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 J/ψ and ψ(2S) are predominantly produced in two-body B meson decays. The prompt results clearly exclude strong transverse polarizations, even for pT exceeding 30 times the J/ψ mass, where λϑ tends to an asymptotic value around 0.3. Taken together with previous measurements, by CMS and LHCb at √s= 7 TeV, the prompt polarizations show a significant variation with pT, at low pT. | ||
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 J/ψ (left) and ψ(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 J/ψ (left) and ψ(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 J/ψ (left) and ψ(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 J/ψ (left) and ψ(2S) (right) event samples, in the mentioned pT bins. The total fit function (blue), the sum of the two CB functions and, only in the J/ψ 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 J/ψ (left) and ψ(2S) (right) event samples, in the mentioned pT bins. The total fit function (blue), the sum of the two CB functions and, only in the J/ψ 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 J/ψ (left) and ψ(2S) (right) event samples, in the mentioned pT bins. The total fit function (blue), the sum of the two CB functions and, only in the J/ψ 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 pT, for the non-prompt J/ψ and ψ(2S) events. |
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Figure 4:
Dimuon mass distributions measured for the prompt J/ψ (left) and ψ(2S) (right) event samples, in the mentioned pT bins. The total fit function (blue), the sum of the two CB functions and (only in the J/ψ 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 J/ψ (left) and ψ(2S) (right) event samples, in the mentioned pT bins. The total fit function (blue), the sum of the two CB functions and (only in the J/ψ 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 J/ψ (left) and ψ(2S) (right) event samples, in the mentioned pT bins. The total fit function (blue), the sum of the two CB functions and (only in the J/ψ 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 pT, for the prompt J/ψ and ψ(2S) events. |
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Figure 6:
Dimuon decay length distributions, integrated in pT, measured for the sideband mass ranges mentioned in the legends, in the J/ψ (left) and ψ(2S) (right) cases. |
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Figure 6-a:
Dimuon decay length distributions, integrated in pT, measured for the sideband mass ranges mentioned in the legends, in the J/ψ (left) and ψ(2S) (right) cases. |
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Figure 6-b:
Dimuon decay length distributions, integrated in pT, measured for the sideband mass ranges mentioned in the legends, in the J/ψ (left) and ψ(2S) (right) cases. |
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Figure 7:
Dimuon decay length distributions measured for the J/ψ (left) and ψ(2S) (right) cases, in their mass signal windows, in the mentioned pT 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 J/ψ (left) and ψ(2S) (right) cases, in their mass signal windows, in the mentioned pT 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 J/ψ (left) and ψ(2S) (right) cases, in their mass signal windows, in the mentioned pT 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 pT of the fraction of events in the PRS region from non-prompt J/ψ and ψ(2S) mesons. |
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Figure 9:
|cosϑHX| distributions measured in the mass sidebands (shifted horizontally for better visibility), and their weighted average, for the prompt J/ψ (left) and non-prompt ψ(2S) (right) samples, in the mentioned pT bins. |
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Figure 9-a:
|cosϑHX| distributions measured in the mass sidebands (shifted horizontally for better visibility), and their weighted average, for the prompt J/ψ (left) and non-prompt ψ(2S) (right) samples, in the mentioned pT bins. |
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Figure 9-b:
|cosϑHX| distributions measured in the mass sidebands (shifted horizontally for better visibility), and their weighted average, for the prompt J/ψ (left) and non-prompt ψ(2S) (right) samples, in the mentioned pT bins. |
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Figure 10:
|cosϑHX| distributions measured in the PRS J/ψ (left) and NPS ψ(2S) (right) samples, of the terms of Eqs. (4) and (3), respectively, in the mentioned pT bins. |
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Figure 10-a:
|cosϑHX| distributions measured in the PRS J/ψ (left) and NPS ψ(2S) (right) samples, of the terms of Eqs. (4) and (3), respectively, in the mentioned pT bins. |
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Figure 10-b:
|cosϑHX| distributions measured in the PRS J/ψ (left) and NPS ψ(2S) (right) samples, of the terms of Eqs. (4) and (3), respectively, in the mentioned pT bins. |
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Figure 11:
Ratios between the measured and simulated |cosϑHX| distributions for the prompt and non-prompt J/ψ (left) and ψ(2S) (right) events, in the pT bins mentioned in the legends. The curves represent fits using Eq. (2) and excluding the largest |cosϑHX| bins. |
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Figure 11-a:
Ratios between the measured and simulated |cosϑHX| distributions for the prompt and non-prompt J/ψ (left) and ψ(2S) (right) events, in the pT bins mentioned in the legends. The curves represent fits using Eq. (2) and excluding the largest |cosϑHX| bins. |
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Figure 11-b:
Ratios between the measured and simulated |cosϑHX| distributions for the prompt and non-prompt J/ψ (left) and ψ(2S) (right) events, in the pT bins mentioned in the legends. The curves represent fits using Eq. (2) and excluding the largest |cosϑHX| bins. |
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Figure 12:
The λϑ parameter measured, as a function of pT, for non-prompt J/ψ and ψ(2S) mesons. The vertical bars represent the total uncertainties. Predicted polarizations of J/ψ mesons produced in B→J/ψX decays are shown for three calculations [48,49], discussed in the text. The low-pT CDF measurement [50] is also shown. |
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Figure 13:
The λϑ parameter measured, as a function of pT, for prompt J/ψ (left) and ψ(2S) (right) mesons, in pp collisions at √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 λϑ parameter measured, as a function of pT, for prompt J/ψ (left) and ψ(2S) (right) mesons, in pp collisions at √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 λϑ parameter measured, as a function of pT, for prompt J/ψ (left) and ψ(2S) (right) mesons, in pp collisions at √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 λϑ values measured in the HX frame, in bins of pT, for the prompt and non-prompt J/ψ mesons, including the statistical (stat), systematic (syst), and total uncertainties. |
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Table 2:
The λϑ values measured in the HX frame, as a function of pT, for the prompt and non-prompt ψ(2S) mesons, indicating the statistical (stat), systematic (syst), and total uncertainties. |
Summary |
The prompt and non-prompt J/ψ and ψ(2S) λϑ polarization parameters have been measured, in the helicity frame and for the |y|< 1.25 interval, using a sample of pp collisions at √s= 13 TeV collected in 2017 and 2018, corresponding to an integrated luminosity of 103.3 fb−1. The results cover pT ranges significantly broader than previous measurements: 25-120 and 20-100 GeV, for the J/ψ and ψ(2S), respectively. The non-prompt J/ψ and ψ(2S) polarization measurements are compatible with each other, regarding the pT dependence and the overall magnitude, plateauing at λϑ≈−0.2 for pT> 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 (λϑ approaching +1), even at pT values exceeding 30 times the J/ψ mass. Using NRQCD concepts, there is no evidence that, at very high pT, the transversely polarized 3S[8]1 and 3P[8]J octet terms become dominant with respect to the unpolarized 1S[8]0 octet. Taken together with previous CMS and LHCb measurements, covering a lower pT domain, we see a significant variation of the prompt polarizations with pT, at low pT. These results will significantly constrain phenomenological analyses of charmonium production, so far mostly focused on pT-differential cross sections. |
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Compact Muon Solenoid LHC, CERN |
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