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Title: Measurement of the target-normal single-spin asymmetry in quasielastic scattering from the reaction He3(e,e')

We report the first measurement of the target single-spin asymmetry, Ay, in quasi-elastic scattering from the inclusive reaction 3He↑ (e,e') on a 3He gas target polarized normal to the lepton scattering plane. Assuming time-reversal invariance, this asymmetry is strictly zero for one-photon exchange. A non-zero Ay can arise from the interference between the one- and two-photon exchange processes which is sensitive to the details of the sub-structure of the nucleon. An experiment recently completed at Jefferson Lab yielded asymmetries with high statistical precision at Q2= 0.13, 0.46 and 0.97 GeV2. These measurements demonstrate, for the first time, that the 3He asymmetry is clearly non-zero and negative with a statistical significance of (8-10)σ. Using measured proton-to-3He cross-section ratios and the effective polarization approximation, neutron asymmetries of -(1-3)% were obtained. The neutron asymmetry at high Q2 is related to moments of the Generalized Parton Distributions (GPDs). Our measured neutron asymmetry at Q2=0.97 GeV2 agrees well with a prediction based on two-photon exchange using a GPD model and in addition provides a new independent constraint on these distributions.
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Publication Date:
OSTI Identifier:
1224078
Report Number(s):
JLAB-PHY--15-2021; DOE/OR/23177--3321; arXiv:1502.02636
Journal ID: ISSN 0031-9007; PRLTAO; National Science Foundation of China and UK STFC grants 57071/1, 50727/1.; TRN: US1600790
Grant/Contract Number:
AC05-06OR23177
Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 115; Journal Issue: 17; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Contributing Orgs:
Jefferson Lab Hall A Collaboration
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS