Possible studies of polarized structure functions for the spin-1 deuteron at hadron accelerator facilities


Seminar of the department “Theory of Fundamental Interactions”

Date and Time: Thursday, 21 May 2020, at 11:00 AM

Venue: Online conference in Zoom, Bogoliubov Laboratory of Theoretical Physics

Seminar topic: «Possible studies of polarized structure functions for the spin-1 deuteron at hadron accelerator facilities»

Speaker: Shunzo Kumano (KEK/J-PARC)


I discuss possible studies of polarized structure functions for the spin-1 deuteron at hadron accelerator facilities, such as NICA (Nuclotron-based Ion Collider fAcility), Fermilab, RHIC, J-PARC, and GSI-FAIR. In particular, I explain tensor-polarized structure functions and gluon transversity. These topics are discussed in the proton-deuteron Drell-Yan processes by taking Fermilab kinematics, so that they may not be used directly for the JINR-NICA spin project, SPD (Spin Physics Detector for physics with polarized beams) [1]. However, measurements should be possible by other observables.

Tensor-polarized structure functions b_{1-4} of a spin-1 hadron are additional observables which do not exist for the spin-1/2 nucleons. Among them, the twist-2 ones are b_1 and b_2. First, we calculated b_1 in the standard convolution description for the deuteron [2] and found large differences between our theoretical results and HERMES data [3]. The large differences may require physics beyond the standard deuteron model. Second, I discuss how the tensor-polarized PDFs could be studied by the proton-deuteron Drell-Yan process [4]. The advantage of the Drell-Yan process is to probe the tensor-polarized antiquark distributions. In particular, the HERMES collaboration indicated a finite antiquark tensor polarization by finding a deviation from the b_1 sum rule of Ref.[5]. We predicted the tensor-polarization asymmetry for the Fermilab-E1039 experiment. We also found a significant tensor-polarized gluon distribution due to the Q^2 evolution.

Next, we proposed to investigate the gluon transversity distribution at hadron accelerator facilities. Although there was recent experimental progress on quark transversity distributions, there is no experimental information on the gluon transversity. In fact, the gluon transversity does not exist for the spin-1/2 nucleons due to the helicity-conservation constraint. One needs a hadron with spin more than or equal to one, so that the helicity flip of two units is allowed. In our work, we proposed the possibility for finding the gluon transversity at hadron-accelerator facilities, especially in the proton-deuteron Drell-Yan process, by showing theoretical formalism and numerical results [6]. This Drell-Yan experiment is under consideration in the Fermilab-E1039 experiment. The NICA project could also contribute to this topic. Since the internal spin-1/2 nucleons within the deuteron cannot contribute directly to the gluon transversity, it could be a good observable to find a new non-nucleonic component beyond the simple bound system of nucleons in nuclei.

[1] A. Guskov, http://theor.jinr.ru/~bystr/SeminarHadronPhysics/2020.html.
[2] W. Cosyn et al., Phys. Rev. D 95 (2017) 074036.
[3] A. Airapetian et al., Phys. Rev. Lett. 95 (2005) 242001.
[4] S. Kumano and Qin-Tao Song, Phys. Rev. D 94 (2016) 054022.
[5] F. E. Close and S. Kumano, Phys. Rev. D 42 (1990) 2377.
[6] S. Kumano and Qin-Tao Song, Phys. Rev. D 101 (2020) 054011 & 094013.