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Charge symmetry breaking in n p --> d pi^0

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
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Abstract

The forward--backward asymmetry in n p --> d pi^0, 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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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. 2003-06-19. Charge symmetry breaking in n p --> d pi^0. https://doi.org/10.1103/physrevlett.91.212302

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