# Study of coherent $J/\psi$ production in lead-lead collisions at $\sqrt{s_{\rm NN}} =5\ \rm{TeV}$ with the LHCb experiment

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## Abstract

Coherent production of ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ mesons is studied in lead-lead collision data at a nucleon-nucleon centre-of-mass energy of $5\mathrm{ Te V}$ collected by the LHCb experiment. The data set corresponds to an integrated luminosity of about $10 {\mathrm{ \upmu b}^{-1}}$. The ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ mesons are reconstructed in the dimuon final state, where the muons are detected within the pseudorapidity region $2.0 < \eta < 4.5$. The ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ mesons are required to have transverse momentum $p_{\mathrm{ T}} <1\mathrm{ Ge V}$ and rapidity $2.0 < {y} < 4.5$. The cross-section times branching fraction within this fiducial region is measured to be $\sigma= 5.3 \pm {0.2} (stat) \pm {0.5} (syst) \pm {0.7} (lumi)\mathrm{ mb}$. The cross-section is also measured in five bins of ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ rapidity. The results are compared to predictions from phenomenological models.

## Figures and captions

 Dimuon invariant mass spectrum in the range between $2.7$ and $4.0\mathrm{ Ge V}$. The contribution of (solid blue line) ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ , (solid green line) $\psi {(2S)}$ and (black dashed line) nonresonant are shown individually and the sum of all contributions is represented by the orange curve. Fig1.pdf [22 KiB] HiDef png [248 KiB] Thumbnail [189 KiB] *.C file Distribution of $\log( p_{\mathrm{ T}}^{2} )$ of dimuon candidates after all requirements have been applied. The orange line represents the fit to the data points; the blue line shows the coherent contribution and the green (black) line shows the incoherent and feed-down (nonresonant) component. A fit is performed to data using three different templates obtained from the STARlight event generator. Fig2.pdf [247 KiB] HiDef png [247 KiB] Thumbnail [188 KiB] *.C file Differential cross-section for coherent ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ production compared to different phenomenological predictions. The LHCb measurements are shown as points, where inner and outer error bars represent the statistical and the total uncertainties respectively. Fig3.pdf [16 KiB] HiDef png [365 KiB] Thumbnail [240 KiB] *.C file Distribution of $\log( p_{\mathrm{ T}} )$ for dimuon candidates after all cuts have been applied before (black) and after (red) using HeRSCheL information. Fig4.pdf [16 KiB] HiDef png [127 KiB] Thumbnail [128 KiB] *.C file Differential cross-section for coherent ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ production compared to NRQCD predictions \cite{Guzey:2016piu}. The LHCb measurements are shown as points, where inner and outer error bars represent the statistical and the total uncertainties respectively. Fig3-guzey.pdf [15 KiB] HiDef png [215 KiB] Thumbnail [151 KiB] *.C file Differential cross-section for coherent ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ production compared to Colour-Dipole based predictions using the boosted Gaussian (BG) wave function \cite{PhysRevC.84.011902,Goncalves:2017wgg} and the Gauss-LC (GLC) wave function \cite{PhysRevC.84.011902,Goncalves:2017wgg}. The LHCb measurements are shown as points, where inner and outer error bars represent the statistical and the total uncertainties respectively. Fig3-g[..].pdf [15 KiB] HiDef png [257 KiB] Thumbnail [177 KiB] *.C file Differential cross-section for coherent ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ production compared to Colour-Dipole based predictions from Ref. \cite{Cepila:2017nef}. The LHCb measurements are shown as points, where inner and outer error bars represent the statistical and the total uncertainties respectively. Fig3-c[..].pdf [14 KiB] HiDef png [143 KiB] Thumbnail [121 KiB] *.C file Differential cross-section for coherent ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ production compared to Colour-Dipole based predictions with and without taking into account initial state fluctuations \cite{Mantysaari:2017dwh}. The LHCb measurements are shown as points, where inner and outer error bars represent the statistical and the total uncertainties respectively. Fig3-m[..].pdf [14 KiB] HiDef png [145 KiB] Thumbnail [122 KiB] *.C file Animated gif made out of all figures. CONF-2018-003.gif Thumbnail

## Tables and captions

 Relative systematic uncertainties considered for the cross-section measurement of coherent ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ production. The first two contributions are taken from Ref. \cite{LHCb-PAPER-2018-011}. Table_1.pdf [26 KiB] HiDef png [109 KiB] Thumbnail [52 KiB] tex code Cross-section measured differentially in ${ J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ rapidity. The first quoted uncertainty is statistical and the second systematic, where the luminosity component (correlated across all bins) has been removed. Table_2.pdf [30 KiB] HiDef png [113 KiB] Thumbnail [56 KiB] tex code

## Supplementary Material [file]

 Supplementary material full pdf Supple[..].pdf [101 KiB] Fig1-S.pdf [15 KiB] HiDef png [215 KiB] Thumbnail [151 KiB] *C file Fig2-S.pdf [15 KiB] HiDef png [257 KiB] Thumbnail [177 KiB] *C file Fig3-S.pdf [14 KiB] HiDef png [143 KiB] Thumbnail [121 KiB] *C file Fig4-S.pdf [14 KiB] HiDef png [145 KiB] Thumbnail [122 KiB] *C file

Created on 18 January 2020.