Quarkonium production in high energy proton-proton and proton-nucleus collisions

TL;DR

This review synthesizes the state of quarkonium production in high-energy pp and pA collisions, highlighting the theoretical tension between color-singlet and color-octet mechanisms and the role of higher-order QCD corrections. It emphasizes cold nuclear matter effects, polarization puzzles, and the crucial link to open heavy-flavor production, proposing new observables such as hadronic activity and associated production to better discriminate production mechanisms. The authors discuss regeneration as a potential explanation for J/psi yields in AA, and stress the need for multi-frame polarization analyses and LHC-era measurements to disentangle CS/CO contributions and CNM effects. Overall, they argue that quarkonia remain powerful probes of QCD and the quark-gluon plasma, contingent on refined measurements and complementary observables.

Abstract

We present a brief overview of the most relevant current issues related to quarkonium production in high energy proton-proton and proton-nucleus collisions along with some perspectives. After reviewing recent experimental and theoretical results on quarkonium production in pp and pA collisions, we discuss the emerging field of polarisation studies. Thereafter, we report on issues related to heavy-quark production, both in pp and pA collisions, complemented by AA collisions. To put the work in a broader perspective, we emphasize the need for new observables to investigate quarkonium production mechanisms and reiterate the qualities that make quarkonia a unique tool for many investigations in particle and nuclear physics.

Figures (30)

• Figure 1: The preliminary mid rapidity inclusive $J/\psi$$p_T$ distributions measured by CMS ($|y|<1.4$) and ATLAS ($|y|<0.75$ and $0.75<|y|<1.5$). Data compilation courtesy of H. Wöhri.
• Figure 2: The preliminary forward rapidity inclusive $J/\psi$$p_T$ distributions measured by CMS ($1.4<|y|<2.4$), ATLAS ($1.5<|y|<2.25$), LHCb ($2.5<y<4.0$) and ALICE ($2.5<y<4.0$). Data compilation courtesy of E. Scomparin and H. Wöhri.
• Figure 3: The preliminary fraction of non-prompt $J/\psi$ as a function of $p_T$ measured by CMS ($|y|<1.4$ & $1.4<|y|<2.4$), ATLAS ($|y|<2.25$) and LHCb ($2.5<y<4$). Data compilation courtesy of H. Wöhri.
• Figure 4: The preliminary measurement of $\langle p_T^2 \rangle$ from ALICE compared with lower energy data Scomparin:QQ10.
• Figure 5: Comparison between the LO CSM prediction for $d\sigma^{direct}_{J/\psi}/dy\times {\rm Br}$ from $gg$ fusion LO contributions in $pp$ collisions at $\sqrt{s}=7$ TeV compared to ALICE boyer, ATLAS ATLAS-JPsi, CMS CMS:2010yr and LHCb LHCb-JPsi results multiplied by the direct fraction (and correcting for the non-prompt component, assumed to be 10%, if applicable). Adapted from Lansberg:2010cn.