Proton Recoil Polarization in the 4 He(e,e’p) 3 H, 2 H(e,e’p)n, and 1 H(e,e’p) Reactions SHMS Commissioning Session, Hall C Workshop. August 20, 2011

Proton Recoil Polarization in the Proton Recoil Polarization in the 44He(e,e’p)He(e,e’p)33H, H, 22H(e,e’p)n, and H(e,e’p)n, and 11H(e,e’p) ReactionsH(e,e’p) Reactions

SHMS Commissioning Session, Hall C Workshop. August 20, 2011.SHMS Commissioning Session, Hall C Workshop. August 20, 2011.

Spokespersons:E.J. Brash, G.M. Huber,R. Ransome, S. Strauch

2Dr. Garth Huber, Dept. of Physics, Univ. of Regina, Regina, SK S4S0A2, Canada.

Scientific ObjectivesScientific Objectives

Investigate the role of nuclear medium modifications via proton Investigate the role of nuclear medium modifications via proton recoil polarization in quasielastic (e,e’p)recoil polarization in quasielastic (e,e’p)

High sensitivity to nucleon structure while at same time least High sensitivity to nucleon structure while at same time least sensitive to conventional nuclear medium effects.sensitive to conventional nuclear medium effects.

4 2 1, , ( , ' )He H H e e p��

Key featuresKey features ImpactImpact

Wide coverage of proton Wide coverage of proton virtualities at Qvirtualities at Q22=1.0 GeV=1.0 GeV22

Study the momentum (virtuality) Study the momentum (virtuality) dependence of nucleon medium effectsdependence of nucleon medium effects

44He, He, 22H, H, 11H targetsH targets Study the density dependence of Study the density dependence of nucleon medium effectsnucleon medium effects

High-precision data point of the High-precision data point of the proton recoil polarization in proton recoil polarization in 44He(e,e’p)He(e,e’p)33H at QH at Q22=1.8 GeV=1.8 GeV22

Compare free and bound proton recoil Compare free and bound proton recoil polarizations where models predict polarizations where models predict largest sensitivity to effect of in-medium largest sensitivity to effect of in-medium form factorsform factors


Kinematic SettingsKinematic Settings

QQ22=1.0:=1.0: 1-pass 2.25 GeV beam, measure 1-pass 2.25 GeV beam, measure 11H, H, 22H, H, 44He(e,e’p)He(e,e’p) Approved for 25 days, beam currents 25-75Approved for 25 days, beam currents 25-75μμAA

QQ22=1.8:=1.8: 2-pass 4.40 GeV beam, measure 2-pass 4.40 GeV beam, measure 11H, H, 44He(e,e’p)He(e,e’p) Approved for 12.4 days, 75Approved for 12.4 days, 75μμAA

Scattered electron in SHMS in undemanding kinematics:Scattered electron in SHMS in undemanding kinematics:

1.68<P1.68<PSHMSSHMS<3.44 GeV/c<3.44 GeV/c 19.8519.85oo<<θθSHMSSHMS<29.75<29.75oo

Hall C Focal Plane Polarimeter in HMS:Hall C Focal Plane Polarimeter in HMS:

0.83<P0.83<PHMSHMS<1.15 GeV/c<1.15 GeV/c 43.9943.99oo<<θθHMSHMS<57.42<57.42oo

HMSHMS(proton)(proton)

SHMSSHMS(electron)(electron)

HMS FPPHMS FPP


11H(e,e’p) Scans a Key Part of the ExperimentH(e,e’p) Scans a Key Part of the Experiment

• Colors Colors indicate 7 indicate 7 different HMS different HMS settings in settings in each scan.each scan.

• SHMS setting SHMS setting could also be could also be varied to give varied to give good good coverage for coverage for optics checks.optics checks.

Coincidence scans at both QCoincidence scans at both Q22=1.0, 1.8 (GeV/c)=1.0, 1.8 (GeV/c)22.. Scans allow instrumental asymmetries of FPP to be studied, and Scans allow instrumental asymmetries of FPP to be studied, and

provide a reference for the polarization-transfer ratios.provide a reference for the polarization-transfer ratios. The e-p coincidence data could also be extremely useful for The e-p coincidence data could also be extremely useful for

understanding the SHMS optics, detector & trigger efficiencies.understanding the SHMS optics, detector & trigger efficiencies.

HMS (p) SHMS (e’)


Our Contributions to Construction/CommissioningOur Contributions to Construction/Commissioning

Construction:Construction: GH building SHMS Heavy Gas Cerenkov.GH building SHMS Heavy Gas Cerenkov.

