CMS-BPH-22-009 ; CERN-EP-2024-155 | ||
Measurement of the polarizations of prompt and non-prompt J/ψ and ψ(2S) mesons produced in pp collisions at √s= 13 TeV | ||
CMS Collaboration | ||
20 June 2024 | ||
Phys. Lett. B 858 (2024) 139044 | ||
Abstract: The polarizations of prompt and non-prompt J/ψ and ψ(2S) mesons are measured in proton-proton collisions at √s= 13 TeV, using data samples collected by the CMS experiment in 2017 and 2018, corresponding to a total integrated luminosity of 103.3 fb−1. Based on the analysis of the dimuon decay angular distributions in the helicity frame, the polar anisotropy, λϑ, is measured as a function of the transverse momentum, pT, of the charmonium states, in the 25-120 and 20-100 GeV ranges for the J/ψ and ψ(2S), respectively. The non-prompt polarizations agree with predictions based on the hypothesis that, for pT≳ 25 GeV, the non-prompt \mathrm{J}/\psi and \psi \text{(2S)} are predominantly produced in two-body B meson decays. The prompt results clearly exclude strong transverse polarizations, even for p_{\mathrm{T}} exceeding 30 times the \mathrm{J}/\psi mass, where \lambda_\vartheta tends to an asymptotic value around 0.3. Taken together with previous measurements, by CMS and LHCb at \sqrt{s} = 7 TeV, the prompt polarizations show a significant variation with p_{\mathrm{T}} , at low p_{\mathrm{T}} . | ||
Links: e-print arXiv:2406.14409 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; |
Figures | |
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Figure 1:
Measured dimuon decay length vs. mass distributions for the \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) samples, showing the rectangular regions used in the analysis. The prompt and non-prompt signal regions are labeled PRS and NPS, respectively, while the remaining regions are non-signal (sideband) regions. |
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Figure 1-a:
Measured dimuon decay length vs. mass distributions for the \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) samples, showing the rectangular regions used in the analysis. The prompt and non-prompt signal regions are labeled PRS and NPS, respectively, while the remaining regions are non-signal (sideband) regions. |
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Figure 1-b:
Measured dimuon decay length vs. mass distributions for the \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) samples, showing the rectangular regions used in the analysis. The prompt and non-prompt signal regions are labeled PRS and NPS, respectively, while the remaining regions are non-signal (sideband) regions. |
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Figure 2:
Dimuon mass distributions measured for the non-prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) event samples, in the mentioned p_{\mathrm{T}} bins. The total fit function (blue), the sum of the two CB functions and, only in the \mathrm{J}/\psi case, the Gaussian function (red), and the background continuum (black) are also shown. |
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Figure 2-a:
Dimuon mass distributions measured for the non-prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) event samples, in the mentioned p_{\mathrm{T}} bins. The total fit function (blue), the sum of the two CB functions and, only in the \mathrm{J}/\psi case, the Gaussian function (red), and the background continuum (black) are also shown. |
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Figure 2-b:
Dimuon mass distributions measured for the non-prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) event samples, in the mentioned p_{\mathrm{T}} bins. The total fit function (blue), the sum of the two CB functions and, only in the \mathrm{J}/\psi case, the Gaussian function (red), and the background continuum (black) are also shown. |
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Figure 3:
Fraction of events in the NPS region due to continuum muon pairs, versus p_{\mathrm{T}} , for the non-prompt \mathrm{J}/\psi and \psi \text{(2S)} events. |
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Figure 4:
Dimuon mass distributions measured for the prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) event samples, in the mentioned p_{\mathrm{T}} bins. The total fit function (blue), the sum of the two CB functions and (only in the \mathrm{J}/\psi case) the Gaussian function (red), and the background continuum (black) are also shown. |
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Figure 4-a:
Dimuon mass distributions measured for the prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) event samples, in the mentioned p_{\mathrm{T}} bins. The total fit function (blue), the sum of the two CB functions and (only in the \mathrm{J}/\psi case) the Gaussian function (red), and the background continuum (black) are also shown. |
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Figure 4-b:
