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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{\,TeV} $ 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{\,GeV} $ 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.

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Dimuon invariant mass spectrum in the range between $2.7$ and $4.0\mathrm{\,GeV} $. 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.

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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.

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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.

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Distribution of $\log( p_{\mathrm{ T}} )$ for dimuon candidates after all cuts have been applied before (black) and after (red) using HeRSCheL information.

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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.

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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.

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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.

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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.

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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}.

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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.

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Supplementary Material [file]

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Created on 09 December 2018.Citation count from INSPIRE on 09 December 2018.