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| CMS-PAS-BPH-21-004 | ||
| Observation of triple $\mathrm{J}\psi$ meson production in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
| CMS Collaboration | ||
| July 2021 | ||
| Abstract: The first observation of the combined production of three $\mathrm{J}\psi$ mesons in proton-proton collisions at a center-of-mass energy of 13 TeV is reported. The analysis is based on a data sample recorded by the CMS experiment at the CERN LHC corresponding to an integrated luminosity of 133 fb$^{-1}$. The search for triple-$\mathrm{J}\psi$ production is performed in final states with three $\mu^{+}\mu^{-}$ pairs that pass fiducial kinematic criteria chosen so as to select high-$p_\mathrm{T}$ $\mathrm{J}\psi$ mesons produced at midrapidity. The $\mathrm{pp}\to\mathrm{J}\psi\,\mathrm{J}\psi\,\mathrm{J}\psi\,\mathrm{X}$ process is observed with a significance in excess of five standard deviations. The fiducial cross section for this process is found to be $\sigma(\mathrm{pp}\to\mathrm{J}\psi\,\mathrm{J}\psi\,\mathrm{J}\psi\,\mathrm{X})= $ 272$^{+141}_{-104}$ (stat) $\pm$ 17 (syst) fb. The result is compared to theoretical expectations for the production of three $\mathrm{J}\psi$ mesons in single (SPS), double- (DPS), and triple- (TPS) parton scattering processes. Under the most economical assumption of factorization of multiple hard scattering probabilities in terms of SPS cross sections, the measured final state is found to be dominated by DPS and TPS contributions. A value of the associated DPS effective cross section parameter of $\sigma_\mathrm{eff,DPS} = $ 2.7$^{+1.4}_{-1.0}$ (exp) $^{+1.5}_{-1.0}$ (theo) mb, related to the transverse distribution of partons in the proton, is derived. | ||
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These preliminary results are superseded in this paper, NP 19 (2023) 338. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Leading diagrams for triple-${\mathrm{J}/\psi}$ production in ${\mathrm{p}} {\mathrm{p}} $ collisions via single- (upper), double- (middle), and triple- (lower) parton scatterings. The leftmost diagrams show the triple prompt-${\mathrm{J}/\psi}$ processes. The remaining diagrams show (left to right) final states with increasing contributions of nonprompt ${\mathrm{J}/\psi}$ 's from B meson decays. The symbols $\sigma ^\mathrm {IpJnp}_\mathrm {NPS}$ are provided to identify each prompt (p) and/or nonprompt (np) diagram to its associated cross section discussed below. |
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Figure 2:
Invariant mass distributions for the three ${\mathrm{J}/\psi}$ muon pairs, ordered (left to right) by increasing transverse momentum of the $\mu^{+} \mu^{-} $ system. In each panel, the data are represented by the points, with the vertical bars showing the statistical uncertainties, the solid curve the overall fit to the data and the dashed curve the widened sideband window. The shaded region corresponds to the fitted signal yield. |
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Figure 2-a:
Invariant mass distributions for the three ${\mathrm{J}/\psi}$ muon pairs, ordered (left to right) by increasing transverse momentum of the $\mu^{+} \mu^{-} $ system. In each panel, the data are represented by the points, with the vertical bars showing the statistical uncertainties, the solid curve the overall fit to the data and the dashed curve the widened sideband window. The shaded region corresponds to the fitted signal yield. |
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Figure 2-b:
Invariant mass distributions for the three ${\mathrm{J}/\psi}$ muon pairs, ordered (left to right) by increasing transverse momentum of the $\mu^{+} \mu^{-} $ system. In each panel, the data are represented by the points, with the vertical bars showing the statistical uncertainties, the solid curve the overall fit to the data and the dashed curve the widened sideband window. The shaded region corresponds to the fitted signal yield. |
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Figure 2-c:
Invariant mass distributions for the three ${\mathrm{J}/\psi}$ muon pairs, ordered (left to right) by increasing transverse momentum of the $\mu^{+} \mu^{-} $ system. In each panel, the data are represented by the points, with the vertical bars showing the statistical uncertainties, the solid curve the overall fit to the data and the dashed curve the widened sideband window. The shaded region corresponds to the fitted signal yield. |
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Figure 3:
Comparison of the effective DPS cross sections $ {\sigma _\mathrm {eff,DPS}} $ extracted in this work (top data point in both panels) to the same parameter derived in measurements of double-quarkonium and electroweak boson plus quarkonium production [10,59,13,58,12,60,61] alone (left), as well as also in final states with jets [54,55,7,23], $\gamma +$jets [56,57], $\mathrm{W} +$jets [17,18], and same-sign W bosons [22] (right). |
