CMS-PAS-HIN-16-004 | ||

Relative modification of prompt $\psi(2\textrm{S})$ and $\textrm{J}/\psi$ yields from pp to PbPb collisions at $\sqrt{s_{NN}} = $ 5.02 TeV | ||

CMS Collaboration | ||

September 2016 | ||

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Abstract:
The ratios between the yields of prompt $\psi(2\textrm{S})$ and $\textrm{J}/\psi$ mesons, reconstructed via their decays into muon pairs, are compared in PbPb and pp collisions at $\sqrt{s_{NN}} = $ 5.02 TeV. The analysis is based on PbPb and pp data samples collected by the CMS experiment at the LHC in late 2015, corresponding to integrated luminosities of 464 $\mu$b$^{-1}$ and 25.8 pb$^{-1}$, respectively. The double ratio of measured yields of prompt charmonia, $(N_{\psi(2\textrm{S})}/N_{\textrm{J}/\psi})_{\textrm{PbPb}} / (N_{\psi(2\textrm{S})}/ N_{\textrm{J}/\psi})_{\textrm{pp}}$, is determined as a function of PbPb collision centrality and charmonium transverse momentum ($p_\text{T}$), in two rapidity intervals: $|y| < $ 1.6 covering 6.5 $ < p_\text{T} < $ 30 GeV/$c$ and 1.6 $< |y| < $ 2.4 extending down to $p_\text{T} = $ 3 GeV/$c$. The centrality-integrated double ratios are 0.36 $\pm$ 0.08 (stat) $\pm$ 0.05 (syst) in the first interval and 0.24 $\pm$ 0.22 (stat) $\pm$ 0.09 (syst) in the second one. The double ratio is lower than unity in all the measured bins, suggesting that the $\psi(2\textrm{S})$ yield is more suppressed than the $\textrm{J}/\psi$ yield in the explored phase space.
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These preliminary results are superseded in this paper, PRL 118 (2017) 162301.The superseded preliminary plots can be found here. |

Figures | Summary | Additional Figures | References | CMS Publications |
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Figures | |

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Figure 1:
Invariant mass spectrum of ${\mu ^+\mu ^-}$ pairs in PbPb collisions for (left) $ |y|< $ 1.6, 9 $< {p_{\mathrm {T}}} < $ 12 GeV/$c$, all centrality, and (right) 1.6 $ < |y| < $ 2.4, 3 $ < {p_{\mathrm {T}}} < $ 30 GeV/$ c $, 0-20% centrality. Also shown is the result of the fit described in the text. |

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Figure 1-a:
Invariant mass spectrum of ${\mu ^+\mu ^-}$ pairs in PbPb collisions for $ |y|< $ 1.6, 9 $< {p_{\mathrm {T}}} < $ 12 GeV/$c$, all centrality. Also shown is the result of the fit described in the text. |

png pdf |
Figure 1-b:
Invariant mass spectrum of ${\mu ^+\mu ^-}$ pairs in PbPb collisions for 1.6 $ < |y| < $ 2.4, 3 $ < {p_{\mathrm {T}}} < $ 30 GeV/$ c $, 0-20% centrality. Also shown is the result of the fit described in the text. |

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Figure 2:
Transverse momentum dependence of ${(N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{ PbPb } / (N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{{ {\mathrm{ p } \mathrm{ p } }} }}$, for mid (squares) and forward (circles) rapidity, with both muons above the ${p_{\mathrm {T}}}$ threshold described in the text. The arrow represents the 95% CL upper limit in the bin where the measurement is consistent with 0. The vertical lines (bands) represent the statistical (systematic) uncertainties. The horizontal lines represent the width of the ${p_{\mathrm {T}}}$ bins. |

png pdf |
Figure 3:
Event centrality dependence of ${(N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{ PbPb } / (N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{{ {\mathrm{ p } \mathrm{ p } }} }} $, for mid (top) and forward (bottom) rapidity, with both muons above the ${p_{\mathrm {T}}}$ threshold described in the text. Integrated values for all centrality are given in the right panels. The arrows represent 95% CL upper limits in the bins where the measurement is consistent with0. The vertical lines (bands) represent the statistical (systematic) uncertainties. The statistical and systematic uncertainties in the ${ {\mathrm{ p } \mathrm{ p } }}$ measurements, common to all points, are represented as boxes at unity. The measurements from CMS at $ {\sqrt {s_{_{\text {NN}}}}} = $ 2.76 TeV [12] are also shown. |

png pdf |
Figure 3-a:
Event centrality dependence of ${(N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{ PbPb } / (N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{{ {\mathrm{ p } \mathrm{ p } }} }} $, for mid rapidity, with both muons above the ${p_{\mathrm {T}}}$ threshold described in the text. Integrated values for all centrality are given in the right panels. The arrows represent 95% CL upper limits in the bins where the measurement is consistent with0. The vertical lines (bands) represent the statistical (systematic) uncertainties. The statistical and systematic uncertainties in the ${ {\mathrm{ p } \mathrm{ p } }}$ measurements, common to all points, are represented as boxes at unity. The measurements from CMS at $ {\sqrt {s_{_{\text {NN}}}}} = $ 2.76 TeV [12] are also shown. |

png pdf |
Figure 3-b:
Event centrality dependence of ${(N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{ PbPb } / (N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{{ {\mathrm{ p } \mathrm{ p } }} }} $, for forward rapidity, with both muons above the ${p_{\mathrm {T}}}$ threshold described in the text. Integrated values for all centrality are given in the right panels. The arrows represent 95% CL upper limits in the bins where the measurement is consistent with0. The vertical lines (bands) represent the statistical (systematic) uncertainties. The statistical and systematic uncertainties in the ${ {\mathrm{ p } \mathrm{ p } }}$ measurements, common to all points, are represented as boxes at unity. The measurements from CMS at $ {\sqrt {s_{_{\text {NN}}}}} = $ 2.76 TeV [12] are also shown. |

