Single-spin asymmetries at two loops

Abstract

We find a novel mechanism for generating transverse single-spin asymmetry (SSA) in semiinclusive deep inelastic scattering, distinct from the known ones which involve the Sivers and Collins functions, or their collinear twist-three counterparts. It is demonstrated that a phase needed for SSA can be produced purely within a parton-level cross section starting at two loops. We identify the complete set of two-loop diagrams for SSA, and discuss their gauge invariance and collinear factorization which features the gT distribution function. In the kT factorization framework, many more sources for SSA exist, and contributions from all possible two-parton transverse-momentumdependent parton distribution functions are presented up to two loops and twist three.

Neutron Stars: A Novel Equation of State with Induced Surface Tension

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Transverse-single-spin asymmetries of charged pions at midrapidity in transversely polarized $p{+}p$ collisions at $\sqrt{s}=200$ GeV

“…Single-spin asymmetries have been measured in hadronic collisions over a wide range of energies for a number of final state particles [1][2][3][4] and at various rapidity regions. Initially, calculations that were based entirely on perturbative quantum chromodynamics (pQCD) expected such asymmetries to be suppressed as they generally required a helicity-flip which would be proportional to the parton mass over the hard scale of the scattering process [5], though recent calculations suggest that perturbative contributions may be possible [6]. In contrast to the pQCD calculations, the measured single-spin asymmetries, A N for pion production in the forward direction were found to be quite sizeable [1][2][3].…”

Transverse Polarization of Hyperons Produced in Semi-Inclusive Deep Inelastic Scattering

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