Measurement of the neutron-neutron scattering lengthannwith the reactionπ−d→nnγin complete kinematics

Abstract
The neutron-neutron scattering length ann is determined from the low energy part of the neutron spectrum of the reaction πd→nnγ with pions at rest. Since neutrons are detected in coincidence with the photon, the kinematics is completely determined. We obtain ann=18.7±0.6 fm, in agreement with a result of a previous experiment based on the analysis the photon spectrum.