Dimuon mass distributions measured for the prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) event samples, in the mentioned p_{\mathrm{T}} bins. The total fit function (blue), the sum of the two CB functions and (only in the \mathrm{J}/\psi case) the Gaussian function (red), and the background continuum (black) are also shown. |
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Figure 5:
Fraction of events in the PRS region due to continuum muon pairs, versus p_{\mathrm{T}} , for the prompt \mathrm{J}/\psi and \psi \text{(2S)} events. |
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Figure 6:
Dimuon decay length distributions, integrated in p_{\mathrm{T}} , measured for the sideband mass ranges mentioned in the legends, in the \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) cases. |
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Figure 6-a:
Dimuon decay length distributions, integrated in p_{\mathrm{T}} , measured for the sideband mass ranges mentioned in the legends, in the \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) cases. |
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Figure 6-b:
Dimuon decay length distributions, integrated in p_{\mathrm{T}} , measured for the sideband mass ranges mentioned in the legends, in the \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) cases. |
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Figure 7:
Dimuon decay length distributions measured for the \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) cases, in their mass signal windows, in the mentioned p_{\mathrm{T}} bins. The vertical dashed lines mark the limits of the PR and NP ranges. The total fit function, as well as the individual contributions, are also shown. |
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Figure 7-a:
Dimuon decay length distributions measured for the \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) cases, in their mass signal windows, in the mentioned p_{\mathrm{T}} bins. The vertical dashed lines mark the limits of the PR and NP ranges. The total fit function, as well as the individual contributions, are also shown. |
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Figure 7-b:
Dimuon decay length distributions measured for the \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) cases, in their mass signal windows, in the mentioned p_{\mathrm{T}} bins. The vertical dashed lines mark the limits of the PR and NP ranges. The total fit function, as well as the individual contributions, are also shown. |
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Figure 8:
Variation with p_{\mathrm{T}} of the fraction of events in the PRS region from non-prompt \mathrm{J}/\psi and \psi \text{(2S)} mesons. |
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Figure 9:
|\cos\vartheta_\mathrm{HX}| distributions measured in the mass sidebands (shifted horizontally for better visibility), and their weighted average, for the prompt \mathrm{J}/\psi (left) and non-prompt \psi \text{(2S)} (right) samples, in the mentioned p_{\mathrm{T}} bins. |
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Figure 9-a:
|\cos\vartheta_\mathrm{HX}| distributions measured in the mass sidebands (shifted horizontally for better visibility), and their weighted average, for the prompt \mathrm{J}/\psi (left) and non-prompt \psi \text{(2S)} (right) samples, in the mentioned p_{\mathrm{T}} bins. |
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Figure 9-b:
|\cos\vartheta_\mathrm{HX}| distributions measured in the mass sidebands (shifted horizontally for better visibility), and their weighted average, for the prompt \mathrm{J}/\psi (left) and non-prompt \psi \text{(2S)} (right) samples, in the mentioned p_{\mathrm{T}} bins. |
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Figure 10:
|\cos\vartheta_\mathrm{HX}| distributions measured in the PRS \mathrm{J}/\psi (left) and NPS \psi \text{(2S)} (right) samples, of the terms of Eqs. (4) and (3), respectively, in the mentioned p_{\mathrm{T}} bins. |
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Figure 10-a:
|\cos\vartheta_\mathrm{HX}| distributions measured in the PRS \mathrm{J}/\psi (left) and NPS \psi \text{(2S)} (right) samples, of the terms of Eqs. (4) and (3), respectively, in the mentioned p_{\mathrm{T}} bins. |
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Figure 10-b:
|\cos\vartheta_\mathrm{HX}| distributions measured in the PRS \mathrm{J}/\psi (left) and NPS \psi \text{(2S)} (right) samples, of the terms of Eqs. (4) and (3), respectively, in the mentioned p_{\mathrm{T}} bins. |
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Figure 11:
Ratios between the measured and simulated |\cos\vartheta_\mathrm{HX}| distributions for the prompt and non-prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) events, in the p_{\mathrm{T}} bins mentioned in the legends. The curves represent fits using Eq. (2) and excluding the largest |\cos\vartheta_\mathrm{HX}| bins. |