Summary |

In summary, the double ratio ${(N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{ PbPb } / (N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{{ {\mathrm{ p } \mathrm{ p } }} }}$ is measured to compare the relative production of $\textrm{J}/\psi$ and $\psi(2\textrm{S})$ mesons in pp and PbPb collisions at $\sqrt{s_{NN}} = $ 5.02 TeV, as a function of transverse momentum and collision centrality. This quantity is below unity in all bins, suggesting that the $\psi(2\textrm{S})$ yield is more suppressed than the $\textrm{J}/\psi$ yield in the entire explored kinematic range. No strong variations are observed, with charmonium ${p_{\mathrm {T}}}$ or collision centrality. These results should trigger further progress in the understanding of the several medium effects at play in $\textrm{J}/\psi$ and $\psi(2\textrm{S})$ production. |

Additional Figures | |

png pdf |
Additional Figure 1:
Invariant mass spectrum of $\mu ^+\mu ^-$ pairs in pp collisions for $ |y|< $ 1.6, 6.5 $ < p_{\mathrm{T}} < $ 30 GeV/$c$. |

png pdf |
Additional Figure 2:
Invariant mass spectrum of $\mu ^+\mu ^-$ pairs in pp collisions for 1.6 $ < |y| < $ 2.4, 3 $ < p_{\mathrm{T}} < $30 \ GeV/$c$. |

png pdf |
Additional Figure 3:
Invariant mass spectrum of $\mu ^+\mu ^-$ pairs in PbPb collisions for $ |y|< $ 1.6, 6.5 $ < p_{\mathrm{T}} < $ 30 GeV/$c$, all centrality. |

png pdf |
Additional Figure 4:
Invariant mass spectrum of $\mu ^+\mu ^-$ pairs in PbPb collisions for 1.6 < |y| < 2.4, 3 $ < p_{\mathrm{T}} < $ 30 GeV/$c$, all centrality. |

png pdf |
Additional Figure 5:
Event centrality dependence of ${(N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{ PbPb } / (N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{{ {\mathrm{ p } \mathrm{ p } }} }} $ with both muons above the $p_{\mathrm{T}}$ threshold described in the text. Integrated values for all centrality are given in the right panel. Arrows represent 95% CL upper limits in the bins where the measurement is consistent with0. Vertical lines (bands) represent the statistical (systematic) uncertainties. The statistical and systematic uncertainties in the pp measurements, common to all points, are represented as boxes at unity. |

png pdf |
Additional Figure 6:
Transverse momentum dependence of ${(N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{ PbPb } / (N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{{ {\mathrm{ p } \mathrm{ p } }} }} $, for mid (squares) and forward (circles) rapidity, with both muons above the $p_{\mathrm{T}}$ threshold described in the text. The arrow represents the 95% CL upper limit in the bin where the measurement is consistent with 0. Vertical lines (bands) represent the statistical (systematic) uncertainties. Horizontal lines represent the width of the $p_{\mathrm{T}}$ bins. The bands represent the predictions from the model of X.Du and R.Rapp [1] (updated from Ref. [2]). |

png pdf |
Additional Figure 7:
Event centrality dependence of ${(N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{ PbPb } / (N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{{ {\mathrm{ p } \mathrm{ p } }} }} $, for midrapidity, with both muons above the $p_{\mathrm{T}}$ threshold described in the text. Integrated values for all centrality are given in the right panels. Arrows represent 95% CL upper limits in the bins where the measurement is consistent with0. Vertical lines (bands) represent the statistical (systematic) uncertainties. The statistical and systematic uncertainties in the pp measurements, common to all points, are represented as boxes at unity. The measurements from CMS at $\sqrt {s_{_{\text {NN}}}} = $ 2.76 TeV [3] are also shown. The hashed boxes represent the predictions from the model of X.Du and R.Rapp [1] (updated from Ref. [2]). |

png pdf |
Additional Figure 8:
Event centrality dependence of ${(N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{ PbPb } / (N_{ {\psi \text {(2S)}} }/ N_{{\mathrm{J}/\psi } })_{{ {\mathrm{ p } \mathrm{ p } }} }} $, for forward rapidity, with both muons above the $p_{\mathrm{T}}$ threshold described in the text. Integrated values for all centrality are given in the right panels. Arrows represent 95% CL upper limits in the bins where the measurement is consistent with0. Vertical lines (bands) represent the statistical (systematic) uncertainties. The statistical and systematic uncertainties in the pp measurements, common to all points, are represented as boxes at unity. The measurements from CMS at $\sqrt {s_{_{\text {NN}}}} = $ 2.76TeV [3] are also shown. The hashed boxes represent the predictions from the model of X.Du and R.Rapp [1] (updated from Ref. [2]). |

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Compact Muon Solenoid LHC, CERN |