The p + p → π+ + d reaction close to threshold at COSY

Abstract Differential and total cross sections of the p + p → π + + d reaction close to threshold were measured employing a magnetic spectrograph with track reconstruction, a very thin liquid hydrogen target and an accelerated proton beam with high phase space density. The data resolve a previous discrepancy between the n + p → π 0 + d and the π + + d → 2 p reaction close to threshold indicating that isospin symmetry may be broken in the s-wave part of the cross section.