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Study of $\psi(2S)$ production and cold nuclear matter effects in $p$Pb collisions at $\sqrt {s_{NN}} = 5$ TeV

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Abstract

The production of $\psi(2S)$ mesons is studied in dimuon final states using proton-lead collision data collected by the LHCb detector. The data sample corresponds to an integrated luminosity of $1.6 \mathrm{nb}^{-1}$. The nucleon-nucleon centre-of-mass energy of the proton-lead collisions is $\sqrt{s_{NN}}=5 \mathrm{TeV}$. The measurement is performed using $\psi(2S)$ mesons with transverse momentum less than $14 \mathrm{GeV}/c$ and rapidity $y$ in the ranges $1.5<y<4.0$ and $-5.0<y<-2.5$ in the nucleon-nucleon centre-of-mass system. The forward-backward production ratio and the nuclear modification factor are determined for $\psi(2S)$ mesons. Using the production cross-section results of $\psi(2S)$ and $J/\psi$ mesons from $b$-hadron decays, the $b\bar{b}$ cross-section in pPb collisions at $\sqrt{s_{NN}}=5 \mathrm{TeV}$ is obtained.

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Projections of the fit results to (top) the dimuon invariant mass $ M_{\mu\mu}$ and (bottom) the pseudo proper decay time $ t_z$ in (left) $ p\mathrm{Pb} $ forward and (right) backward data. In all plots the total fitted function is shown by the (black) solid line, the combinatorial background component is shown as the (green) hatched area, the prompt signal component by the (blue) shaded area, and the $b$-component by the (red) light solid line.

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Differential cross-section of $\psi {(2S)}$ meson production as a function of (left) $p_{\mathrm{ T}}$ and (right) $ y$ in $ p\mathrm{Pb}$ forward collisions. The (black) dots represent inclusive $\psi {(2S)}$ , the (blue) triangles indicate prompt $\psi {(2S)}$ , and the (red) squares show $\psi {(2S)}$ from $b$. The error bars indicate the total uncertainties.

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Differential cross-section of $\psi {(2S)}$ meson production as a function of (left) $p_{\mathrm{ T}}$ and (right) $ y$ in $ p\mathrm{Pb}$ backward collisions. The error bars indicate the total uncertainties.

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Forward-backward production ratios $ R_{ {FB}} $ as functions of (left) $|y|$ and (right) $p_{\mathrm{ T}}$ for inclusive $\psi {(2S)} $ mesons, together with inclusive $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ results [19] and the theoretical predictions [3,4,5], only some of which are available for $|y|$. The inner error bars (delimited by the horizontal lines) show the statistical uncertainties; the outer ones show the statistical and systematic uncertainties added in quadrature.

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Ratio (left) between nuclear modification factors of $\psi {(2S)}$ and $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ as a function of $y$ for prompt $\psi {(2S)} $ mesons and $\psi {(2S)}$ from $ b $ . The blue triangles represent prompt $\psi {(2S)}$ and the red rectangles indicate $\psi {(2S)}$ from $ b $ . Ratio (right) between nuclear modification factors of $\psi {(2S)}$ and $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ as a function of $y$ for inclusive $\psi {(2S)} $ mesons. The black dots show the LHCb result, the hollow circles indicate the ALICE result, and the brown triangle is the PHENIX result at $0.2\mathrm{\,TeV} $. The inner error bars (delimited by the horizontal lines) show the statistical uncertainties; the outer ones show the statistical and systematic uncertainties added in quadrature.

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Nuclear modification factor $ R_{p\mathrm{Pb}}$ as a function of $y$ for inclusive $\psi {(2S)} $ and $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ mesons. The black dots represent the $\psi {(2S)}$ result, the red squares indicate the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ result, and the blue hollow circles show the ALICE result for $\psi {(2S)}$ . The inner error bars (delimited by the horizontal lines) show the statistical uncertainties; the outer ones show the statistical and systematic uncertainties added in quadrature.

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Nuclear modification factor $ R_{p\mathrm{Pb}}$ as a function of $y$ for (left) prompt $\psi {(2S)} $ and (right) $\psi {(2S)}$ from $b$, together with the theoretical predictions from (yellow dashed line and brown band) Refs. [3,47], (blue band) Ref. [5], and (green solid and blue dash-dotted lines) Ref. [4], where only those from Ref. [47] are available for $\psi {(2S)}$ from $ b $ . The inner error bars (delimited by the horizontal lines) show the statistical uncertainties; the outer ones show the statistical and systematic uncertainties added in quadrature.

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Tables and captions

Summary of the relative systematic uncertainties on cross-section measurements (%).

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Integrated production cross-sections for prompt $\psi {(2S)}$ , $\psi {(2S)}$ from $b$, and inclusive $\psi {(2S)}$ in the forward region and the backward region. The $p_{\mathrm{ T}}$ range is $ p_{\mathrm{ T}} <14 {\mathrm{\,GeV\!/}c} $. The first uncertainty is statistical and the second is systematic.

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Production cross-sections $\sigma( b \overline b )$ of $ b \overline b $ pairs in $ p\mathrm{Pb}$ collisions obtained from the production cross-sections of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and $\psi {(2S)}$ from $b$. The superscript $\psi$ denotes $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ or $\psi {(2S)}$ . The first uncertainties are statistical, the second are systematic, and the third are due to the production branching fractions. The last row gives the averaged results, with the first uncertainty uncorrelated and the second correlated.

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Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.