Collins effect and single spin azimuthal asymmetriesin the HERMES and COMPASS experiments

Abstract

Predictions are made for single spin azimuthal asymmetries due to the Collins effect in pion production from semi-inclusive deeply inelastic scattering off transversely and longitudinally polarized targets for the HERMES and COMPASS experiments. The x-dependence of the asymmetries is evaluated using the parton distribution functions from the chiral quark-soliton model. The overall normalization of the predicted asymmetries is determined by the information on the Collins fragmentation function extracted from previous HERMES data on azimuthal asymmetries A sin φ U L from a longitudinally polarized target. The single spin asymmetries AUT from the transversely polarized proton target are found to be about 20% for positive and neutral pions both at HERMES and COMPASS. For a longitudinally polarized target we obtain for COMPASS A sin φ U L ∼ 1% and A sin 2φ U L ∼ 3%.

Transversity distribution in spin asymmetries in semi-inclusive DIS and in the Drell-Yan process

“…5 . It should be noted that the prediction of A sin φ 0L (x, π) = 0 at x ≃ (0.4 − 0.5) is sensitive to the approximation of favoured flavour fragmentation (11). In principle one could conclude from data, how well this approximation works.…”

“…The first suspicion is favoured fragmentation approximation (11). First of all, pay attention to the negative and large A sin(φ+φs) 0T (π 0 ).…”

“…To access these chiral-odd structure functions one needs either to scatter two polarized protons and to measure the transversal spin correlation A N N in Drell-Yan process that is the problem for running RHIC and future PAX (GSI) experiments (see e.g. [11,12]) or to know the transverse polarization of a quark scattered from transversely polarized target. There are several ways to do this:…”

“…In this review we present the results of the works [26]- [31], [11] on spin asymmetries in SIDIS and the Drell-Yan process, which are based on predictions for the transversity distributions from the χQSM [32], c.f. also the overview given in Ref.…”

Spin-polarized high-energy scattering of charged leptons on nucleons

“…Once this normalization has been determined, it can be used to determine the normalization of sea quarks in pp scattering. Plans are being laid at several laboratories to exploit this reaction to measure transversity [88,89]. All existing experimental constraints on transversity are based on the sensitivity of fragmentation to the transverse polarization of the struck quark in processes other than DY, as manifested in single-spin asymmetries.…”