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Prompt and nonprompt J/$\psi$ production and nuclear modification in $p$Pb collisions at $\sqrt{s_{\text{NN}}}= 8.16$ TeV

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Abstract

The production of J/$\psi$ mesons is studied in proton-lead collisions at the centre-of-mass energy per nucleon pair $\sqrt{s_{\text{NN}}}=8.16$ TeV with the LHCb detector at the LHC. The double differential cross-sections of prompt and nonprompt J/$\psi$ production are measured as functions of the J/$\psi$ transverse momentum and rapidity in the nucleon-nucleon centre-of-mass frame. Forward-to-backward ratios and nuclear modification factors are determined. The results are compared with theoretical calculations based on collinear factorisation using nuclear parton distribution functions, on the colour glass condensate or on coherent energy loss models.

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(left) Invariant mass and (right) pseudo proper time distributions for $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ candidates in the bin $6< p_{\mathrm{ T}} <7 {\mathrm{ Ge V /}c} $ and $3.5<|y^*|<4.0$ for the (top) $p$Pb and (bottom) Pb$p$ samples respectively. The black circles with error bars represent the LHCb data. The projection of the result of the fit described in the text is drawn on each distribution: the red solid line is the total fit function, the blue dashed line is the prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ signal component, the purple solid line is the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons signal component and the green dashed line is the combinatorial background component.

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Total $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ detection efficiency, $\epsilon_{\text{tot}}$, as a function of the $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ $p_{\mathrm{ T}}$ in different $y^*$ bins for (left) $p$Pb and (right) Pb$p$.

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Production cross-section for (top left) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ in $p$Pb, (top right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons in $p$Pb, (bottom left) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ in Pb$p$ and (bottom right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons in Pb$p$. The data points are placed at the centre of the $p_{\mathrm{ T}}$ bins, the horizontal error bars indicate the bin widths and the vertical error bars the total uncertainties, calculated as quadratic sums of the statistical and systematic uncertainties.

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Fraction of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons, $f_b$, as a function of $p_{\mathrm{ T}}$ for (from top to bottom) $1.5<|y^*|<2.0$, $2.0<|y^*|<2.5$, $2.5<|y^*|<3.0$, $3.0<|y^*|<3.5$, $3.5<|y^*|<4.0$, $4.0<|y^*|<4.5$ and $4.5<|y^*|<5.0$. The data points are placed at the centre of the $p_{\mathrm{ T}}$ bins, the horizontal error bars indicate the bin widths and the vertical error bars the total uncertainties, calculated as quadratic sums of the statistical and systematic uncertainties. Blue circles are for $p$Pb collisions, red squares for Pb$p$ collisions and black triangles for $pp$ collisions at $8 {\rm TeV}$ taken from Ref. [64].

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Absolute production cross-sections of (left) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and (right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons, as a function of $y^*$, integrated over the range $0< p_{\mathrm{ T}} <14 {\mathrm{ Ge V /}c} $. The black circles are the $p$Pb and Pb$p$ values and the red open squares the values for $pp$ collisions at the same energy, multiplied by the Pb mass number $A=208$. The horizontal error bars are the bin widths and vertical error bars the total uncertainties.

