Search

Prospects for quarkonium-production studies accessible during the upcoming high-luminosity phases of the CERN Large Hadron Collider operation after 2021 are reviewed. Current experimental and theoretical open issues in the field are assessed together with the potential for future studies in quarkonium-related physics. This will be possible through the exploitation of the huge data samples to be collected in proton-proton, proton-nucleus and nucleus-nucleus collisions, both in the collider and fixed-target modes. Such investigations include, among others, those of: (i) J/psi and Upsilon produced in association with other hard particles; (ii) chi(c,b) and eta(c,b) down to small transverse momenta; (iii) the constraints brought in by quarkonia on gluon PDFs, nuclear PDFs, TMDs, GPDs and GTMDs, as well as on the low-x parton dynamics; (iv) the gluon Sivers effect in polarised-nucleon collisions; (v) the properties of the quark-gluon plasma produced in ultra-relativistic heavy-ion collisions and of collective partonic effects in general; and (vi) double and triple parton scatterings., Comment: Latex, 115 pages, 55 figures, 4 tables. v2: Review published in Progress in Particle and Nuclear Physics

We consider the transverse single-spin asymmetry (SSA) for $J/\ensuremath{\psi}$ production in ${p}^{\ensuremath{\uparrow}}p\ensuremath{\rightarrow}J/\ensuremath{\psi}+X$ within a phenomenological transverse momentum dependent scheme in nonrelativistic QCD. Extending a previous study [U. D'Alesio et al., Eur. Phys. J. C 79, 1029 (2019)], we employ here the color-gauge invariant generalized parton model (CGI-GPM), in which spin and intrinsic transverse momentum effects are taken into account, together with leading-order initial- and final-state interactions (ISIs and FSIs). We find that, even when the heavy-quark pair is produced in a color-octet state, ISIs and FSIs lead to a nonvanishing SSA, allowing us, in principle, to test the process dependence of the gluon Sivers function (GSF). We show that of the two independent contributions, due to the so-called $f$- and $d$-type GSFs, appearing in the CGI-GPM, the $d$-type one turns out to be dynamically suppressed. Therefore, as already found adopting the Color-Singlet Model approach for the $J/\ensuremath{\psi}$ formation [U. D'Alesio et al., Phys. Rev. D 96, 036011 (2017)], only the $f$-type GSF could play a role in phenomenology. A comparison with the corresponding results obtained in the generalized parton model, without the inclusion of ISIs and FSIs, is also carried out.

We calculate the Sivers and $$\cos 2\phi $$ azimuthal asymmetries in $$J/\psi $$ production in the polarized and unpolarized semi-inclusive ep collision, respectively, using the formalism based on the transverse momentum-dependent parton distributions (TMDs). The non-relativistic QCD-based color octet model is employed in calculating the $$J/\psi $$ production rate. The Sivers asymmetry in this process directly probes the gluon Sivers function. The estimated Sivers asymmetry at $$z=1$$ is negative, which is in good agreement with the COMPASS data. The effect of TMD evolution on the Sivers asymmetry is also investigated. The $$\cos 2\phi $$ asymmetry is sizable and probes the linearly polarized gluon distribution in an unpolarized proton.

We calculate the transverse single-spin asymmetry (SSA) for $$J/\psi $$J/ψ production in proton-proton collisions, within non-relativistic QCD, employing the transverse momentum dependent, generalized parton model, which includes both spin and intrinsic motion effects. In particular, we study the role of the color octet mechanism in accessing the gluon Sivers function. In doing that, we also show, within this approach, how the singularities coming from color octet terms in the low-$$P_T$$PT region can be handled, leading to finite cross sections. Predictions for both unpolarized cross sections and SSAs are given and compared against PHENIX data. Estimates for LHCb in the fixed target mode are also presented.

The prediction of single-spin asymmetry in inelastic photoproduction of $J/\ensuremath{\psi}$ in $e{p}^{\ensuremath{\uparrow}}$ collision is presented. At next-to-leading order, the dominating process is photon-gluon fusion, $\ensuremath{\gamma}+g\ensuremath{\rightarrow}J/\ensuremath{\psi}+g$ for the production of $J/\ensuremath{\psi}$ in $e+{p}^{\ensuremath{\uparrow}}\ensuremath{\rightarrow}J/\ensuremath{\psi}+X$, which directly probes the gluon Sivers function. Using the nonrelativistic QCD based color octet model, the color octet states ${^{3}S}_{1}^{(8)}$, ${^{1}S}_{0}^{(8)}$ and ${^{3}P}_{J(0,1,2)}^{(8)}$ contribution to $J/\ensuremath{\psi}$ production is calculated. Sizable asymmetry is estimated as a function of transverse momentum ${P}_{T}$ and energy fraction $z$ of $J/\ensuremath{\psi}$ in the range $0l{P}_{T}\ensuremath{\le}1\text{ }\text{ }\mathrm{GeV}$ and $0.3lz\ensuremath{\le}0.9$. The unpolarized differential cross section of inelastic $J/\ensuremath{\psi}$ photoproduction is found to be in good agreement with H1 and ZEUS data.

We study the possibility to probe the unpolarized and linearly polarized transverse momentum- dependent gluon distributions in unpolarized pp collision in charmonium and bottomonium produc- tion, employing non-relativistic QCD (NRQCD) based color octet model within transverse momentum dependent (TMD) factorization framework. The transverse momentum (p T ) and rapidity distributions of J/{\psi} and {\Upsilon}(1S) at LHCb, RHIC and AFTER energies are estimated. Significant modulations in transverse momentum spectrum of quarkonium in the low p T region is obtained when contributions of linearly polarized gluons inside an unpolarized proton are taken into account. The results of quarko- nium production in color octet model and color evaporation model are compared., Comment: Replaced with the revised version, to appear in PRD

We propose the study of unpolarized transverse momentum dependent gluon parton distributions as well as the effect of linearly polarized gluons on transverse momentum and rapidity distributions of $J/\psi$ and $\Upsilon$ production within the framework of transverse momentum dependent factorization employing color evaporation model (CEM) in unpolarized proton-proton collision. We estimate the transverse momentum and rapidity distributions of $J/\psi$ and $\Upsilon$ at LHCb, RHIC and AFTER energies using TMD evolution formalism., Comment: 25 pages, 10 figures