Quarkonia and heavy-flavour production in CMS

TL;DR

This paper reports CMS measurements of quarkonium suppression in PbPb collisions at 2.76 TeV, revealing significant suppression patterns that shed light on quark-gluon plasma properties and heavy-flavor quark energy loss.

Contribution

It provides new detailed measurements of quarkonium suppression across different states, rapidities, and transverse momenta in heavy-ion collisions at LHC energies.

Findings

Strong suppression of non-prompt J/psi indicating b-quark energy loss.

Prompt J/psi shows centrality-dependent suppression at high p_T.

Excited bottomonium states are more suppressed than the ground state.

Abstract

The Compact Muon Solenoid (CMS) has measured numerous quarkonium states via their decays into muon pairs in pp and PbPb collisions at sqrt(s_NN) = 2.76 TeV. Quarkonia are especially relevant for studying the quark-gluon plasma since they are produced at early times and propagate through the medium, mapping its evolution. Non-prompt J/psi from b-hadron decays show a strong suppression in the transverse momentum range (6.5 < p_T < 30 GeV/c) when compared to the yield in pp collisions scaled by the number of inelastic nucleon-nucleon collisions. This suppression is related to the in-medium b-quark energy loss. In the same kinematic region, for prompt J/psi, a strong, centrality-dependent suppression is observed in PbPb collisions. Such strong suppression at high p_T has previously not been observed at RHIC. At midrapidity (|y| < 1.6) and the same p_T region, inclusive psi(2S) are even stronger suppressed than J/psi, whereas psi(2S) at forward rapidity (1.6 < |y| < 2.4) and lower p_T (3 < p_T < 30 GeV/c) appear to be less suppressed than J/psi, however, with large uncertainties that prevent a conclusion. Furthermore, low-p_T Y(2S) and Y(3S) mesons are strongly suppressed in PbPb collisions. The suppression of the Y(1S) state is smaller than the suppression of the excited states and consistent with the suppression of the feed-down contribution only.