CERN/SPC/336/Draft CERN LIBRARIES, GENEVA CM-P00095230 ...cds.cern.ch/record/1124485/files/CM-P00095230-e.pdf · CERN/SPC/336 Page 10 The immediate measures now being considered were:

CERN LIBRARIES, GENEVA

CM-P00095230

CERN/SPC/336/Draft 18 April, 1973

ORGANISATION EUROPÉENNE POUR LA RECHERCHE NUCLÉAIRE

CERN EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

SCIENTIFIC POLICY COMMITTEE

Seventy-second Meeting

Geneva - 13 February, 1973

DRAFT MINUTES

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DRAFT MINUTES

The Scientific Policy Committee was composed of the following:

Chairman : Professor A.G. Ekspong

Vice-Chairman: Professor M. Conversi

Members : Professor B.P. Gregory

Professor L. Leprince-Ringuet

Professor P.T. Matthews

Professor C. MØller

Professor F. Perrin

Professor S.A. Wouthuysen

Ex officio Members : Professor D.H. Wilkinson Chairman, Physics III Committee

Professor M. Cresti Chairman, Track Chamber Experiments Committee

Professor F. Amman Chairman, 300 GeV Machine Committee

Dr P. Lehmann Chairman, Super Proton

Synchrotron Committee

Professor W. Gentner President of the Council Mr P. Levaux Chairman of the Finance

Committee

Professor G. Salvini invited in his capacity as Acting Chairman of ECFA

CERN Officials:

Laboratory I : P rofessor W. Jen t schke Di rec to r -Genera l

Mr G.H. Hampton Director, Administration Department

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CERN Officials:

Laboratory I : (Cont'd)

Professor K. Johnsen Director, ISR Department

Professor C. Peyrou Director, Physics II Department

Professor H. Schopper Assistant to the Director-General for the Co-ordination of the Experimental Programme

Professor J. Steinberger Director, Physics I Department

Dr C.J. Zilverschoon Director, Proton Synchrotron Department

Laboratory II:

Dr J.B. Adams Director-General

Dr H.O. Wüster Deputy to the Director-General

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1. APPROVAL OF THE DRAFT MINUTES OF THE SEVENTY-FIRST MEETING (Item 1 of the Agenda) (CERN/SPC/33/Draft )

The CHAIRMAN said that he was glad to welcome Professor Lehmann, the Chairman of the new Committee (SPSC). He had been informed that, unfortunately, Professors Amaldi, Mannelli, Paul and Weisskopf would be unable to attend the meeting.

He invited the Committee to consider the Draft Minutes of the Seventy-first Meeting (CERN/SPC/334/Draft).

The Minutes of the Seventy-first Meeting (CERN/SPC/334) were approved.

2. ADOPTION OF THE AGENDA (Item 2 of the Agenda) (CERN/SPC/336)

The Agenda (CERN/SPC/336) was adopted.

3. REPORT OF THE WORKING GROUP ON APPOINTMENT POLICY - PAPER BY THE DIRECTORS-GENERAL (Item 3 of the Agenda) (CERN/SPC/335)

Professor JENTSCHKE said that Mr Ullmann would give an introductory talk. There was no need to reach final conclusions at this stage, but it was desirable for the Scientific Policy Committee to be informed of the many important problems connected with this matter.

Mr ULLMANN, commenting on document CERN/SPC/335 and on the Report of the Working Group on Appointment Policy, said that the Working Group had been set up in 1970 for three major reasons:

(1) To review a policy which had not been reviewed for ten years.

(2) To re-examine the Organization's policies concerning recruitment, advancement and indefinite appointments at a time when staff numbers were levelling off.

(3) To take account of changes which had occurred outside the Laboratory.

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Two observations could be made in connection with this review:

(a) The needs and the possibilities of the Organization were often contradictory:

(i) there were a large number of specialists in the Laboratory;

(ii) many people had emigrated from their own country to come to CERN;

(iii) the time-scale of projects impeded the steady flow of staff through the Organization.

(b) Many erroneous ideas had been and were being expressed on what CERN's purpose and work really were:

(i) few people realized the industrial nature of CERN which comprised many engineers and technicians,

(ii) a wide variety of views had been expressed on the relevance of the age of the staff to the policy as a whole; it was clear, in this connection, that the age of individuals was not of fundamental importance; it was better to eliminate cases of limited efficiency than set up artificial barriers.

An examination of European trends outside the Laboratory had shown the following to be particularly relevant:

(a) the stability of employment;

(b) permanent schemes for retraining and education;

(c) participation.

In collecting information inside the Laboratory, the Working Group had looked at demographic data such as staff distribution, the departure rates and the mortality and invalidity rates (Fig. 1).

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Demographic Data Present Policies

1. Present Staff Distribution: 1. Recruitment a) Age b) Profession 2. Contracts

2. Departures: 3. Termination/Retirement a) Leavers b) Invalidity + Mortality

3. 1980 Staff Distribution

Projection Guide-lines

Projection Guide-lines

Projection Guide-lines

Figure 1

Projections had then been made to develop guide-lines on the effect of these data on the variables in the flow chart (Fig. 1), i.e. the policies concerning recruitment, contracts and termination/ retirement.

Age distribution charts had been prepared and the distribution for the total staff showed that the average age was now 37 and would naturally increase by 12 over the next 15 years (Fig. 2).

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Figure 2

Indefinite appointments

Figure 3 represented the total CERN population, 20% being visitors and 80% being staff and supernumeraries:

Tota l Populat ion

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Figure 4 showed the composition of the CERN staff, on 31 December 1971, excluding visitors.

Figure 4

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Figure 5 showed the rate of departures.

Departures

a. Leavers = 1% p.a. (Indef. Contr.)

b. Invalidity + Mortality:

Figure 5

Figure 6 showed the projected staff numbers in 1980.

1980 Staff Numbers

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The Working Group had found that the personnel practices and policies had been valid. It was desirable, however, to see where they would lead. Accordingly, the Group had looked at the CERN staff data under the following headings:

General Population Research Applied Physics and Engineering Programmers and Mathematicians Others.

He proposed to use the first three headings and examples.

With regard to the general population, its number in 1980 would be around 2000 (present average age about 37). It was proposed to try to recruit people under 30 in that category and adequate arrangements would have to be made to keep the average age down by mobility, with the consequences such arrangements might have. For instance, the young people might treat CERN as their first employer which they would leave after a few years. Indefinite contracts would continue to be awarded, but on a more selective basis and people would be encouraged to leave the Organization to a greater extent than now. This policy of mobility would cost money and cause extra work. It would also call for suitable administrative and social arrangements.

With regard to research staff, on the other hand, the average age was likely to remain somewhere between 30 and 35, with about 50% of the population on indefinite contracts. The policy in this case should be to keep the percentage of indefinite contracts to about 45%, to give these contracts to a limited number of younger people, and to encourage one physicist per annum to leave research.

For applied physicists and engineers, i.e. the category between the other two, with indefinite appointments reaching a level of 65% in 1973, the average age would be advancing significantly with the years. The way of keeping it down would be to give indefinite contracts to only 50% of the new staff recruited for projects.

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The immediate measures now being considered were:

(i) to reduce the average age of recruitment; (ii) to apply stricter selection criteria; (iii) to facilitate mobility; (iv) to survey training needs; (v) to extend personnel appraisal schemes and, finally,

to make sure that the policy of the Organization was clearly known.

During the discussion that ensued, it was emphasized by the CHAIRMAN and Professor CONVERSI that careful consideration would have to be given to many of the points raised, and it was pointed out by Mr ULLMANN, in reply to Professor Gentner, that the question of visitors was considered to be outside the terms of reference of the Group.

Professor AMMAN remarked that it was desirable to avoid considering CERN as a closed system and that some formal ways ought to be found of connecting the CERN system with national institutes.

It was pointed out by Professor LEHMANN that the research physicists with an indefinite appointment at CERN were mostly engaged in work of general interest, and mobility was a problem which was more relevant to engineering and applied physics than to the few research physicists on the staff. National institutes were rather small compared to CERN. It was difficult to make suitable arrangements with industry. Therefore, personal incentives seemed to be the best way of dealing with this problem.

Professor MATTHEWS observed that mobility among the research staff was achieved owing to the fact that the ratio of visitors to research physicists with an indefinite appointment was of the order of 12 to 1. The rest of the staff need not be young, provided they were good.

Professor PERRIN said that quality should be the main concern. Promotion should be on the grounds of ability rather that seniority and compensation payments should be used to facilitate the departure of those who were not worth promoting.

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Dr ADAMS said that the problem was whether CERN could operate a system which was not in balance with the outside world. National laboratories were also trying to replace older people by young ones, but this sort of policy was not easily put into practice in a field which was tending to contract rather than expand. The best solution seemed to be to recruit young people, to be very selective in recruiting and not to give indefinite contracts too easily. He did not think that the CERN staff came out badly in comparison with staff in industry. Furthermore, experience had shown that, in the accelerator world at least, there did not seem to be a marked fall off in quality with age.

Professor JENTSCHKE said that it was desirable to have a good proportion of young research physicists on the staff as they were bound to play an important part in keeping up the quality of the physics output.

Professor WILKINSON said that to achieve mobility inside the Laboratory the principle of rotation should not be limited to senior posts and the concept of viscosity in the staff structure should be introduced.

Dr ZILVERSCHOON pointed out that the principle of the mobility was already applied on quite a considerable scale. For instance, in the PS Department, out of 11 Group Leaders, 5 had less than three years' service in that position. Moreover, in the last few years 5 former Department Directors or Division or Group Leaders had reverted to leading a section or even less.

