Fe b 20 07 Measurement of the dp → 3 He η reaction near threshold

Total and differential cross sections for the dp → Heη reaction have been measured near threshold for He center-of-mass momenta in the range from 17.1 MeV/c to 87.5 MeV/c. The data were taken during a slow ramping of the COSY internal deuteron beam scattered on a proton target detecting the He ejectiles with the COSY-11 facility. The forward-backward asymmetries of the differential cross sections deviate clearly from zero for center-of-mass momenta above 50 MeV/c indicating the presence of higher partial waves in the final state. Below 50 MeV/c centerof-mass momenta a fit of the final state enhancement factor to the data of the total cross sections results in the He−η scattering length of a = |2.9±0.6|+i(3.2±0.4) fm.