Bernard Gabioud

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

The neutron-neutron scattering length a/sub nn/ is determined from the low energy part of the neutron spectrum of the reaction ..pi../sup -/d..-->..nn..gamma.. with pions at rest. Since neutrons are detected in coincidence with the photon, the kinematics is completely determined. We obtain a/sub nn/ = -18.7 +- 0.6 fm, in agreement with a result of a previous experiment based on the analysis the photon spectrum.

Measurement of the neutron-neutron scattering length a nn with the reaction π − d → nn γ in complete kinematics

The neutron-neutron scattering length a/sub nn/ is determined from the low energy part of the neutron spectrum of the reaction ..pi../sup -/d..-->..nn..gamma.. with pions at rest. Since neutrons are detected in coincidence with the photon, the kinematics is completely determined. We obtain a/sub nn/ = -18.7 +- 0.6 fm, in agreement with a result of a previous experiment based on the analysis the photon spectrum.

π− d → γnn and the Effective Range Theory Parameters ann and rnn

Among all reactions used to determine ann, π− d → γnn and μ− d → υnn are unique to study the two neutrons final state interactions since no other strong interacting particle is present. This fact makes the theoretical calculations necessary to extract ann more reliable. The “complete” experiment of R.M. Salter, R.P. Haddock et al.1) yielded a value of −16.7 ± 1.3 fm. To this uncertainty mainly coming from the detection of the two neutrons must be added the theoretical uncertainty of the Bander’s theory2) (1 fm) used to extract ann. Two recent calculations3,4) give lower uncertainties of about 0.3 fm if the neutron-neutron relative momentum is restricted to about a few tens of MeV/c.