IP crossing-angle and LC technology recommendation Philip Bambade LAL, Orsay 5 th ITRP meeting, Caltech, USA Session on detector & physics issues June.

IP crossing-angle and LC technology recommendation

Philip BambadeLAL, Orsay

5th ITRP meeting, Caltech, USA Session on detector & physics issues

June 28, 2004

Philip Bambade LAL/Orsay

x-angle & LC technology choice ITRP 28/6/2004

2

Context warm LC c [mrad] 20 , 7

cold LC c [mrad] 20 , 7 , 0• magnitude important aspect of machine design

• TRC recommended (R2 item) that the technical pros / cons of the TESLA head-on scheme – especially the extraction – be critically reviewed and to consider also designs with a finite c – e.g. 20, 7 mrad or eventually other possibilities (0.6 and 2 mrad)

• LC scope calls for 2 ee IR with similar energy and luminosity, one of which with c ~ 30 mrad to enable a future -collider option

Importance for detector & physics ?



3

ITRP crossing-angle questions1. “The presence of a crossing angle, while not fully correlated with

the technology choice, will have experimental impacts upon the precision of measurement of energy, energy-wtd luminosity, and polarization. Discuss physics consequences of having 0 crossing angle with no final beam measurements possible, versus a finite crossing angle, which permits measurements of the spent beam.”

2. “In the case of a crossing angle, the beam axes differ from the magnetic field direction. What complication does this cause for the experiments? Does it argue for keeping the crossing angle as small as possible?”

3. “Are there differences in the coverage dictated by differences in the final focus elements for the two technologies?”



4

Energy and polarization from beam-based measurements



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BPMs

E/E ~ (1 – 2) 10-4

linac E spread dL/dE

also from Bhabhaanalyses

post – IP more difficult without large c

SPECTROMETRY pre – IP all designs

E/E ~ (1 – 2) 10-4

linac E spread with other pre-IP device



6

P/P ~ (2.5 – 5) 10-3

Compton scattering extrapolation

clearance from spent beam probes beam-beam effects

post – IP requires large c

POLARIMETRY pre – IP all designs

P/P ~ (2.5 – 5) 10-3

Compton scattering extrapolation

optics constraints

M. Woods et al. SLAC-PUB-10353



7

How important are additional post – IP spectrometer and polarimeter ?

Different systematics ! Errors Beam-beam effects correlations

21~

Physics needs : ~ 5 10-3 searches 2 10-3 HE SM

tests < 1 10-3 GigaZ

Precision of each pre- & post-IP measurement (1 – 2) 10-4 (2.5 – 5) 10-3

E P 2 10-4 mtop, mhiggs

5 10-5 mW , ALR



8

Full beam-beam effect ~ 3 - 4 lumi-weightedK. Mönig

• Post-IP can compare with / without collisions • Post-IP “magnifying glass” for beam-beam effect• Real conditions : must correlate to offsets, currents,...

mrad50 if P,S 0P,S

xx

x

x

0.0025

0.008



9

Effects from misalignment of solenoid and beam axes

steering and spin precession backgrounds



10

c 0 solenoid steers spin precesses

IP

IP y angle ~ 100 radIP y offset ~ - 20 m

(y) ~ 85 rad (y) ~ 3 nm

spin precession ~ 60 mrad if uncorrected ~ 0.2 % depolarization with perfect beams (or else larger)

c = 20 mrad

must compensate !

A.Seryi and B. Parker



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• Adds ~ 0.01 of Bz along x in detector• TPC tracking map Bz to 0.0005 to control distortions• Larger backgrounds and steering of the spent beam

Option for local correction with extra dipole fields within the detector + before + after

IP

With compensation

IP



12

New TESLA design, K. Büsser and A. Stahl

Beam – beam pairs in instrumented mask / BeamCAL

T. MaruyamaTotal pair statistics



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• c 20 mrad twice more energy from pairs in BeamCAL• Complex shapes, beam param. extraction more complicated

GeV / cm2 GeV / cm2

TESLA head-on TESLA c = 20 mrad

Cold head-on / c 20 mrad



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GeV / cm2 GeV / cm2

TESLA head-on TESLA c = 20 mrad

• for crossing angle, smaller background enhancement wrt headon if outgoing hole is increased ; also helps relax collimation requirements• if collimation requirements impose to increase the exit hole, then the vertex detector radius would increase as well in the head-on case

Collimation exit hole radius vertex detector radius



15

Total pair energy in Warm / Cold c 20 , 7 , 0 mrad

• Warm / R2cm / 20mrad with Serpentine ~ Cold / R1.2cm / 0mrad • Smallest effects for Warm / 7mrad• Total pair energy can be used for luminosity monitoring in all cases

