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

Rohini M Godbole,Anuradha Misra,Abhiram Kaushik

doi:10.1103/physrevd.97.076001

Rohini M Godbole, Anuradha Misra + Show 1 more

Open Access

https://doi.org/10.1103/physrevd.97.076001

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Abstract

We study the low-virtuality inclusive leptoproduction of open charm, $p^\uparrow l\rightarrow D^0+X$ as a probe of the gluon Sivers function. We perform the analysis in a generalised parton model framework. At leading order, this process is sensitive only to the gluon content of the proton. Hence any detection of a transverse single-spin 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\%.

Highlights

Transverse single-spin asymmmetries (SSA) can provide crucial information on the three-dimensional structure of hadrons and have been a subject of increasing interest in the past two decades
We present estimates of the upper bound on the asymmetry as obtained with a maximal gluon Sivers function
Before going into the results, we should first make a note on the differing kinematic conventions of the two experiments: As COMPASS is a fixed target experiment, by convention the lepton is taken to be along the þz direction

Summary

INTRODUCTION

Transverse single-spin asymmmetries (SSA) can provide crucial information on the three-dimensional structure of hadrons and have been a subject of increasing interest in the past two decades. An extraction of the GSF using large-pT hadron production is contaminated by the quark contributions to the SSA and would depend on the extent to which these different processes can be separated in a data sample With this being the first significant evidence for a nonzero GSF, it is important to study processes such as closed and open charm production which probe the gluon channel cleanly and directly. While present data on open-charm production in COMPASS is limited due to statistics, the proposed Electron-Ion Collider [19] would have a significantly higher luminosity and should be able to provide better data on open/closed charm production For both experiments, we present estimates for the maximum magnitude of SSA as obtained using the saturated GSF, and the expected values of SSA obtained using the fits of Ref. IV, we discuss results for both the COMPASS and the EIC kinematics

THE GPM FORMALISM

PARAMETRIZATION OF THE TMDS

RESULTS

COMPASS

Single-spin asymmetry in open-charm decay muons

CONCLUSIONS