Commissioning:Commissioning: General assistance with Hall C commissioning, manpower.General assistance with Hall C commissioning, manpower. We will in addition help the Hall C Collaboration understand We will in addition help the Hall C Collaboration understand

the SHMS optics, coincidence trigger, and detector the SHMS optics, coincidence trigger, and detector efficiencies through the analysis of our data (particularly the efficiencies through the analysis of our data (particularly the 11H(e,e’p) elastic coincidence scans).H(e,e’p) elastic coincidence scans).

We We are openare open to inviting additional hall users and staff to to inviting additional hall users and staff to participate in the experiment.participate in the experiment.

→ → Already working with Gep CollaborationAlready working with Gep Collaboration


Because of low proton momentum in the HMS, need thinner CHBecause of low proton momentum in the HMS, need thinner CH22 analyzers for some kinematic settings.analyzers for some kinematic settings.

S0 scintillator which replaced S2 in Gep-III is also not optimal.S0 scintillator which replaced S2 in Gep-III is also not optimal. covers too little of HMS focal plane and increases multiple covers too little of HMS focal plane and increases multiple

scattering.scattering.

Readiness: Planned work on FPP CHReadiness: Planned work on FPP CH22 Analyzers Analyzers

Will provide efficient triggering across focal plane while preserving Will provide efficient triggering across focal plane while preserving

good missing mass resolution.good missing mass resolution. Improved triggering also desirable for other FPP experiments.Improved triggering also desirable for other FPP experiments.

A straightforward project expected to take ~6 months.A straightforward project expected to take ~6 months.

Plan new FPP analyzers:Plan new FPP analyzers: Each FPP analyzer will consist of Each FPP analyzer will consist of

two removable 20cm CH2 layers, two removable 20cm CH2 layers, and a 5cm scintillator layer.and a 5cm scintillator layer.

Can restack existing CH2, but need Can restack existing CH2, but need 8 scintillator bars for each layer.8 scintillator bars for each layer.


Double Ratio Experiment insensitive to Double Ratio Experiment insensitive to absolute flux uncertainties absolute flux uncertainties (luminosity, (luminosity, global detector efficiencies, solid angles)global detector efficiencies, solid angles)

Our `signal’ is the modulation of Our `signal’ is the modulation of φφ-distribution relative to flat, unpolarized -distribution relative to flat, unpolarized baselinebaseline

A Potential Commissioning ExperimentA Potential Commissioning Experiment

' '

' 'x x

z zA H

P PR

P P

SHMS optics requirements not particularly demandingSHMS optics requirements not particularly demanding:: p(e,e’p) coincidences easier to understand than single arm (e,e’)p(e,e’p) coincidences easier to understand than single arm (e,e’) Only need SHMS to determine q-vector to 5mrad to know POnly need SHMS to determine q-vector to 5mrad to know P ’x’x to 1%. to 1%. SHMS settings:SHMS settings:

P<3.5 GeV/c, P<3.5 GeV/c, θθ>19>19oo

Missing mass resolution Missing mass resolution requirements are modestrequirements are modest

ππ00


Broader Benefits to Hall CBroader Benefits to Hall C

Although our experiment is able to meet its physics goals without a Although our experiment is able to meet its physics goals without a

detailed knowledge of detector efficiencies and electron spectrometer detailed knowledge of detector efficiencies and electron spectrometer

optics, the data we acquire will be very useful for the calibration of those optics, the data we acquire will be very useful for the calibration of those

experiments to follow.experiments to follow.

Detailed scans needed to determine FPP instrumental Detailed scans needed to determine FPP instrumental

asymmetries very useful for:asymmetries very useful for: Debugging SHMS+HMS coincidence trigger.Debugging SHMS+HMS coincidence trigger.

Determining SHMS detection efficiencies (both global and local).Determining SHMS detection efficiencies (both global and local).

Can we reproduce previously measured cross sections?Can we reproduce previously measured cross sections?

For similar reasons, an experiment was one of the HRSFor similar reasons, an experiment was one of the HRS22

commissioning experiments in Hall A.commissioning experiments in Hall A.

16 ( , ' )O e e p��

1 ( , ' )H e e p��


ProsPros Cons Cons

Polarization transfer technique Polarization transfer technique insensitive to most errors.insensitive to most errors.

11H(e,e’p) coincidence scans H(e,e’p) coincidence scans useful for detailed determination useful for detailed determination of SHMS optics, efficiencies, etc.of SHMS optics, efficiencies, etc.

We desire 1-2 pass beam, which We desire 1-2 pass beam, which is otherwise undersubscribed.is otherwise undersubscribed.

