CMS-HIN-21-008

CMS-HIN-21-008 ; CERN-EP-2023-052
Measurements of the azimuthal anisotropy of prompt and nonprompt charmonia in PbPb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 5.02 TeV
CMS Collaboration
25 May 2023
JHEP 10 (2023) 115
Abstract: The second-order ( $v_{2}$ ) and third-order ( $v_{3}$ ) Fourier coefficients describing the azimuthal anisotropy of prompt and nonprompt (from b-hadron decays) J/ $\psi$ , as well as prompt $\psi$ (2S) mesons are measured in lead-lead collisions at a center-of-mass energy per nucleon pair of $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 5.02 TeV. The analysis uses a data set corresponding to an integrated luminosity of 1.61 nb $^{-1}$ recorded with the CMS detector. The J/ $\psi$ and $\psi$ (2S) mesons are reconstructed using their dimuon decay channel. The $v_{2}$ and $v_{3}$ coefficients are extracted using the scalar product method and studied as functions of meson transverse momentum and collision centrality. The measured $v_{2}$ values for prompt J/ $\psi$ mesons are found to be larger than those for nonprompt J/ $\psi$ mesons. The prompt J/ $\psi$ $v_{2}$ values at high $p_{\mathrm{T}}$ are found to be underpredicted by a model incorporating only parton energy loss effects in a quark-gluon plasma medium. Prompt and nonprompt J/ $\psi$ meson $v_{3}$ and prompt $\psi$ (2S) $v_{2}$ and $v_{3}$ values are also reported for the first time, providing new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions.
Links: e-print arXiv:2305.16928 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Invariant mass (left) and $\ell_{\mathrm{J}/\psi}$ (right) distributions for the bin of 3.0 $< p_{\mathrm{T}} <$ 4.5 GeV/ $c$ and 0.0 $< v_{2} <$ 0.3 in centrality 10-60%. The solid lines represent the total fit, while the dashed and dash-dotted lines represent the prompt and nonprompt components, respectively. The background contributions are shown by the filled blue histograms.
png pdf	Figure 1-a: Invariant mass distribution for the bin of 3.0 $< p_{\mathrm{T}} <$ 4.5 GeV/ $c$ and 0.0 $< v_{2} <$ 0.3 in centrality 10-60%. The solid line represents the total fit, while the dashed and dash-dotted lines represent the prompt and nonprompt components, respectively. The background contributions are shown by the filled blue histogram.
png pdf	Figure 1-b: $\ell_{\mathrm{J}/\psi}$ distribution for the bin of 3.0 $< p_{\mathrm{T}} <$ 4.5 GeV/ $c$ and 0.0 $< v_{2} <$ 0.3 in centrality 10-60%. The solid line represents the total fit, while the dashed and dash-dotted lines represent the prompt and nonprompt components, respectively. The background contributions are shown by the filled blue histogram.
png pdf	Figure 2: Simultaneous fits of the dimuon invariant mass spectrum and the $v_{2}^{\text{Sig+Bkg}}$ (left) and $v_{3}^{\text{Sig+Bkg}}$ (right) distributions for $\psi$ (2S) mesons, as defined by Eq. (5), for 6.5 $< p_{\mathrm{T}} <$ 10 GeV/ $c$ and centrality 10-60%. In the upper panel, the solid black (signal + background) and dashed blue (background only) lines show the result of the mass fit. In the lower panel, the vertical lines of the $v^{\text{Sig}}_{n}$ points represent the statistical uncertainty. The solid ( $v_{n}$ signal + background) and the dashed ( $v_{n}$ background) lines indicate the corresponding fit to the $v_{n}$ distributions.
png pdf	Figure 2-a: Simultaneous fits of the dimuon invariant mass spectrum and the $v_{2}^{\text{Sig+Bkg}}$ distribution for $\psi$ (2S) mesons, as defined by Eq. (5), for 6.5 $< p_{\mathrm{T}} <$ 10 GeV/ $c$ and centrality 10-60%. In the upper panel, the solid black (signal + background) and dashed blue (background only) lines show the result of the mass fit. In the lower panel, the vertical lines of the $v^{\text{Sig}}_{2}$ points represent the statistical uncertainty. The solid ( $v_{2}$ signal + background) and the dashed ( $v_{2}$ background) lines indicate the corresponding fit to the $v_{2}$ distribution.
png pdf	Figure 2-b: Simultaneous fits of the dimuon invariant mass spectrum and the $v_{2}^{\text{Sig+Bkg}}$ distribution for $\psi$ (2S) mesons, as defined by Eq. (5), for 6.5 $< p_{\mathrm{T}} <$ 10 GeV/ $c$ and centrality 10-60%. In the upper panel, the solid black (signal + background) and dashed blue (background only) lines show the result of the mass fit. In the lower panel, the vertical lines of the $v^{\text{Sig}}_{3}$ points represent the statistical uncertainty. The solid ( $v_{3}$ signal + background) and the dashed ( $v_{3}$ background) lines indicate the corresponding fit to the $v_{3}$ distribution.
png pdf	Figure 3: The $v_{2}$ (upper) and $v_{3}$ (lower) values, as functions of $p_{\mathrm{T}}$ (left) and $\langle\mathrm{N}_\text{part}\rangle$ (right) for prompt and nonprompt J/ $\psi$ mesons. The results for 3 $< p_{\mathrm{T}} <$ 6.5 and 6.5 $< p_{\mathrm{T}} <$ 50 GeV/ $c$ are studied in the rapidity range of 1.6 $< \|y\| <$ 2.4 and $\|y\| <$ 2.4, respectively (left). The kinematic range for the right panel is 6.5 $< p_{\mathrm{T}} <$ 50 GeV/ $c$ and $\|y\| <$ 2.4. The data points are positioned in the middle of each $p_{\mathrm{T}}$ bin. The vertical bars denote the statistical uncertainties and the rectangular bands show the systematic uncertainties.
png pdf	Figure 4: The $v_{2}$ values of prompt J/ $\psi$ mesons (blue circles) as a function of $p_{\mathrm{T}}$ in the 10-60% centrality range compared with a model calculation in Ref. [31] (green dashed line). The results for 3 $< p_{\mathrm{T}} <$ 6.5 and 6.5 $< p_{\mathrm{T}} <$ 50 GeV/ $c$ are studied in the rapidity range of 1.6 $< \|y\| <$ 2.4 and $\|y\| <$ 2.4, respectively. The vertical bars denote the statistical uncertainties and the rectangular bands show the systematic uncertainties.
png pdf	Figure 5: The $v_{2}$ (upper) and $v_{3}$ (lower) values, as functions of $p_{\mathrm{T}}$ (left) and $\langle\mathrm{N}_\text{part}\rangle$ (right) for prompt J/ $\psi$ (blue circles) and prompt $\psi$ (2S) (green squares) mesons. The results for $p_{\mathrm{T}} <$ 6.5 and $p_{\mathrm{T}} >$ 6.5 GeV/ $c$ are studied in the rapidity range of 1.6 $< \|y\| <$ 2.4 and $\|y\| <$ 2.4, respectively (left). The kinematic range for the right panel is 6.5 $< p_{\mathrm{T}} <$ 50 GeV/ $c$ and $\|y\| <$ 2.4. The data points are positioned in the middle of each $p_{\mathrm{T}}$ bin. The vertical bars denote the statistical uncertainties and the rectangular bands show the systematic uncertainties.

