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Title: Search for Proton Medium Modifications in the 4He(e,e'p)3H Reaction

Abstract

Polarization transfer in quasi-elastic nucleon knockout is sensitive to the properties of the nucleon in the nuclear medium, including possible modification of the nucleon form factor and/or spinor. In our recently completed experiment E03-104 at Jefferson Lab we measured the proton recoil polarization in the 4He(e,e'p)3H reaction at a Q^2 of 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision. These data complement earlier data between 0.4 and 2.6 (GeV/c)^2 from both Mainz and Jefferson Lab. The measured ratio of polarization-transfer coefficients differs from a fully relativistic calculation, favoring either the inclusion of a medium modification of the proton form factors predicted by a quark-meson coupling model or strong charge-exchange final-state interactions. The measured induced polarizations agree well with the fully relativistic calculation and indicate that these strong final-state interactions may not be applicable.

Authors:
Publication Date:
Research Org.:
Thomas Jefferson National Accelerator Facility, Newport News, VA
Sponsoring Org.:
USDOE - Office of Energy Research (ER)
OSTI Identifier:
917016
Report Number(s):
JLAB-PHY-07-724; DOE/OR/23177-0153; arXiv:0709.4034
TRN: US0804409
DOE Contract Number:
AC05-06OR23177
Resource Type:
Conference
Resource Relation:
Conference: NuInt07, May 30-June 2, 2007, Batavio, IL
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; CHARGE EXCHANGE; FINAL-STATE INTERACTIONS; FORM FACTORS; MODIFICATIONS; NUCLEONS; POLARIZATION; PROTONS

Citation Formats

S. Strauch. Search for Proton Medium Modifications in the 4He(e,e'p)3H Reaction. United States: N. p., 2007. Web.
S. Strauch. Search for Proton Medium Modifications in the 4He(e,e'p)3H Reaction. United States.
S. Strauch. Wed . "Search for Proton Medium Modifications in the 4He(e,e'p)3H Reaction". United States. doi:. https://www.osti.gov/servlets/purl/917016.
@article{osti_917016,
title = {Search for Proton Medium Modifications in the 4He(e,e'p)3H Reaction},
author = {S. Strauch},
abstractNote = {Polarization transfer in quasi-elastic nucleon knockout is sensitive to the properties of the nucleon in the nuclear medium, including possible modification of the nucleon form factor and/or spinor. In our recently completed experiment E03-104 at Jefferson Lab we measured the proton recoil polarization in the 4He(e,e'p)3H reaction at a Q^2 of 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision. These data complement earlier data between 0.4 and 2.6 (GeV/c)^2 from both Mainz and Jefferson Lab. The measured ratio of polarization-transfer coefficients differs from a fully relativistic calculation, favoring either the inclusion of a medium modification of the proton form factors predicted by a quark-meson coupling model or strong charge-exchange final-state interactions. The measured induced polarizations agree well with the fully relativistic calculation and indicate that these strong final-state interactions may not be applicable.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Wed May 30 00:00:00 EDT 2007},
month = {Wed May 30 00:00:00 EDT 2007}
}

Conference:
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  • Polarization transfer in quasi-elastic nucleon knockout is sensitive to the properties of the nucleon in the nuclear medium, including possible modification of the nucleon form factor and/or spinor. In our recently completed experiment E03-104 at Jefferson Lab we measured the proton recoil polarization in the 4He(e,e'p)3H reaction at a Q^2 of 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2 with unprecedented precision. These data complement earlier data between 0.4 and 2.6 (GeV/c)^2 from both Mainz and Jefferson Lab. The measured ratio of polarization-transfer coefficients differs from a fully relativistic calculation, favoring either the inclusion of a medium modification of the proton form factorsmore » predicted by a quark-meson coupling model or strong charge-exchange final-state interactions. The measured induced polarizations agree well with the fully relativistic calculation and indicate that these strong final-state interactions may not be applicable.« less
  • In the recent experiment E97-111 at Jefferson Lab the unseparated cross section for the (e,e{prime}p) reaction on {sup 4}He was measured at recoil momenta up to 530 MeV/c. In the plane-wave impulse approximation, many calculations predict a sharp minimum in the cross section for recoil momenta around 450 MeV/c and show that its location is sensitive to the short-range part of the internucleon potential. However, reaction dynamic effects such as final-state interactions and meson-exchange currents can obscure such a minimum. To distinguish and study these effects data were taken at several different kinematic points. The preliminary results of the experimentmore » are presented and compared to recent model calculations.« less
  • Polarization observables in the {sup 4}He({rvec e}, e{prime} {rvec p}){sup 3}H reaction are calculated using accurate three- and four-nucleon bound-state wave functions, a realistic model for the nuclear electromagnetic current operator, and a treatment of final-state-interactions with an optical potential model constrained by p {sup 3}H elastic and charge-exchange cross section data. In contrast to earlier studies, no significant discrepancies are found between theory and experiment both for the ratio of transverse to longitudinal polarization transfers and for the induced polarization, when free-nucleon electromagnetic form factors are used in the current operator. The present results challenge the current interpretation ofmore » the experimental data in terms of medium-modified form factors.« less
  • The cross section of the {sup 4}He(e,e'p){sup 3}H reaction has been measured for missing momenta 220 {le}p{sub m}{le}690 MeV/c to study high-momentum components of the nuclear wave function and the reaction mechanism for this transition. The zero predicted in the plane-wave impulse approximation (PWIA) cross section, due to the underlying pt momentum distribution, is found to be washed out. Three types of calculations indicate that this is caused by final-state interactions and contributions from two-body currents. The calculations reproduce the high p{sub m} (600-690 MeV/c) data, although due to different ingredients in the models.
  • We measured with unprecedented precision the induced polarization Py in 4He(e,e'p)3H at Q^2 = 0.8 (GeV/c)^2 and 1.3 (GeV/c)^2. The induced polarization is indicative of reaction-mechanism effects beyond the impulse approximation. Our results are in agreement with a relativistic distorted-wave impulse approximation calculation but are over-estimated by a calculation with strong charge-exchange effects. Our data are used to constrain the strength of the spin independent charge-exchange term in the latter calculation.