Low energy pion reactions

The s-wave amplitude for pion production in pp-collisions has been deduced from a recently updated data set, α0=0.230±0.019 mb. The new number is in agreement with data from pionic deuterium width applying basic symmetries and known ratios, yielding a value b1=(-80.5±6.8) x 10-3/mπ f or the πN isovector scattering length. A compilation of all results for the isovector scattering length from analysis of data from reactions with real pions yields a new mean value, b1=(-87.3±2.4) x 10-3/mπ.The main source of uncertainty seems to be the ratio T=w(π-+d→n+n+γ)/w(π-+p→n+γ) whic h has to be 0.74±0.12 in order to lead to this mean value of b1. (orig.)