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Study of $\Upsilon$ production in $p$Pb collisions at $\sqrt{s_{NN}}=8.16$ TeV

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Abstract

The production of $\Upsilon(nS)$ mesons ($n=1,2,3$) in $p$Pb and Pb$p$ collisions at a centre-of-mass energy per nucleon pair $\sqrt{s_{NN}}=8.16$ TeV is measured by the LHCb experiment, using a data sample corresponding to an integrated luminosity of 31.8 nb$^{-1}$. The $\Upsilon(nS)$ mesons are reconstructed through their decays into two opposite-sign muons. The measurements comprise the differential production cross-sections of the $\Upsilon(1S)$ and $\Upsilon(2S)$ states, their forward-to-backward ratios and nuclear modification factors, performed as a function of the transverse momentum \pt and rapidity in the nucleon-nucleon centre-of-mass frame $y^*$ of the $\Upsilon(nS)$ states, in the kinematic range $p_{\rm{T}}<25$ GeV/$c$ and $1.5<y^*<4.0$ ($-5.0<y^*<-2.5$) for $p$Pb (Pb$p$) collisions. In addition, production cross-sections for $\Upsilon(3S)$ are measured integrated over phase space and the production ratios between all three $\Upsilon(nS)$ states are determined. The measurements are compared to theoretical predictions and suppressions for quarkonium in $p$Pb collisions are observed.

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Invariant-mass distribution of $\mu^+\mu^-$ pairs from the (left) $p$Pb and (right) Pb$p$ samples after the trigger and off\-line selections.

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Total efficiency $\varepsilon_{\mathrm{tot}} $ of the { $\Upsilon{(1S)}$ } meson as a function of its $p_{\mathrm{ T}}$ in different $y^*$ bins in (left) $p$Pb and (right) Pb$p$ collisions. The horizontal locations of the markers are roughly the centroids of the bins, with offsets from centre to aid in readability.

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Double-differential cross-section for the { $\Upsilon{(1S)}$ } meson as a function of $p_{\mathrm{ T}}$ for different values of $y^*$ for the (left) forward $p$Pb and (right) backward Pb$p$ samples. The uncertainties are the sums in quadrature of the statistical and systematic components. The horizontal locations of the markers are roughly the centroids of the bins, with offsets from centre to aid in readability.

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Cross-section of (left) { $\Upsilon{(1S)}$ } and (right) { $\Upsilon{(2S)}$ } production as a function of $y^*$ integrated over $p_{\mathrm{ T}}$ for the backward (negative $y^*$) and forward (positive $y^*$) samples, compared to the cross-section measured in $pp$, interpolated to $\sqrt{s_{\scriptscriptstyle\rm NN}} =8.16\mathrm{\,TeV} $. In this and subsequent figures, the uncertainties shown are the sums in quadrature of the statistical and systematic components.

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Cross-section of (top) { $\Upsilon{(1S)}$ } and (bottom) { $\Upsilon{(2S)}$ } production as a function of $p_{\mathrm{ T}}$ integrated over $y^*$ for the (left) forward and (right) backward samples compared to the cross-section measured in $pp$, interpolated to $\sqrt{s_{\scriptscriptstyle\rm NN}} =8.16\mathrm{\,TeV} $.

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Nuclear modification factors of the (left) { $\Upsilon{(1S)}$ } and (right) { $\Upsilon{(2S)}$ } mesons as a function of $y^*$ integrated over $p_{\mathrm{ T}}$ for the forward and backward samples. The bands correspond to the theoretical predictions for the nCTEQ15 and EPPS16 nPDFs sets, and the comovers model as reported in the text.

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Nuclear modification factors of the (top) { $\Upsilon{(1S)}$ } and (bottom) { $\Upsilon{(2S)}$ } mesons as a function of $p_{\mathrm{ T}}$ integrated over $y^*$ for the (left) forward and (right) backward samples. The bands correspond to the theoretical predictions for the nCTEQ15 and EPPS16 nPDFs sets as reported in the text.

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Forward-backward ratio for the { $\Upsilon{(1S)}$ } as a function of (left) $p_{\mathrm{ T}}$ integrated over $y^*$ and (right) as a function of $|y^*|$ integrated over $p_{\mathrm{ T}}$ . The bands correspond to the theoretical calculations for the nCTEQ15 and EPPS16 nPDFs sets as reported in the text.

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Forward-backward ratio for the { $\Upsilon{(2S)}$ } compared with theoretical calculations for the nCTEQ15 and EPPS16 nPDFs sets as reported in the text.

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Ratios between { $\Upsilon{(2S)}$ } and { $\Upsilon{(1S)}$ } cross-sections as a function of (top) $p_{\mathrm{ T}}$ integrated over $y^*$, and as function of (bottom) $y^*$ integrated over $p_{\mathrm{ T}}$ , for $p$Pb and Pb$p$ collisions. The bands correspond to the theoretical predictions for the nCTEQ15 and EPPS16 nPDFs sets as reported in the text.

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Double ratios for (left) { $\Upsilon{(2S)}$ } and (right) { $\Upsilon{(3S)}$ }. The bands correspond to the theoretical prediction for the comovers model as reported in the text.

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Ratio of { $\Upsilon{(1S)}$ } to nonprompt $ { J \mskip -3mu/\mskip -2mu\psi \mskip 2mu}$ cross-sections as a function of $y^*$ integrated over $p_{\mathrm{ T}}$ , for $p$Pb and Pb$p$ collisions.

