TMDs of Spin-one Targets: Formalism and Covariant Calculations

TL;DR

This paper develops a covariant formalism and model calculations for transverse momentum-dependent quark distributions in spin-one hadrons, revealing their sensitivity to quark orbital angular momentum and the effects of chiral symmetry breaking.

Contribution

It introduces a covariant description of TMDs for spin-one hadrons and applies it to $ ho$ mesons within the NJL model, highlighting novel insights into tensor polarized distributions.

Findings

Tensor polarized TMDs are highly sensitive to quark orbital angular momentum.

Approximately 44% of the $ ho$ meson's spin is from quark orbital angular momentum.

Tensor polarized quark distributions are about 30% of unpolarized distributions.

Abstract

We present a covariant formulation and model calculations of transverse momentum-dependent quark distribution functions (TMDs) for spin-one hadrons. Emphasis is placed on a description of these 3-dimensional distribution functions which is independent of any constraints on the spin quantization axis. We apply our covariant spin description to all nine leading-twist time-reversal even $\rho$ meson TMDs in the framework provided by the Nambu--Jona-Lasinio model, incorporating important aspects of quark confinement via the infrared cut-off in the proper-time regularization scheme. In particular, the behavior of the 3-dimensional TMDs in a tensor polarized spin-one hadron are illustrated. Sum rules and positivity constraints are discussed in detail. Results of particular interest include the finding that the tensor polarized TMDs -- associated with spin-one hadrons -- are very sensitive to quark orbital angular momentum, and that the TMDs associated with the quark operator $\gamma^+\boldsymbol{\gamma}_T\gamma_5$ would vanish were it not for dynamical chiral symmetry breaking. In addition, we find that 44% of the $\rho$ meson's spin is carried by the orbital angular momentum of the quarks, and that the magnitude of the tensor polarized quark distribution function is about 30% of the unpolarized quark distribution. A qualitative comparison between our results for the tensor structure of a quark-antiquark bound state is made to previous experimental and theoretical results for the two-nucleon (deuteron) bound state.