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

Abstract

Tensor-polarized structure functions of a spin-1 hadron are additional observables, which do not exist for the spin-1=2 nucleon. They could probe novel aspects of the internal hadron structure. Twist-2 tensor-polarized structure functions are b 1 and b 2 , and they are related by the Callan-Gross-like relation in the Bjorken scaling limit. In this work, we theoretically calculate b 1 in the standard convolution description for the deuteron. Two different theoretical models, a basic convolution description and a virtual nucleon approximation, are used for calculating b 1 , and their results are compared with the HERMES measurement. We found large differences between our theoretical results and the data. Although there is still room to improve by considering higher-twist effects and in the experimental extraction of b 1 from the spin asymmetry A zz , there is a possibility that the large differences require physics beyond the standard deuteron model for their interpretation. Future b 1 studies could shed light on a new field of hadron physics. In particular, detailed experimental studies of b 1 will start soon at the Thomas Jefferson National Accelerator Facility. In addition, there are possibilities to investigate tensorpolarized parton distribution functions and b 1 at Fermi National Accelerator Laboratory and a future electron-ion collider. Therefore, further theoretical studies are needed for understanding the tensor structure of the spin-1 deuteron, including a new mechanism to explain the large differences between the current data and our theoretical results.

ρ meson unpolarized generalized parton distributions with a light-front constituent quark model

“…It should be mentioned that the spin-1 particle, different from the spin-1/2 one, has the tensor structure function b 1 . It triggers great interest [58][59][60][61][62]. The sum rule of this structure function is dxb 1 (x) = 0 [58].…”

The energy-momentum tensor of spin-1 hadrons: formalism

“…On the other hand, its internal structure and dynamics are the ultimate effect of the interactions between the elementary constituents, and this makes the deuteron a promising avenue towards understanding how QCD produces the force that binds nucleons together in nuclei [23]. After the first measurement by the HERMES collaboration of a tensor polarized collinear structure function of the deuteron [24], the so-called b 1 function defined in [25], it became clearer that going beyond the single-nucleon formulation is needed to describe the experimental data, especially in specific regions of the parton momentum range [26][27][28][29][30].…”

Theoretical perspective for the future experiments on parton densities

“…The deuteron structure has been investigated for a long time at low energies and it is described as a bound system of proton and neutron in mainly S wave with small D-wave admixture. Using this standard model with a convolution formalism for the deuteron structure function b 1 , we obtained the solid curve [12], which is very different from the HERMES measurements, as shown in Fig. 9.…”