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| CMS-PAS-SMP-19-014 | ||
| Observation of heavy triboson production in leptonic final states in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| Avril 2020 | ||
| Abstract: An observation of the combined production of three massive vector bosons (VVV with V = W, Z) 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 a total integrated luminosity of 137 fb$^{-1}$. The searches for individual WWW, WWZ, WZZ, and ZZZ production processes are performed in final states with three, four, five, and six leptons (electrons or muons), or with two same-charge leptons plus one or two jets. The observed (expected) significance of the combined VVV production signal is 5.7 (5.9) standard deviations (sd) and the corresponding measured signal strength is 1.02$^{+0.26}_{-0.23}$. The significances of the individual WWW and WWZ channels are 3.3 and 3.4 sd, respectively. The measured production cross sections for the individual triboson final states are also reported. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PRL 125 (2020) 151802. The superseded preliminary plots can be found here. |
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| Figures & Tables | Summary | Additional Figures & Tables | References | CMS Publications |
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| Figures | |
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Figure 1:
Comparison of the observed numbers of events from the BDT-based selections to the predicted yields after fitting. The VVV signal is shown stacked on top of the total background and is based on theoretical SM cross sections. The expected significance $L$ in the middle panel represents the number of sd with which the null hypothesis (no signal) is rejected. The lower panel shows the pulls for the fit result. |
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Figure 2:
Best fit values of the signal strengths for the BDT-based analyses (blue) and the sequential-cut analyses (black). For ZZZ production, a 95% CL upper limit is shown. The stated numerical values correspond to the BDT-based analysis. |
| Tables | |
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Table 1:
Measured cross sections obtained with the BDT-based analyses. The uncertainties listed are statistical and systematic. The VVV cross section is calculated from the fit for $ {\mu _{\text {comb}}} $. For the ZZZ channel, 95% confidence level upper limits are reported. |
| Summary |
| In summary, data recorded with the CMS experiment during the LHC Run~2 amounting to 137 fb$^{-1}$ of pp collisions at $\sqrt{s} = $ 13 TeV were used to search for the production of triple heavy gauge bosons observed in leptonic final states. The significance of the observation is 5.7 standard deviations (sd) with 5.9 sd expected. For WWW (WWZ) production, the observed significance is 3.3 sd (3.4 sd) compatible with 3.1 sd (4.1 sd) expected. Measured cross sections for individual production processes for WWW, WWZ, and WZZ and an upper limit for ZZZ were reported and are in agreement with the expectations of the standard model. This note documents the first evidence for WWW and WWZ production and the first observation of the combined heavy triboson production by the CMS Collaboration. |
| Additional Figures | |
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Additional Figure 1:
Distribution of the dijet invariant mass, ${m_{\mathrm {jj}}}$, for events with two same-charged leptons (e or $\mu$) and at least two jets for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 2:
Distribution of the maximal transverse mass, ${{m_{\mathrm {T}}} ^{\mathrm {max}}}$, for events with two same-charged leptons (e or $\mu$) and at least two jets for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 3:
Distribution of the nonprompt lepton-BDT score for events with two same-charged leptons (e or $\mu$) and at least two jets for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 4:
Distribution of the number of b-tagged jets, ${n_{{\mathrm {b}}}}$, for events with three charged leptons (e or $\mu$) with no same-flavor opposite-charged lepton pair (0 SFOS) for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 5:
Distribution of the prompt lepton-BDT score for events with three charged leptons (e or $\mu$) with no same-flavor opposite-charged lepton pair (0 SFOS) for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 6:
Distribution of the invariant mass of the two leptons not forming a Z boson candidate, ${m_{{\mathrm {e}} {\mu}}}$, for events with four charged leptons (e or $\mu$) in the e${\mu}$ category for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 7:
Distribution of ${m_{\mathrm {T2}}}$ for events with four charged leptons (e or $\mu$) in the e${\mu}$ category for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 8:
