Transverse single-spin asymmetry in the low-virtuality leptoproduction of open charm as a probe of the gluon Sivers function

Abstract

We study the low-virtuality inclusive leptoproduction of open charm, p ↑ l → D 0 þ X as a probe of the gluon Sivers function. We perform the analysis in a generalized parton model framework. At leading order, this process is sensitive only to the gluon content of the proton. Hence any detection of a transverse singlespin asymmetry in this process would be clear indication of a non-zero gluon Sivers function (GSF). Considering COMPASS and a future Electron-Ion Collider (EIC), we present predictions for asymmetry using fits for the GSF available in literature. Predictions for peak asymmetry values lie in the range of 0.8% to 13%. We also present estimates of the upper bound on the asymmetry as obtained with a maximal gluon Sivers function. Further, for the case of the Electron-Ion Collider, we evaluate the asymmetry in the muons decaying from the D-meson and find that the asymmetry is well preserved in the kinematics of the muons. Peak values of the muon asymmetry are close to those obtained for the D-meson and lie in the range 0.75% to 11%.

Computing the gluon Sivers function at small-x

“…Finally in this section we make a connection to observables. An interesting process in which the dipole gluon Sivers function plays a role is single spin asymmetry in open charm production ep ↑ → D 0 X,D 0 X in semi-inclusive DIS [7,11,13]. The spin-dependent part of the differential cross section of charm quark production reads…”

“…While most of the literature deals with the quark Sivers function f ⊥q 1T (x, k ⊥ ), there is a growing interest in the gluon Sivers function f ⊥g 1T (x, k ⊥ ) and its possible manifestation at RHIC and the future Electron-Ion Collider (EIC) and AFTER@LHC [5][6][7][8][9][10][11][12][13][14][15][16][17][18] (see also a review [19]). On general grounds, one expects that the gluon Sivers function is an important or even dominant source of SSA for the production of high mass states such as D-mesons, J/ψ's or dijets.…”

Probing the gluon Sivers function through direct photon production at RHIC

“…In Ref. [26], we proposed the low-virtuality leptoproduction of open charm and studied it in the context of the GPM framework. Unlike hadroproduction, this process does not involve any contributions from quarks and hence can probe the gluon Sivers function effectively.…”

“…We find that after the inclusion of these effects, the dominance of the gluon contribution in the backward region continues even though the SSAs are suppressed. In this work, following our earlier studies of the GSF in open charm production [25,26], we consider estimates for the asymmetry obtained using saturated quark and gluon Sivers functions. The use of saturated QSFs and GSF gives the upper bound on the possible asymmetry and further allows us to study the general kinematic dependencies of the asymmetry and the relative importances of the quark and gluon contributions to the asymmetry.…”

Quarkonium production to explore hadron 3D structure

“…Refs. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]), which encode the rich three-dimensional inner structure of the hadrons in momentum space (see e.g. Ref.…”