Inclusive, prompt and non-prompt ${\rm J}/ψ$ production at midrapidity in p$-$Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

A measurement of inclusive, prompt, and non-prompt ${\rm J}/\psi$ production in p$-$Pb collisions at a nucleon--nucleon centre-of-mass energy $\sqrt{s_{\mathrm{NN}}} = 5.02$ TeV is presented. The ${\rm J}/\psi$ mesons are reconstructed in the dielectron decay channel at midrapidity down to a transverse momentum $p_{\rm T} = 0$. The inclusive ${\rm J}/\psi$ nuclear modification factor $R_{\rm pPb}$ is calculated by comparing the results in p$-$Pb collisions to a measured proton$-$proton reference at the same centre-of-mass energy. Non-prompt ${\rm J}/\psi$ mesons, which originate from the decay of beauty hadrons, are separated from promptly produced ${\rm J}/\psi$ on a statistical basis for $p_{\rm T}$ larger than 1.0 GeV/$c$. These results are based on the data sample collected by the ALICE detector during the 2016 LHC p$-$Pb run, corresponding to an integrated luminosity ${\cal L}_{\rm int} = 292 \pm 11 \; {\rm \mu b}^{-1}$, which is six times larger than the previous publications. The total uncertainty on the $p_{\rm T}$-integrated inclusive ${\rm J}/\psi$ and non-prompt ${\rm J}/\psi$ cross section are reduced by a factor 1.7 and 2.2, respectively. The measured cross sections and $R_{\rm pPb}$ are compared with theoretical models that include various combinations of cold nuclear matter effects. From the non-prompt ${\rm J}/\psi$ production cross section, the ${\rm b\overline{b}}$ production cross section at midrapidity, $\mathrm{d}\sigma_{\rm b\overline{b}}/\mathrm{d}y$, and the total cross section extrapolated over full phase space, $\sigma_{\rm b\overline{b}}$, are derived.

 

JHEP06 (2022) 011
HEP Data
e-Print: arXiv:2105.04957 | PDF | inSPIRE
CERN-EP-2021-077
Figure group

Figure 1

Opposite-sign dielectron invariant mass distributions for the \pt-intervals used for this analysis. The signal (blue), combinatorial background (red), and correlated background (green) components, evaluated as described in the text, are shown separately in each panel.

Figure 2

Invariant mass (left panel) and pseudoproper decay length (right panel) distributions for \JJpsi candidates with $\pt > 1$ GeV/$c$. The latter distribution is limited to the \JJpsi candidates under the signal peak region $2.92~

Figure 3

Fraction of \JJpsi from b-hadron decays at midrapidity as a function of the \JJpsi \pt in p--Pb collisions at $\snn = 5.02$ TeV (red closed circles) compared with results from the ALICE~ and ATLAS~ collaborations in the same collision system (blue and green closed circles, and the blue arrow that shows an upper limit at 95\%~CL in the range $1.3

Figure 4

$\textup{d}\sigma_{\rm prompt\ \JJpsi}/\textup{d}y$ as a function of the rapidity in the centre-of-mass frame (left panel) as obtained in this work at midrapidity and by the LHCb collaboration in the forward and backward rapidity regions~, and $\textup{d}^2\sigma_{\rm prompt\ \JJpsi}/\textup{d}y\textup{d}p_{\rm T}$ as a function of \pt (right panel) compared with ATLAS results~ (reported up to $\pt = 20$ GeV/$c$). The results for inclusive \JJpsi are also shown superimposed in the right hand panel. The vertical error bars and the boxes on top of each point represent the statistical and systematic uncertainties. For the measurements as a function of \pt, the data symbols are placed within each bin at the mean of the \pt distribution determined from MC simulations. The results of a model~ including nuclear shadowing based on the EPPS16~ and nCTEQ15~ nPDFs are shown superimposed on both panels (see text for details). In the right panel, the computations refer only to the ALICE rapidity range.

Figure 5

$\textup{d}\sigma_{\rm \JJpsi\ from\ h_{\rm b}}/\textup{d}y$ as a function of rapidity (left panel) as obtained at midrapidity in this work and by the LHCb collaboration in the forward and backward rapidity regions~, and $\textup{d}^2\sigma_{\rm \JJpsi\ from\ h_{\rm b}}/\textup{d}y\textup{d}p_{\rm T}$ as a function of \pt (right panel) compared with ATLAS measurements~ (shown up to $\pt = 20$ GeV/$c$). The statistical and systematic uncertainties are shown as vertical error bars and hollow boxes, respectively. For the measurements as a function of \pt, data symbols are placed at the mean value of the \pt distribution within each bin The results are compared to FONLL computations~ with EPPS16~ nPDFs, highlighting the total theoretical uncertainty (empty band) and the contribution from EPPS16 (coloured band). In the right panel, model computations are obtained in the same rapidity range of the ALICE results.

Figure 6

$R_{\rm pPb}$ of prompt \JJpsi as a function of rapidity (left panel) and as a function of \pt along with that of inclusive \JJpsi at midrapidity (right panel). Results are shown in comparison with LHCb measurements~ at backward and forward rapidity in the left panel and with ATLAS results~ (shown up to $\pt = 20$ GeV/$c$) in the right-hand plot Statistical uncertainties are represented by vertical error bars, while open boxes correspond to systematic uncertainties. The filled box around $R_{\rm pPb} = 1$ in the right panel indicates the size of the global relative uncertainty of the ALICE measurements. The results of various model predictions implementing different CNM effects are also shown~.

Figure 7

Nuclear modification factor $R_{\rm pPb}$ of non-prompt \JJpsi as a function of rapidity (left panel) and as a function of \pt at midrapidity (right panel). The results are compared with similar measurements from the LHCb~ and ATLAS~ experiments Vertical bars and the open boxes indicate the statistical and systematic uncertainties, respectively. The uncertainty due to the extrapolation to $\pt = 0$ GeV/$c$ for the ALICE measurement is reported as a shaded box in left panel, while the filled box around $R_{\rm pPb} = 1$ in the right-hand panel denotes the size of the global normalisation uncertainty The predicted nuclear modification factors according to the nDSg~ (central value shown in the left panel only) and EPPS16~ parameterisations (including a reweighted computation from~) are shown superimposed on both panels.