Measurement of the longitudinal spin transfer to Λ and ̄ hyperons in polarised muon DIS

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