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Figure 3-a:
Comparison of the effective DPS cross sections $ {\sigma _\mathrm {eff,DPS}} $ extracted in this work (top data point in both panels) to the same parameter derived in measurements of double-quarkonium and electroweak boson plus quarkonium production [10,59,13,58,12,60,61] alone (left), as well as also in final states with jets [54,55,7,23], $\gamma +$jets [56,57], $\mathrm{W} +$jets [17,18], and same-sign W bosons [22] (right). |
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Figure 3-b:
Comparison of the effective DPS cross sections $ {\sigma _\mathrm {eff,DPS}} $ extracted in this work (top data point in both panels) to the same parameter derived in measurements of double-quarkonium and electroweak boson plus quarkonium production [10,59,13,58,12,60,61] alone (left), as well as also in final states with jets [54,55,7,23], $\gamma +$jets [56,57], $\mathrm{W} +$jets [17,18], and same-sign W bosons [22] (right). |
| Tables | |
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Table 1:
Definition of the fiducial phase space for the triple-${\mathrm{J}/\psi}$ cross section measurement. |
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Table 2:
Contributions to the systematic uncertainty of the $\sigma ({\mathrm{p}} {\mathrm{p}} \to {\mathrm{J}/\psi} \, {\mathrm{J}/\psi} \, {\mathrm{J}/\psi} \, \mathrm {X})$ measurement, in percent. The last row gives the sum in quadrature of all components. |
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Table 3:
Predictions for single-, double-, and triple-${\mathrm{J}/\psi}$ production cross sections in SPS processes, which pass the fiducial criteria listed in Table 1, derived from the HELAC-Onia (ho) and MadGraph 5\_amc@nlo (mg5nlo) matrix element calculators, complemented with the PYTHIA 8 (py8) parton shower, as described in the text. |
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Table 4:
Central predictions for triple-${\mathrm{J}/\psi}$ production cross sections and yields from SPS, DPS (for $ {\sigma _\mathrm {eff,DPS}} = $ 2.7 mb), and TPS (for $ {\sigma _\mathrm {eff,TPS}} =$ 0.82, $ {\sigma _\mathrm {eff,DPS}} = $ 2.2 mb) processes, and their sums. The DPS and TPS results are derived via Eqs. (3) and (4) from the SPS cross sections listed in Table 3 with $ {\sigma _\mathrm {eff,DPS}} $ chosen so that the sum of contributions yields a total cross section equal to the experimental value of $\sigma ^{3{\mathrm{J}/\psi}}_\mathrm {tot}$. The expected yield, $N^{3{\mathrm{J}/\psi}}_\mathrm {NPS}$, is given for $\varepsilon \, {\mathcal {L}} _\mathrm {int}=$ 87 fb$^{-1} $ for each contributing process. The last column lists the total DPS and TPS cross sections and yields. |
| Summary |
| The first observation of the concurrent production of three ${\mathrm{J}/\psi}$ mesons in proton-proton collisions at $\sqrt{s} = $ 13 TeV has been reported. Events with three ${\mathrm{J}/\psi}$ mesons, each decaying into two muons, have been reconstructed including prompt as well as nonprompt (i.e., coming from B decays) production. After all selection requirements, five events are found that are consistent with triple-${\mathrm{J}/\psi}$ production, plus one event assigned to possible combinatorial background, through a three-dimensional unbinned extended maximum likelihood fit of the dimuons invariant mass distributions. The statistical significance of the signal relative to the background-only expectation corresponds to a significance above five standard deviations. The cross section for triple-${\mathrm{J}/\psi}$ production, within the fiducial region defined in Table 1, is $\sigma(\mathrm{pp}\to{\mathrm{J}/\psi}\,{\mathrm{J}/\psi}\,{\mathrm{J}/\psi} \,\mathrm{X})= $ 272$^{+141}_{-104}$ (stat) $\pm$ 17 (syst) fb. This result is compared to the theoretical expectations for triple-${\mathrm{J}/\psi}$ production via a sum of contributions from single- (SPS), double- (DPS), and triple- (TPS) parton scatterings. Under the most economical assumption of factorization of multiple hard scattering probabilities in terms of SPS cross sections, the measured triple-${\mathrm{J}/\psi}$ cross section is consistent with the production via DPS ($\sim$74%), TPS ($\sim$20%), and SPS ($\sim$6%) processes for a value of the effective DPS cross section parameter, closely related to the transverse distribution of partons in the proton, of $ \sigma_\mathrm{eff,DPS} = $ 2.7$ ^{+1.4}_{-1.0}$ (exp) $^{+1.5}_{-1.0}$ (theo) mb. Within its large uncertainty, this value is consistent with similarly extracted parameters from double-quarkonium measurements, but significantly smaller than the effective DPS cross sections derived from double-particle final states that include high-$p_{\mathrm{T}}$ jets, photons, and electroweak bosons. The present analysis provides a novel approach to study multiple hard scatterings in pp collisions exploiting, for the first time, the production of three heavy particles. |
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