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Charge symmetry breaking in n p --> d pi0

A. K. Opper, E. Korkmaz, D. A. Hutcheon, R. Abegg, C. A. Davis, R. W. Finlay, P. W. Green, L. G. Greeniaus, D. V. Jordan, J. A. Niskanen, G. V. O'Rielly, T. A. Porcelli, S. D. Reitzner, P. L. Walden, S. Yen

nucl-exarXiv:nucl-ex/0306027

Abstract

The forward--backward asymmetry in n p --> d pi0, which must be zero in the center-of-mass system if charge symmetry is respected, has been measured to be [17.2 +/- 8 (stat) +/- 5.5 (sys)] * 10-4, at an incident neutron energy of 279.5 MeV. This charge symmetry breaking observable was extracted by fitting the data with GEANT-based simulations and is compared to recent chiral effective field theory calculations, with implications regarding the value of the u d quark mass difference.

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