Professor GREGORY observed that he was very pleased with the results achieved by the Working Group which he had set up before relinquishing his appointment as Director-General. He felt that the Scientific Policy Committee should support the proposals made on page 17 of the Report, whereby the Directors-General should have more latitude than at present to negotiate resignations with adequate compensation.

Professor SALVINI proposed that ECFA should also be informed of the findings of the Working Group on Appointment Policy.

Professor GENTNER supported this proposal.

It was so agreed.

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5. ORAL REPORT ON THE LATEST PHYSICS RESULTS AT THE ISR (Item 5 of the Agenda)

Professor GREGORY reported that the ISR Construction Group had reached its goal just before the Council session. This time it had achieved a better luminosity than the design value 4 × 1030 cm-2s-1 and there was still good hope of improving the luminosity as the full intensity of the machine had not yet been reached. Moreover, by accelerating protons up to 31.5 GeV, it was now possible to make some measurements at lower luminosities at an energy equivalent to 2000 GeV in the laboratory system. Five out of eight intersection regions were being used for experiments and a sixth was due to be opened in a few months. Thanks to the effeciency of the Machine Group and the Support Group and the ability of the co-ordinator, the eleven physics experiments could run with a maximum of flexibility and little interference from the ISRC.

Professor Gregory then went on to comment on the experiments running at the ISR* and particularly on the results obtained in the two experiments on:

(a) the energy dependence of the proton-proton total cross-section for centre-of-mass energies between 23 and 53 GeV**

and

(b) measurements of the total proton-proton cross-section at the ISR***.

Concluding his report, Professor Gregory said that there was strong pressure from the physicists for further experiments and a clear possibility of increasing the luminosity of the ISR. Accordingly, ISR physics was likely to remain a very active and rich field of research for many years to come.

In the discussion which followed,Professor Gregory said that it was too early to make a good guess about the behaviour of the p-p cross-section beyond the energies reached so far, and it was pointed out by Professor Johnsen that it was difficult for the time being to make measurements with the ISR at less than 11 GeV in the centre-of-mass. Accordingly, it was not easy for the moment to link up the ISR results with the Serpukhov results.

*For details see CERN/ISRC/Exp.4 attached as Annex I. **Attached as Annex II. ***Attached as Annex III.

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Replying to a question by Dr Adams, Professor STEINBERGER said that he did not think the results obtained so far on the ISR would significantly affect the 300 GeV programme.

The CHAIRMAN thanked Professor Gregory for his very interesting report.

6. ORAL REPORT ON THE FIRST MEETING OF THE SPSC (Item 6 of the Agenda)

Professor LEHMANN reported that the SPSC had held its first meeting on 9 January, the Minutes of which had been distributed to the Members of the Scientific Policy Committee. As the Committee would see, an attempt had been made to keep as much balance as possible in the composition of the SPSC. A second meeting had been held on 9 February.

The starting point for the SPSC was the work of ECFA and its Working Group and the final report of the Executive Committee of the ECFA 300 GeV Working Group presented by Professor Falk-Vairant.

At the first meeting, Dr Adams had told the Committee about the important points on which an early decision would have to be taken. The most important decisions to be taken in this connection were:

(1) the decision on construction schedules A, B or C;

(2) the decision on whether the proton energy on the neutrino target in the West area should be 200 or 400 GeV;

(3) the decision on the master plan for the North hall as civil engineering work had to start before the end of 1973.

The SPSC had decided to carry on its work with a limited number of working groups with which it would keep close links, i.e.:

The West area neutrino working group under K. Winter (CERN). The North area neutrino working group under Lipmann (Saclay). The working group on neutrino detectors under Turlay (Rutherford).

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It would be necessary to take decisions by the end of the year on the large equipment to be built for the West and North halls, as the time schedule for building this kind of equipment was of the order of three years and the first beams were expected to be available in the West hall in 1976, and in the North hall in 1977. It was also desirable to foresee as soon as possible how this equipment would fit into the total financial provisions available. Accordingly, the SPSC had discussed at its last meeting a letter to be sent to about 800 people, who would be asked to write letters of intent to the SPSC that would help to show what general facilities were expected by the physics community. These letters of intent should also facilitate the financial planning and the setting-up of priorities. The SPSC's letter asked for information about the equipment which groups were willing to build or contribute to, for the names of the physicists interested and for those of the contact men. It was planned to hold an open meeting of potential users on 25 April and it was hoped some letters of intent would be in by June, so that first recommendations might be made by the SPSC in the autumn.

The two dangers to be avoided were the construction of large equipment by purely national teams and the elimination of the smaller laboratories.

It was already known that groups of physicists were being formed with a view to writing these letters of intent. The only decision which probably should be taken before September was that on the accelerator construction schedule. In any event, the SPSC hoped to be in a position to make recommendations to the NPRC early in 1974, so that there was enough time to build the large items for the experimental programme.

During the discussion which followed, Dr ADAMS said that he hoped the decision on the machine schedule would be taken in accordance with the following time-scale:

(i) preliminary GESSS report ready in April; (ii) discussion of the report in the 300 GeV Machine Committee

(Chairman Professor Amman) in April; (iii) discussions in the SPSC and NPRC early in May; (iv) discussion in the Scientific Policy Committee and ECFA

in May; (v) if all went well, announcement to the Council in June,

probably as part of the Progress Report, since there was no need for the Council to take a decision on the matter.

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magnets in June or J u l y , firms concerned i n t e r r u p t their magnet p roduc t ion .

Replying q u e s t i o n by Professor LEHMANN t h a t , on b a l a n c e , it would be to proposals to a l l the of the letter, but p roposa l s were bound to known a t open meetings of p r o s p e c t i v - use r s or c i r c u l a t e d as a b s t r a c t s .

Replying t o a ques t ion by Professor P e r r i n , P ro fes so r Lehmann sa id t h a t the p o s s i b i l i t y of having a s i n g l e channel in the North a rea for muons and from pion decay was s t u d i e d e x t e n s i v e l y .

The CHAIRMAN thanked P ro fes so r Lehmann for h i s r e p o r t .

7. OTHER BUSINESS ( I t e m of the Agenda)

P ro fe s so r pa id t o the of P ro fe s so r who had d i e d suddenly

The meeting was adjourned a t 1.30 p.m.

The meeting was resumed in c losed a t 3 p.m.

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8. PRELIMINARY DISCUSSION ON SENIOR STAFF APPOINTMENTS, LABORATORY I - JUNE 1973 (Letter CERN/14.988) (Item 4 of the Agenda)

The Scientific Policy Committee considered the situation of four Division Leaders whose appointments came to an end on 30 June, 1973, namely:

- Professor B. Zumino, Leader of TH Division - Dr G.R. Macleod, Leader of DD Division - Mr C. Tièche, Leader of Finance Division - Mr G. Ullmann, Leader of Personnel Division.

The Scientific Policy Committee concurred with Professor Jentschke's suggestion to nominate Professor D. Amati as successor to Professor B. Zumino, for a three-year period.

The Committee also agreed with Professor Jentschke's proposal to renew the appointments of Dr Macleod, Mr Tièche and Mr Ullmann for a further three-year period.

9. MEMBERSHIP OF THE SCIENTIFIC POLICY COMMITTEE (Item 7 of the Agenda)

The Scientific Policy Committee was extremely glad to learn from Professor Møller that Professor A. Bohr would be happy to become a Member of the Committee.

With regard to the other vacancy in the Scientific Policy Committee, the Committee was unanimous in deciding to invite Professor G.H. Stafford to join in the near future.

The Chairman of the Scientific Policy Committee would therefore submit these nominations to Council for formal approval at its June session.

Finally, the Scientific Policy Committee agreed to discuss at its next meeting May the matter of france Chairmen of the Experiments .

In this , a table giving the names of former Chairmen dates the various Committees had been set up would be circulated in advance by Professor .

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10. OTHER BUSINESS (Item 9 of the Agenda) (resumed)

(a) Items for the May Meeting Agenda

The Scientific Policy Committee agreed to discuss at its next meeting the decision to be taken about the selection of magnets for the second stage of the SPS and to review the work done in the superconducting field at CERN.

(b) The SC Future Programme

Professor Wilkinson informed the Scientific Policy Committee that, provided the rotating condensor was available by 10 March, the shut-down was planned to take place on 19 April, 1973.

(c) Record of Closed Sessions

It was agreed that the conclusions of the discussions held in closed session would henceforth be included in the Minutes of the open meetings.

The meeting rose at 5.20 p.m.

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CERN/ISR/EXP/4 October 1972

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

PROGRAMME OF ACCEPTED EXPERIMENTS

CERN INTERSECTING STORAGE RINGS

October 1972.

Table 1 : ISR Experiments running or accepted

Table 2 : ISR Experiments completed at 1.10.1972

Fig. 1 : General Layout of Experiments at the ISR

Fig. 2 : Layout of Intersection 1

Fig. 3 : Layout of Intersection 2

Fig. 4 : Details of Experiment R-201 and R-203

Fig. 5 : Layout of Intersection 4

Fig. 6 : Layout of Intersection 6

Fig. 7 : Details of Experiment R-801

Fig. 8 : Details of Experiment R-802.

K.M. Potter ISR Co-ordinator.

- 1 -

Table 1

ACCEPTED CERN ISR EXPERIMENTS

Area Expt. Code ISRC Reference Number Description of Experiment Present composition of group Date of

NPRC Acceptance Status

I-1 R-103 CERN/ISRC/69-43, and Add.1 Search for Massive Dileptons CERN-Columbia-Rockefeller:Büsser, Camilleri,DiLella,Pope,A. Smith,Yoh, Zavattini;Blumenfeld,Lederman;Cool, L.Litt,Segler

NPRC 85 5.11.1969

In Production

I-1 R-104T CERN/ISRC/70-19, Add.1, 2 Search for High Energy multigamma events

Brookhaven-Grumman - Rome: L.C.L. Yuan; Ed.Amaldi, Borgia,Beneventano, Pistilli, Dell, Dooher, Uto

NPRC 98 4. 6. 1971

Parasitic on Experiment R-103

I-1 R-105 CERN/ISRC/72-13 and Add.1 To measure high transverse momentum charged particles

Saclay: Banner, Cheze, Hamel, Pansart, Stirling, Teiger, Zaccone

NPRC 110 30.8.1972

Installation during shut­down

T Test experiment.

