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Title: Precision Measurement of the p(e, e´p) π⁰ Reaction at Threshold

New results are reported from a measurement of $$\pi^0$$ electroproduction near threshold using the p(e, e´p) π⁰ reaction. The experiment was designed to determine precisely the energy dependence of $s-$ and $p-$wave electromagnetic multipoles as a stringent test of the predictions of Chiral Perturbation Theory (ChPT). The data were taken with an electron beam energy of 1192 MeV using a two-spectrometer setup in Hall A at Jefferson Lab. For the first time, complete coverage of the $$\phi^*_{\pi}$$ and $$\theta^*_{\pi}$$ angles in the $$p \pi^0$$ center-of-mass was obtained for invariant energies above threshold from 0.5 MeV up to 15 MeV. The 4-momentum transfer $Q^2$ coverage ranges from 0.05 to 0.155 (GeV/c)$^2$ in fine steps. A simple phenomenological analysis of our data shows strong disagreement with $p-$wave predictions from ChPT for $Q^2>0.07$ (GeV/c)$^2$, while the $s-$wave predictions are in reasonable agreement.
 [1] ;  [2] ;  [3] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Univ. of Virginia, Charlottesville, VA (United States); Chiang Mai Univ. (Thailand)
  2. Univ. of Virginia, Charlottesville, VA (United States); Mississippi State Univ., Mississippi State, MS (United States)
  3. Univ. of Virginia, Charlottesville, VA (United States);
  4. Univ. of Glasgow, Scotland (United Kingdom)
  5. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
  6. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States), et. al.
Publication Date:
OSTI Identifier:
Report Number(s):
JLAB/PHY-15-2013; DOE/OR-23177-3313
Journal ID: ISSN 0031-9007; PRLTAO; FG02-97ER41025; NSF MRI Award No. 021635; JLAB-E04-007; TRN: US1600762
Grant/Contract Number:
FG02-97ER41025; AC05-06OR23177; 021635
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 114; Journal Issue: 19; Journal ID: ISSN 0031-9007
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 Hall A Collaboration
Country of Publication:
United States