Single Transverse Spin Asymmetry for Large-p_T Pion Production in Semi-Inclusive Deep Inelastic Scattering
Hisato Eguchi, Yuji Koike, Kazuhiro Tanaka
TL;DR
The paper addresses the origin of large single transverse spin asymmetries (SSAs) in SIDIS at large transverse momentum by employing twist-3 collinear QCD dynamics. It derives the twist-3 cross sections for the two contributions (A) nucleon G_F and pion D, and (B) transversity δq and pion E_F, focusing on soft-gluon-pole pieces and their hard parts. The nonperturbative inputs G_F, E_F, and δq are constrained by SSA data from $p^rrow p\to\pi X$, enabling simple phenomenological estimates of the two twist-3 effects in SIDIS. This work provides a concrete framework to quantify large SSAs in SIDIS at high $p_T$, linking nucleon and fragmentation twist-3 dynamics within collinear factorization and informing future phenomenology and data comparisons.
Abstract
We study the single spin asymmetry (SSA) for the pion production with large transverse momentum p_T in semi-inclusive deep inelastic scattering $ep^\uparrow\to eπX$. We derive the twist-3 cross section formula for SSA, focussing on the soft-gluon-pole contributions associated with the twist-3 distribution for the nucleon and with the twist-3 fragmentation function for the pion. We present a simple estimate of the asymmetries due to each twist-3 effect from nucleon and pion, respectively, by fixing the overall strength of the relevant nonperturbative quantities by the data on the SSA A_N in $p^\uparrow p\toπX$ collision.