Jonathan DeGange (UG), Simona Malace (Post Doc), Michael Paolone (GS), and Steffen Strauch

1. E03-104: Probing the Limits of the Standard Model of Nuclear Physics with the 4He(e,e’p)3H Reaction Experiment Status Report Jonathan DeGange (UG), Simona Malace (Post Doc), Michael Paolone (GS), and Steffen Strauch University of South Carolina and the Hall A Collaboration Hall A Collaboration Meeting, December 13-14, 2007Jefferson Lab, Newport News, VA Hall A Collaboration Meeting, December 13-14, 2007

2. Motivation A(e,e’p)B reactions 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 medium QCD: - nucleons: composite objects of quarks and gluons Are the experimental results described by conventional nuclear physics theories? If not… ? Is it because there are not enough higher order corrections to the Born+IA ? ? Is it because the possible medium modification of the nucleons structure is ignored in the conventional nuclear physics theories ? ? ? Which approach would be more economical ? Hall A Collaboration Meeting, December 13-14, 2007

3. Theory: Overview Born + Impulse Approximation(IA) • Theoretical calculations have to take into account the presence of the nuclear medium. Hall A Collaboration Meeting, December 13-14, 2007

4. In-Medium Effects Electron-photon vertex current: • Coulomb distortion of the electron wave function. Photon-nucleon 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? => • 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

5. E03-104 in Hall A Targets: 4He: • 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… 1H: • 1H is baseline when estimating the effect of the medium on the polarization transfer ratio in 4He(e,e’p)3H . Kinematics: • Quasielastic scattering + low pm + symmetry about pm=0; Q2 = 0.8, 1.3 GeV2 . Beam: • Longitudinally polarized electron beam; incoming electron helicity flipped • to access both the transfer and induced polarization. Detection system: • Hall A High Resolution Spectrometers (HRS): FPP used to determine the polarization of the recoiling protons. Hall A Collaboration Meeting, December 13-14, 2007

6. 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 Induced polarization. Instrumental asymmetries complicate the extraction of induced polarization and are typically caused by: - detector misalignment - detector inefficiencies - tracking problems Also… Input the available theoretical calculation in a new MC simulation: SIMC. Analysis Status Mike Paolone S. Malace 1H(e,e’p) Q2 = 0.8 GeV2 Hall A Collaboration Meeting, December 13-14, 2007

7. xFP(A) Analyzer xTGT COSY xFP(C) Compare COSY Transport Mike Paolone • Already good agreement between Analyzer and COSY. -10/+10 mm -5/+5 mm • Small deviation due to higher order correction terms in the COSY transport matrix. Hall A Collaboration Meeting, December 13-14, 2007

8. 1 2 3  Instrumental Asymmetries Drift Chamber Inefficiencies • 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 Hall A Collaboration Meeting, December 13-14, 2007

9. Instrumental Asymmetries “Mirror” Test • Use only events for which Track(φ)andTrack(φ+π) fall in an equally efficient region of the rear chambers. • Given a track, we need to reconstruct the “mirror” track: “Real” track reconstruction: wire hits “Mirror” track reconstruction: wire hits + proton-Carbon vertex. • The reconstruction resolution of the “real” and “mirror” tracks not comparable => method not good enough. 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

10. Inefficiency Corrections • Inefficiency = Nseen/Nshould • The inefficiency correction is applied event by event. v_r at z=403 cm, FPP [4,35] deg vz [-3,+3] deg Depending on the angle at which the proton hits the chambers, the inefficiency correction is different! vz [-45,-11] deg vz [-11,-3] deg We would need an angle dependent inefficiency correction for each event in the “bad region”! Nshould vz [+3,+11] deg vz [+11,+45] deg Nseen * Instrumental Asymmetries But it does not work! Hall A Collaboration Meeting, December 13-14, 2007

11. “relaxed” tracking algorithm standard tracking algorithm Work in progress.. Instrumental 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 = track • To 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) • … Hall A Collaboration Meeting, December 13-14, 2007

12. Polarization-Transfer in 4He(e,e’p)3H • RDWIA calculation: no MEC and no charge-exchange FSI terms. • Study shows: effect of MEC ~ 3-4%. • 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. Hall A Collaboration Meeting, December 13-14, 2007

13. Polarization-Transfer in 4He(e,e’p)3H Schiavilla et al. calculation provides for alternative explanation: • R is suppressed ~ 4% from MEC. • Spin-dependent charge-exchange FSI suppresses R ~ 6%. • Charge-exchange term not well constrained => need precise Py data. Hall A Collaboration Meeting, December 13-14, 2007

14. Induced Polarization • RDWIA used to correct data for HRS acceptance (30% - 40% effect). • Py (measure of FSI) small and with only very weak Q2 dependence. • Spin-dependent charge-exchange terms not well constrained by N-N scattering and possibly overestimated. • RDWIA results consistent with data. • E03-104 data will set tight constraints on FSI. Hall A Collaboration Meeting, December 13-14, 2007

15. Summary 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 Hall A Collaboration Meeting, December 13-14, 2007