Distribution of the BDT score of the ZZ and ${{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}$ BDT for events with four charged leptons (e or $\mu$) in the e${\mu}$ category for simulation for WWZ, ZZ, and ${{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}$ events. |
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Additional Figure 9:
Distribution of the missing transverse momentum, ${{p_{\mathrm {T}}} ^\text {miss}}$, for events with four charged leptons (e or $\mu$) in the ${{\mathrm {e}} {\mathrm {e}}/ {\mu} {\mu}}$ category for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 10:
Distribution of transverse momentum of the four-lepton system, ${{p_{\mathrm {T}}} ^{4\ell}}$, for events with four charged leptons (e or $\mu$) in the ${{\mathrm {e}} {\mathrm {e}}/ {\mu} {\mu}}$ category for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 11:
Distribution of transverse mass, ${m_{\mathrm {T}}}$, of the lepton assigned as W boson candidate and the ${{p_{\mathrm {T}}} ^\text {miss}}$ for events with five charged leptons (e or $\mu$) for data and simulation corresponding to 137 fb$^{-1}$. The VVV signal is stacked on top of the background. |
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Additional Figure 12:
Distribution of the scalar sum of the lepton transverse momenta, $ \sum {p_{\mathrm {T}}} ^{\ell}$, for events with at least six charged leptons (e or $\mu$) for data and simulation corresponding to 137 fb$^{-1}$ in the six lepton signal region. The VVV signal is stacked on top of the background. The uncertainties shown are only statistical. |
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Additional Figure 13:
Distribution of the dijet invariant mass, ${m_{\mathrm {jj}}}$, for events with two same-charged leptons (e or $\mu$) and at least two jets for the WWW signal simulation. The signal events are seperated into a category where the two jets are matched to a quark from the W boson decay (red), and another category for all other events. The uncertainties shown are only statistical. |
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Additional Figure 14:
Distribution of the subleading parton transverse momentum for a quark from the W boson decay for the WWW signal simulation. The signal events are seperated into a category where all W bosons were generated onshell, and a category of ${{\mathrm {W}} {\mathrm {H}} \to {\mathrm {W}} {\mathrm {W}} {\mathrm {W}}}$. |
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Additional Figure 15:
Distribution of the dijet invariant mass, ${m_{\mathrm {jj}}}$, for events with two same-charged leptons (e or $\mu$) and at least two jets in the lost-lepton control region for data and simulation corresponding to 137 fb$^{-1}$. The uncertainties shown are only statistical. |
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Additional Figure 16:
Distribution of the nonprompt lepton BDT score for events with three charged leptons (e or $\mu$) with no same-flavor opposite-charged lepton pair (0 SFOS) in the loose-lepton control region for data and simulation corresponding to 137 fb$^{-1}$. The uncertainties shown are only statistical. |
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Additional Figure 17:
Distribution of the missing transverse momentum, ${{p_{\mathrm {T}}} ^\text {miss}}$, for events with four charged leptons (e or $\mu$) in the ZZ control region for data and simulation corresponding to 137 fb$^{-1}$. The uncertainties shown are only statistical. |
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Additional Figure 18:
Distribution of ${m_{\mathrm {T2}}}$ for events with four charged leptons (e or $\mu$) in the ZZ control region for data and simulation corresponding to 137 fb$^{-1}$. The uncertainties shown are only statistical. |
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Additional Figure 19:
Distribution of the BDT score of the ${{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}$ BDT for events with four charged leptons (e or $\mu$) in the ZZ control region for data and simulation corresponding to 137 fb$^{-1}$. The uncertainties shown are only statistical. |
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Additional Figure 20:
Distribution of the invariant mass of the two leptons not forming a Z boson candidate, ${m_{{\mathrm {e}} {\mu}}}$, for events with four charged leptons (e or $\mu$) in the ${{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}$ control region for data and simulation corresponding to 137 fb$^{-1}$. The uncertainties shown are only statistical. |
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Additional Figure 21:
Distribution of the transverse momentum of the four-lepton system, ${{p_{\mathrm {T}}} ^{4\ell}}$, for events with four charged leptons (e or $\mu$) in the ${{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}$ control region for data and simulation corresponding to 137 fb$^{-1}$. The uncertainties shown are only statistical. |
