Measurement of quarkonium production in proton-lead and proton-proton collisions at 5.02 TeV with the ATLAS detector

Abstract

The modification of the production of $J/\psi$ , $\psi \left(2S\right)$ , and ${\rm Y}\left(nS\right)$ ( $n=1,2,3$ ) in p+Pb collisions with respect to their production in pp collisions has been studied. The p+Pb and pp datasets used in this paper correspond to integrated luminosities of $28{\mathrm{nb}}^{-1}$ and $25{\mathrm{pb}}^{-1}$ respectively, collected in 2013 and 2015 by the ATLAS detector at the LHC, both at a centre-of-mass energy per nucleon pair of 5.02 TeV. The quarkonium states are reconstructed in the dimuon decay channel. The yields of $J/\psi$ and $\psi \left(2S\right)$ are separated into prompt and non-prompt sources. The measured quarkonium differential cross sections are presented as a function of rapidity and transverse momentum, as is the nuclear modification factor, $R_{p\mathrm{Pb}}$ for $J/\psi$ and ${\rm Y}\left(nS\right)$ . No significant modification of the $J/\psi$ production is observed while ${\rm Y}\left(nS\right)$ production is found to be suppressed at low transverse momentum in p+Pb collisions relative to pp collisions. The production of excited charmonium and bottomonium states is found to be suppressed relative to that of the ground states in central p+Pb collisions.

Fig. 1

Projections of the charmonium fit results onto dimuon invariant mass $m_{\mu \mu }$ (left) and pseudo-proper lifetime ${\tau }_{\mu \mu }$ (right) for pp collisions at $\sqrt{s}=5.02\mathrm{TeV}$ (top) for the kinematic ranges $10<p_{\text{T}}^{\mu \mu }<11\text{GeV}$ and $|y|<2.0$, and $p$+Pb collisions at $\sqrt{s_{{}_{\text{NN}}}}=5.02\mathrm{TeV}$ (bottom) for the kinematic ranges $10<p_{\text{T}}^{\mu \mu }<11\text{GeV}$ and $-2.0<y^{\ast }<1.5$. The goodnesses of the invariant mass fits with $\text{ndof}=63$ and the pseudo-proper lifetime fits with $\text{ndof}=153$ are also presented

Fig. 2

Bottomonium fit results in dimuon invariant mass $m_{\mu \mu }$ for pp collisions at $\sqrt{s}=5.02\mathrm{TeV}$ (top) and $p$+Pb collisions at $\sqrt{s_{{}_{\text{NN}}}}=5.02\mathrm{TeV}$ (bottom) for one typical low $p_{\text{T}}^{\mu \mu }$ interval of $1.5<p_{\text{T}}^{\mu \mu }<3\text{GeV}$ (left) and one high $p_{\text{T}}^{\mu \mu }$ interval of $14<p_{\text{T}}^{\mu \mu }<20\text{GeV}$ (right). For all the shown fits, ${\rm Y}(\text{1S})$ acceptance weights are assigned. The goodness of the bottomonium fit with $\text{ndof}=24$ is also presented

Fig. 3

The differential non-prompt production cross section times dimuon branching fraction of $J/\psi$ (left) and $\psi (\text{2S})$ (right) as a function of transverse momentum $p_{\text{T}}$ for three intervals of rapidity y in pp collisions at $5.02\text{TeV}$. For each increasing rapidity slice, an additional scaling factor of 10 is applied to the plotted points for visual clarity. The horizontal position of each data point indicates the mean of the weighted $p_{\text{T}}$ distribution. The horizontal bars represent the range of $p_{\text{T}}$ for the bin, and the vertical error bars correspond to the combined statistical and systematic uncertainties. The FONLL theory predictions (see text) are also shown, and the error bands in the prediction correspond to the combined factorisation scale, quark mass and parton distribution functions uncertainties

Fig. 4

The differential prompt production cross section times dimuon branching fraction of $J/\psi$ (left) and $\psi (\text{2S})$ (right) as a function of transverse momentum $p_{\text{T}}$ for three intervals of rapidity y in pp collisions at $5.02\text{TeV}$. For each increasing rapidity slice, an additional scaling factor of 10 is applied to the plotted points for visual clarity. The horizontal position of each data point indicates the mean of the weighted $p_{\text{T}}$ distribution. The horizontal bars represent the range of $p_{\text{T}}$ for the bin, and the vertical error bars correspond to the combined statistical and systematic uncertainties. The NRQCD theory predictions (see text) are also shown, and the error bands in the prediction correspond to the combined scale, quark mass and LDMEs uncertainties

