Theoretical estimate on tensor-polarization asymmetry in proton-deuteron Drell-Yan process

Abstract

Tensor-polarized parton distribution functions are new quantities in spin-one hadrons such as the deuteron, and they could probe new quark-gluon dynamics in hadron and nuclear physics. In charged-lepton deep inelastic scattering (DIS), they are studied by the twist-two structure functions b1 and b2. The HERMES collaboration found unexpectedly large b1 values than a naive theoretical expectation based on the standard deuteron model. The situation should be significantly improved in the near future by an approved experiment to measure b1 at JLab (Thomas Jefferson National Accelerator Facility). There is also an interesting indication in the HERMES result that finite antiquark tensor polarization exists. It could play an important role in solving a mechanism on tensor structure in the quark-gluon level. The tensor-polarized antiquark distributions are not easily determined from the charged-lepton DIS; however, they can be measured in a proton-deuteron Drell-Yan process with a tensor-polarized deuteron target. In this article, we estimate the tensorpolarization asymmetry for a possible Fermilab Main-Injector experiment by using optimum tensorpolarized PDFs to explain the HERMES measurement. We find that the asymmetry is typically a few percent. If it is measured, it could probe new hadron physics, and such studies could create an interesting field of high-energy spin physics. In addition, we find that a significant tensorpolarized gluon distribution should exist due to Q 2 evolution, even if it were zero at a low Q 2 scale. The tensor-polarized gluon distribution has never been observed, so that it is an interesting future project.

Tensor-polarized structure function b1 in the standard convolution description of the deuteron

“…Fortunately, a JLab experiment was approved for measuring b 1 accurately at a medium x [28], and also an experiment to measure the tensor-polarization asymmetry A zz at a large x is possible [29], so that the situation should become much clearer in a few years. There is also a possibility to measure the tensor-polarized antiquark distributions in a proton-deuteron Drell-Yan process with the tensor-polarized deuteron target at Fermilab [8][9][10]. Furthermore, it should be an interesting topic to investigate b 1 at the future electron-ion-collider project [30] and other hadron facilities such as Brookhaven National Laboratory-RHIC, CERN-COMPASS, Japan Proton Accelerator Research Complex [46], Gesellschaft für Schwerionenforschung-Facility for Antiproton and Ion Research, and Institute for High Energy Physics in Russia.…”

“…Furthermore, shadowing mechanisms contribute significantly to b 1 at small x [5,6], and pions in the deuteron could also play a role [7]. There are related studies to the spin-1 hadron structure on a polarized proton-deuteron Drell-Yan process [8][9][10], leptoproduction of a spin-one hadron [11], fragmentation functions [12], generalized parton distributions [13], target-mass corrections [14], positivity constraints [15], lattice QCD estimates [16], and angular momenta for the spin-1 hadron [17]. The spin-1 deuteron structure can be also investigated by tagging the final state proton [18].…”

Gluon transversity in polarized proton-deuteron Drell-Yan process

“…In addition to the transversity, there are related studies on polarized deuteron structure functions. For example, the tensor-polarized structure function b 1 will be measured in the near future at JLab [28,29], and polarized proton-deuteron reactions [30] could be investigated at Fermilab for measuring tensor-polarized distribution functions [25,31]. Since the conventional deuteron model cannot explain existing experimental measurements by the HERMES collaboration [32], a new hadronic mechanism would be needed for their interpretation [33].…”

Estimate on Spin Asymmetry for Drell-Yan Process at Fermilab with Tensor-Polarized Deuteron

“…Fortunately, it is possible in the Fermilab-E1039 experiment by the Drell-Yan process with a tensor-polarized deuteron target. The purpose of our research is to calculate the tensor-polarized spin asymmetries of the Drell-Yan process [10] because there was no theoretical estimate to be used for an experimental proposal and future comparison with the data.…”