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Additional Figure 22:
Distribution of the BDT score of the ZZ BDT for events with four charged leptons (e or $\mu$) in the ${{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}$ control region for data and simulation corresponding to 137 fb$^{-1}$. The uncertainties shown are only statistical. |
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Additional Figure 23:
Comparison of the observed numbers of events from the BDT-based selections to the predicted yields after fitting. The VVV signal is shown stacked on top of the total background and is based on theoretical SM cross sections times the signal strengths shown in the legend. The significance $L$ in the middle panel represents the expected number of sd with which the null hypothesis (no signal) is rejected. The lower panel shows the pulls for the fit result. |
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Additional Figure 24:
Comparison of the observed numbers of events from the sequential-cut selections to the predicted yields after fitting. The VVV signal is shown stacked on top of the total background and is based on theoretical SM cross sections times the signal strengths shown in the legend. The significance $L$ in the middle panel represents the expected number of sd with which the null hypothesis (no signal) is rejected. The lower panel shows the pulls for the fit result. |
png pdf |
Additional Figure 25:
Comparison of the observed numbers of events from the sequential-cut selections to the predicted yields after fitting. The VVV signal is shown stacked on top of the total background and is based on theoretical SM cross sections times the signal strengths shown in the legend. The significance $L$ in the middle panel represents the expected number of sd with which the null hypothesis (no signal) is rejected. The lower panel shows the pulls for the fit result. |
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Additional Figure 26:
Event display of candidate WWW event in same-sign dilepton plus two jets final states. In this event, there are two positively charged muons (red) along with two jets (orange cones) with an invariant mass consistent with the W mass. The neutrinos are represented by ${{p_{\mathrm {T}}} ^\text {miss}}$ (pink arrow). The tracks reconstructed in the event are represented by the yellow trajectories. The CMS detector depicted in the figure shows the muon system from one side of the hemisphere. The rest of the detector components are omitted for illustration purpose. The corresponding muon chambers that detected the muons in the event are depicted. The beam pipe can be seen in the center where the two proton beams approach from each side. On the right, the transverse view of the same event is shown. |
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Additional Figure 27:
Event display of candidate WWW event in three lepton final states. In this event, there are two positrons and one muon where no pair of leptons consist an oppositely charged same flavor dilepton pair. The green tracks are the tracks from the positrons, and the green towers represent the electromagnetic calorimeter energy deposits from the positrons. The neutrinos are represented by ${{p_{\mathrm {T}}} ^\text {miss}}$ (pink arrow). The tracks reconstructed in the event are represented by the yellow trajectories. The CMS detector depicted in the figure shows the muon system from one side of the hemisphere. The rest of the detector components are omitted for illustration purpose. The corresponding muon chambers that detected the muons in the event are depicted. The beam pipe can be seen in the center where the two proton beams approach from each side. On the right, the transverse view of the same event is shown. |
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Additional Figure 28:
Event display of candidate WWZ event in four lepton final states. In this event, there is a pair of oppositely charged muons (red) with an invariant mass consistent with the Z mass. There is an additional oppositely charged e$\mu $ pair in the event as well. The green track is the track from the electron in the event. The green towers represent the electromagnetic calorimeter energy deposits from the positrons. The neutrinos are represented by ${{p_{\mathrm {T}}} ^\text {miss}}$ (pink arrow). The tracks reconstructed in the event are represented by the yellow trajectories. The $ {m_{\mathrm {T2}}} $ computed from the e$\mu $ system and the ${{p_{\mathrm {T}}} ^\text {miss}}$ is $64$ GeV and the invariant mass of the e$\mu $ system is $128$ GeV. The CMS detector depicted in the figure shows the muon system from one side of the hemisphere. The rest of the detector components are omitted for illustration purpose. The corresponding muon chambers that detected the muons in the event are depicted. The beam pipe can be seen in the center where the two proton beams approach from each side. On the right, the transverse view of the same event is shown. |
