Speaker
Description
Prompt heavy quarkonium production is well described within the collinear parton model in the next-to-leading order of perturbaive QCD at kinematical region of $p_T^{} \gg M$ where $M$ is a mass of a quarkonium state. But the region of small $p_T^{}$ is still being researched and the factorisation approach which is valid here is TMD-factorisation (transverse-momentum dependent). We studied $J/\psi$ production in collision of protons at $\sqrt{s} = 200, 27$ and $19.4$ GeV. Certainly, we used Nonrelativistic QCD (NRQCD) as a standard hadronisation model for charmonium production, and we extracted nonperturbative matrix elements for octet color states of the NRQCD from a set of experimental data on prompt $J/\psi$ production because color singlet model can't be considered as sufficient for experimental data description.
The TMD approach is a general factorisation model for $p_T^{} \ll M$ region [1]. One of the realisations of the TMD-factorisation is a so called Soft Gluon Resummation approach [2] where soft gluon emission by partons is considered, evolution of the TMD parton distribution functions is controlled by the Collins -- Soper equations [3] though the TMD distribution is partly reduced to the collinear one. We perform our study at the LO$+$LL approximation for now. We describe data from PHENIX Collaboration at $\sqrt{s} = 200$ GeV and from NA3 Collaboration at $\sqrt{s} = 19.4$ GeV and do predictions for future SPD NICA experiments at $\sqrt{s} = 27$ GeV. We considered both gluons and quarks as initial partons, we also estimated a contribution of $P$-wave charmonium production and calculated polarised $J/\psi$ production as an angular coefficient $\lambda$. The Inverse-Error Weighting Scheme [4] is used as an approach for matching of collinear and TMD factorisations.
References:
[1] J. C. Collins. Foundations of Perturbative QCD, Cambridge Univ. Press, Cambridge (2011).
[2] J. Bor and D. Boer. TMD evolution study of the $\cos 2\phi$ azimuthal asymmetry in unpolarized $J/\psi$ production at EIC, Phys. Rev. D 106, 1 (2022).
[3] J. C. Collins, D. E. Soper, and G. Sterman. Transverse momentum distribution in Drell-Yan pair and $W$ and $Z$ boson production, Nuclear Physics B 250 (1-4), 199--224 (1985).
[4] M. G. Echevarria, T. Kasemets, J.-P. Lansberg, C. Pisano, A. Signori. Matching factorization theorems with an inverse-error weighting, Phys. Lett. B 781, 161--168 (2018).
