Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons

Abstract

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise

Modelling the nucleon structure

“…With these assumptions, as well as the very plausible assumption that the FSI is on average attractive, one finds that f ⊥u 1T < 0, while f ⊥d 1T > 0. Both signs have been confirmed by a flavor analysis based on pions produced in a semi-inclusive DIS experiment on a proton target by the Hermes collaboration [144] and are consistent with a vanishing isoscalar Sivers function observed by Compass [145] as well as more recent Compass proton data [146]. A similar mechanism can be invoked to explain the Boer Mulders effect, where the transverse spin of the nucleon is replaced by the transverse spin of the struck quark.…”

Deep Inelastic Scattering with the SPS Muon Beam

“…Figure 11 (top) shows the Collins asymmetry for the proton as measured for positive and negative hadrons (dominantly pions). Similar measurements exist for identified pions and kaons 67 and from HERMES. The corresponding asymmetries for the deuteron are compatible with zero due to a cancellation of the up and down quark contributions.…”

Double Collins effect in e+e−→ΛΛ¯Wang1, Yang2, Lü3 2018Phys. Rev. D9030View full textAdd to dashboardCite

“…As a time-reversal-odd (T-odd) function, the Collins function can be served as a quark spin analyzer and can also be used to explore the nonperturbative fragmentation mechanism of hadrons. The experimental measurements of the pion Collins function came from several single transverse spin asymmetries in semi-inclusive deep inelastic scattering (SIDIS) [2][3][4][5][6][7][8] from the HERMES and the COMPASS Collaborations, and the azimuthal asymmetry in the e þ e − annihilating process [9][10][11][12][13] from the BABAR and Belle Collaborations. Combining the experimental data from SIDIS and e þ e − annihilating processes, one can extract the Collins function as well as the transversity distribution function [14][15][16][17], which makes the Collins function a useful tool to investigate the internal structure for hadrons.…”