T. Maruyama

out-going hole radius [cm] out-going hole radius [cm]

cold: Rincoming = Routgoingcold: Rincoming = Routgoing



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Forward Tracking Disks FTD

Hits on vertex detector

• Detector occupancies are up to factor 2 larger if c 20 mrad and the outgoing hole is not enlarged with respect to the head-on case• Still at tolerable levels • More on occupancies in H. Yamamoto’s talk on pile-up issues

c 20 mrad more backscattering into main

detector asymmetrical distributions Hits on forward chamber

New TESLA design, K. Büsser and A. Stahl



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Reduction in SUSY coverage from IR geometries with c 0

scenarios with quasi – degenerate mass spectra



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signal major background

ee 0 0 ee (e)(e) ~ 10 fb ~ 106 fb

Transverse view

Dark matter SUSY scenarios slepton & neutralino masses often very close (co-annihilation mechanism)

e.g. search & measure stau with m - 3 – 9 GeV

c 0 harder to eliminate signal – like - processes

P.B. et al. hep-ph/0406010

M. Battaglia et al. hep-ph/0306219

~



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Preliminary result benchmark point D’ with m- = 12 GeV

signal efficiency ~ 80% spectrum end-points preserved

ms= 0.18 GeV and and m = 0.17 GeV for this benchmark point smallest ms- detectable as function of veto angle and quality ?

After requiring N=2 Normalized for L=500fb-1

Same performance for both head-on and crossing-angle collisions




20

Preliminary resultbenchmark point D’ with m- = 5 GeV

Thrust axis angle in 3-dim

PT wrt thrust axisin the transverse plane

Azimuthal dependence of the transverse momentum

head-on crossing-angle

efficiency ~ 11 % ~ 8 %

Effect of 2nd hole after re-optimizing the analysis


c 20 mrad



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Luminosity, ECM and efficiency optimization benchmark point D’ with m- = 5 GeV mass precision wrt efficiency effect from 2nd hole only

Relative mass precision from cross-section measurements near the production threshold with negligible background

8%11%



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Importance of high veto efficiency BeamCAL

ee 0 0 ee (e)(e)

~ 10 fb ~ 106 fb

analysis ~ 1 fb ~ 600 fb

analysis + veto ~ 1 fb ~ 0.7 fb

veto ~ 0.999

S/N ~ 1

10 mrad

m - 5 GeV

~

S / B depends crucially on VETO for the HE electron superimposed on the pairs

c 20 mrad factor 2 increase in deposited pair background energy

Potential additional effects from pile-up will be addressed in K. Mönig’s and H. Yamamoto’s talks



23

Summary : post-IP diagnostics• Post-IP energy spectrometry is desirable to complement the pre-IP

calibration and to give another handle on the luminosity spectrum. • It will be important to reach, together with analyses of dedicated

physics calibration channels, ultimate SM measurement precision. • The design of a post-IP spectrometer is more difficult without a

large enough c .• The same is true for post-IP polarimetry. A design seems quasi-

impossible in this case without a large enough c .• A post-IP polarimeter, correlated with other measurements of the

spent beam (orbits, intensities,…) is important to probe beam-beam depolarizing effects, in order to validate the simulation and assist in controlling the systematics involved.



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Summary : solenoid / c

• Steering and spin precession from the solenoid with c 20 mrad must be corrected.

• Adding steering dipoles within, before and after the detector can compensate for these effects. The additional B field must be taken into account in the tracking, especially in the context of correcting distortions in a TPC.

• For c 20 mrad, pair deposition in the instrumented mask and backscattering in the detector increase by factors 1.5 - 2, from the solenoid and beam axes misalignment and additionally from the compensating steering.

• Occupancies remain tolerable though some hit distributions become asymmetrical and contain structures complicating the interpretation.

• Such effects are less important for c 7 mrad.



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Summary : hermeticity• To enable precise mass measurements in SUSY models with

degenerate spectra typical of scenarios proposed to explain Dark Matter, it is critical to tag forward high energy electrons very well.

• The slepton detection efficiency and mass measurement precision are reduced for c 20 mrad , because of the 2nd hole for the in-coming beam and because of larger pair background.

• The reduction strongly depends on the mass difference between the sparticle considered and the lightest SUSY particle (the neutralino). It is largest for the smallest mass differences.

• In a realistic case study with stau (smuon) mass 5 (12) GeV heavier than the neutralino, efficiency losses from the 2nd hole were 25% (negligible), after re-optimizing the analysis.

• Meaningful estimates of further losses from the increased pair background, taking into account an appropriate optimization of the electron veto algorithm, are not yet available.

IP crossing-angle and LC technology recommendation Philip Bambade LAL, Orsay 5 th ITRP meeting, Caltech, USA Session on detector & physics issues June.

Documents

ip crossingangle

itrp crossingangle questions

finite crossing angle

beam axes

mrad lc scope

cold lc c mrad

beambased measurements

preip device slide