Tables
png pdf	Table 1: Summary of the absolute total systematic uncertainty and its dominant contributions, in units of 10 $^{-3}$ .
png pdf	Table 2: A Summary of the kinematic regions for J/ $\psi$ and $\psi$ (2S) in the centrality interval 10-60%.
png pdf	Table 3: The centrality classes and $\langle\mathrm{N}_\text{part}\rangle$ values for PbPb collisions at $\sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} =$ 5.02 TeV used in this study.

Summary

The second-order (

$v_{2}$ ) and third-order (

$v_{3}$ ) Fourier coefficients of azimuthal distributions for prompt and nonprompt J/

$\psi$ , and prompt

$\psi$ (2S) mesons are measured in PbPb collisions as functions of transverse momentum (

$p_{\mathrm{T}}$ ) and event centrality. The

$v_{2}$ values for prompt and nonprompt J/

$\psi$ mesons both indicate a decreasing trend from mid-central towards central collision events. Within present experimental uncertainties, these

$v_{2}$ values show no clear

$p_{\mathrm{T}}$ dependence between 3 and 50 GeVc. The prompt J/

$\psi$ meson

$v_{2}$ values are found to be larger than those of nonprompt J/

$\psi$ mesons throughout the studied kinematic region, suggesting different in-medium effects for charm and bottom quarks. The prompt J/

$\psi$ meson

$v_{2}$ values are larger than those from a model calculation which considered the prompt J/

$\psi$ production above 10 GeVc from jet fragmentation. This discrepancy indicates additional effects are required to describe the observed sizable

$v_{2}$ at high

$p_{\mathrm{T}}$ for prompt J/

$\psi$ mesons. The

$v_{3}$ values for prompt and nonprompt J/

$\psi$ mesons are reported for the first time, and found to be consistent with zero in the measured

$p_{\mathrm{T}}$ and centrality intervals. The

$v_{2}$ and

$v_{3}$ values are also measured for prompt

$\psi$ (2S) mesons and are compatible with, although slightly larger than, those of prompt J/

$\psi$ mesons. These J/

$\psi$ and

$\psi$ (2S) meson measurements provide new information about heavy quark interactions in the hot and dense medium created in heavy ion collisions.

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