Scheduling flexiblity:Scheduling flexiblity: Since QSince Q22=1.0, 1.8 =1.0, 1.8

measurements have separate measurements have separate hydrogen elastics scans, they hydrogen elastics scans, they do notdo not need to be run need to be run consecutively.consecutively.

Don’t even need to keep FPP Don’t even need to keep FPP in HMS between the two runs.in HMS between the two runs.

Require installation of FPP in Require installation of FPP in HMS, with straightforward HMS, with straightforward modifications to optimize the modifications to optimize the FPP analyzers for low FPP analyzers for low momentum.momentum.

Otherwise, the experiment is Otherwise, the experiment is relatively simple, with little relatively simple, with little concern that the experiment concern that the experiment cannot run early.cannot run early.



44He(e,e’p)He(e,e’p)33H H QQ22 Distribution Distribution

Polarization-transfer data Polarization-transfer data effectively described by effectively described by in-medium in-medium electromagnetic form electromagnetic form factorsfactors or or charge-charge-exchange FSIexchange FSI..

For QFor Q22≥1.3 GeV≥1.3 GeV22 Madrid Madrid RWDIARWDIA and and Schiavilla Schiavilla (2010)(2010) results seem to results seem to agree.agree.

Our data will allow the Our data will allow the precision of the polarization precision of the polarization double ratios at Q2=1.0, 1.8 double ratios at Q2=1.0, 1.8 to be greatly improved.to be greatly improved.

Will R be reduced by 7% Will R be reduced by 7% with respect to with respect to Madrid Madrid RWDIA RWDIA / / SchiavillaSchiavilla??

≈7%


Compare knock-out from Compare knock-out from 44He and He and 22HH

Compare Compare 44He(e,e’p)He(e,e’p)33H and H and 22H(e,e’p)n Double RatiosH(e,e’p)n Double Ratios Previous Previous 22H data (H data (ΔΔ) are ) are

suggestively close to suggestively close to virtuality dependence of virtuality dependence of 44He (○) data.He (○) data.

Modern, rigorousModern, rigorous 22H(e,e’p)n H(e,e’p)n calculations including calculations including rescattering effects available.rescattering effects available. Reaction-dynamics Reaction-dynamics

effects and FSI will effects and FSI will change the ratio up to 5-change the ratio up to 5-8% in this kinematics8% in this kinematics

Any larger effects (35%?) Any larger effects (35%?) should be attributed to should be attributed to something else…something else…

Medium Effect (QMC)35% 4%

?


Broad Broad 44He(e,e’p) Virtuality CoverageHe(e,e’p) Virtuality Coverage

Probe the Probe the expected strong expected strong dependence of medium dependence of medium effects on the momentum of effects on the momentum of the bound nucleonthe bound nucleon

Significant improvement over Significant improvement over previous dataprevious data

QQ22=1.0 GeV=1.0 GeV22

Parallel kinematicsParallel kinematics ppmm=0, 140, 220 MeV/c=0, 140, 220 MeV/c Scan emphasizes x>1 region, Scan emphasizes x>1 region,

to reduce inelastic channels to reduce inelastic channels and probe genuine quasielastic and probe genuine quasielastic scatteringscattering

Medium Effect (QMC)Medium Effect (QMC)35% 4%35% 4%

2 2

p2

2 2 2 2A A-1 m m p

ν = p - m

= M - M + p - p - m

Proton off-shellness can be Proton off-shellness can be quantified via the nucleon virtualityquantified via the nucleon virtuality


KinematicsKinematics

Quasielastic scatteringQuasielastic scattering Parallel kinematicsParallel kinematics x>1, spectator forward to reduce x>1, spectator forward to reduce

inelastic channels and probe inelastic channels and probe genuine quasielastic scatteringgenuine quasielastic scattering

The off-shellness can be The off-shellness can be quantified as the nucleon quantified as the nucleon virtuality:virtuality:

Nucleon virtuality is a function of Nucleon virtuality is a function of the nucleon momentum only.the nucleon momentum only.

* ,q

2 2

22 2 2 2

1

p

A A m m p

p m

M M p p m

INITIAL STATE:

FINAL STATE:

3H

p

mp q p

4He

QQ2 2

(GeV(GeV22))ppmm

(MeV/c)(MeV/c)

TargetsTargets

1.01.0 0, +140, 0, +140, +220+220

44He, He, 22H, H, 11HH

1.81.8 00 44He, He, 11HH

Documents

Proton Recoil Polarization in the 4 He(e,e’p) 3 H, 2 H(e,e’p)n, and 1 H(e,e’p) Reactions SHMS Commissioning Session, Hall C Workshop. August 20, 2011