The European Physical Journal A

, Volume 38, Issue 1, pp 27–33 | Cite as

Separated cross-sections in \( \pi^{0}_{}\) electroproduction at threshold at Q2 = 0.05GeV2/c2

  • The A1 Collaboration
  • M. Weis
  • P. Bartsch
  • D. Baumann
  • J. Bermuth
  • A. M. Bernstein
  • K. Bohinc
  • R. Böhm
  • M. Ding
  • M. O. Distler
  • I. Ewald
  • J. M. Friedrich
  • J. Friedrich
  • M. Kahrau
  • M. Kohl
  • K. W. Krygier
  • A. Liesenfeld
  • H. Merkel
  • P. Merle
  • U. Müller
  • R. Neuhausen
  • M. M. Pavan
  • Th. Pospischil
  • M. Potokar
  • G. Rosner
  • H. Schmieden
  • M. Seimetz
  • S. Širca
  • A. Wagner
  • Th. Walcher
Regular Article - Experimental Physics

Abstract

The differential cross-sections σ0 = σT + εσL , σLT , and σTT of \( \pi^{0}_{}\) electroproduction from the proton were measured from threshold up to an additional center-of-mass energy of 40MeV, at a value of the photon four-momentum transfer of Q 2 = 0.05 GeV2/c2 and a center-of-mass angle of θ = 90° . By an additional out-of-plane measurement with polarized electrons σLT' was determined. This showed for the first time the presence of an imaginary part of the s -wave above the \( \pi^{+}_{}\) threshold, which is usually interpreted as a unitary cusp. The predictions of the Heavy Baryon Chiral Perturbation Theory (HBChPT) are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological model and are in good agreement with the dynamical model DMT.

PACS

25.30.Rw Electroproduction reactions 13.60.Le Meson production 

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Copyright information

© SIF, Springer-Verlag Berlin Heidelberg 2008

Authors and Affiliations

  • The A1 Collaboration
  • M. Weis
    • 1
  • P. Bartsch
    • 1
  • D. Baumann
    • 1
  • J. Bermuth
    • 2
  • A. M. Bernstein
    • 3
  • K. Bohinc
    • 4
  • R. Böhm
    • 1
  • M. Ding
    • 1
  • M. O. Distler
    • 1
  • I. Ewald
    • 1
  • J. M. Friedrich
    • 1
  • J. Friedrich
    • 1
  • M. Kahrau
    • 1
  • M. Kohl
    • 5
  • K. W. Krygier
    • 1
  • A. Liesenfeld
    • 1
  • H. Merkel
    • 1
  • P. Merle
    • 1
  • U. Müller
    • 1
  • R. Neuhausen
    • 1
  • M. M. Pavan
    • 3
  • Th. Pospischil
    • 1
  • M. Potokar
    • 4
  • G. Rosner
    • 1
  • H. Schmieden
    • 1
  • M. Seimetz
    • 1
    • 6
  • S. Širca
    • 4
    • 6
  • A. Wagner
    • 1
  • Th. Walcher
    • 1
  1. 1.Institut für KernphysikJohannes Gutenberg-Universität MainzMainzGermany
  2. 2.Institut für PhysikJohannes Gutenberg-Universität MainzMainzGermany
  3. 3.Laboratory for Nuclear ScienceMassachusetts Institute of TechnologyCambridgeUSA
  4. 4.Jožef Stefan InstituteLjubljanaSlovenia
  5. 5.Institut für KernphysikTechnische Universität DarmstadtDarmstadtGermany
  6. 6.Department of PhysicsUniversity of LjubljanaLjubljanaSlovenia

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