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Absolute production cross-sections of (top left) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ in $p$Pb, (top right) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ in Pb$p$, (bottom left) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons in Pb$p$ and (bottom left) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons in Pb$p$, as a function of $ p_{\mathrm{ T}} $ and integrated over the rapidity range of the analysis. The black circles are the $p$Pb and Pb$p$ values and the red open squares the values for $pp$ collisions at the same energy, multiplied by the Pb mass number $A=208$, integrated over the same rapidity ranges. The horizontal error bars are the bin widths and vertical error bars the total uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ nuclear modification factor, $R_{p{\rm Pb}}$, integrated over $y^*$ in the analysis range, as a function of $p_{\mathrm{ T}}$ for (top left) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ in $p$Pb, (bottom left) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons in $p$Pb, (top right) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ in Pb$p$ and (bottom right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons in Pb$p$. Horizontal error bars are the bin widths, vertical error bars the total uncertainties. The black circles are the values measured in this letter and the coloured areas the theoretical predictions from the models detailed in the text with their uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ nuclear modification factor, $R_{p{\rm Pb}}$, integrated over $p_{\mathrm{ T}}$ in the range $0< p_{\mathrm{ T}} <14 {\mathrm{ Ge V /}c} $, as a function of $y^*$ for (left) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and (right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons. The horizontal error bars are the bin widths and vertical error bars the total uncertainties. The black circles are the values measured in this letter, the red squares the values measured at $\sqrt{s_{NN}}=5 {\rm TeV}$ from Ref. [27] and the coloured areas the theoretical computations from the models detailed in the text, with their uncertainties.

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Forward-to-backward ratios, $R_{{\rm FB}}$, integrated over the common rapidity range $2.5<|y^*|<4.0$ as a function of $p_{\mathrm{ T}}$ for (left) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and (right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons. The horizontal error bars are the bin widths and the vertical error bars the total uncertainties. The black circles are the values measured in this letter, the red squares the values measured at $\sqrt{s_{NN}}=5 {\rm TeV}$ from Ref. [27] and the coloured areas the theoretical computations from the models detailed in the text, with their uncertainties.

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Forward-to-backward ratios, $R_{{\rm FB}}$, integrated over $p_{\mathrm{ T}}$ in the range $0< p_{\mathrm{ T}} <14 {\mathrm{ Ge V /}c} $ as a function of $|y^{*}|$ for (left) prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and (right) $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons. The horizontal error bars are the bin widths and the vertical error bars the total uncertainties. The black circles are the values measured in this letter, the red squares the values measured at $\sqrt{s_{NN}}=5 {\rm TeV}$ from Ref. [27] and the coloured areas the theoretical computations from the models detailed in the text, with their uncertainties.

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Tables and captions

Summary of relative systematic uncertainties in $p$Pb and Pb$p$ on the cross-section of prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ and $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons. Uncertainties that are computed bin-by-bin are expressed as ranges giving the minimum to maximum values. The last column indicates the correlation between bins within the same beam configuration.

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Prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ absolute production cross-section in $p$Pb, as a function of $p_{\mathrm{ T}}$ and $y^*$. The quoted uncertainties are the total uncertainties, and the breakdown into statistical uncertainties, and correlated and uncorrelated systematic uncertainties.

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Prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ absolute production cross-section in $p$Pb, as a function of $p_{\mathrm{ T}}$ and $y^*$. The quoted uncertainties are the total uncertainties, and the breakdown into statistical uncertainties, and correlated and uncorrelated systematic uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons absolute production cross-section in $p$Pb, as a function of $p_{\mathrm{ T}}$ and $y^*$. The quoted uncertainties are the total uncertainties, and the breakdown into statistical uncertainties, and correlated and uncorrelated systematic uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons absolute production cross-section in $p$Pb, as a function of $p_{\mathrm{ T}}$ and $y^*$. The quoted uncertainties are the total uncertainties, and the breakdown into statistical uncertainties, and correlated and uncorrelated systematic uncertainties.

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Prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ absolute production cross-section in Pb$p$, as a function of $p_{\mathrm{ T}}$ and $y^*$. The quoted uncertainties are the total uncertainties, and the breakdown into statistical uncertainties, and correlated and uncorrelated systematic uncertainties.

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Prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ absolute production cross-section in Pb$p$, as a function of $p_{\mathrm{ T}}$ and $y^*$. The quoted uncertainties are the total uncertainties, and the breakdown into statistical uncertainties, and correlated and uncorrelated systematic uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons absolute production cross-section in Pb$p$, as a function of $p_{\mathrm{ T}}$ and $y^*$. The quoted uncertainties are the total uncertainties, and the breakdown into statistical uncertainties, and correlated and uncorrelated systematic uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons absolute production cross-section in Pb$p$, as a function of $p_{\mathrm{ T}}$ and $y^*$. The quoted uncertainties are the total uncertainties, and the breakdown into statistical uncertainties, and correlated and uncorrelated systematic uncertainties.

