# 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.

## Figures and captions

 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. Fig1a.pdf [19 KiB] HiDef png [668 KiB] Thumbnail [135 KiB] *.C file Fig1b.pdf [19 KiB] HiDef png [701 KiB] Thumbnail [145 KiB] *.C file Fig1c.pdf [17 KiB] HiDef png [410 KiB] Thumbnail [93 KiB] *.C file Fig1d.pdf [17 KiB] HiDef png [303 KiB] Thumbnail [75 KiB] *.C file 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. Fig2a.pdf [15 KiB] HiDef png [126 KiB] Thumbnail [52 KiB] *.C file Fig2b.pdf [15 KiB] HiDef png [128 KiB] Thumbnail [53 KiB] *.C file 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. Fig3a.pdf [14 KiB] HiDef png [76 KiB] Thumbnail [18 KiB] *.C file Fig3b.pdf [14 KiB] HiDef png [75 KiB] Thumbnail [19 KiB] *.C file 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. Fig4a.pdf [16 KiB] HiDef png [463 KiB] Thumbnail [79 KiB] *.C file Fig4b.pdf [17 KiB] HiDef png [258 KiB] Thumbnail [74 KiB] *.C file 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. Fig5a.pdf [14 KiB] HiDef png [124 KiB] Thumbnail [54 KiB] *.C file Fig5b.pdf [14 KiB] HiDef png [148 KiB] Thumbnail [63 KiB] *.C file 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. Fig6.pdf [14 KiB] HiDef png [139 KiB] Thumbnail [62 KiB] *.C file 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. Fig7a.pdf [17 KiB] HiDef png [666 KiB] Thumbnail [102 KiB] *.C file Fig7b.pdf [15 KiB] HiDef png [411 KiB] Thumbnail [69 KiB] *.C file Animated gif made out of all figures. PAPER-2015-058.gif Thumbnail

## Tables and captions

 Summary of the relative systematic uncertainties on cross-section measurements (%). Table_1.pdf [51 KiB] HiDef png [75 KiB] Thumbnail [11 KiB] tex code 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. Table_2.pdf [34 KiB] HiDef png [45 KiB] Thumbnail [8 KiB] tex code 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. Table_3.pdf [47 KiB] HiDef png [44 KiB] Thumbnail [6 KiB] tex code

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