Measurement of the Longitudinal Spin Transfer to Lambda and Anti-Lambda Hyperons in Polarised Muon DIS

The longitudinal polarisation transfer from muons to Lambda and (Lambda) over bar hyperons, D-LL(Lambda(Lambda) over bar), has been studied in deep-inelastic scattering off an unpolarised isoscalar target at the COMPASS experiment at CERN. The spin transfers to Lambda and (Lambda) over bar produced in the current fragmentation region exhibit different behaviours as a function of x and x(F). The measured x and xF dependences of D-LL(Lambda) are compatible with zero, while D-LL((Lambda) over bar) tends to increase with x(F), reaching values of 0.4-0.5. The resulting average values are D-LL(Lambda) = -0.012 +/- 0.047 +/- 0.024 and D-LL((Lambda) over bar) = 0.249 +/- 0.056 +/- 0.049. These results are discussed in the frame of recent model calculations.