Abstract
Motivated by a novel origin of transverse single spin asymmetry (SSA) in semi-inclusive Deep Inelastic Scattering (SIDIS) uncovered by some of us, we quantitatively investigate its impact on the theoretical understanding of the mechanism responsible for SSA. This new contribution from the quark-initiated channel first appears in two-loop perturbation theory and involves the $g_T(x)$ distribution. We point out another entirely analogous piece from the gluon-initiated channel proportional to the gluon helicity distribution $\Delta G(x)$. Both contributions are solely expressed in terms of twist-two polarized parton distribution functions and twist-two fragmentation functions in the Wandzura-Wilczek approximation, such that they can be unambiguously evaluated without introducing free parameters. We make predictions for measurements of the asymmetries $A_{UT}$ at the future Electron-Ion Collider (EIC), and find that $A_{UT}$ associated with the $\sin (\phi_h-\phi_S)$, $\sin \phi_S$ and $\sin (2\phi_h-\phi_S)$ harmonics can reach up to 1-2\% even at the top EIC energy.
Highlights
Motivated by a novel origin of transverse single spin asymmetry (SSA) in semi-inclusive deep inelastic scattering (SIDIS) uncovered by some of us, we quantitatively investigate its impact on the theoretical understanding of the mechanism responsible for SSA
NUMERICAL RESULTS With all the analytical results presented in the previous sections, we are ready to make predictions for electron-ion collider (EIC) measurements
At the EIC, AUT for pions can reach 1-2% for the three harmonics sinðφh − φSÞ, sinðφhÞ and sinð2φh − φSÞ
Summary
J. Yang, have proposed a novel mechanism for generating transverse single-spin asymmetry (SSA) in semi-inclusive deep inelastic scattering (SIDIS) ep↑ → e0hX [1]. It has been demonstrated that an imaginary phase necessary for SSA can be produced purely within a parton-level cross section starting at two loops. The spin-dependent part of the cross section at high transverse momentum PhT > 1 GeV (measured with respect to the virtual photon direction) can be schematically written as dΔσ ∼ gTðxÞ ⊗ H ⊗ D1ðzÞ þ Á Á Á ; ð1Þ dPhT where gTðxÞ is the twist-three parton distribution function (PDF) associated with a transversely polarized proton, D1 is the unpolarized twist-two fragmentation function (FF) for the observed hadron h, and H is the hard kernel starting at Oðα2sÞ (see an earlier related work [2]). The terms omitted in (1) are proportional to the “genuine twist-three” quark-gluon correlation functions ∼hψgFψi commonly
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