Measurement of the longitudinal spin transfer to Λ and $\bar{\varLambda}$ hyperons in polarised muon DIS

The longitudinal polarisation transfer from muons to Λ and \(\bar{\varLambda}\)  hyperons, \(D_{LL}^{\varLambda(\bar{\varLambda})}\) , has been studied in deep-inelastic scattering off an unpolarised isoscalar target at the COMPASS experiment at CERN. The spin transfers to Λ and \(\bar{\varLambda}\)  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 LL Λ are compatible with zero, while \(D_{LL}^{\bar{\varLambda}}\) tends to increase with x F , reaching values of 0.4–0.5. The resulting average values are D LL Λ = −0.012±0.047±0.024 and \(D_{LL}^{\bar{\varLambda}}\) = 0.249±0.056±0.049. These results are discussed in the frame of recent model calculations.