Double spin asymmetriesALTcosϕSandA

Abstract

We investigate the double spin asymmetries of pion production in semi-inclusive deep inelastic scattering with a longitudinal polarized beam off a transversely polarized proton target. Particularly, we consider the cos φS and cos(2φ h − φS) modulations, which can be interpreted by the convolution of the twist-3 transverse momentum dependent distributions and twist-2 fragmentation functions. Three different origins are taken into account simultaneously for each asymmetry: the gT D1 term, the eT H , and e ⊥ T (x, k 2 T ) in a spectator-diquark model including vector diquarks. Then we predict the two corresponding asymmetries for charged and neutral pions at the kinematics of HERMES, JLab, and COMPASS for the first time. The numerical estimates indicate that the two different angular-dependence asymmetries are sizable by several percent at HERMES and JLab, and the cos φS asymmetry has a strong dependence on the Bjorken x. Our predictions also show that the dominant contribution to the cos φS asymmetry comes from the gT D1 term, while the g ⊥ T D1 term gives the main contribution to the cos(2φ h − φS) asymmetry; the other two T -odd terms almost give negligible contributions. In particular, the cos(2φ h − φS) asymmetry provides a unique opportunity to probe the distribution g ⊥ T .

Transverse Spin Azimuthal Asymmetries in SIDIS at COMPASS: Multidimensional Analysis

“…This is the only DSA which appears to be non-zero at COMPASS and the last TSA for which a statistically significant signal has been detected. Remaining four asymmetries are found to be small or compatible with zero within available statistical accuracy which is in agreement with available predictions [19,20,28]. As an example the "3D: x-z-p T " results for A sin(3φ h −φ S ) UT asymmetry are presented in Figure 7.…”

“…Remaining four asymmetries are so-called "higher-twist" effects 2 . Corresponding structure functions enter at sub-leading order (Q −1 ) and contain terms given as various mixtures of twisttwo and twist-three (induced by quark-gluon correlations) parton distribution and fragmentation functions [2]- [20]. However, applying wildly used "Wandzura-Wilczek approximation" this higher twist objects can be simplified to the twist-two order (see [2,3] for more details).…”

Semi-inclusive deep-inelastic scattering in Wandzura-Wilczek-type approximation

“…asymmetry was also studied in a different spectator model in ref. [199] predicting asymmetries of the same sign but of smaller magnitudes of O(1 %).…”

Semi-inclusive deep inelastic scattering in Wandzura-Wilczek-type approximation

“…Let us remark that the A cos(2φ h −φ S ) LT asymmetry was also studied in a different spectator model in Ref. [197] predicting asymmetries of the same sign but of smaller magnitudes of O(1 %).…”