- 2 -

Table 1 (cont'd)

Area Expt. Code ISRC Reference Number Description of Experiment Present composition of group Date of

NPRC Acceptance Status

I-2 R-201 CERN/ISRC/69-5, and Add.1, 2, 3, 4 CERN/ISRC/69-9

Production of stable particles at small angles

CERN-Holland-Lancaster-Manchester-Coll. (CHLM):Albrow,Bacchus,Barber,Bogaerts, Bosnjakovic,Erné,Sens,v.d. Veen, Clegg,Locke,Loebinger,Gee,Murphy,Rudge

NPRC 84 4.7.1969

In Produc­tion

I-2 R-202 CERN/ISRC/69-7, and Add.1 Study of particle production in high energy proton-proton collisions at medium angles

Argonne-Bologna: Antinucci, Bussière,Bertin,Capiluppi, D'Agostino-Bruno,Giacomelli,Maroni, Rossi, Vannini

NPRC 84 4.7.1969

1stPhase complete a), 2nd Phase in product.

I-2 R-203 CERN/ISRC/69-2 CERN/ISRC/69-3 CERN/ISRC/69-44 CERN/ISRC/70-32 CERN/ISRC/71-9

a) Experiment to determine production spectra of Π±,K±, p, d... etc. at large angles.

b) Search for "Quarks" at large angles

The collaboration mentioned below and the Scandinavian Coll.:Boggild,Damgaard, (Hansen), Jarlskog, Jönsson, Klovning, Leistam, Lillethun, Lynch, Von Dardel, Korder, Weiss

NPRC 84 4.7.1969

Installing high momentum mode

I-2 R-204 CERN/ISRC/69-3 Measurement of muons with large trans­verse momentum as a search for the intermediate boson

British Universities coll.: Alper, Birge(Bulos),(Carrol), Cence, Duff, Potter, Sharp, Sharrock, (Manning), (Heymann), (Quarrie), (Malos), (Booth), Prentice (Jackson)

NPRC 84 4.7.1969 In Prod.

(...) = participating in experiment but not now at CERN.

a) See Table of completed Experiments (Table 2).

- 3 -

Table 1 (cont'd) ACCEPTED CERN ISR EXPERIMENTS

Area Expt. Code ISRC Reference Number Description of Experiment Present composition Date of

NPRC Acceptance Status

I-4 R-401 CERN/ISRC/69-14 Measurement of energy dependence of iso­bar excitation in proton-proton colli­sions

CERN-Hamburg-Orsay-Vienna(CHOV) Coll.: Aubert,Bartl,Broil,Coignet,Dibon,

Favier,Flügge,Gottfried,Massonet,Neuhofer, Niebergall,Regler,Schmidt-Parze-fall,

Schubert,Schumacher,Smith, Vivargent, Winter

NPRC 83 4.7.1969

Expt.to be per­formed in Split-Field Magnet (Magnet Instal­lation Jan.'73)

I-4 R-403 T CERN/ISRC/70-5 S.F.M. Test and Survey Collaboration: (S.F.M. = Split Field Magnet)

S.F.M.: Charpak, Fischer, Flügge, Gottfried,Minten,Schwille NPRC 95

3.2.1971 Test Experiment in progress

I-4 R-404 T CERN/ISRC/70-18 and add. 1, 2

Test of a proposal to search for Heavy Baryon Isomers

CERN-Hamburg-Vienna Coll.: Flüngge, Gottfried,Neuhofer,Niebergal1,Regler, Schnidt-Parzefall, K.R. Schubert, Winter

-Test Expt. in progress

T = Test Experiment

- 4 -

Table 1 (cont'd) ACCEPTED CERN ISR EXPERIMENTS

Area Expt. Code ISRC Reference Number Description of Experiment Present composition

Date of NPRC Approval Status

I-4 R-406 CERN/ISRC/70-31 and Add.1 and 2

Search for fractionally charged or massive particles at the ISR

Bologna - CERN Coll:Basile,Bollini, Brurini,Fiorentino,Frabetti,Massam, Monari,Navarria,Palmonari,Zichichi

NPRC 110 30.8.1972

No time allocation yet

I-4 R-407 CERN/ISRC/71-30 and Add.1

To measure two-particle correlations in multiparticle events in the fragmentation region with the SFM spectrometer

Karlsruhe- CERN Collaboration:Moritz, Schmidt,Schneider,Schopper, Wegener

NPRC 110 30.8.1972

No time allocation yet

I-4 R-408 CERN/ISRC/71-34 To measure inelastic proton-proton scattering at the ISR

Charpak,Drijard,Dunwoodie, Fischer,Innocenti,Minten,Sauli

NPRC 110 30.8.1972

No time allocation yet

R-409 CERN/ISRC/71-36 A minimum-bias-trigger experiment using the SFM to study typical beam-beam events

Breidenbach,Fabjan,Gjesdal, Steinberger,williams,Winstein

NPRC 110 30.8.1972

No time allocation yet

I-4 R-410 CERN/ISRC/71-37, 72-7 and Add.1

Study of particle correlations at large angles

MIT-Orsay-Scandinavian Collaboration: Becker,Busza,Cheng,Sadrozinski,Ting, Sau Lan Wu, Wu

NPRC 110 30.8.1972

No time allocation yet

- 5 -

Table 1 (cont'd) ACCEPTED CERN ISR EXPERIMENTS

Area Expt. Code ISRC Ref.Number Description of Experiment Present composition of group

Date of NPRC Acceptance Status

I-6 R-601 CERN/ISRC/69-20, and add. 1, 2 CERN/ISRC/70-7, and add. 1, 2

The measurement of proton-proton differential cross section in the Coulomb interference region

CERN-Rome Coll.: Allaby, Bartel,Cocconi, Diddens, Dimcovski, Dobinson, Litt,J., Wetherell; U.Amaldi,Biancastelli,Bosio, Matthiae

NPRC 83 4.7.1969

In Prod.

I-6 R-602 CERN/ISRC/69-19, and add.1, 2, 3

a) Measurement of the elastic scattering cross section beyond the Coulomb inter­ference region.

b) Search for "Quarks" at small angles.

CERN-Aachen-Uni.Calif.-Genova-Harvard-Torino: Baksay,Boehm,Bozzo,DiZorzi,Ellis,Ferrero,Foeth, Maderni,Meyer,Naroska,Pilcher,Rubbia,Schlein, Sette,Staude,Strolin,Sulak,Trippe,Webb

NPRC 83 4.7.1969

Elastic Scatter­ing measu­rements. In Prod.

I-6 R-603 CERN/ISRC/71-45 and add.1

∆++ Spectroscopy Studies CERN-Aachen-UCLA-Harvard Coll.:Baksay,Boehm, Drickey,Ellis,Hansroul ,Foeth,Lockman,Meyer, Muller,Naroska,Palazzi,Pilcher,Rander,Rubbia, Schlein,Staude,Strolin,Sulak,Trippe,Webb

NPRC 104 2.2.1972

Install. after com­pletion of R-602

- 6 -

Table 1 (cont'd) ACCEPTED CERN ISR EXPERIMENTS

Area Expt. Code ISRC Ref. Number Description of Experiment Composition of group Date of

NPRC Acceptance Status

I-7 R-701 CERN/ISRC/72-17 Observation of inelastic proton-proton collisions with streamer chambers

Aachen,CERN,Münich Collaboration: Eggert, Holder; Darriulat,Gygi, Schneider, Tittel; Derado,Eckardt, Schmitz, Seyboth,Mc Donald, Pugh

NPRC 110 30.8.1972

Installation during shut­down

- 7 -

Table 1 (Cont'd) ACCEPTED CERN ISR EXPERIMENTS

Area Expt. Code

ISRC Reference Number Description of Experiment Present composition of group Date of NPRC Acceptance

Status

I-8 R-801 CERN/ISRC/69-12 Measurement of the p-p total cross section

Pisa-Stony Brook Coll.: Amendolia, Bellettini, Braccini,Bradaschia, Castaldi,Cerri,Ciancaglini,Del Prete, Finocchiaro, Foà, Giromini,Grannis, D. Green, Laurelli,Menzione,Mustard, Ristori,Sanguinetti, Valada, Thun

NPRC 83 4.7.1969

In Production

I-8 R-802 CERN/ISRC/71-41 and Add. 1 and 2

Particle Production in the forward direction

CERN-Rome Coll.:Allaby,Bartel, Cocconi,Diddens,Dimcovski,Dobinsor, Wetherell; U.Amaldi,Biancastelli, Bosio,Matthiae

NPRC 107 3.5.1972

In Preparation, starting anti­cipated after shut-down

- 8 -

Table 2 ISR Experiments completed at October

Area Expt. Code Description of Experiment Authors Completion of

Data-taking Status

I-1 R-101 Emulsion Exposures giving:-a) Angular distribution of charged particles between 35° and 90° b) Stopping particles at 90°

CERN-Cracow-Bucharest-Tata emulsion collaboration: Annoni,Cordaillat,Czyzewski, Friedländer,Gierula,Gurtu, Haiduc,Herz,Marin,Vicky,Wolter

September 1971 a) Published

b) Submitted to Phys.Letters.

