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Title: Separated response functions in exclusive, forward π± electroproduction on deuterium

Background: Measurements of forward exclusive meson production at different squared four-momenta of the exchanged virtual photon, Q2, and at different four-momentum transfer, t, can be used to probe QCD's transition from meson-nucleon degrees of freedom at long distances to quark-gluon degrees of freedom at short scales. Ratios of separated response functions in π⁻ and π⁺ electroproduction are particularly informative. Ratio for transverse photons may allow this transition to be more easily observed, while the ratio for longitudinal photons provides a crucial verification of the assumed pole dominance, needed for reliable extraction of the pion form factor from electroproduction data. Method: Data were acquired with 2.6-5.2 GeV electron beams and the HMS+SOS spectrometers in Jefferson Lab Hall C, at central Q2 values of 0.6, 1.0, 1.6 GeV2 at W=1.95 GeV, and Q2=2.45 GeV2 at W=2.22 GeV. There was significant coverage in Φ And ϵ, which allowed separation of σL,T,LT,TT. Results: σL shows a clear signature of the pion pole, with a sharp rise at small -t. In contrast, σT is much flatter versus t. The longitudinal/transverse ratios evolve with Q2 and t, and at the highest Q2=2.45 GeV2 show a slight enhancement for π⁻ Production compared to π⁺. The π⁻/π⁺+ ratiomore » for transverse photons exhibits only a small Q2-dependence, following a nearly universal curve with t, with a steep transition to a value of about 0.25, consistent with s-channel quark knockout. The σTTT ratio also drops rapidly with Q2, qualitatively consistent with s-channel helicity conservation. The π⁻/π⁺ ratio for longitudinal photons indicates a small isoscalar contamination at W=1.95 GeV, consistent with what was observed in our earlier determination of the pion form factor at these kinematics.« less
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Publication Date:
OSTI Identifier:
1167105
Report Number(s):
JLAB-PHY--14-1996; DOE/OR/23177--3258; arXiv:1412.5140
Journal ID: ISSN 0556-2813; PRVCAN; ArticleNumber: 015202
Grant/Contract Number:
AC05-84ER40150
Type:
Accepted Manuscript
Journal Name:
Physical Review. C, Nuclear Physics
Additional Journal Information:
Journal Volume: 91; Journal Issue: 1; Journal ID: ISSN 0556-2813
Publisher:
American Physical Society (APS)
Research Org:
Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
Contributing Orgs:
Jefferson Lab F π Collaboration
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS