Narrow Results

The study of Drell–Yan (DY) processes involving the collision of an (un)polarised hadron beam on an (un)polarised proton target can result in a fundamental improvement of our knowledge on the transverse momentum dependent (TMDs) parton distribution functions (PDFs) of hadrons. The production mechanism of J/ψ and J/ψ - DY duality can also be addressed. One of the forthcoming polarised DY experiments (COMPASS (SPS, CERN)) is discussed in this context. The most important features of this project are briefly reviewed, as well as its sensitivity to the various transverse momentum dependent spin asymmetries.

Heavy flavor production is a sensitive probe of the initial gluon density in the nucleon and is modified by the entire evolution of the hot quark and gluon medium created in high-energy nucleus–nucleus collisions. Besides, it is a process that can be calculated by perturbative QCD because of their large mass. The PHENIX experiment at RHIC studied the heavy flavor productions for a broad momentum and rapidity ranges using single leptons from the semileptonic decay of charm and bottom hadrons, and dileptons from $J/\psi$ decays in $p+p$, $p+$A, and Au$+$Au collisions at $\sqrt{s_{NN}}$$=$200GeV. In these proceedings, the recent experimental results in $p+p$, Au$+$Au, and the small collision systems are presented and the heavy flavor productions and their modifications are discussed.

Recent measurements of charm production at HERA are presented. They include measurements of charm fragmentation fractions, of charm production in DIS and of inelastic and exclusive J/ψ photoproduction. Charm measurements have been combined and analysed in the framework of a QCD fit to inclusive and charm data.

A significant excess of $J/\psi$ yield at very low transverse momentum ($p_T<0.3$ GeV/c) has been observed by the ALICE Collaboration in peripheral Pb+Pb collisions, which points to evidence of coherent photoproduction of $J/\psi$ in violent hadronic interactions. The survival of photoproduced $J/\psi$ merits more experimental investigations. In this article, we report on the STAR measurements of $J/\psi$ production at very low transverse momenta ($p_T$) in hadronic Au+Au collisions at $\sqrt{s_{\text{NN}}}$ = 200 GeV and U+U collisions at $\sqrt{s_{\text{NN}}}$ = 193 GeV at mid-rapidity. Centrality dependence of $J/\psi$ yields and nuclear modification factors at very low $p_T$ are presented.

In this article we discuss the science enabled by heavy quarkonium production in electro-and photo-production on a proton, its possible relation to the determination of the trace anomaly contribution to the proton mass, and the search of LHCb charm pentaquark. We describe the elastic threshold J/ψ production experiments carried out or planned at Jefferson Lab. We also discuss a possible elastic threshold ϒ electroproduction measurement on a proton at a future electron ion collider (EIC).