Malace_e03104.ppt - Hall A - Jefferson Lab

Document Sample
Malace_e03104.ppt - Hall A - Jefferson Lab Powered By Docstoc
					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, 2007
                     Jefferson Lab, Newport News, VA




                                         Hall A Collaboration Meeting, December 13-14, 2007
                           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
                            Theory: Overview
             Born + Impulse Approximation(IA)

                                                 P N  ( EN , PN )
               k       f    ( f , k f )

                                                          P A1  (EA1, PA1 )
                                 q   ( , q )
                                                          P A  (EA , PA )

               k  i  ( i , ki )
                                     dq                              ( 1)
          Wif   dx  dy                 j e ( x )e  iq ( x  y ) 2 J N  ( y )
                                   (2 ) 2                            q
           j e (r )   f e (r )  i e (r ) J N  (r )   F N (r ) J N  B N (r )

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

                                                          Hall A Collaboration Meeting, December 13-14, 2007
                               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. => •T. De Forest, Jr. Nucl. Phys. A392, 232 (1983)
                                      •D. Debruyne, et al. ,Phys. Rev. C 62, 024611 (2000)


• Many-body currents: IA = “zero order approximation” but realistically we
need higher-order corrections to IA. => •A. Meucci et al., Phys. Rev. C 66, 034610 (2002)
                                                   •R. Schiavilla et al., Phys. Rev. Lett. 94, 072303 (2005)



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


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

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.                                                    1H(e,e’p)
Instrumental asymmetries complicate
                                                                         Q2 = 0.8 GeV2
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.
                                              Hall A Collaboration Meeting, December 13-14, 2007
                                    COSY Transport
xFP(C)                 •Already good agreement between Analyzer and COSY.



                     -10/+10 mm
COSY




                     -5/+5 mm
           Compare
xTGT
Analyzer
xFP(A)




                     •Small deviation due to higher order correction terms in
                     the COSY transport matrix.
                                                     Hall A Collaboration Meeting, December 13-14, 2007
                   Instrumental Asymmetries
Drift Chamber Inefficiencies
•FPP chambers performance: inefficient
regions cause of instrumental
                                                        1 2 3
asymmetries.

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

         A( )  A(   )

•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
                                    Instrumental Asymmetries
“Mirror” Test
 • 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:




 “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
                               Instrumental Asymmetries
Inefficiency Corrections
• Inefficiency = Nseen/Nshould

• The inefficiency correction is applied event
by event.
                                                                            Nshould
v_r at z=403 cm, FPP [4,35] deg   vz [-3,+3] deg                      * Nseen




                                                                    But it does not work!

vz [-11,-3] deg                   vz [-45,-11] deg          Depending on the angle at
                                                                which the proton hits the
                                                                chambers, the inefficiency
                                                                correction is different!

vz [+3,+11] deg                   vz [+11,+45] deg
                                                                 We would need an angle
                                                                 dependent inefficiency
                                                                 correction for each event in
                                                                 the “bad region”!
                                                         Hall A Collaboration Meeting, December 13-14, 2007
                      Instrumental Asymmetries

Standard tracking algorithm              “relaxed” tracking algorithm
                                         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                   Work in progress..

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
             Polarization-Transfer in 4He(e,e’p)3H

• RDWIA calculation: no MEC                P                      P 
and no charge-exchange FSI              R x                       x 
                                           P                      P 
terms.                                     z e Nbound             z e  N free
• 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
                  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
                         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
                          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

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:2
posted:10/15/2012
language:English
pages:15