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Fraction of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons, $f_b$, in $p$Pb in bins of $p_{\mathrm{ T}}$ and $y^*$. The uncertainty is the quadratic sum of statistical and systematic uncertainties.

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Fraction of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons, $f_b$, in $p$Pb in bins of $p_{\mathrm{ T}}$ and $y^*$. The uncertainty is the quadratic sum of statistical and systematic uncertainties.

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Fraction of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons, $f_b$, in Pb$p$ in bins of $p_{\mathrm{ T}}$ and $y^*$. The uncertainty is the quadratic sum of statistical and systematic uncertainties.

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Fraction of $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons, $f_b$, in Pb$p$ in bins of $p_{\mathrm{ T}}$ and $y^*$. The uncertainty is the quadratic sum of statistical and systematic uncertainties.

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Prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ nuclear modification factor, $R_{p{\rm Pb}}$, in $p$Pb and Pb$p$ as a function of $p_{\mathrm{ T}}$ integrated over $y^*$ in the range $1.5<y^*<4.0$ for $p$Pb and $-5.0<y^*<-2.5$ for Pb$p$. The quoted uncertainties are the quadratic sums of statistical and systematic uncertainties.

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Prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ nuclear modification factor, $R_{p{\rm Pb}}$, in $p$Pb and Pb$p$ as a function of $y^*$ integrated over $p_{\mathrm{ T}}$ in the range $0< p_{\mathrm{ T}} <14 {\mathrm{ Ge V /}c} $. The quoted uncertainties are the quadratic sums of statistical and systematic uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons nuclear modification factor, $R_{p{\rm Pb}}$, in $p$Pb and Pb$p$ as a function of $p_{\mathrm{ T}}$ integrated over $y^*$ in the range $1.5<y^*<4.0$ for $p$Pb and $-5.0<y^*<-2.5$ for Pb$p$. The quoted uncertainties are the quadratic sums of statistical and systematic uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons nuclear modification factor, $R_{p{\rm Pb}}$, in $p$Pb as a function of $y^*$ integrated over $p_{\mathrm{ T}}$ in the range $0< p_{\mathrm{ T}} <14 {\mathrm{ Ge V /}c} $. The quoted uncertainties are the quadratic sums of statistical and systematic uncertainties.

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Prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ forward-to-backward ratio, $R_{{\rm FB}}$, as a function of $p_{\mathrm{ T}}$ integrated over $|y^*|$ in the range $2.5<|y^*|<4.0$. The quoted uncertainties are the quadratic sums of statistical and systematic uncertainties.

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Prompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ forward-to-backward ratio, $R_{{\rm FB}}$, as a function of $y^*$ integrated over $p_{\mathrm{ T}}$ in the range $0< p_{\mathrm{ T}} <14 {\mathrm{ Ge V /}c} $. The quoted uncertainties are the quadratic sums of statistical and systematic uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons forward-to-backward ratio, $R_{{\rm FB}}$, as a function of $p_{\mathrm{ T}}$ integrated over $|y^*|$ in the range $2.5<|y^*|<4.0$. The quoted uncertainties are the quadratic sums of statistical and systematic uncertainties.

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$ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ -from-$b$-hadrons forward-to-backward ratio, $R_{{\rm FB}}$, as a function of $y^*$ integrated over $p_{\mathrm{ T}}$ in the range $0< p_{\mathrm{ T}} <14 {\mathrm{ Ge V /}c} $. The quoted uncertainties are the quadratic sums of statistical and systematic uncertainties.

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Created on 06 March 2021.