Abstract
The ratio between the prompt ψ(2S) and J/ψ yields, reconstructed via their decays into μ+ μ-, is measured in Pb-Pb and p-p collisions at sqrt[sNN]=2.76 TeV. The analysis is based on Pb-Pb and p-p data samples collected by CMS at the Large Hadron Collider, corresponding to integrated luminosities of 150 μb(-1) and 5.4 pb(-1), respectively. The double ratio of measured yields (Nψ(2S)/N(J/ψ))(Pb-Pb)/(Nψ(2S)/N(J/ψ))(p-p) is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, |y|<1.6, covering the transverse momentum range 6.5<pT<30 GeV/c, and the other at forward rapidity, 1.6<|y|<2.4, extending to lower pT values, 3<pT<30 GeV/c. The centrality-integrated double ratio changes from 0.45±0.13(stat)±0.07(syst) in the first range to 1.67±0.34(stat)±0.27(syst) in the second. This difference is most pronounced in the most central collisions.
Highlights
The ratio measured between the prompt ψð2SÞ andpJffiffi=ffiffiψffiffiffi in Pb-Pb and p-p collisions at sNN yields, 1⁄4 2.76 reconstructed via their decays TeV
The double ratio of measured yields ðNψð2SÞ=NJ=ψ ÞPb-Pb= ðNψð2SÞ=NJ=ψ Þp-p is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, jyj < 1.6, covering the transverse momentum range 6.5 < pT < 30 GeV=c, and the other at forward rapidity, 1.6 < jyj < 2.4, extending to lower pT values, 3 < pT < 30 GeV=c
Charmonia should dissociate when the Debye screening radius of this medium, which decreases with increasing quark-gluon plasma temperature, becomes smaller than the binding radius of the charmonium state [2]
Summary
The ratio measured between the prompt ψð2SÞ andpJffiffi=ffiffiψffiffiffi in Pb-Pb and p-p collisions at sNN yields, 1⁄4 2.76 reconstructed via their decays TeV. The double ratio of measured yields ðNψð2SÞ=NJ=ψ ÞPb-Pb= ðNψð2SÞ=NJ=ψ Þp-p is computed in three Pb-Pb collision centrality bins and two kinematic ranges: one at midrapidity, jyj < 1.6, covering the transverse momentum range 6.5 < pT < 30 GeV=c, and the other at forward rapidity, 1.6 < jyj < 2.4, extending to lower pT values, 3 < pT < 30 GeV=c. This Letter presents a measurement of the prompt ψð2SÞ and J=ψ hadrons) yields In the Pb-Pb fits, instead, the double ratio replaces the ψð2SÞ to J=ψ ratio as one of the free parameters Given their smaller signal-to-background ratio, the Pb-Pb data are fitted fixing the σG=σCB ratio to the value obtained in fits to MC distributions. The simultaneous fit directly provides the three double ratios (one per centrality class) for each rapidity interval
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