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Figure 11-a:
Ratios between the measured and simulated |\cos\vartheta_\mathrm{HX}| distributions for the prompt and non-prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) events, in the p_{\mathrm{T}} bins mentioned in the legends. The curves represent fits using Eq. (2) and excluding the largest |\cos\vartheta_\mathrm{HX}| bins. |
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Figure 11-b:
Ratios between the measured and simulated |\cos\vartheta_\mathrm{HX}| distributions for the prompt and non-prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) events, in the p_{\mathrm{T}} bins mentioned in the legends. The curves represent fits using Eq. (2) and excluding the largest |\cos\vartheta_\mathrm{HX}| bins. |
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Figure 12:
The \lambda_\vartheta parameter measured, as a function of p_{\mathrm{T}} , for non-prompt \mathrm{J}/\psi and \psi \text{(2S)} mesons. The vertical bars represent the total uncertainties. Predicted polarizations of \mathrm{J}/\psi mesons produced in {\mathrm{B}} \to {\mathrm{J}/\psi} \, X decays are shown for three calculations [48,49], discussed in the text. The low- p_{\mathrm{T}} CDF measurement [50] is also shown. |
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Figure 13:
The \lambda_\vartheta parameter measured, as a function of p_{\mathrm{T}} , for prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) mesons, in pp collisions at \sqrt{s} = 13 TeV, compared to measurements made at 7 TeV by CMS [10] and LHCb [11,12]. The vertical bars represent the total uncertainties. The curves on the left panel are described in the text. |
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Figure 13-a:
The \lambda_\vartheta parameter measured, as a function of p_{\mathrm{T}} , for prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) mesons, in pp collisions at \sqrt{s} = 13 TeV, compared to measurements made at 7 TeV by CMS [10] and LHCb [11,12]. The vertical bars represent the total uncertainties. The curves on the left panel are described in the text. |
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Figure 13-b:
The \lambda_\vartheta parameter measured, as a function of p_{\mathrm{T}} , for prompt \mathrm{J}/\psi (left) and \psi \text{(2S)} (right) mesons, in pp collisions at \sqrt{s} = 13 TeV, compared to measurements made at 7 TeV by CMS [10] and LHCb [11,12]. The vertical bars represent the total uncertainties. The curves on the left panel are described in the text. |
Tables | |
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Table 1:
The \lambda_\vartheta values measured in the HX frame, in bins of p_{\mathrm{T}} , for the prompt and non-prompt \mathrm{J}/\psi mesons, including the statistical (stat), systematic (syst), and total uncertainties. |
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Table 2:
The \lambda_\vartheta values measured in the HX frame, as a function of p_{\mathrm{T}} , for the prompt and non-prompt \psi\mathrm{(2S)} mesons, indicating the statistical (stat), systematic (syst), and total uncertainties. |
Summary |
The prompt and non-prompt \mathrm{J}/\psi and \psi\mathrm{(2S)} \lambda_\vartheta polarization parameters have been measured, in the helicity frame and for the |y| < 1.25 interval, using a sample of pp collisions at \sqrt{s} = 13 TeV collected in 2017 and 2018, corresponding to an integrated luminosity of 103.3 fb ^{-1} . The results cover p_{\mathrm{T}} ranges significantly broader than previous measurements: 25-120 and 20-100 GeV, for the \mathrm{J}/\psi and \psi \text{(2S)} , respectively. The non-prompt \mathrm{J}/\psi and \psi \text{(2S)} polarization measurements are compatible with each other, regarding the p_{\mathrm{T}} dependence and the overall magnitude, plateauing at \lambda_\vartheta \approx - 0.2 for p_{\mathrm{T}} > 30 GeV. The measured trends agree with predictions based on the hypothesis that these charmonia are predominantly produced by two-body B meson decays, through colour-singlet processes. Regarding the prompt results, we see no evidence of strong transverse polarizations ( \lambda_\vartheta approaching + 1), even at p_{\mathrm{T}} values exceeding 30 times the \mathrm{J}/\psi mass. Using NRQCD concepts, there is no evidence that, at very high p_{\mathrm{T}} , the transversely polarized ^3 S_1^{[8]} and ^3 P_J^{[8]} octet terms become dominant with respect to the unpolarized ^1 S_0^{[8]} octet. Taken together with previous CMS and LHCb measurements, covering a lower p_{\mathrm{T}} domain, we see a significant variation of the prompt polarizations with p_{\mathrm{T}} , at low p_{\mathrm{T}} . These results will significantly constrain phenomenological analyses of charmonium production, so far mostly focused on p_{\mathrm{T}} -differential cross sections. |
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Compact Muon Solenoid LHC, CERN |
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