/ nucl-ex CMS-HIN-12-007

Measurement of prompt $\psi(2\mathrm{S})$ to $\mathrm{J}/\psi$ yield ratios in $\mathrm{Pb}\mathrm{Pb}$ and $\mathrm{p}\mathrm{p}$ collisions at $\sqrt{s_\mathrm{NN}} = 2.76~\mathrm{TeV}$

Pages: 27

Abstract: The ratio between the prompt $\psi(2\mathrm{S})$ and $\mathrm{J}/\psi$ yields, reconstructed via their decays into $\mu^+\mu^-$, is measured in $\mathrm{Pb}\mathrm{Pb}$ and $\mathrm{p}\mathrm{p}$ collisions at $\sqrt{s_\mathrm{NN}} = 2.76~\mathrm{TeV}$. The analysis is based on $\mathrm{Pb}\mathrm{Pb}$ and $\mathrm{p}\mathrm{p}$ data samples collected by CMS at the LHC, corresponding to integrated luminosities of $150~\mu\mathrm{b}^{-1}$ and $5.4~\mathrm{pb}^{-1}$, respectively. The double ratio of measured yields, $(N_{\psi(2\mathrm{S})} / N_{\mathrm{J}/\psi})_{\mathrm{Pb}\mathrm{Pb}} / (N_{\psi(2\mathrm{S})} / N_{\mathrm{J}/\psi})_{\mathrm{p}\mathrm{p}}$, is computed in three $\mathrm{Pb}\mathrm{Pb}$ collision centrality bins and two kinematic ranges: one at midrapidity, $|y|$ < $1.6$, covering the transverse momentum range $6.5$ < $p_{\mathrm{T}}$ < $30~\mathrm{GeV}/c$, and the other at forward rapidity, $1.6$ < $|y|$ < $2.4$, extending to lower $p_{\mathrm{T}}$ values, $3$ < $p_{\mathrm{T}}$ < $30~\mathrm{GeV}/c$. The centrality-integrated double ratio changes from $0.45 \pm 0.13~\mathrm{(stat)} \pm 0.07~\mathrm{(syst)}$ in the first range to $1.67 \pm 0.34~\mathrm{(stat)} \pm 0.27~\mathrm{(syst)}$ in the second. This difference is most pronounced in the most central collisions.

Note: Submitted to Phys. Rev. Lett

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