Measurement of the longitudinal spin asymmetries for weak boson production in proton-proton collisions at s=510  GeV

Abstract

We report new STAR measurements of the single-spin asymmetries AL for W + and W − bosons produced in polarized proton-proton collisions at √ s = 510 GeV as a function of the decay-positron and decay-electron pseudorapidity. The data were obtained in 2013 and correspond to an integrated luminosity of 250 pb −1 . The results are combined with previous results obtained with 86 pb −1 . A comparison with theoretical expectations based on polarized lepton-nucleon deep-inelastic scattering and prior polarized proton-proton data suggests a difference between the ū and d quark helicity distributions for 0.05 < x < 0.25. In addition, we report new results for the double-spin asymmetries ALL for W ± , as well as AL for Z/γ * production and subsequent decay into electron-positron pairs.

What we know and what we don’t know about the proton spin after 30 years

“…However, for sea quark polarizations including u, d and s (s), there exist larger uncertainties, in particular, in the strange quark polarization [110][111][112] , where the constraints mainly come from SIDIS measurements by the HERMES and COMPASS experiments. It was also found that the W boson spin asymmetries at centre-of-mass energy s = 510 GeV at the RHIC have also improved the constraints on the u and d polarization 113 . Exciting results, in particular, for the double spin asymmetries in inclusive jet production from the RHIC experiments have provided a stronger constraint on the gluon helicity 114 (FIG.…”

Electron-ion collider in China

“…The theories and models which explain this asymmetry also predict the asymmetry for polarized light sea quarks [41][42][43]. Moreover, the measurement of the longitudinal spin asymmetries for weak boson production in proton-proton collisions at RHIC [44] suggests a difference between the ∆ū and ∆d helicity distributions as well. Another interesting issue is the polarized distribution of the strange (s) quark and its contribution to the proton spin.…”

“…Another interesting issue is the polarized distribution of the strange (s) quark and its contribution to the proton spin. Assuming the SU (3) flavor symmetry, one finds that the analysis of DIS data [45,46] indicates that the strange quark contribution to the proton spin is roughly −0.1. It is well-known that the strange quark contribution can be directly probed by semi-inclusive DIS (SIDIS).…”

Working Group 6 Summary: Spin and 3D Structure

“…These results include a full underlying event correction and they have since been published [41]. In conclusion of first part of the W-boson program, parity violating single spin asymmetries from PHENIX and STAR have been published and are available for the inclusion in global analyses to improve the determination of the sea quark polarization [42,43,44]. New theoretical tools have been developed to extract ∆g in polarized semi-inclusive deep inelastic scattering using heavy quark production at NLO [45,46], which will be important for the study of the gluon fusion process at a future EIC.…”