Hall A Collaboration Meeting, December 13-14, 2007

E03-104: Probing the Limits of the Standard Model of Nuclear Physics with

the 4He(e,e’p)3H ReactionExperiment Status Report

Jonathan DeGange (UG), Simona Malace (Post Doc),

Michael Paolone (GS), and Steffen StrauchUniversity of South Carolinaand the Hall A Collaboration

Hall A Collaboration Meeting, December 13-14, 2007Jefferson Lab, Newport News, VA

Hall A Collaboration Meeting, December 13-14, 2007

MotivationMotivation

Conventional Nuclear Physics: - we probe “point-like” nucleons + form-factors - reaction mechanisms: theoretically parameterized ignoring that the nucleon’s inner structure may be changed in the nuclear mediumQCD:

- nucleons: composite objects of quarks and gluons

A(e,e’p)B reactions

Is it because the possible medium modification of the nucleons structure is ignored in the conventional nuclear physics theories ?

Are the experimental results described by conventional nuclear physics theories?

If not…

Which approach would be more economical ?

Is it because there are not enough higher order corrections to the Born+IA ?

Hall A Collaboration Meeting, December 13-14, 2007

Theory: OverviewTheory: OverviewBorn + Impulse Approximation(IA)

( ) ( ) ( )e e ef ij r r r

( ) ( ) ( )N NN F N BJ r r J r

( )2 2

( 1)( ) ( )(2 )

e iq x yif N

dqW dx dy j x e J yq

•Theoretical calculations have to take into account the presence of the nuclear medium.

( , )f f fk k

( , )i i ik k

( , )q q

( , )N N NP E P

1 1 1( , )A A AP E P

( , )A A AP E P

Hall A Collaboration Meeting, December 13-14, 2007

In-Medium EffectsIn-Medium Effects

• Coulomb distortion of the electron wave function.Electron-photon vertex current:

• Off-shell effects (no unambiguous treatment): various prescriptions to impose current conservation. =>

• Many-body currents: IA = “zero order approximation” but realistically we need higher-order corrections to IA. =>

• Final-State Interactions: the nucleon can interact with its neighbors after has been struck by the photon. =>

• Medium modified form-factors: free or medium modified form-factors in the electromagnetic current operator? =>

Photon-nucleon vertex current:

•T. De Forest, Jr. Nucl. Phys. A392, 232 (1983) •D. Debruyne, et al. ,Phys. Rev. C 62, 024611 (2000)

•A. Meucci et al., Phys. Rev. C 66, 034610 (2002)•R. Schiavilla et al., Phys. Rev. Lett. 94, 072303 (2005)

•J. Udias et al., Phys. Rev. Lett. 83, 5451 (1999)•R. Schiavilla et al., Phys. Rev. Lett. 94, 072303 (2005)•P. Lava et al., Phys. Rev. C 71, 014605 (2005)

•D.H. Lu et al., Phys. Rev. C 60, 068201 (1999) •J. R. Smith and G. Miller, Phys. Rev. Lett. 91, 212301 (2003)

Hall A Collaboration Meeting, December 13-14, 2007

E03-104 in Hall AE03-104 in Hall A

• High density nucleus => any possible medium effects are enhanced.• Its relative simplicity allows realistic microscopic calculations.• Variety of calculations show that polarization-transfer observables in 4He(e,e’p)3H are influenced little by FSI, MEC…

4He:

1H:• 1H is baseline when estimating the effect of the medium on the polarization transfer ratio in 4He(e,e’p)3H .

Kinematics:

Targets:

Beam:

Detection system:

• Quasielastic scattering + low pm + symmetry about pm=0; Q2 = 0.8, 1.3 GeV2 .

• Longitudinally polarized electron beam; incoming electron helicity flipped to access both the transfer and induced polarization.

• Hall A High Resolution Spectrometers (HRS): FPP used to determine the polarization of the recoiling protons.

Hall A Collaboration Meeting, December 13-14, 2007

Analysis Analysis Status Status

Induced polarization.Instrumental asymmetries complicate the extraction of induced polarization and are typically caused by: - detector misalignment - detector inefficiencies - tracking problemsAlso…Input the available theoretical calculation in a new MC simulation: SIMC.

1H(e,e’p)Q2 = 0.8 GeV2

Polarization transfer. - spectrometer pointing and kinematics - maintenance of analysis code - implementation of COSY spin transport into PALMETTO code - study of systematic uncertainties - verification of COSY transport model

Hall A Collaboration Meeting, December 13-14, 2007

COSY COSY TransportTransport

xFP(A)

Analyzer

xTGT

COSY

xFP(C)

Compare

-10/

+10

mm

-5/+

5 m

m

•Small deviation due to higher order correction terms in the COSY transport matrix.