Fig. 5

The differential production cross section times dimuon branching fraction of ${\rm Y}(\text{1S})$ as a function of transverse momentum $p_{\text{T}}$ for three intervals of rapidity y in pp collisions at $5.02\text{TeV}$. For each increasing rapidity slice, an additional scaling factor of 10 is applied to the plotted points for visual clarity. The horizontal position of each data point indicates the mean of the weighted $p_{\text{T}}$ distribution. The horizontal bars represent the range of $p_{\text{T}}$ for the bin, and the vertical error bars correspond to the combined statistical and systematic uncertainties. The NRQCD theory predictions (see text) are also shown, and the error bands in the prediction correspond to the combined scale, quark mass and LDMEs uncertainties

Fig. 6

The differential production cross section times dimuon branching fraction of ${\rm Y}(\text{2S})$ (left) and ${\rm Y}(\text{3S})$ (right) as a function of transverse momentum $p_{\text{T}}$ for three intervals of rapidity y in pp collisions at $5.02\text{TeV}$. For each increasing rapidity slice, an additional scaling factor of 10 is applied to the plotted points for visual clarity. The horizontal position of each data point indicates the mean of the weighted $p_{\text{T}}$ distribution. The horizontal bars represent the range of $p_{\text{T}}$ for the bin, and the vertical error bars correspond to the combined statistical and systematic uncertainties. The NRQCD theory predictions (see text) are also shown, and the error bands in the prediction correspond to the combined scale, quark mass and LDMEs uncertainties

Fig. 7

The differential cross section times dimuon branching fraction of prompt and non-prompt $J/\psi$ (left) and $\psi (\text{2S})$ (right) as a function of transverse momentum $p_{\text{T}}$ in $p$+Pb collisions at $\sqrt{s_{{}_{\text{NN}}}}=5.02\mathrm{TeV}$. The horizontal position of each data point indicates the mean of the weighted $p_{\text{T}}$ distribution. The horizontal bars represent the range of $p_{\text{T}}$ for the bin, and the vertical error bars correspond to the combined statistical and systematic uncertainties

Fig. 8

The differential cross section times dimuon branching fraction of prompt and non-prompt $J/\psi$ (left) and $\psi (\text{2S})$ (right) as a function of centre-of-mass rapidity $y^{\ast }$ in $p$+Pb collisions at $\sqrt{s_{{}_{\text{NN}}}}=5.02\mathrm{TeV}$. The horizontal position of each data point indicates the mean of the weighted $y^{\ast }$ distribution. The vertical error bars correspond to statistical uncertainties. The vertical sizes of coloured boxes around the data points represent the systematic uncertainties, and the horizontal sizes of coloured boxes represent the range of $y^{\ast }$ for the bin

Fig. 9

Left: the differential cross section times dimuon branching fraction of ${\rm Y}(n\text{S})$ as a function of transverse momentum $p_{\text{T}}$ in $p$+Pb collisions at $\sqrt{s_{{}_{\text{NN}}}}=5.02\mathrm{TeV}$. The horizontal position of each data point indicates the mean of the weighted $p_{\text{T}}$ distribution. The horizontal bars represent the range of $p_{\text{T}}$ for the bin, and the vertical error bars correspond to the combined statistical and systematic uncertainties. Right: the differential cross section times dimuon branching fraction of ${\rm Y}(n\text{S})$ as a function of centre-of-mass rapidity $y^{\ast }$ in $p$+Pb collisions. The horizontal position of each data point indicates the mean of the weighted $y^{\ast }$ distribution. The vertical error bars correspond to statistical uncertainties. The vertical sizes of coloured boxes around the data points represent the systematic uncertainties, and the horizontal sizes of coloured boxes represent the range of $y^{\ast }$ for the bin

Fig. 10

The nuclear modification factor, $R_{p\mathrm{Pb}}$, as a function of transverse momentum $p_{\text{T}}$ for prompt $J/\psi$ (left) and non-prompt $J/\psi$ (right). The horizontal position of each data point indicates the mean of the weighted $p_{\text{T}}$ distribution. The vertical error bars correspond to the statistical uncertainties. The vertical sizes of coloured boxes around the data points represent the uncorrelated systematic uncertainties, and the horizontal sizes of coloured boxes represent the $p_{\text{T}}$ bin sizes. The vertical sizes of the leftmost grey boxes around $R_{p\mathrm{Pb}}=1$ represent the correlated systematic uncertainty