I-2 R-202 Study of positive particle product­ion with a single arm spectrometer at medium angles

Argonne-Bologna-Michigan Collaboration: Ratner,Ellis,Vannini,Babcock,Krisch, Roberts

September 1971 Published (Study of negative particle production continuing. See Table 1).

I-1 R-102 a) Study of interactions in which gamma rays and electrons with large transverse momentum are emitted.

b) Search for "Quarks" at large angles

Saclay-Strasbg.: Banner,Cheze,Hamel Stirling,Teiger,Zaccone,Pansart; Bassompierre,Croissiau,Gresser, Morand,Schneegans,Riedinger

April 1972 Submitted to Physics Letters.

I-1 R-402 Search for fractionally charged particles

CERN-Munich Collaboration: Caldwell, Fabjan,Bruhn,Hyams,Sauli,Zahniser, Bott-Bodenhausen,Stierlin,Rochester, Winstein,Tirler

August 1972 Preliminary results submit­ted to Phys.Letters. (Analysis continuing).

I-5 R-405 Neutron Production at small angles CERN-Karlsruhe Coll.: Engler,Flauger, Gibbard,Monnig,Schopper, Bartel,Schmidt

October 1972

FIG : 1 ISR EXPERIMENTS October 1972

FIG : 2

FIG : 3

FIG : 4

FIG : 5

FIG: 6

FIG : 7

FIG : 8

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

THE ENERGY DEPENDENCE OF THE PROTON-PROTON TOTAL CROSS-SECTION FOR CENTRE-OF-MASS ENERGIES BETWEEN 23 AND 53 GeV

U. Amaldi*) , R. Biancastelli, C. Bosio and G. Matthiae, Physics Laboratory, Istituto Superiore di Sanità

and INFN, Sezione Sanità, Rome, Italy.

J.V. Allaby, W. Bartel, G. Cocconi, A.N. Diddens, R.W. Dobinson and A.M. Wetherell,

CERN, Geneva, Switzerland.

ABSTRACT

Measurements of proton-proton elastic scattering at angles around 6 mrad have been made at centre-of-mass energies of 23, 31, 45 and 53 GeV using the CERN Intersecting Storage Rings. The absolute scale of the cross-section was established by determination of the effective density of the colliding beams in their overlap region. Proton-proton total cross sections were deduced by extrapolation of the elastic differential cross-section to the forward direction and by application of the optical theorem. The results indicate that over the energy range studied the proton-proton total cross-section increases from about 39 to about 43 mb.

Geneva - January 1973

*) At present CERN Visiting Scientist.

The measurements of the strong interaction proton-proton total cross-section, σt, presently being performed at the CERN Intersecting Storage Rings (ISR) use methods other than the conventional transmission technique, which is not directly applicable to colliding beams. In one method σt is obtained from a measurement of the differential elastic scattering cross-section by application of the optical theorem1,2), in another the

total number of proton-proton interactions is counted3) . In applying the first method two different approaches have been used to fix the absolute scale of the elastic cross-section: measurement of the elastic cross-section at very small momentum transfers1), where Coulomb scattering is dominant and known in absolute value,and determination of the machine luminosity by the Van der Meer method4,2).

This Letter presents measurements of σt at centre-of-mass energies, √s, of 23, 31, 45 and 53 GeV using the first method. The various steps involved may be summarized as follows:

a) Measurement of proton-proton elastic scattering at angles around 6 mrad.

b) Determination of the effective density of the colliding beams in their overlap region (machine luminosity)by the Van der Meer method, which establishes the absolute scale of the differential cross-section dσ/dΩ.

c) Extrapolation to = 0 using the measured dependence of d / σ t . d) Calculation of σt from the optical theorem.

The apparatus consisted of small scintillation counter hodoscopes measuring elastic scattering and of three monitor systems of large scin­tillators, detecting inelastic events at angles of about 50 mrad, to de­termine the ISR luminosity. At the beginning of each run the monitors were calibrated by means of the Van der Meer metho4) , which may be described as follows.

The relationship between the counting rate R of a detector, registering events produced by two beams crossing in the horizontal plane, the cross-section ∆σ corresponding to the events counted by the detector and the vertical density distributions of the stored beam currents i1(z-zi) and i2(z-z2) may be written

- 2 -

R ( δ ) = ∆σ K

i1(z) i2(z + δ) dz, (1)

where δ = z1-z2 is the vertical displacement between the centres z1 and z2 of the two beams. The constant K is given by

K = e2 βc tg (α/2), (2)

α being the crossing angle of the beams at the ISR (α = 14.79° ± 0.01°) and βc the velocity of the protons. Since the beams do not meet head-on, but each crosses the full horizontal width of the other, the collision probability does not depend on the shape of the density distribution in the horizontal direction, hence only the convolution of vertical density distributions is needed in Eq. (1). Following a suggestion of Van der Meer4) a simple method has been used to determine the normalising factor ∆σ/K in Eq.(1). This method consists in measuring the counting rate R(δ) as a function of the vertical displacement δ between the two beams. The following relation then holds

R(δ) dδ = ∆σ K

I1 I2 (3)

because I1 and I2 , the currents of the two circulating beams, are given by the expression I = i(z) dz.

In this experiment the integral R(δ) dδ was measured by means of a monitor system which detected events from beam-beam collisions while the two beams were displaced vertically, one re­lative to the other, in small and precise steps (typically ∆δ = 0.50 ± 0.01 mm; the absolute value of this displacement was checked, at all energies, by the ISR machine group using pick—up electrodes). The experimentally deter­mined integral, normalized to the product of the measured circulating currents (known to better than 10-4) gives, using Eq.(3), the cross-section ∆σM for events which are within the acceptance of the monitor system. The procedure is valid only if the beam shapes are invariant during their displacements and only if the monitor rate is independent of the position of the source. To meet the second requirement a monitor which detects inelastic events is essential.

- 3 -

The relation between the "monitor constant" ∆σM and the elastic scattering cross-section ∆σE integrated over ∆Ω is given by

∆σE = (dσE/dΩ) ∆Ω = ∆σM NE/NM, (4)

where NE and NM are the elastic and the monitor rates counted simultaneously. For Eq. (4) to be valid it is only necessary that the ISR energies are equal to those used for the calibration and that the monitor efficiency remains constant. The other parameters (such as beam currents, beam shapes etc.) can be changed at will and need not stay constant dur­ing the measurement of elastic scattering.

The counter arrangement used to measure elastic scattering events is shown schematically in Fig. 1. Protons scattered in the vertical plane were detected in coincidence by means of the two systems of scin­tillation counters A and B, each consisting of one hodoscope and two trigger counters, placed 9 m from the intersection region. Each hodo­scope covered an area of 30 × 70 mm2 and was formed by two separate ar­rays of horizontal and vertical scintillators. The horizontal scintil­lators Hi (i = 1, ...,5) were 6 mm high and 70 mm wide, while the vertical scintillators Vi (i = 1, ...,7) were 30 mm high and 10 mm wide. The effective size of each hodoscope element was thus determined by the height of the horizontal and the width of the vertical scintillators. The two arrays of horizontal and vertical scintillators were placed in between two trigger counters (called A', A" and B', B" for the A and B systems, respectively) of dimensions 35 × 75 mm2, sufficient to cover the hodoscope scintillators.

A and B were placed in special, thin-wall sections (0.2 mm stain­less steel) of the ISR vacuum chamber which could be displaced vertical­ly towards the beams. The two hodoscopes were set symmetrically with respect to the crossing region to observe elastic scattering at angles around 6 mrad with the ISR operating at equal beam momenta.

The four-fold coincidence combination A'A"B'B" was used to gate pattern units which registered the signals from the hodoscope

- 4 -

counters. The data, together with the time-of-flight between conjugate trigger counters and the pulse-heights of all counters, were recorded for each event. The rates of the three monitor systems were also recorded. A CAMAC system and a small on-line computer were used for data collection and storage on magnetic tape.

In order to have the crossing region small with respect to the size of the hodoscopes the data were taken with the machine working in the Terwilliger mode5). In this scheme, which uses special quadrupoles in the machine lattice, the width of the beams is determined only by the betatron oscillations. The distribution of the interaction points was approximately gaussian in shape with r.m.s. values of about 3 mm in the radial direction and about 1.5 mm in the vertical direction. Thus for the elastic (collinear) events, in which one of the scattered protons was detected close to the centre of one of the hodoscopes, the coincident proton was practically always detected by the other hodoscope. With stored currents of about 5 A the coincident rate at (22.6 + 22.6) GeV/c was about 20 events/sec; the accidental rate between hodoscopes A and B was always less than 1%.

In the data analysis only those triggers were used in which at least one array element of each hodoscope (out of twelve) had fired. This corresponded to the requirement of at least a six-fold coincidence. At all energies, about 72% of these triggers were events with one firing on a horizontal and a vertical counter in both hodoscopes. The events which fired two counters of the same array were about 16%. These events were interpreted as mostly due to δ-rays produced in the trigger counters or in the hodoscope scintillators. This interpretation agreed with measurements performed in a particle beam in connection with a previous experiment1). Six per cent of the triggers were multiple firings, which were attributed either to interactions in the vacuum chamber of elastically scattered protons or to true inelastic processes coming from the source. In about 6% of the events one of the four ar­rays gave no signal. The number of these "incomplete" events agreed with estimates based on the measured spacing between adjacent counters of the arrays.

