APS » PROLA » Phys. Rev. Lett. » Volume 88 » Issue 1

Phys. Rev. Lett. 88, 012301 (2001) [4 pages]

Neutral Pion Threshold Production at Q2  =  0.05 GeV2/c2 and Chiral Perturbation Theory
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H. Merkel et al. (A1 Collaboration)
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Received 20 August 2001; published 20 December 2001

New data are presented on the p(e,e′p)π0 reaction at threshold at a four-momentum transfer of Q2  =  0.05 GeV2/c2. The data were taken with the three-spectrometer setup of the A1 Collaboration at the Mainz Microtron MAMI. The complete center of mass solid angle was covered up to a center of mass energy of 4 MeV above threshold. Combined with measurements at three different values of the virtual photon polarization ε, the structure functions σT, σL, σTT, and σTL are determined. The results are compared with calculations in heavy baryon chiral perturbation theory and with a phenomenological model. The measured cross section is significantly smaller than both predictions.


©2002 The American Physical Society

URL: http://link.aps.org/abstract/PRL/v88/e012301
DOI: 10.1103/PhysRevLett.88.012301
PACS: 25.30.Rw, 13.60.Le, 12.39.Fe

* Email address: Merkel@kph.uni-mainz.de http://wwwa1.kph.uni-mainz.de/
† Present address: TU München, Garching, Germany.
‡ Present address: INFN Sezione di Pisa, Pisa, Italy.
§ Present address: TRIUMF, Vancouver, B.C., Canada.
** Present address: University of Glasgow, Glasgow, U.K.
†† Present address: M.I.T., Cambridge, MA 02139.

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