Charge symmetry breaking in n p --> d pi0

The forward-backward asymmetry in np → dπ 0 , which must be zero in the center-of-mass system if charge symmetry is respected, has been measured to be [17.2 ′ 8.0(stat) ′ 5.5(syst)] × 10 - 4 , at an incident neutron energy of 279.5 MeV. This observable is compared to recent chiral effective field theory calculations, with implications regarding the du quark mass difference.