- 5 -

The events (with the exclusion of"incomplete" events) were displaced in matrices according to the following procedure. Consider the centre ele­ment of hodoscope A as the element defining the solid angle ∆Ω, i.e. the element (H3V4)A. Elastic events registering in this element have their conjugate proton distributed over hodoscope B. The events in which only this element of hodoscope A was fired and, on the opposite hodoscope B, there was only one firing of a horizontal counter Hi and one firing of a vertical counter Vj, were added with weight 1 to the ma­trix element ij. For multiple events (both of A and/or B hodoscopes) weights smaller than 1 were attributed to each possible AB combination in such a way that each detected event was counted only once. In this manner the total number of elastic events in the sample was not altered, independent of whether a δ-ray was produced or the scattered proton had interacted in the chamber wall or in the counters. An example of a (HiVj)B matrix obtained in a run at (26.6 + 26.6), GeV/c selecting the central element (H3V4)A of the A hodoscope, is shown in Fig. 2. The total number of events in this matrix is about 5500. The kinematic cor­relation typical of elastic scattering events produced a prominent peak over a small background, caused by inelastic processes. The dimensions of the source and of the counters fixed the definition of elastic events, which corresponded to the criterion that two charged particles were collinear with an r.m.s. angle of ±1 mrad in the horizontal and ±0.4 mrad in the vertical plane. These angles correspond to transverse momenta of about 20 MeV/c, small enough to ensure that the contribution of any other known physical process has a much wider distribution. In particu­lar, since the typical transverse momenta in the decay of a diffractively produced resonance are about 200 MeV/c, the distribution of the decay particles is practically constant below the peak of Fig. 2 and contributes to the uniform background, which is subtracted. Unknown phenomena of sizeable cross-sections, having characteristic transverse momenta smaller than ~ 20 MeV/c, would invalidate the present definition of elastic events.

The procedure described above for the central element (H3V4)A of hodoscope A has been applied to the nine central elements of hodoscopes A and B. The elastic event rate NE introduced in Eq. (4) was then

- 6 -

obtained by subtracting a common background from the matrices correspond­ing to these nine central elements HiVj (i = 2,3,4 and j = 3,4,5) of the hodoscopes. The percentage values of the background, subtracted at the four different ISR momenta of (11.8 + 11.8), (15.4 + 15.4), (22.6 + 22.6) and (26.6 + 26.6) GeV/c were 3.5%, 5.0%, 7.5% and 10%, respectively, and were obtained by means of a computer program which fitted the shape of the peak in the matrix. For the nine combinations chosen the elastic peak was quite well centred on the matrix itself so that the border los­ses due to the finite extension of the hodoscope arrays were small (less than 2%) and could be safely estimated.

In applying Eq. (4) the main source of error turned out to be the uncertainty in the monitor constant ∆σM so that three independent moni­tor systems, M1, M2 and M3, were used. Each monitor consisted of two pairs of scintillation counters placed about 5 m from the intersection region to detect mainly inelastic beam-beam collisions. The dimensions of these counters were 20 × 30 cm2 for monitor M1, 40 × 40 cm2 for M2, and 50 × 50 cm2 for M3. In order to avoid orbit distortions induced by simultaneous displacements of the beams in the other intersection regions, many special calibration runs were performed, at the four ISR energies, by displacing vertically the beams only in the intersection region where the apparatus was mounted. The absence of beam blow-up effects for high intensities (i.e. beam currents >5A) was established by calibration runs at (26.6 + 26.6) GeV/c in which the product of currents (I1 × I2) was varied by a factor of ten and in which the vertical heights of the beams was changed by a factor of two. The observed maximum spread of the most stable monitor at any given energy in any condition was ±2% over a period of about two months. The cross-sections were computed using this monitor and attributing to the determination of the monitor con­stant ∆σM a standard deviation of 2%, equal to the observed maximum spread.

Having obtained the elastic differential cross-section at angles around 6 mrad the Coulomb contribution, which varied from ~ 5% at (11.8 + 11.8) GeV/c to ~ 0.2% at (26.6 + 26.6) GeV/c, was subtracted and

- 7 -

the extrapolation of the nuclear scattering differential cross-section dσ/dt = (π/p2) dσ/dΩ to the forward direction was performed using the ex­pression

(dσ/dt) = (dσ/dt)t=0 e b t . (5)

The forward scattering cross-section was then related to the total cross-section σt through the optical theorem:

σt= √ 16π

(

dσ

) t=0. √ ( 1 + ρ 2 ) ( d t ) t=0. (6)

The previous equations are based on the assumptions that the nuclear differential cross-section depends exponentially on the square of the four-momentum transfer,t, with a constant slope parameter b down to zero scattering angles, and that spin effects are negligible. The validity of these assumptions was discussed in Ref. 1. The ratio of the real to the imaginary part of the nuclear amplitude, ρ, has been previously measured1) and its average value between √s = 23 and 31 GeV was found to be ρ = 0.025 ± 0.035. Since the result is compatible with ρ = 0, this value has been assumed in applying Eq. (6). The presence of a small real part does not affect the determination of σt. In fact an uncertainty of ∆ρ = ±0.05 would cause a decrease of σt of only 0.05 mb.

Table 1 gives the momentum transfers |t| at which the elastic scattering was measured, the values of the differential cross-section dσ/dt, the parameters b used, the extrapolation factors eb|t| and the forward nuclear cross-section (dσ/dt)t=0.

The values of b used in Eq. (5) and shown in Table 1 were obtained) by interpolation of previous measurements6,7) taken together with new values obtained at √s = 45 and 53 GeV with the apparatus described in a

previous publication1). The new results are: b = (12.6 ± 0.4) GeV-2

in the range 0.01 ≤ |t| ≤ 0.05 GeV at √s = 45 GeV and b = 13.1 ± 0.3 GeV-2

in the range 0.01 ≤ |t| ≤ 0.06 GeV2 at 53 GeV. These values agree well with the figures obtained at somewhat larger momentum

- 8 -

transfers6), which supports the assumption that for |t| 0.1 GeV the value of b in Eq. (5) remains constant.

The sources of the errors on the extrapolated differential cross-sections are listed in Table 2. As discussed previously, the biggest contribution arises from the uncertainty in the measurement of the moni­tor constant. A safe estimate has been made for the error introduced by the inelastic background subtraction, since the error has been taken equal to 15% of the background itself. In addition, the effect of a generous error ∆b = ±0.5 GeV - 2, which is about twice the experimental error, has been taken into account in Table 2.

The errors appearing in Tables 1 and 2 are point-to-point errors. In addition there is a scale error which affects equally the measured differential cross sections at the four momenta, with an estimated standard deviation of 3%. It was obtained by combining estimated errors of ±2% due to calibration of the magnets which displace vertically the beams in the ISR, ±2% due to uncertainty in the knowledge of the solid angle ∆Ω, ±0.5% due to possible counter inefficiencies, and ±1% due to the uncertainty in the background subtraction of the "incomplete" events and in the estimate of the border losses.

Table 3 contains the total cross-section obtained from Eq.(6). Note that percentage-wise the errors in σt are one-half of the errors in (dσ/dt)t=0 because this enters under the square root in Eq.(6). The fifth column of the table gives the total elastic cross-sections σe1 computed using the extrapolated values of the forward cross-section with the quoted slopes for |t| ≤ 0.1 GeV2, and an exponential behaviour of smaller slope for |t| 0.1 GeV2 as measured by Barbiellini et a17). In the last column the total inelastic cross section σin = σt - σe1 is given.

The values of the total cross-sections are plotted in Fig. 3 together with other published data 1,8) as well as the antiproton-proton cross-section up to 50 GeV/c. The present results at √s = 23 and 51 GeV,(σt = (39.1 ± 0.7) mb and σt = (40.5± 0.8) mb, respectively) can be compared with the values obtained at the same energies by using Coulomb scattering to normalize the cross-section scale1): (38.9 ± 0.7) mb and (40.2 ± 0.8) mb, re­spectively. The average difference is (0.25 ± 0.75) mb, well within the

- 9 -

errors. This good agreement demonstrates that at these two energies the evaluations of the luminosity by the Van der Meer and the Coulomb scattering methods agree within (1 ± 4)%.

The present data are in excellent agreement with the results of Amendolia et a13). who measured σt by counting the to ta l number of proton-proton in te rac t ions .

The main conclusion of the present experiment is that the proton-proton cross-section increases by

∆σt = (4.1 ± 0.7) mb (7)

when the centre-of-mass energy increases from 23 to 53 GeV. The present ISR data alone may be fitted by a linear increase with s. On the other hand, Fig. 3 indicates that σt goes through a shallow minimum around s0 = 200 GeV2 where σt = σ0=(38.4 ± 0.3) mb. Thus, over a wider energy range, 100 s 2800 GeV2 an expression of the form

σ = σ0 + σ1 [n (s/s0]n (8)

provides a good fit to the data with σ1 = (0.9 ± 0.3) mb and n = 1.8 ± 0.4. Such an increase of the total nuclear cross-section with energy agrees, within a large error and over this energy range, with the Froissart limit, n = 2, which corresponds to the maximum rate of increase allowed by unitarity9).

Cosmic-ray data have recently been interpreted as suggesting a similar behaviour10) for σt. An increase of σin proportional to (n s)2 was first suggested by Heisenberg11) as a consequence of his bremsstrahlung model of multiple production.

The present results, together with previous data, lead to the following picture of proton-proton interactions at the highest energies attainable with present accelerators.

i) The slope b of the forward elastic differential cross section in-creases monotonically with energy 6,7). In the ISR energy range explored the increase is (11 ± 3)%.

ii) The ratio ρ of the real to the imaginary parts of the forward scattering amplitude increases from about -0.1 at Ös = 10 GeV 12) to a value consistent with zero, ρ = 0.025 ± 0.035 at Ös = 25 GeV 1).