Fig. 11

The nuclear modification factor, $R_{p\mathrm{Pb}}$, as a function of centre-of-mass rapidity $y^{\ast }$ for prompt $J/\psi$ (left) and non-prompt $J/\psi$ (right). The horizontal position of each data point indicates the mean of the weighted $y^{\ast }$ distribution. The vertical error bars correspond to the statistical uncertainties. The vertical sizes of coloured boxes around the data points represent the uncorrelated systematic uncertainties, and the horizontal sizes of coloured boxes represent the $y^{\ast }$ bin sizes. The vertical sizes of the leftmost grey boxes around $R_{p\mathrm{Pb}}=1$ represent the correlated systematic uncertainty

Fig. 12

The nuclear modification factor, $R_{p\mathrm{Pb}}$, as a function of transverse momentum $p_{\text{T}}$ (left) and centre-of-mass rapidity $y^{\ast }$ (right) for ${\rm Y}(\text{1S})$. The horizontal position of each data point indicates the mean of the weighted $p_{\text{T}}$ or $y^{\ast }$ distribution. The vertical error bars correspond to the statistical uncertainties. The vertical sizes of coloured boxes around the data points represent the uncorrelated systematic uncertainties, and the horizontal sizes of coloured boxes represent the bin sizes. The vertical size of the rightmost (left) and leftmost (right) grey boxes around $R_{p\mathrm{Pb}}=1$ represent the correlated systematic uncertainty

Fig. 13

Prompt and non-prompt $J/\psi$, prompt $\psi (\text{2S})$ and ${\rm Y}(\text{1S})$ to Z boson yield ratio, $R_{p\mathrm{Pb}}^Z$, as a function of event centrality in $p$+Pb collisions. The ratio is normalised to the ratio integrated in the centrality range 0–$90\%$. The error bars represent statistical uncertainties. The vertical sizes of coloured boxes around the data points represent the uncorrelated systematic uncertainties, and the vertical size of the leftmost grey box around $R_{p\mathrm{Pb}}^Z=1$ represents the correlated systematic uncertainty

Fig. 14

Self-normalised yield for prompt $J/\psi$, non-prompt $J/\psi$ and ${\rm Y}(\text{1S})$, compared to ${\rm Y}(\text{1S})$ self-normalised yield ratio measured by CMS [26]. The horizontal position of each data point represents the normalised mean value of the $\mathrm{\Sigma }{E}_{\text{T}}^{\mathrm{Backwards}}$ distribution in minimum-bias data sample. The error bar represents statistical uncertainties, and the vertical size of box underneath the data point represents the systematic uncertainties. The dotted line is a linear function with a slope equal to unity

Fig. 15

The prompt charmonium production double ratio, ${\rho }_{p\mathrm{Pb}}^{\psi (\text{2S})/J/\psi }$, as a function of the centre-of-mass rapidity, $y^{\ast }$. The vertical error bars correspond to the statistical uncertainties. The horizontal position of each data point indicates the mean of the weighted $y^{\ast }$ distribution. The vertical sizes of coloured boxes around the data points represent the uncorrelated systematic uncertainties, and horizontal sizes of the coloured boxes represent the bin sizes

Fig. 16

The bottomonium double ratio, ${\rho }_{p\mathrm{Pb}}^{{\rm Y}(n\text{S})/{\rm Y}(\text{1S})}$, integrated in the whole measured $p_{\text{T}}$ and $y^{\ast }$ range. The vertical error bars correspond to the statistical uncertainties. The vertical sizes of boxes around the data points represent the systematic uncertainties

Fig. 17

The prompt charmonium double ratio, ${\rho }_{p\mathrm{Pb}}^{\psi (\text{2S})/J/\psi }$, (left) and the bottomonium double ratio, ${\rho }_{p\mathrm{Pb}}^{{\rm Y}(n\text{S})/{\rm Y}(\text{1S})}$, (right) as a function of event centrality in $p$+Pb collisions . The vertical error bars correspond to the statistical uncertainties, and the vertical sizes of coloured boxes around the data points represent the uncorrelated systematic uncertainties in $p$+Pb collisions. The vertical size of the leftmost yellow box around ${\rho }_{p\mathrm{Pb}}^{\mathcal{O}(n\text{S})/\mathcal{O}(\text{1S})}=1$ represents the total uncertainty of the pp reference which is the same for all centralities