MIT Symposium on the Quark Discovery 50 Years · MIT Symposium on the Quark Discovery 50 Years Friday October 25, 2019, 4:00 pm ... • Currently, George E. PakeProfessor of Physics,

Evidence for fractional charge of partons

MIT Symposium on the Quark Discovery50 Years

Friday October 25, 2019, 4:00 pmMIT Wong Auditorium, Tang Center (Building E51)

eP vs eN and electron vs neutrino scattering

Arie BodekUniversity of Rochester

https://whereis.mit.edu/?go=E51

My background• Started working for Jerry Friedman and Henry Kendall, as an undergraduate at MIT

in 1967

• Spent summer 1967 at SLAC working with John Litt on a first look at electron-deuteron quasielastic scattering and resonance production data.

• Wrote a MIT undergraduate (phenomenological) senior thesis in Spring 1968 on the extraction of neutron cross sections from deuterium data (Fermi motion)

• Continued as a graduate student in Fall 1968. Graduated with a PhD thesis in 1972. “Inelastic electron-deuteron scattering and the structure of the neutron’ (E49B)- which required an extensive study of Fermi motion effects in the deuteron an provided the evidence for fractionally charged quarks.

• Moved on to Caltech as Millikan Fellow and worked on Neutrino Experiment at Fermilab which provided more evidence for fractional charged quarks.

• Currently, George E. Pake Professor of Physics, University of Rochester, on CMS experiment at LHC and MINERvA neutrino experiment at Fermilab.

Quark Symposiuim MIT Oct. 2019 A. Bodek 2

(1) Measurement of Parton ChargesComparison of electron scattering from neutrons and protons

• Quark model - Isospin symmetry u, d in proton = d, u in neutron

Proton: (u u d) = (!"!"#$"); Neutron: (d d u) = (#$"

#$"

!")

and at low x add : u-ubar, d-dbar, s-sbar sea

Prediction F2N/F2P = 1 at small x (sea dominates)

Naïve quark model: average F2N/F2P = '( )

'()

*(

*( )

*()

'(

= +, = -.

If d quark dominates F2N/F2P > '(*(

= /0


1970 (1)

Resonance model (non partonic) can account for scaling by letting the number of resonances that are excited increase sufficiently with W (final state mass)

P. V. Landhsoff and J. C. Polkinghorne, Nucl. Phys. B19, 432 (1970)

Everywhere: F2N/F2P = !"

G. Domokos, S. Kovesi-Domokos, E. Schonberg, Phys. Rev. D3, 1184, and 1191 (1971).

Everywhere: F2N/F2P =0.70 to 0.78


1970 (2)Integrally charged partons (bare nucleons and bare pions):

T. D. Lee and S. D. Drell, Phys Rev. D5, 1738 (1972) • F2N/F2P =0 x à 1


End Station A spectrometers

8 GeV spectrometerHigh momentum transfer large angle, hydrogen and deuterium.Experiments E49B (grad student),

E87 (Postdoc).Bodek, Riordan {PhD. Theses)

6

20 GeV spectrometer(E49A).

Quark Symposiuim MIT Oct. 2019 A. Bodek

The SLAC primary e- beam was momentum analyzed, collimated, and transported to a liquid hydrogen and deuterium targets.

7

Entire allocated beam time was about 3 weeksQuark Symposiuim MIT Oct. 2019

A. Bodek

8

Entire allocated beam time was about 3 weeks

Within a day we found that the circulation fan of the deuterium target was not working. The beam heated the target (boiling), and the density was affected by the intensity of the electron beam.

Quark Symposiuim MIT Oct. 2019 A. Bodek

1.6 GeV spectrometer to the rescue: We quickly set it up to detect recoil protons from quasielastic electron-deuteron scattering, and serve as a density monitor.