- 10 -

iii) The total nuclear cross-section goes through a shallow minimum at Ös 15 GeV and then increases by nearly 5 mb as the energy in­creases to Ös = 53 GeV. In the ISR energy range the increase is (10 ± 2)%.

iv) The elastic cross-section σe1 starts to increase from a similar shallow minimum at a similar value of the centre-of-mass energy. In the ISR range the increase is (12 ± 4)%. This is understandable from points (i) and (iii) above, since integration of Eq. (5) gives σe1 σt2/b. (The change of slope beyond |t| 0.1 GeV2 gives a correction of a few per cent to this expression.)

v) The inelastic cross-section, σin = σt - σe1, thus also increases by about (10 ± 2)% in the ISR range.

The approximate equality of the relative increases of b, σt, σe1 and σin in the ISR energy range is consistent with a naïve optical model of an absorbing disc of constant opacity, since in such a picture all four quantities are proportional to R2, where R is the interaction radius of the scattering particles. Within this framework the data in­dicate that the radius R increases by about 5% when the centre-of-mass energy increases from Ös = 23 to 53 Gev.

The following final remarks may be made. It has been found by Denisov et a1. that the K+ - p cross-section increases, from a constant plateau of 17 mb below 20 GeV/c, to about 18 mb at 55 GeV/c. Considering the trend of the antiproton-proton cross-section shown in Fig. 3 it is conceivable that this cross-section passes through a minimum at a value of s 300 GeV2 before rising towards the p-p cross section, if there is a common high-energy limit as required by the Pomeranchuk theorem. One may then speculate that the K+ - p, p-p and -p total cross-sections begin to increase at energies connected with the magnitude of their plateau cross-sections, the rise appearing at lower energy the smaller the cross-section of the plateau. One would thus expect that the total cross-sections for K- - p, Π+ - p and Π- - p will also rise appreciably at laboratory momenta above 60 GeV/c, but in all three cases at momenta lower than that at which the p-p cross section begins to rise.

- 11 -

We are indebted to the staff of the various sections of the ISR Department for having provided the precise and stable beams vital to this experiment. In particular we are grateful to P. Bryant and K.M. Potter for their work in improving the precision of the luminosity measurements, and to J.-C. Brunet, J.-C. Godot, E. Jones and G. Rollinger for their essential contribution in the construction of the special vacuum chamber. We are very grateful for the help in data analysis given by Mme C. Busi. The excellent technical support of R. Donnet, M. Ferrat and C.A. Ståhlbrandt of CERN and of P. Gricia, R. Orlando and P. Veneroni of Rome is acknow­ledged. We also thank the Aachen-CERN-Genova-Harvard-Torino group for the use of one of their monitors and for useful discussions. Z. Dimcovski is thanked for valuable contributions to the experiment.

Table 1 Measured elastic differential cross section

ISR Momentum (GeV/c)

|t| (GeV2)

(dσ/dt) (mb/GeV2)

b (GeV-2)

eb|t| extrapol­ation factor (dσ/dt)t=0 (mb/GeV2)

(11.8+11.8) 8.1 10-3 71.0±1.5 11.8 1.10 78.1±1.7

(15.4+15.4) 13.5 10-3 71.0±1.6 12.3 1.18 83.8±1.9

(22.6+22.6) 17.5 10-3 73.8±1.7 12.8 1.25 92.3±2.2

(26.6+26.6) 23.0 10-3 70.6±1.8 13.1 1.35 95.4±2.6

Table 2 Point-to-point errors

Source of error Percentage standard deviation on (dσ/dt)t=0 Source of error

11.8 GeV/c

15.4 GeV/c

22.6 GeV/c

26.6 GeV/c

Monitor constant ∆σM ± 2.0% ±2.0% ±2.0% ±2.0%

Statistics < 0.5% <0.5% <0.5% <0.5%

Subtraction of in­elastic background

± 0.5% ±0.7% ±1.0% ±1.5%

Coulomb subtraction ± 0.3% ±0.1% - -

Error in the slope parameter (∆b = ± 0.5 GeV-2)

± 0.4% ±0.6% ±0.7% ±1.0%

Overall error ± 2.2% ±2.3% ±2.4% ±2.7%

REFERENCES

1. U. Amaldi, R. Biancastelli, C. Bosio, G. Matthiae, J.V. Allaby, W. Bartel, M.M. Block, G. Cocconi, A.N. Diddens, R.W. Dobinson, J. Litt and A.M. Wetherell, Phys.Letters (in print).

2. M. Holder, E. Radermacher, A. Staude, G. Barbiellini, P. Darriulat, M. Hansroul, S. Orito, P. Palazzi, A. Santroni, P. Strolin, K. Tittel, J. Pilcher, C. Rubbia, G. De Zorzi, M. Macri, G. Sette, C. Grosso-Pilcher, A. Fainberg and G. Maderni, Phys.Letters 35B (1971) 361.

3. S.R. Amendolia, G. Bellettini, P.L. Braccini, C. Bradaschia,R. Castaldi, V. Cavasinni, C. Cerri, T. Del Prete, L. Foà, P. Giromini, P. Laurelli, A. Menzione, L. Ristori, G. Sanguinetti, M. Valdata, G. Finocchiaro, P. Grannis, D. Green, R. Mustard, R. Thun, Phys. Letters (1973)

4. S. Van der Meer, CERN Internal Report ISR-PO/68-31 (1968), unpublished.

5. K.M. Terwilliger, Proceedings of the International Conference on High Energy Accelerators (CERN), p. 53 (1959).

6. U. Amaldi, R. Biancastelli, C. Bosio, G. Matthiae, J.V. Allaby, W. Bartel, G. Cocconi, A.N. Diddens, R.W. Dobinson, V. Elings, J. Litt, L.S. Rochester and A.M. Wetherell, Phys.Letters 36B (1971) 504.

7. M. Holder, E. Radermacher, A. Staude, G. Barbiellini, P. Darriulat, M. Hansroul, S. Orito, P. Palazzi, A. Santroni, P. Strolin, K. Tittel, J. Pilcher, C. Rubbia, G. De Zorzi, M. Macri, G. Sette,C.Grosso-Pilcher, A. Fainberg and G. Maderni, Phys.Letters 35B (1971) 355.

M. Holder, E. Radermacher, A. Staude, G. Barbiellini, P. Darriulat, P. Palazzi, A. Santroni, P. Strolin, K. Tittel, J. Pilcher, C. Rubbia, M. Bozzo, G. De Zorzi, M. Macri, S. Orito, G. Sette, A. Fainberg, C. Grosso-Pilcher and G. Maderni, Phys.Letters 36B (1971) 400.

G. Barbiellini, M. Bozzo, P. Darriulat, G. Diambrini-Palazzi, G. De Zorzi, A. Fainberg, M.I. Ferrero, M. Holder, A. McFarland, G. Maderni, S. Orito, J. Pilcher, C. Rubbia, A. Santroni, G. Sette, A. Staude, P. Strolin and K. Tittel, Phys.Letters 39B (1972) 663.

Table 3 Total, elastic and inelastic cross sections

ISR momenta GeV/c

c.m. energy Ös (GeV)

Equivalent laboratory momentum (GeV/c) σt

(scale error=±0.6 mb)*)

(mb)

σe1 (scale error=±0.3 mb)*)

(mb)

σin (scale error=±0.5 mb)*)

(mb)

(11.8+11.8) 23.5 290 39.1±0.4 6.8±0.2 32.3±0.4

(15.4+15.4) 30.6 500 40.5±0.5 7.0±0.2 33.5±0.4

(22.6+22.6) 44.9 1070 42.5±0.5 7.5±0.3 35.0±0.5

(26.6+26.6) 52.8 1480 43.2±0.6 7.6±0.3 35.6±0.5

*) When comparing with results of other experiments the point-to-point errors should be combined quadratically with the scale errors.

REFERENCES (cont'd)

8. S.P. Denisov, S.V. Donskov, Yu.P. Gorin, A.I. Petrukhin, Yu.D.Prokoshkin, D.A. Stoyanova, J.V. Allaby and G. Giacomelli, Phys.Letters 36B (1971) 415.

J.W. Chapman, N. Green, B.P. Roe, A.A. Seidl, D. Sinclair, J.C. Van der Velde, C.M. Bromberg, D. Cohen, T. Ferbel, P. Slattery, S. Stone and B. Werner, Phys.Rev.Letters 29 (1972) 1686.

G. Charlton, Y. Cho, M. Derrick, R. Engelmann. T. Fields, L. Hyman, K. Jaeger, U. Mehtani, B. Musgrave, Y. Oren, D. Rhines. P. Schreiner, H. Yuta, L. Voyvodic, R. Walker, J. Whitmore, H.B.Crawley, Z. Ming Ma and R.G. Glasser, Phys.Rev.Letters 29 (1972) 515.

F.T. Dao, D. Gordon, J. Lach, E. Malamud, T. Meyer, R. Poster and W. Slater, Phys.Rev.Letters 29 (1972) 1627.

9. M. Froissart, Phys.Rev. 123 (1961) 1053.

A. Martin, Phys.Rev. 129 (1963) 1432 and Nuovo Cimento 42 (1966) 930.

10. G.B. Yodh, Yash Pal and J.S. Trefil, Phys.Rev.Letters 28 (1972) 1005.

11. W. Heisenberg, in Kosmische Strahlung (Springer Verlag 1953) p. 148.

12. G.C. Beznogikh, A. Bujak, L.F. Kirillova, B.A. Morozov, V.A. Nikitin, P.V. Nomokonov, A. Sandacz, M.G. Shafranova, V.A. Sviridov, Truong Bien, V.I. Zayachki, N.K. Zhidkov and L.S. Zolin, Phys.Letters 39B (1972), 411, and Dubna preprint E1-6613 (1972), to be published in Nucl.Physics.

Figure captions

Fig. 1 : General layout of the experimental apparatus and sketch of the disposition of hodoscopes in the special vacuum chamber sections.