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Additional Figure 29:
Event display of candidate WZZ event in five lepton final states. Tracks from the positrons and electrons in the event are represented by green tracks. The green tower represents the electromagnetic calorimeter energy deposits from the positrons or electrons. In this event, there are two pairs of oppositely charged electrons with their invariant masses consistent with Z mass. The neutrino in the event is represented by ${{p_{\mathrm {T}}} ^\text {miss}}$ (pink arrow). In addition there is an extra electron in the event. The $ {m_{\mathrm {T}}} $ of the fifth electron and the ${{p_{\mathrm {T}}} ^\text {miss}}$ system is 65 GeV. |
| Additional Tables | |
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Additional Table 1:
Event selection for the SS channel for the sequential-cut analysis: for each category (${{m_{\mathrm {jj}}}}$-in, ${{m_{\mathrm {jj}}}}$-out, and 1j) we define three signal regions depending on the lepton flavor: ${{\mathrm {e}^\pm} {\mathrm {e}^\pm}}$, ${{\mathrm {e}^\pm} {\mu ^\pm}}$, and ${{\mu ^\pm} {\mu ^\pm}}$. This results in 3$\times$3$=$9 signal region for the SS channel. |
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Additional Table 2:
Event selection for the 3$\ell $ channel for the sequential-cut analysis: We define 3 signal regions depending on the number of SFOS lepton pairs: 0, 1, or 2 SFOS. |
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Additional Table 3:
Comparison of the observed numbers of events to the predicted yields after fitting of the BDT-based selections for the SS and 3$\ell $ final states. The VVV signal is shown both as a sum as well as separated into different production modes based on theoretical standard model cross sections. |
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Additional Table 4:
Comparison of the observed numbers of events to the predicted yields after fitting of the BDT-based selection for the 4$\ell $ final state and the sequential-cut selections for the $\geq $5$\ell $ final states. The VVV signal is shown both as a sum as well as separated into different production modes based on theoretical standard model cross sections. The signal regions in the 4$\ell $ final state are defined through orthogonal selections in the two-dimensional plane of the ZZ and ${{{\mathrm {t}\overline {\mathrm {t}}}} {\mathrm {Z}}}$ BDT scores. |
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Additional Table 5:
Comparison of the observed numbers of events to the predicted yields after fitting of the sequential-cut selections for the SS and 3$\ell $ final states. The VVV signal is shown both as a sum as well as separated into different production modes based on theoretical standard model cross sections. |
png pdf |
Additional Table 6:
Comparison of the observed numbers of events to the predicted yields after fitting of the sequential-cut selections for the $\geq 4\ell $ final states. The VVV signal is shown both as a sum as well as separated into different production modes based on theoretical standard model cross sections. The signal regions in the e${\mu}$ category are defined as (bins 1-4) $ {m_{{\mathrm {e}} {\mu}}} = $ 0-40, 40-60, 60-100, and $\geq$ 100 GeV. For events with $ {m_{{\mathrm {e}} {\mu}}} < $ 100 GeV, we require $ {m_{\mathrm {T2}}} > $ 25 GeV. The signal regions in the ${{\mathrm {e}} {\mathrm {e}}/ {\mu} {\mu}}$ category are defined as $ {{p_{\mathrm {T}}} ^\text {miss}} \geq $ 120 GeV (bin A) or 70 $\leq {{p_{\mathrm {T}}} ^\text {miss}} < $ 120 GeV and $ {{p_{\mathrm {T}}} ^{4\ell}} \geq $ 70 GeV (bin B) or 40 $\leq {{p_{\mathrm {T}}} ^{4\ell}} < $ 70 GeV (bin C). |
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Additional Table 7:
Values of the observed (expected) significances (in sd) with respect to the SM background-only hypothesis for the production of three massive vector bosons. When obtaining the significances of the individual processes, the four processes (WWW, WWZ, WZZ, and ZZZ) are fitted simultaneously. When obtaining the combined significances (VVV), all processes are treated to have relative cross sections as according to the standard model. |
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Additional Table 8:
Values of the observed (expected) upper limits at 95% confidence on the signal strengths of the WZZ and ZZZ processes. The signal strength is defined as the measured cross section divided by the theoretical cross section. As the processes are fitted together with the WWW and WZZ processes that dominate the $\leq 4\ell $ final states, different values for the sequential-cut and BDT-based analyses are obtained, even though fpr the $\geq 4\ell $ final states we apply only sequential-cut selections. |
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