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| CMS-PAS-HIN-24-001 | ||
| Observation of the multiplicity dependence of $ \sigma_{\psi(2S)}/\sigma_{J/\psi} $ in pPb collisions at 8.16 TeV | ||
| CMS Collaboration | ||
| 12 June 2024 | ||
| Abstract: The ratio of $ \psi(2S) $ and J/$ \psi $ meson production cross sections is measured as a function of the charged-particle multiplicity in pPb collisions at center-of-mass energy per nucleon pair of $ \sqrt {\smash [b]{s_{_{\mathrm {NN}}}}} = $ 8.16 TeV using the CMS detector. The data corresponds to an integrated luminosity of 175 nb$^{-1}$. Both charmonium states are measured using the dimuon decay channel. The ratio is measured for both prompt and nonprompt $ \psi(2S) $ and J/$ \psi $ mesons separately. A multiplicity-dependent modification of the ratio is observed for prompt mesons. The ratio of the nonprompt $ \psi(2S) $ to J/$ \psi $ cross sections show no dependency on multiplicity. No significant rapidity-dependence is observed within the charmonium rapidity range $ -$2.865 $ < y_{CM} < $ 1.935 and transverse momentum range probed, 3 $ < p_{T} < $ 30 GeV. These measurements constrain hadronization models of heavy quarks in nuclear collisions and support a picture in which co-moving particles may preferentially dissociate weakly-bound charmonia excited states as compared to the ground state during the evolution of the system. | ||
| Links: CDS record (PDF) ; CADI line (restricted) ; | ||
| Figures | |
png pdf |
Figure 1:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ 1 < y_{CM} < 1.935 $ (upper left), $ -1 < y_{CM} < $ 1 (upper right), $ -2 < y_{CM} < - $1 (lower left), and $ -2.865 < y_{CM} < - 2$ (lower right) for 6.5 $ < p_{\mathrm{T}} < $ 30 GeV. |
png pdf |
Figure 1-a:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ 1 < y_{CM} < 1.935 $ (upper left), $ -1 < y_{CM} < $ 1 (upper right), $ -2 < y_{CM} < - $1 (lower left), and $ -2.865 < y_{CM} < - 2$ (lower right) for 6.5 $ < p_{\mathrm{T}} < $ 30 GeV. |
png pdf |
Figure 1-b:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ 1 < y_{CM} < 1.935 $ (upper left), $ -1 < y_{CM} < $ 1 (upper right), $ -2 < y_{CM} < - $1 (lower left), and $ -2.865 < y_{CM} < - 2$ (lower right) for 6.5 $ < p_{\mathrm{T}} < $ 30 GeV. |
png pdf |
Figure 1-c:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ 1 < y_{CM} < 1.935 $ (upper left), $ -1 < y_{CM} < $ 1 (upper right), $ -2 < y_{CM} < - $1 (lower left), and $ -2.865 < y_{CM} < - 2$ (lower right) for 6.5 $ < p_{\mathrm{T}} < $ 30 GeV. |
png pdf |
Figure 1-d:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ 1 < y_{CM} < 1.935 $ (upper left), $ -1 < y_{CM} < $ 1 (upper right), $ -2 < y_{CM} < - $1 (lower left), and $ -2.865 < y_{CM} < - 2$ (lower right) for 6.5 $ < p_{\mathrm{T}} < $ 30 GeV. |
png pdf |
Figure 2:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ -2.865 < y_{CM} < - 2$ (left) for 6.5 $ < p_{\mathrm{T}} < $ 30 GeV. The trend-line slope for both prompt and nonprompt double ratio is plotted (right) with respect to the $ y_{CM} $. |
png pdf |
Figure 2-a:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ -2.865 < y_{CM} < - 2$ (left) for 6.5 $ < p_{\mathrm{T}} < $ 30 GeV. The trend-line slope for both prompt and nonprompt double ratio is plotted (right) with respect to the $ y_{CM} $. |
png pdf |
Figure 2-b:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ -2.865 < y_{CM} < - 2$ (left) for 6.5 $ < p_{\mathrm{T}} < $ 30 GeV. The trend-line slope for both prompt and nonprompt double ratio is plotted (right) with respect to the $ y_{CM} $. |
png pdf |
Figure 3:
Dimuon invariant mass distribution showing the J/$ \psi $ and $ \psi $(2S) peaks in pPb data, after applying the $ l^{3D} \mathrm{J}/\psi $ selection, for $ -2.865 < y_{CM} < - 2$ (left) and $ 1 < y_{CM} < 1.935 $ (right) for 3 $ < p_{\mathrm{T}} < $ 30 GeV. The invariant mass fits are performed using the unbinned maximum extended likelihood method in the region of 2.5 $ < m_{\mu^{+} \mu^{-}} < $ 4.3 GeV. Both the J/$\psi$ and $\psi$(2S) nominal signal shapes are defined by the sum of two Crystal Ball (CB) functions. The background is described by a third-order Chebyshev polynomial. The total fit is shown with a solid blue line, and the dotted blue line represents the background. |
png pdf |
Figure 3-a:
Dimuon invariant mass distribution showing the J/$ \psi $ and $ \psi $(2S) peaks in pPb data, after applying the $ l^{3D} \mathrm{J}/\psi $ selection, for $ -2.865 < y_{CM} < - 2$ (left) and $ 1 < y_{CM} < 1.935 $ (right) for 3 $ < p_{\mathrm{T}} < $ 30 GeV. The invariant mass fits are performed using the unbinned maximum extended likelihood method in the region of 2.5 $ < m_{\mu^{+} \mu^{-}} < $ 4.3 GeV. Both the J/$\psi$ and $\psi$(2S) nominal signal shapes are defined by the sum of two Crystal Ball (CB) functions. The background is described by a third-order Chebyshev polynomial. The total fit is shown with a solid blue line, and the dotted blue line represents the background. |