9

8 GeV spectrometer1.6 GeV spectrometer

20 GeV spectrometer

Electron beamQuark Symposiuim MIT Oct. 2019

A. Bodek

Extended Data

• 1 ≤ q2 ≤ 20 GeV2; W2 ≤ 25 Gev2

• Extensive data sets with good statistics

• More measurements of proton W1 & W2 and first test of

neutron scaling

• Neutron measurements involved subtracting the Fermi motion

smeared proton values from the deuteron, and then

un-smearing the neutron.*

• *W. Atwood and G. B. West, A. Bodek,

Period Spectrometer Angle 0 Target

1967-1968 20 6, 10 Hydrogen

1970 8 18, 26, 34 Hydrogen, deuterium

1970 20 6, 10 Deuterium

~1975 1.6, 8, 20 many Hydrogen & Deuterium


Neutron

Proton, neutron, and deuteron exhibit similar scaling behavior



Discovery of gluon

Extraction of neutron cross sections from deuterium data


Neutron (extracted from deuterium data) to Proton Ratio• Data do not agree with

predictions of non-partonic models such as resonance models which predict

F2N/F2P =0.66 to 0.78


P. V. Landhsoff and J. C. Polkinghorne, Nucl. Phys. B19, 432 (1970)

F2N/F2P = !"

G. Domokos, S. Kovesi-Domokos, E. Schonberg, Phys. Rev. D3, 1184, and 1191 (1971).: F2N/F2P =0.70 to 0.78

Data do not agree with Integrally charged partons (bare nucleons and bare pions):T. D. Lee and S. D. Drell, Phys Rev. D5, 1738 (1972)

which predict

F2N/F2P =0 x à 1


Neutron (extracted from deuterium data) to Proton Ratio

• Quark model lower bound is 0.25

• Low value of 0.25 implies only d quark from neutron and u quark from proton contribute (at large x).


Neutron (extracted from deuterium data) to Proton Ratio1970-1974 partons have fractional charges (as expected for quarks)A. Bodek, MIT PhD 1972

180, 260, 340 SLAC E49Physical Review Letters. 30, 1087 (1973)

150, 190, 340 SLAC E87Physics Letters B51, 417 (1974)


Rejection letter from Physical Review Letters


Consequently: The definitive confirmation of fractional quark charges was published in Physics Letters in 1974

The story on the publication of our observation of scaling violations is similar.

(2) Measurement of Parton ChargesComparison of electron (N+P) and neutrino (N+P) scattering

neutrino scattrering is on nuclear targets (N+P)

• Proton: (u u d) = (!"!"#$"); Neutron: (d d u) = (#$"

#$"

!")

Neutrino scattering: quark weak charge = 2 (vector plus axial)

F2'(N+P)/ F2e(N+P)= = ()* +

,*

= )-. = 3.6

does not depend very much on x because it is on a nuclear targets(equal number of d type and u type quarks)



View of Gargamelle bubble chamber detector in the West Hall at CERN, February 1977 (Heavy Liquid Freon)

https://en.wikipedia.org/wiki/CERN


The chamber of Gargamelle is currently on exhibition at CERN


Experimental Study of Structure Functions and Sum Rules in Charge Changing Interactions of Neutrinos and anti-neutrinos on Nucleons -( Low Energy Neutrino Beam - Used a modified scaling variable)CERN Gargamelle Neutrino Collaboration (H. Deden (Aachen, Tech. Hochsch.) et al.).Nucl.Phys. B85 (1975) 269-288Consistent with fractional quark charges – but low Q2 meant large fraction of elastic events.

1975

Fractional Quark Charges Confirmed by the Higher Energy Caltech Fermilab Neutrino Experiment – 1978

(B. C. Barish, J. F. Bartlett, A. Bodek et al) Iron Target Sampling Calorimeter – spark chambers



Confirmed by High Energy Caltech-Fermilab Neutrino Experiment(Barish, Bodek, et al). 1978

CERN Gargamelle low energyNeutrino Beam 1975

Parton charges

By end of 1975 both:• The ratio of neutron/proton structure functions in

electron scattering (1974)• And the ratio of neutrino and electron structure

functions on nuclei (low energy 1975) , and high energy (1978)

Provide evidence that partons are fractionally charged (e.g. quarks)


Extra Slides (to be covered in Riordan’s Talk)


Neutron

Proton, neutron, and deuteron exhibit ~same scaling behavior

Scatter of point indicate some deviations from scaling



MIT Symposium on the Quark Discovery 50 Years · MIT Symposium on the Quark Discovery 50 Years Friday October 25, 2019, 4:00 pm ... • Currently, George E. PakeProfessor of Physics,

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