Neutral pion threshold production at Q^2=0.05 GeV^2/c^2 and Chiral Perturbation Theory

Harald Merkel; Peter Bartsch; Dagmar Baumann; Jörg Bermuth; Aron M. Bernstein; Klemen Bohinc; Ralph Böhm; Norbert Clawiter; Sabine Derber; Matthias Ding; Michael O. Distler; Ingo Ewald; Jan M. Friedrich; Jörg Friedrich; Peter Jennewein; Marco Kahrau; Michael Kohl; Klaus Werner Krygier; Michael Kuss; Arnd Liesenfeld; Pascal Merle; Rory A. Miskimen; Ulrich Müller; Reiner Neuhausen; Marcello M. Pavan; Thomas Pospischil; Milan Potokar; Günther Rosner; Hartmut Schmieden; Michael Seimetz; Simon Širca; Axel Wagner; Thomas Walcher; Markus Weis

doi:10.1103/physrevlett.88.012301

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Neutral pion threshold production at Q^2=0.05 GeV^2/c^2 and Chiral Perturbation Theory

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Abstract

New data are presented on the p(e,e'p)π^0 reaction at threshold at a four-momentum transfer of Q^2=0.05 GeV^2/c^2. 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 σ_T, σ_L, σ_{TT}, and σ_{TL} 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.

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Harald Merkel, Peter Bartsch, Dagmar Baumann, Jörg Bermuth, Aron M. Bernstein, Klemen Bohinc, Ralph Böhm, Norbert Clawiter, Sabine Derber, Matthias Ding, Michael O. Distler, Ingo Ewald, Jan M. Friedrich, Jörg Friedrich, Peter Jennewein, Marco Kahrau, Michael Kohl, Klaus Werner Krygier, Michael Kuss, Arnd Liesenfeld, Pascal Merle, Rory A. Miskimen, Ulrich Müller, Reiner Neuhausen, Marcello M. Pavan, Thomas Pospischil, Milan Potokar, Günther Rosner, Hartmut Schmieden, Michael Seimetz, Simon Širca, Axel Wagner, Thomas Walcher, Markus Weis. 2001-11-02. Neutral pion threshold production at Q^2=0.05 GeV^2/c^2 and Chiral Perturbation Theory. https://doi.org/10.1103/physrevlett.88.012301

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