Measurement of the Collins and Sivers asymmetries on transversely polarised protons

Abstract

The Collins and Sivers asymmetries for charged hadrons produced in deeply inelastic scattering on transversely polarised protons have been extracted from the data collected in 2007 with the CERN SPS muon beam tuned at 160 GeV/c. At large values of the Bjorken x variable non-zero Collins asymmetries are observed both for positive and negative hadrons while the Sivers asymmetry for positive hadrons is slightly positive over almost all the measured x range. These results nicely support the present theoretical interpretation of these asymmetries, in terms of leading-twist quark distribution and fragmentation functions.

Transverse single-spin asymmetries of pion production in semi-inclusive DIS at subleading twist

“…11 and 12, respectively. In this calculation, we adopt the following kinematical cuts [16]: 0.004 < x < 0.7, 0.1 < y < 0.9, z > 0.2,…”

“…A remarkable feature of the above mentioned asymmetries is that they appears at leading twist, thereby those effects should not be unsuppressed at high energies. Indeed significant asymmetries were measured by the HERMES Collaboration [10][11][12], the COMPASS Collaboration [13][14][15][16][17][18] and Jefferson Lab (JLab) Hall A Collaboration [19,20]. The corresponding data have been utilized to extract [21][22][23][24] the Sivers function and transversity distribution, within the TMD factorization [25].…”

Azimuthal asymmetries in single polarized proton-proton Drell-Yan processes

“…The shaded regions give the ranges of the asymmetries by considering the additional contribution from the distributions h1, h ⊥ 1T , and h ⊥ 1L of sea quarks constrained by the positivity bounds given in Eqs. (27), (28) and (29). The upper and lower limits of the bands correspond to the asymmetries by saturating the positivity bounds.…”

“…The thick solid and dashed lines correspond to the contribution merely from the combinations of the valence transversity distributions and the sea Boer-Mulders distributions, that is, ignoring the transversity distributions of sea quarks. The shaded regions give the ranges of A sin(2φ−φS) T U by considering the additional contribution of the transversity distributions of sea quarks constrained by positivity bound (27). The upper and lower limits of the bands correspond to the asymmetries by saturating the positivity bound.…”

“…Substantial SSAs contributed by the Sivers effect in SIDIS processes [21][22][23][24][25][26][27][28], with one colliding nucleon transversely polarized, have been measured by several experiments during recent years. The asymmetries are identified by the angular dependence sin(φ h − φ S ), where φ h and φ S denote, respectively, the azimuthal angles of the produced hadron and of the nucleon spin polarization, with respect to the lepton scattering plane.…”