Transverse momentum dependent shape function for J/ψ production in SIDIS

18 Auguts 2023

 
It has been shown previously that the transverse momentum dependent (TMD) factorization of heavy quarkonium production requires a TMD shape function. Its perturbative tail can be extracted by matching the cross sections valid at low and high transverse momenta. In this article we compare the order-αs TMD expressions with the order-αs² collinear ones for J/ψ production in semi-inclusive deep inelastic scattering (SIDIS), employing nonrelativistic QCD in both cases. In contrast to previous studies, we find that the small transverse momentum limit of the collinear expressions contains discontinuities. We demonstrate how to properly deal with them and include their finite contributions to the TMD shape functions. Moreover, we show that soft gluon emission from the low transverse momentum Born diagrams provide the same leading order TMD shape functions as required for the matching. Their revised perturbative tails have a less divergent behavior as compared to the TMD fragmentation functions of light hadrons. Finally, we investigate the universality of TMD shape functions in heavy quarkonium production, identify the need for process dependent factorization and discuss the phenomenological implications.

TMD evolution study of the cos 2ϕ azimuthal asymmetry in unpolarized J/ψ production at EIC

29 July 2022

Semi-inclusive J/ψ production in electron-proton collisions is a promising process to study gluon transverse momentum distributions (TMDs) at the future electron-ion collider (EIC). In this article, we improve on previous studies of the cos 2ϕ azimuthal asymmetry that arises from the linear polarization of gluons inside unpolarized protons by including TMD evolution. We find that in the TMD regime the asymmetry grows monotonically with increasing transverse momentum of the outgoing J/ψ, in contrast to tree level calculations with Gaussian TMDs. Our predictions for the asymmetry at the EIC can become very large at larger x, Q, and transverse momenta, even larger than the positivity bound. This problem stems from the very small b region and implies a range of validity of TMD factorization that is more restricted than usually expected. We also include an estimate of the nonperturbative uncertainty from the large b region and we conclude that it is smaller than the largest source of uncertainty, which stems from the choice of color octet long-distance matrix elements.

Conferences and Seminars

  • Sardinian Workshop on Spin (June 2023, Cagliari, Italy): TMD evolution study of the azimuthal asymmetry in unpolarized J/ψ production at EIC.
  • Heavy Flavours from small to large systems joint Strong-2020 session ‘Recent results and perspectives in hadron physics’ (October 2022, Orsay, France): Studying gluon TMDs via double J/ψ production in proton-proton collisions.
  • Journal Club Van Swinderen Institute (June 2022, Groningen, Netherlands): TMD evolution study of the cos 2ϕ azimuthal asymmetry in unpolarized J/ψ production at EIC.
  • Quarkonia as Tools (January 2022, Aussois, France): Studies of Gluons TMDs and their evolution using J/ψ production.
  • Quarkonium & QCD Meeting (June 2021, Aussois, France): Low-PT gluon induced J/ψ production at the EIC.