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Tables and captions

Yields of ${\Upsilon{(1S)} }$, ${\Upsilon{(2S)} }$, ${\Upsilon{(3S)} }$ mesons in $p$Pb and Pb$p$ samples as given by the fit. The uncertainties are statistical only.

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Systematic uncertainties (in percent) on the cross-section measurements. The ranges indicate the minimum and maximum values in different bins, among all \Y nS states.

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Ratio $R(\Y nS)$ in $pp$, $p$Pb, and Pb$p$ samples. The uncertainties are combinations of statistical and systematical components.

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{ $\Upsilon{(1S)}$ } production cross-section in $p$Pb, as a function of $ p_{\mathrm{ T}} $ and $y^*$.

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{ $\Upsilon{(1S)}$ } production cross-section in Pb$p$, as a function of $ p_{\mathrm{ T}} $ and $y^*$.

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{ $\Upsilon{(1S)}$ } production cross-section in $p$Pb and Pb$p$, as a function of $ p_{\mathrm{ T}} $.

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{ $\Upsilon{(1S)}$ } production cross-section in $p$Pb and Pb$p$, as a function of $y^*$.

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{ $\Upsilon{(2S)}$ } production cross-section in $p$Pb and Pb$p$, as a function of $ p_{\mathrm{ T}} $.

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{ $\Upsilon{(2S)}$ } production cross-section in $p$Pb, as a function of $y^*$.

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Scaled $pp$ differential cross-section in $p_{\mathrm{ T}}$ at $\sqrt{s_{\scriptscriptstyle\rm NN}} =8.16$ TeV. The first uncertainty is statistical, the second is systematic, which includes the systematic uncertainty from the $pp$ measurement and that estimated by changing the interpolation function.

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Scaled $pp$ differential cross-section in $y$ at $\sqrt{s_{\scriptscriptstyle\rm NN}} =8.16$ TeV. The first uncertainty is statistical, the second is systematic, which includes the systematic uncertainty from the $pp$ measurement and that estimated by changing the interpolation function.

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$\Upsilon(1S)$ nuclear modification factor, $R_{p{\rm Pb}}^{\Upsilon(1S)}$, 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$p$.

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$\Upsilon(1S)$ nuclear modification factor, $R_{p{\rm Pb}}^{\Upsilon(1S)}$, in $p$Pb and Pb$p$ as a function of $y^*$ integrated over $ p_{\mathrm{ T}} $ in the range $0 < p_{\mathrm{ T}} < 25$ $ {\mathrm{\,GeV\!/}c} $ .

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$\Upsilon(2S)$ nuclear modification factor, $R_{p{\rm Pb}}^{\Upsilon(2S)}$, 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$p$.

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$\Upsilon(2S)$ nuclear modification factor, $R_{p{\rm Pb}}^{\Upsilon(2S)}$, in $p$Pb and Pb$p$ as a function of $y^*$ integrated over $ p_{\mathrm{ T}} $ in the range $0 < p_{\mathrm{ T}} < 25$ $ {\mathrm{\,GeV\!/}c} $ .

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$\Upsilon(1S)$ forward-to-backward ratio, $R_{{\rm FB}}^{\Upsilon(1S)}$, as a function of $ p_{\mathrm{ T}} $ integrated over $\vert y^* \vert$ in the range $2.5 < \vert y^* \vert < 4.0$.

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$\Upsilon(1S)$ forward-to-backward ratio, $R_{{\rm FB}}^{\Upsilon(1S)}$, as a function of $\vert y^* \vert$ integrated over $ p_{\mathrm{ T}} $ in the range $0 < p_{\mathrm{ T}} < 25$ $ {\mathrm{\,GeV\!/}c} $ .

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$\Upsilon(2S)$ forward-to-backward ratio, $R_{{\rm FB}}^{\Upsilon(2S)}$, as a function of $ p_{\mathrm{ T}} $ integrated over $\vert y^* \vert$ in the range $2.5 < \vert y^* \vert < 4.0$.

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$\Upsilon(2S)$ forward-to-backward ratio, $R_{{\rm FB}}^{\Upsilon(2S)}$, as a function of $\vert y^* \vert$ integrated over $ p_{\mathrm{ T}} $ in the range $0 < p_{\mathrm{ T}} < 25$ $ {\mathrm{\,GeV\!/}c} $ .

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$\Upsilon(2S)$ to $\Upsilon(1S)$ ratio, $R({\Upsilon{(2S)} })$, 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$p$.

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$\Upsilon(2S)$ to $\Upsilon(1S)$ ratio, $R({\Upsilon{(2S)} })$, in $p$Pb and Pb$p$ as a function of $y^*$ integrated over $ p_{\mathrm{ T}} $ in the range $0 < p_{\mathrm{ T}} < 25$ $ {\mathrm{\,GeV\!/}c} $ .

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$\Upsilon(1S)$ to nonprompt $J/\psi$, in $p$Pb and Pb$p$ as a function of $y^*$ integrated over $ p_{\mathrm{ T}} $ in the range $0 < p_{\mathrm{ T}} < 25$ $ {\mathrm{\,GeV\!/}c} $ . The quoted uncertainties are the sum in quadrature of the statistical and systematic components.

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Created on 17 February 2019.Citation count from INSPIRE on 17 February 2019.