Abstract
The COMPASS Collaboration at CERN has investigated the reaction at center-of-momentum energy below five pion masses, , embedded in the Primakoff reaction of 190 GeV pions impinging on a lead target. Exchange of quasireal photons is selected by isolating the sharp Coulomb peak observed at smallest momentum transfers, . Using partial-wave analysis techniques, the scattering intensity of Coulomb production described in terms of chiral dynamics and its dependence on the -invariant mass were extracted. The absolute cross section was determined in seven bins of with an overall precision of 20%. At leading order, the result is found to be in good agreement with the prediction of chiral perturbation theory over the whole energy range investigated.
- Received 25 November 2011
DOI:https://doi.org/10.1103/PhysRevLett.108.192001
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