Abstract
The transversity and the Sivers distribution functions of quarks incorporate important information about the transverse-spin and transverse-momentum structure of nucleons. We show how these distributions can be directly determined point by point from leptoproduction asymmetry data collected for various targets and produced hadrons by the COMPASS Collaboration. Only simple symmetry relations are used in the extraction.
Highlights
We can use Equations (31) and (32) to extract point-by-point the valence Sivers distributions from asymmetry data
The uv Sivers distribution is determined more precisely than the dv distribution, as the asymmetry measurements on the proton are considerably more accurate than the corresponding ones on the deuteron, in particular in the valence region
Taking advantage of the variety of processes investigated by the COMPASS experiment with the same kinematics, we extracted the quark distributions point by point by combining only observable quantities on the basis of isospin symmetry
Summary
A non-zero Sivers function dependent distribution (TMD), the “Sivers function” f 1T causes the distributions of quark transverse momentum to be asymmetric with respect to the plane given by the directions of nucleon spin and momentum This asymmetry, known as the Sivers effect, has been experimentally observed by the HERMES [6,16] and COMPASS collaborations [8,10,11,12,13,17] in the case of pion and kaon production. An alternative way to determine the transversity from the Collins asymmetries alone is via the so-called “difference asymmetries”, which allow extracting combinations of the u and d valence quark transversity without knowing the Collins fragmentation function This method was proposed long time ago [27,28,29] to access the helicity distribution functions. We report the results of a recent paper of ours [31], where, using again the COMPASS measurements with proton and deuteron targets, we determined the transversity ratio h1uv /h1dv
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