Abstract
The production yields of ϒ(1S), ϒ(2S), and ϒ(3S) quarkonium states are measured through their decays into muon pairs in the CMS detector, in PbPb and pp collisions at the centre-of-mass energy per nucleon pair of 2.76 TeV. The data correspond to integrated luminosities of 166μb−1 and 5.4pb−1 for PbPb and pp collisions, respectively. Differential production cross sections are reported as functions of ϒ rapidity y up to 2.4, and transverse momentum pT up to 20GeV/c. A strong centrality-dependent suppression is observed in PbPb relative to pp collisions, by factors of up to ≈2 and 8, for the ϒ(1S) and ϒ(2S) states, respectively. No significant dependence of this suppression is observed as a function of y or pT. The ϒ(3S) state is not observed in PbPb collisions, which corresponds to a suppression for the centrality-integrated data by at least a factor of ≈7 at a 95% confidence level. The observed suppression is in agreement with theoretical scenarios modeling the sequential melting of quarkonium states in a quark gluon plasma.
Highlights
At large energy density and high temperature, strongly interacting matter is predicted by lattice QCD calculations to consist of a deconfined system of quarks and gluons [1]
The suppression of Υ(1S) production in heavy ion collisions relative to pp yields scaled by the number of binary nucleon–nucleon (NN) collisions was first measured by CMS [15] in the midrapidity range | y| < 2.4, by ALICE at forward rapidities 2.5 < y < 4
To put the pp and PbPb data on a comparable scale, the corrected yields are normalized by the measured integrated luminosity in pp collisions, and by the product of the number of corresponding minimum bias (MB) events and the centrality-integrated the nuclear overlap function (TAA) value for PbPb collisions
Summary
At large energy density and high temperature, strongly interacting matter is predicted by lattice QCD calculations to consist of a deconfined system of quarks and gluons [1] This state, often referred to as “quark gluon plasma” (QGP) [2], constitutes the main object of studies using high energy heavy ion collisions. The suppression of Υ(1S) production in heavy ion collisions relative to pp yields scaled by the number of binary nucleon–nucleon (NN) collisions was first measured by CMS [15] in the midrapidity range | y| < 2.4, by ALICE at forward rapidities 2.5 < y < 4. In pPb [20] reported collisions at Υ(1S) yields that are slightly suppressed along the p-going forward direction, possibly indicating√the reference data at sNN importance = 5.02 TeV, of nuclear effects. The yields in PbPb and pp events are used to extract nuclear modification factors, RAA
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