Fig. 2 : Three-dimensional representation of the coincidence rate be­tween the central element of hodoscope A and the 35 ele­ments of hodoscope B obtained in a run of about one hour at (26.6 + 26.6) GeV/c.

Fig. 3 : Total proton-proton cross-sections as a function of the square of the centre-of-mass energy, s, and of the equivalent laboratory momentum. The general trends of the proton-proton data below 15 GeV/c and of the antiproton-proton cross-sections are indicated by smooth curves. The previous high-energy data are taken from references 1, 2 and 8. When comparing the results of the present experi­ment with lower energy data, a systematic error of ±0.6 mb should be combined with the point-to-point errors shown in the figure.

FIG. 1

FIG: 2

FIG: 3

EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH

MEASUREMENT OF THE TOTAL PROTON-PROTON CROSS-SECTION AT THE ISR*)

S.R. Amendolia, G. Bellettini**), P.L. Braccini, C. Bradaschia, R. Castaldi†), V. Cavasmni, C. Cerri**), T. Del Prete,

L. Foa**), P. Giromini, P. Laurelli, A. Menzione, L. Ristori, G. Sanguinetti and M. Valdata

Istituto Nazionale di Fisica Nucleare, Sezione di Pisa Istituto di Fisica dell'Università, Pisa

Scuola Normale Superiore, Pisa G. Finocchiaro, P. Grannis**), D. Green, R. Mustard and R. Thun

State University of New York Stony Brook, New York

ABSTRACT

We present the first results of a measurement of the total cross-section σT in proton-proton collisions at equivalent laboratory momenta between 291 and 1480 GeV/c at the CERN Intersecting Storage Rings (ISR). The method is based on the measurement of the ratio of the total inter­action rate and the machine luminosity. The data show an increase of about 10% in σT in this energy interval.

Geneva - February 1973 (Submitted to Physics Letters)

*) Work supported in part by the Consiglio Nazionale delle Ricerche of Italy, and by the National Science Foundation, USA.

**) These authors have held CERN visiting scientist positions. †) Present address: State University of New York, Stony Brook, New York.

The simplest and most fundamental measure of the size of the proton as observed in very high energy p-p collisions is the total cross-section. The lower energy accelerator data have resulted in the expectation that σT should remain essentially constant through the ISR energies, and much of the phenomenological description of strong interactions in the ISR range has been based on the notion that we have nearly reached the energy-independent regime of hadron physics. In this paper we report a measure­ment of σT at four energies and find that there is an appreciable increase between 291 and 1480 GeV/c equivalent laboratory momentum.

At a machine with two colliidng beams, one cannot measure σT with a traditional transmission experiment. We instead find σT from the detected rate RT of all interactions through the expression

RT = σT L , (1)

where L is the luminosity of the beams. The luminosity represents the overlap of the two beam fluxes in the intersection region, and replaces the product of beam intensity times number of targets/cm2 in a conventional transmission experiment. In terms of the ISR parameters,

L I 1 I 2

1

c e2 tg α/2 heff

, (2)

where I 1 and I2 are the beam currents, e is the charge of the proton, c the velocity of light, and α the crossing angle of the two beams. The effective height h e f f is defined in terms of integrals over the direction (vertical) perpendicular to the plane of the two beams, as

1 h e f f

Ö ρ1(z) ρ2(z) dz Ö ρ1(z) dz Ö ρ2(z) dz.

(3)

Here ρ1 and ρ2 are the beam densities as a function of z, the vertical coordinate. Inasmuch as all parameters in Eq. (2) except heff are known or measured during ISR operation to better than 0.1%, the determination of becomes the most delicate task in measuring L.

In the present letter, a brief description of the experimental appara­tus and most relevant information on the procedure followed to measure σT are given. More details, both on the detectors and on the data reduction, can be found in a forthcoming paper1).

- 2 -

The general layout of the experiment is shown in Fig. 1. The basic trigger requires at least one charged particle in cones surrounding each beam emerging from the interaction region. Each arm of the apparatus con­sists of hodoscopes H1, H2, H3, H4. Hodoscopes H1 and H2 are in coinci­dence and detect particles produced at angles 4° q 30°. In a similar way, the coincidence of H3 and H4 covers angles 0.8° q 7°. Each hodoscope consists of eight triangular counters, dividing the total azimuth into octants (Fig. 2a).

Two large-angle hodoscopes (L and Ls ) surround the interaction region and cover the angular interval from ~ 40° to 90° over nearly the full azi­muth (see Figs. 1 and 2b). In order to detect those events in which the charged particles are emitted at q 40° in one hemisphere, the coincidence (L • Ls ) is used in the trigger. This signal is set in coincidence with one of the forward cones and added to the main trigger; by symmetry one knows the contribution of these large-angle particles in coincidence with the other cone.

The trigger is completed by small hodoscopes (TB) on each arm, posi­tioned downstream of hodoscope H4 in the region where the vacuum pipe has narrowed to an elliptical cross-section (see Fig. 2c). These hodoscopes are treated logically as small-angle elements of (H3 • H4).

In order to measure the emission angle of the produced particles, used to calculate the fraction of events lost by the trigger (see below), two additional hodoscopes H2q and H4q are set behind the trigger hodoscopes H2 and H4. The structure of these counters is shown in Fig. 2d. The **********L-hodoscope is also split into approximate q-bins (see Fig. 2b).

When a trigger occurs, the information pertinent to an event is trans­ferred to an on-line computer via a CAMAC data acquisition system. This information includes a bit (fired or not fired) for each counter of the hodoscopes, clock readings of live time, and several digitized time-of-flight (TOF) differences between hodoscopes (H4left - H4right, H4left - H2right, H2left - H4right, H2left - H2right, H4left - L, H2left - L). The fast logic is inhibited during data acquisition. The event rate entering into the cross-section was computed as the inverse of the average live time before a beam-beam event was recorded.

- 3 -

The resolving time of the main trigger was kept rather wide, ±30 nsec, and accepted an appreciable amount of background events due to jets of secondaries generated in beam-gas or beam-pipe interactions and accompany­ing the two beams. The separation of beam-beam events from single-beam background was obtained by analysing the previously mentioned TOF distri­butions, in which background events were concentrated in peaks well se­parated from those of beam-beam events. The shapes of the TOF spectra for background events were measured in separate runs with only one beam circula­ting in the machine. These spectra were normalized to the background peaks in the beam-beam runs and subtracted. We have checked the accuracy of the background subtraction by altering the procedure for extracting events from the various TOF spectra.

A flat background of less than 1% due to accidental hodoscope counts has been subtracted from the sample. The loss of good events owing to accidental start or stop of the TOF circuits was monitored in test runs taken in normal beam conditions, but triggering the electronics with a pulse generator. This loss was typically 1% and was added to the measured beam-beam rate.

Because of the central importance in our experiment of knowing the luminosity, we now discuss three independent approaches to the determina­tion of heff, related to L by Eq. (2).

Before each data-taking run, three separate sets of scintillator monitors selecting different samples of beam-beam events were calibrated to give heff by the Van der Meer method 2). In analogy with Eqs. (1) and (2)

RM = KM I1I2

heff, (4)

where RM is the monitor rate of beam-beam events and KM is the calibration constant. The Van der Meer (VDM) method consists in displacing the beams vertically with respect to each other and measuring RM as a function of re­lative beam displacement δ. The value of heff (t = 0) is then given as the ratio of the area under the displacement curve to the rate at the top of the curve, so that

KM = 1

I 1 I 2 ∫ RM(δ) dδ = 1 I1 I2

RMtop heff(t = 0) (5)

- 4 -

The area under the displacement curve was obtained by numerical integra­tion and also by fitting the data with simple functions such as a Gaussian The calibration constants were insensitive to within 1% to the method used to calculate the area. The heff value at any later time was obtained from the measured time dependences of RM and I1, I 2 and Eq. (4). The values obtained from our different monitors agreed to within 1%.

In order to check the displacement scale used in the Van der Meer method, we have employed a counter-spark chamber telescope, positioned in the horizontal plane, viewing the intersection region at 90° from inside the ISR rings. Nearly horizontal tracks can be projected back to the ver­tical plane at the beam centre. We have displaced the two beams equally in the same direction and measured the centre of the beam-beam profile. In addition, we have displaced a single beam through a dilute gas of ti­tanium atoms evaporated from a source near the interaction region and have determined the centre of the distribution. These measurements give for the ratio of spark chamber scale to ISR scale 1.012 ± 0.010 and 1.000 ± 1.012, respectively. We thus assign an energy-independent normalization to the luminosity (and hence σT) of ±2%.

The second method of obtaining heff employs the spark chamber telescope. Using the titanium source, we measure the individual beam profiles r1(z) and r2(z) which from Eq. (3) yield h e f f . The trigger for this measurement selects a recoil proton from quasi-elastic beam-gas scattering with momen­tum greater than 600 MeV/c in the telescope and a small-angle particle along one of the beams. Events with particles elsewhere are rejected. The trig­ger topology allows identification of beam 1 (B1) or beam 2 (B2) events with a probability of misidentifying the beam of less than 3%. Values of heff obtained in this way are given in Table 1 and compared with the VDM values for the same time.

The third approach is provided by observing the beam-beam (BB) over­lap r1(z)r2(z) directly. The spark chambers are triggered during normal beam conditions by a pion of momentum greater than 190 MeV/c in the tele­scope and small-angle particles in both hemispheres to ensure BB events. This method is not fully independent of the second one, since one must know the relative widths and central positions of the two beams in order to extract heff from the observed BB overlap. The usual sequence of spark chamber runs was BB, B1,B2, and again BB. The widths and centres of Bl and

- 5 -

B2 profiles are used to calculate the correction factor, usually close to one, required to analyse the BB profiles. Table 1 gives heff values from the BB measurements.

