Transversity and Collins functions from SIDIS ande+e−data

Abstract

A global analysis of the experimental data on azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS), from the HERMES and COMPASS Collaborations, and in e + e − → h1h2X processes, from the Belle Collaboration, is performed. It results in the extraction of the Collins fragmentation function and, for the first time, of the transversity distribution function for u and d quarks. These turn out to have opposite signs and to be sizably smaller than their positivity bounds. Predictions for the azimuthal asymmetry A sin(φ h +φ S ) U T , as will soon be measured at JLab and COMPASS operating on a transversely polarized proton target, are then presented.

Azimuthal and single spin asymmetries in hard scattering processes

“…13 we show the quality of the fit to the asymmetry, as defined by the Belle Collaboration for the two experimental setups, according to Ref. [268]. This allowed to extract the first independent parameterization of the Collins function, that was then used to extract, in combination with HERMES and COMPASS results on azimuthal asymmetries, the u and d quark transversity distribution function (see also section 5.5).…”

“…(96) with the parameterizations of Ref. [268]. The shaded areas correspond to the theoretical uncertainty on the parameters.…”

“…[266], where their phenomenological interest was pointed out, and more recently in Refs. [267,268], where Belle results were used to extract additional information on the Collins function. Both Refs.…”

“…The azimuthal asymmetry, as defined by the Belle collaboration (setup 1), can be obtained from here by the following steps: i) Performing a change of angular variables from (φ 1 , φ 2 ) to (φ 1 , φ 1 + φ 2 ) and then integrating over the moduli of the intrinsic transverse momenta, p ⊥1 , p ⊥2 , and over the azimuthal angle φ 1 ; ii) Normalizing the result to the azimuthally averaged cross section; iii) Taking the ratio R [268]. The shaded area corresponds to the theoretical uncertainty on the parameters.…”

“…In Ref. [268] both kinematical setups were considered, and SIDIS and e + e − data were combined to get a simultaneous fit of the Collins and the transversity distribution functions.…”