Gluodissociation and Screening of Upsilon States in PbPb Collisions at sqrt (s_NN) = 2.76 TeV

TL;DR

This paper investigates the suppression of excited Upsilon states in lead-lead collisions at the LHC, attributing it to gluon-induced dissociation and screening effects, and compares the theoretical calculations with CMS experimental data.

Contribution

It introduces a combined model of gluodissociation and screening effects to explain Upsilon suppression, with calculations based on a screened Cornell potential and thermal gluon distributions.

Findings

The suppression pattern of Y(2S) and Y(3S) states matches CMS observations.

Screening causes the dissolution of the 3S state before significant gluodissociation.

Gluodissociation accurately explains the suppression of the Y(1S) state.

Abstract

We suggest that gluon-induced dissociation and screening of the Y(nS) states explain the suppression of the Y(2S+3S) states relative to the Y(1S) ground state that has been observed by CMS in PbPb collisions at sqrt(s_NN)= 2.76 TeV at the CERN LHC. The minimum-bias gluodissociation cross sections of the 1S-3S states are calculated using a screened Cornell potential and a thermal gluon distribution. The 3S state dissolves due to screening before sizeable gluodissociation occurs, but for the 2S and 1S states there is an interplay between screening, gluodissociation, and feed-down from the chi_b(2P) and chi_b(1P) states. Based on a schematic approach, we find that the calculated suppression of the Y(2S) and Y(3S) states relative to Y(1S) is consistent with the CMS result, but allows for additional suppression mechanisms. The Y(1S) suppression through gluodissociation is, however, in good agreement with the CMS data.