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Hall A Collaboration Meeting, December 13-14, 2007 E03-104: Probing the Limits of the Standard Model of Nuclear Physics with the 4 He(e,ep) 3 H Reaction.

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Presentation on theme: "Hall A Collaboration Meeting, December 13-14, 2007 E03-104: Probing the Limits of the Standard Model of Nuclear Physics with the 4 He(e,ep) 3 H Reaction."— Presentation transcript:

1 Hall A Collaboration Meeting, December 13-14, 2007 E03-104: Probing the Limits of the Standard Model of Nuclear Physics with the 4 He(e,ep) 3 H 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, 2007 Jefferson Lab, Newport News, VA

2 Hall A Collaboration Meeting, December 13-14, 2007 Motivation Conventional Nuclear Physics: - we probe point-like nucleons + form-factors - reaction mechanisms: theoretically parameterized ignoring that the nucleons inner structure may be changed in the nuclear medium QCD: - nucleons: composite objects of quarks and gluons A(e,ep)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 ?

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

4 Hall A Collaboration Meeting, December 13-14, 2007 In-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, (2000) A. Meucci et al., Phys. Rev. C 66, (2002) R. Schiavilla et al., Phys. Rev. Lett. 94, (2005) J. Udias et al., Phys. Rev. Lett. 83, 5451 (1999) R. Schiavilla et al., Phys. Rev. Lett. 94, (2005) P. Lava et al., Phys. Rev. C 71, (2005) D.H. Lu et al., Phys. Rev. C 60, (1999) J. R. Smith and G. Miller, Phys. Rev. Lett. 91, (2003)

5 Hall A Collaboration Meeting, December 13-14, 2007 E 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 4 He(e,ep) 3 H are influenced little by FSI, MEC… 4 He: 1 H: 1 H is baseline when estimating the effect of the medium on the polarization transfer ratio in 4 He(e,ep) 3 H. Kinematics: Targets: Beam: Detection system: Quasielastic scattering + low p m + symmetry about p m =0; Q 2 = 0.8, 1.3 GeV 2. 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.

6 Hall A Collaboration Meeting, December 13-14, 2007 Analysis Status 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. 1 H(e,ep) Q 2 = 0.8 GeV 2 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

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

8 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 Drift Chamber Inefficiencies 123

9 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 Test Real track reconstruction: wire hits Mirror track reconstruction: wire hits + proton-Carbon vertex. Instrumental 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)

10 Hall A Collaboration Meeting, December 13-14, 2007 But it does not work! * N seen N should Inefficiency = N seen /N should The inefficiency correction is applied event by event. Inefficiency Corrections 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 Asymmetries

11 Hall A Collaboration Meeting, December 13-14, 2007 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 shouldnt see in the u/v event distribution the bad regions originating from the chamber left aside) - … Work in progress.. relaxed tracking algorithm standard tracking algorithm

12 Hall A Collaboration Meeting, December 13-14, 2007 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 E possibly hint an unexpected trend in Q 2. Study shows: effect of MEC ~ 3-4%. Polarization-Transfer in 4 He(e,ep) 3 H

13 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 P y data. Polarization-Transfer in 4 He(e,ep) 3 H

14 Hall A Collaboration Meeting, December 13-14, 2007 Induced Polarization P y (measure of FSI) small and with only very weak Q 2 dependence. RDWIA results consistent with data. Spin-dependent charge-exchange terms not well constrained by N-N scattering and possibly overestimated. E data will set tight constraints on FSI. RDWIA used to correct data for HRS acceptance (30% - 40% effect).

15 Hall A Collaboration Meeting, December 13-14, 2007 Summary Previous data on polarization transfer in 4 He(e,ep) – E significant deviation from RDWIA results; data effectively described by proton medium modifications -alternative interpretation in terms of strong charge-exchange FSI; possibly inconsistent with P y E high statistics data at Q 2 = 0.8 GeV 2 and 1.3 GeV 2 -polarization transfer can be studied in detail -much improved induced polarization data will be crucial to better constrain FSI -preliminary results from E already challenge available models -final results in 2008


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