The resolution in the vertical beam coordinate z in the spark chamber measurements is mostly due to multiple scattering in the vacuum pipe wall and in the chambers themselves. It is to a lesser extent due to the in­trinsic chamber resolution and the track projection error across the beam width. These effects have been computed with detailed Monte Carlo cal­culations. The probable error in the resolution is estimated to be ≤ 10%, which causes a possible systematic error in spark chamber values of heff of ≤ 3%.

The listed errors in Table 1 for spark chamber measurements are stat­istical only, while those on the VDM method are not only statistical, but also include the uncertainties arising from fitting the VDM displacement curves. Agreement between spark chambers and VDM is generally within 3% and consistent with the errors. Only VDM values of heff have been used to obtain σT in this paper and have an estimated accuracy of ±2%. The spark chamber measurements have a somewhat greater uncertainty but exclude the possibility of large (> 3%) errors in the luminosity.

The ratio of the measured rate of beam-beam interactions and the luminosity gives the partial cross-section detected by the apparatus. The fourth column of Table 2 shows the values obtained at incident beam momen­ta of 11.8, 15.4, 22.6, and 26.6 GeV/c.

In order to obtain the total cross-section, a correction must be made for events not accepted by the trigger. The most important loss is due to protons scattered elastically at angles smaller than the inner edge of the TB counters. It should be observed that such protons emitted towards the small-angle detectors can also fail to give a trigger, owing to mul­tiple scattering and interactions in the pipes. The over-all loss was calculated with the Monte Carlo method and with known parameters of elastic scattering3). The results are given in column 5 of Table 2. Quoted errors are due to uncertainties in the elastic cross-section, in the geometry of detectors and interaction diamond, and in the model adopted to describe proton-pipe interactions.

- 6 -

A small fraction of inelastic events fail to trigger because the charged particles are all emitted towards the beam exit holes in H4 or towards the gaps 30° q < 40° between H2 and L.

The loss of inelastic events due to charged particles directed inside the beam exit holes has been estimated by plotting the trigger rate as a function of the maximum angle of the produced prongs in either cone. The amount of elastic events contained in this sample was subtracted. The dis­tribution of the remaining events was extrapolated to zero angle, and was used to calculate the loss inside the pipes. The result at the various energies is given in the sixth column of Table 2. The errors include an estimate of possible systematic effects. The loss of events due to all charged particles of one hemisphere being produced in the gap between H2

and L has been studied and found to correspond to less than 0.05 mb at all momenta. This loss has been neglected.

The final values for σT are quoted in the seventh column of Table 2 and are shown in Fig. 3, together with values from Serpukhov4) and NAL5-7). The errors correspond to root-mean-square addition of the errors on the entries of columns 4, 5, and 6 of Table 2. They are dominated by the 2% error taken for the luminosity determination. In addition, as explained before, we associate a ±2% over-all normalization error common to all momenta arising from possible systematic effects in the luminosity scale.

We note the increase in total cross-section of nearly 4 mb within the energy interval studied. These data are in excellent agreement with recently available measurements8) at the ISR which employ the elastic cross-section and the optical theorem to obtain σT . They also agree at our lowest momentum with the highest energy data at NAL7). The existence of a rise in σT at energies above the ISR range has already been suggested from cosmic-ray measurements9). The possibility of rapidly rising total cross-sections at very high energies has been considered theoretically by Heisenberg10), and by Cheng and Wu11). The presence of an energy dependence in σT indicates that if an asymptotic limit exists, it has not been reached at ISR energies, and points up the interest in extending all total cross-section measurements to higher energies.

- 7 -

We would like to thank all the people who have contributed to the success of this experiment, and in particular the ISR staff for the ex­cellent operation of the machine and the CERN Directorate for their warm support. We appreciate the encouragement and the help in Italy given by Professors C. Villi and G. Stoppini, and the advice of Professors M.L. Good, J. Kirz and C.N. Yang in Stony Brook. The help of J. Renaud has been es­sential for the smooth running of the experiment. Our group technicians A. Bechini and G. Mugnai, and all technicians of the Physics Department of the University of Pisa, have given a decisive and essential contribution. Dr. G. Ciancaglini has led the design and installation of the counter hodoscopes with great enthusiasm and competence.

- 8 -

Table 1

Measured effective heights referred to a common time

Beam momentum (GeV/c)

Date (1972)

heff (mm) Beam momentum (GeV/c)

Date (1972) Van der Meer

method a) Beam 1 and

beam 2 profiles Beam 1 - beam 2 overlap profile

11.8 14 Nov. 8.12 ± 0.14 8.11 ± 0.14 8.47 ± 0.30

15.4 18 Dec. 7.90 ± 0.08 7.60 ± 0.11 7.63 ± 0.13

22.6 15 Dec. 6.10 ± 0.12 6.12 ± 0.19 5.83 ± 0.08

26.6 19 Nov. 6.15 ± 0.09 6.42 ± 0.18 6.16 ± 0.12

a) There is a possible ±2% scale error common to all Van der Meer values.

- 9 -

Table 2

Summary of results on total cross-section

Beam momentum

c.m. energy squared

Equivalent lab. beam momentum

Detected cross-section

Increment for elastic loss

Increment for inelastic loss σT

(GeV/c) (GeV)2 (GeV/c) (mb) (mb) (mb) (mb)

11.8 548 291 38.66 ± 0.79 0.54 ± 0.10 0.10 ± 0.02 39.30 ± 0.79

15.4 932 496 39.93 ± 0.81 0.75 ± 0.10 0.17 ± 0.04 40.85 ± 0.82

22.6 2005 1068 40.69 ± 0.84 1.54 ± 0.15 0.34 ± 0.10 42.57 ± 0.86

26.6 2776 1480 40.53 ± 0.83 1.95 ± 0.20 0.50 ± 0.12 42.98 ± 0.84

- 10 -

REFERENCES

1) Pisa-Stony Brook Collaboration, "Total cross-section measurement at the ISR", submitted to Nuovo Cimento.

2) S. Van der Meer, CERN Internal Report ISR-PO/68-31 (1968), unpublished.

3) U. Amaldi, R. Biancastelli, C. Bosio, G. Matthiae, J.V. Allaby, W. Bartl, G. Cocconi, A.N. Diddens, R.W. Dobinson and A.M. Wetherell, submitted to Physics Letters.

G. Barbiellini, M. Bozzo, P. Darriulat, G. Diambrini-Palazzi, G. De Zorzi, A. Fainberg, M.I. Ferrero, M. Holder, A. McFarland, G. Maderni, S. Orito, J. Pilcher, C. Rubbia, A. Santroni, G. Sette, A. Staude, P. Strolin and K. Tittel, Phys. Letters 39 B, 663 (1972).

4) S.P. Denisov, S.V. Donskov, Yu.P. Gorin, A.I. Petrukhin, Yu.D. Prokoshkin, D.A. Stoyanova, J.V. Allaby and G. Giacomelli, Phys. Letters 36 B, 415 (1971).

5) J.W. Chapman, N. Green, B.P. Roe, A.A. Seidl, D. Sinclair, J.C. Van der Velde, C M . Bromberg, D. Cohen, T. Ferbel, P. Slattery, S. Stone and B. Werner, Phys. Rev. Letters 29, 1686 (1972). (100 GeV/c data.)

6) G. Charlton, Y. Cho, M. Derrick, R. Engelmann, T. Fields, L. Hyman, K. Jaeger, U. Mehtani, B. Musgrave, Y. Oren, D. Rhines, P. Schreiner, H. Yuta, L. Voyvodic, R. Walker, J. Whitmore, H.B. Crawley, Z. Ming Ma and R.G. Glasser, Phys. Rev. Letters 29, 515 (1972). (200 GeV/c data.)

7) F.T. Dao, D. Gordon, J. Lach, E. Malamud, T. Meyer, R. Poster and

W. Slater, Phys. Rev. Letters 29, 1627 (1972). (300 GeV/c data.)

8) See U. Amaldi et a1., Reference 3.

9) G.B. Yodh, Yash Pal and J.S. Trefil, Phys. Rev. Letters 2 8 , 1005 (1972). 10) W. Heisenberg, Kosmische Strahlung (Springer Verlag, Berlin, 1953),

p. 148.

11) H. Cheng and T.T. Wu, Phys. Rev. Letters 24, 1456 (1970).

- 11 -

Figure captions

Fig. 1 : Schematic layout of the experiment. H1, ..., H4, counter hodoscopes, binned in f-octants. H2q, H4q, counter hodoscopes comprising four quadrants split into q-bins. L, double-layer counter hodoscope box (four planes of scintillator/lead/scintillator sandwich). Ls, small counter box (four counters) surrounding the intersection. TB, scintillation counters leav­ing minimum clearance for the beam pipes. Some additional monitor counters are not shown in the figure.

Fig. 2 : Schematic drawing of hodoscope counters.

a) H1 hodoscope. Hodoscope H2 is similar, but the f-bins are rotated by Π/16. Hodoscopes H3 and H4 are like H1, H2, but with no off-centre hole.

b) L-box. Only the first layer is shown. The second layer is behind it, with a lead plate in between.

c) TB counters.

d) q-hodoscopes. The outer rings are split into octants, the inner rings into quadrants.

Fig. 3 : Plot of the results versus equivalent beam momentum. The Serpukhov (Ref. 4) and NAL (Refs. 5-7) data are shown for com­parison.

: Data of Ref. 4; O : Data of Refs. 5-7; : This experiment.

FIG. 1

PISA-STONY BROOK SKETCH OF COUNTERS OF TOTAL CROSS-SECTION EXPERIMENT

a ) -hodoscope b) L - box

c) TB counters d ) - hodoscope

FIG. 2

FIG. 3