png pdf |
Figure 3-b:
Dimuon invariant mass distribution showing the J/$ \psi $ and $ \psi $(2S) peaks in pPb data, after applying the $ l^{3D} \mathrm{J}/\psi $ selection, for $ -2.865 < y_{CM} < - 2$ (left) and $ 1 < y_{CM} < 1.935 $ (right) for 3 $ < p_{\mathrm{T}} < $ 30 GeV. The invariant mass fits are performed using the unbinned maximum extended likelihood method in the region of 2.5 $ < m_{\mu^{+} \mu^{-}} < $ 4.3 GeV. Both the J/$\psi$ and $\psi$(2S) nominal signal shapes are defined by the sum of two Crystal Ball (CB) functions. The background is described by a third-order Chebyshev polynomial. The total fit is shown with a solid blue line, and the dotted blue line represents the background. |
png pdf |
Figure 4:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ -2.865 < y_{CM} < - 2$ (left) and $ 1 < y_{CM} < 1.935 $ (right) for 3 $ < p_{\mathrm{T}} < $ 6.5 GeV are shown. Both prompt and nonprompt cross-section ratios are fitted with straight lines (shown in solid red for prompt and solid blue for nonprompt), considering statistical and systematic uncertainties added in quadrature. The color bands represent the 1$ \sigma $ confidence intervals. In both regions, the prompt ratio shows a dependence on multiplicity, whereas the nonprompt ratio remains independent across multiplicity. A stronger relative suppression in the Pb-going ($ -2.865 < y_{CM} < - 2$) direction compared to the p-going ($ 1 < y_{CM} < 1.935 $) direction is found for the prompt ratio, but any firm conclusion is limited by the larger uncertainty. |
png pdf |
Figure 4-a:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ -2.865 < y_{CM} < - 2$ (left) and $ 1 < y_{CM} < 1.935 $ (right) for 3 $ < p_{\mathrm{T}} < $ 6.5 GeV are shown. Both prompt and nonprompt cross-section ratios are fitted with straight lines (shown in solid red for prompt and solid blue for nonprompt), considering statistical and systematic uncertainties added in quadrature. The color bands represent the 1$ \sigma $ confidence intervals. In both regions, the prompt ratio shows a dependence on multiplicity, whereas the nonprompt ratio remains independent across multiplicity. A stronger relative suppression in the Pb-going ($ -2.865 < y_{CM} < - 2$) direction compared to the p-going ($ 1 < y_{CM} < 1.935 $) direction is found for the prompt ratio, but any firm conclusion is limited by the larger uncertainty. |
png pdf |
Figure 4-b:
Prompt and nonprompt normalized $ \sigma_{$ \psi (\text{2S}) $} / \sigma_{\mathrm{J}/\psi} $ for $ -2.865 < y_{CM} < - 2$ (left) and $ 1 < y_{CM} < 1.935 $ (right) for 3 $ < p_{\mathrm{T}} < $ 6.5 GeV are shown. Both prompt and nonprompt cross-section ratios are fitted with straight lines (shown in solid red for prompt and solid blue for nonprompt), considering statistical and systematic uncertainties added in quadrature. The color bands represent the 1$ \sigma $ confidence intervals. In both regions, the prompt ratio shows a dependence on multiplicity, whereas the nonprompt ratio remains independent across multiplicity. A stronger relative suppression in the Pb-going ($ -2.865 < y_{CM} < - 2$) direction compared to the p-going ($ 1 < y_{CM} < 1.935 $) direction is found for the prompt ratio, but any firm conclusion is limited by the larger uncertainty. |
| Summary |
| In summary, this note presents a measurement of the normalized production cross-section ratio of $ \psi $(2S) over J/$ \psi $ mesons as a function of charged-particle multiplicity in pPb collisions at center-of-mass energy per nucleon pair of $ \sqrt{\smash[b]{s_{_{\mathrm{NN}}}}} = $ 8.16 TeV with a data sample collected by the CMS detector, corresponding to an integrated luminosity of 175 nb$^{-1}$. The ratio is measured for both prompt and nonprompt $ \psi $(2S) and J/$ \psi $ mesons separately. A multiplicity-dependent modification of the ratio is observed for prompt mesons, indicating a decreasing trend with increasing multiplicity. The ratio of the nonprompt $ \psi $(2S) to J/$ \psi $ cross sections show no dependency on multiplicity. No significant rapidity-dependence is observed within the charmonium rapidity range $ -2.865 < y_{CM} < 1.935 $ and transverse momentum range, 3 $ < p_{\mathrm{T}} < $ 30 GeV probed. The observations in this study suggest that co-moving particles may dissociate weakly-bound excited state of charmonia more than the ground state. These findings provide valuable new constraints for understanding the mechanisms of hadronization in nuclear collisions involving heavy quarks. |
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