•Already good agreement between Analyzer and COSY.

Hall A Collaboration Meeting, December 13-14, 2007

•FPP chambers performance: inefficient regions cause of instrumental asymmetries.

•Instrumental asymmetries do not cancel, unless we have for the FPP acceptance and efficiency:

•Several attempts to correct for false asymmetries:-“mirror” test- inefficiency correction- revision of tracking algorithm: work in progress

Instrumental Asymmetries Instrumental Asymmetries Drift Chamber InefficienciesDrift Chamber Inefficiencies

( ) ( )A A

1 2 3

Hall A Collaboration Meeting, December 13-14, 2007

• The reconstruction resolution of the “real” and “mirror” tracks not comparable => method not good enough.

• Use only events for which Track(φ) and Track(φ+π) fall in an equally efficient region of the rear chambers. • Given a track, we need to reconstruct the “mirror” track:

““Mirror” TestMirror” Test

“Real” track reconstruction: wire hits “Mirror” track reconstruction: wire hits + proton-Carbon vertex.

Instrumental AsymmetriesInstrumental Asymmetries

J. Degange et al., “Study of instrumental asymmetries in Focal Plane Polarimeter (CEU Poster Session)”, Bull. Am. Phys. Soc. 52, Nr. 9, 55 (2007)

Hall A Collaboration Meeting, December 13-14, 2007

But it does not work!

* NseenNshould

• Inefficiency = Nseen/Nshould

• The inefficiency correction is applied event by event.

Inefficiency Inefficiency CorrectionsCorrections

vz [-3,+3] deg

vz [-45,-11] deg

vz [+11,+45] deg

vz [-11,-3] deg

vz [+3,+11] deg

v_r at z=403 cm, FPP [4,35] deg

Depending on the angle at which the proton hits the chambers, the inefficiency correction is different!

We would need an angle dependent inefficiency correction for each event in the “bad region”!

Instrumental AsymmetriesInstrumental Asymmetries

Hall A Collaboration Meeting, December 13-14, 2007

Instrumental AsymmetriesInstrumental Asymmetries

Standard tracking algorithm

To reconstruct a track: at least 1 hit in CH3 and CH4 and at least 3 in total.“Relaxed” tracking algorithm

To reconstruct a track: at least 1 hit in CH3 or CH4.- if 1 hit in each chamber => track- if 1 hit just in one of the chambers => hit + pC vertex = trackTo do:- apply the relaxed tracking algorithm to all events (same reconstruction resolution for all events)- use just one of the chambers for track reconstruction (=> we shouldn’t see in the u/v event distribution the “bad” regions originating from the chamber left aside)- …

Work in progress..

“relaxed” tracking algorithmstandard tracking algorithm

Hall A Collaboration Meeting, December 13-14, 2007

bound free

x x

z ze N e N

P PRP P

• RDWIA calculation: no MEC and no charge-exchange FSI terms.

• RMSGA calculation: similar procedure as RDWIA but different treatment of FSI =>FSI underestimated.• RDWIA and RMSGA models cannot describe the data.• Data effectively described by medium modified form factors (QMC, CQSM).

Preliminary data from E03-104 possibly hint an unexpected trend in Q2.

• Study shows: effect of MEC ~ 3-4%.

Polarization-Transfer in Polarization-Transfer in 44He(e,e’p)He(e,e’p)33HH

Hall A Collaboration Meeting, December 13-14, 2007

• R is suppressed ~ 4% from MEC.• Spin-dependent charge-exchange FSI suppresses R ~

6%.

Schiavilla et al. calculation provides for alternative explanation:

• Charge-exchange term not well constrained => need precise Py data.

Polarization-Transfer in Polarization-Transfer in 44He(e,e’p)He(e,e’p)33HH

Hall A Collaboration Meeting, December 13-14, 2007

Induced Induced PolarizationPolarization

• Py (measure of FSI) small and with only very weak Q2 dependence.

• RDWIA results consistent with data.

• Spin-dependent charge-exchange terms not well constrained by N-N scattering and possibly overestimated.

• E03-104 data will set tight constraints on FSI.

• RDWIA used to correct data for HRS acceptance (30% - 40% effect).

Hall A Collaboration Meeting, December 13-14, 2007

SummarySummary

Previous data on polarization transfer in 4He(e,e’p) – E93-094

-significant deviation from RDWIA results; data effectively described by proton medium modifications-alternative interpretation in terms of strong charge-exchange FSI; possibly inconsistent with Py

E03-104

-high statistics data at Q2 = 0.8 GeV2 and 1.3 GeV2

-polarization transfer can be studied in detail-much improved induced polarization data will be crucial to better constrain FSI-preliminary results from E03-104 already challenge available models-final results in 2008