CMS-PAS-EXO-20-007

CMS-PAS-EXO-20-007
Search for high mass trijet resonances using final states with boosted dijet resonances in proton-proton collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
June 2021

Abstract: A novel search is reported for high mass trijet resonances that decay to a jet and a boosted dijet resonance. The search uses 138 fb $^{-1}$ of integrated luminosity collected by the CMS detector in proton-proton collisions at $\sqrt{s}=$ 13 TeV. The boosted dijet resonance is reconstructed as a single jet, containing jet substructure consistent with a two-body decay. The jet substructure information and the kinematics of cascade resonance decays are exploited to disentangle the signal from the large QCD multijet background. The dijet mass spectra are analyzed for the presence of new resonances, and are found to be consistent with standard model expectations. Results are interpreted in a warped extra dimension model where the first resonance is a Kaluza-Klein (KK) gluon, the second resonance is a radion, and final state partons are all gluons. Limits on the production cross section are set as a function of KK gluon and radion masses. These limits exclude at 95% confidence level a KK gluon with a mass of 4.2TeV for a radion mass of 0.42 TeV, and a radion with a mass of 0.74 TeV for a KK gluon mass of 3.7 TeV. By exploring a novel experimental signature, we extend significantly the discovery potential of this benchmark model of new physics compared to previous searches at the LHC.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ; These preliminary results are superseded in this paper, Submitted to PLB. The superseded preliminary plots can be found here.

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Feynam diagram of the process $\rm {pp} \rightarrow \rm {R}_1 \rightarrow \rm {R}_2+\rm {P}_3 \rightarrow (\rm {P}_1+\rm {P}_2)+\rm {P}_3$ involving the cascade decays of two new massive resonances. The particles in the final state are partons (quarks, antiquarks or gluons).
png pdf	Figure 2: Left) Simulation of the second resonance vs the parton candidate masses (points), for trijet resonance events originating from a KK gluon with a mass $M_{GKK}=$ 4 TeV, decaying to a radion with a mass $M_{\phi}=$ 0.4 TeV and a gluon. The 22 event categories in this plane, within which the search in the dijet mass distribution is conducted, are shown with red boxes. Right) Same for $M_{GKK}=$ 5 TeV, and $M_{\phi}=$ 1 TeV , for which the number of event categories is 9. For both plots, the cross-like shape is approximately centered on the second resonance pole mass $M(R_{2})$ for both horizontal and vertical axes.
png pdf	Figure 2-a: Left) Simulation of the second resonance vs the parton candidate masses (points), for trijet resonance events originating from a KK gluon with a mass $M_{GKK}=$ 4 TeV, decaying to a radion with a mass $M_{\phi}=$ 0.4 TeV and a gluon. The 22 event categories in this plane, within which the search in the dijet mass distribution is conducted, are shown with red boxes. Right) Same for $M_{GKK}=$ 5 TeV, and $M_{\phi}=$ 1 TeV , for which the number of event categories is 9. For both plots, the cross-like shape is approximately centered on the second resonance pole mass $M(R_{2})$ for both horizontal and vertical axes.
png pdf	Figure 2-b: Left) Simulation of the second resonance vs the parton candidate masses (points), for trijet resonance events originating from a KK gluon with a mass $M_{GKK}=$ 4 TeV, decaying to a radion with a mass $M_{\phi}=$ 0.4 TeV and a gluon. The 22 event categories in this plane, within which the search in the dijet mass distribution is conducted, are shown with red boxes. Right) Same for $M_{GKK}=$ 5 TeV, and $M_{\phi}=$ 1 TeV , for which the number of event categories is 9. For both plots, the cross-like shape is approximately centered on the second resonance pole mass $M(R_{2})$ for both horizontal and vertical axes.
png pdf	Figure 3: Weighted sum of the number of events divided by bin width within each category as a function of dijet mass (points) for the search for a trijet resonance with mass $M_{R_{1}} = M_{GKK} = 2.9 TeV$ decaying to a second resonance with mass $M_{R_{2}} = M_{\phi} =$ 0.4 TeV ( $\rho _m \sim$ 0.14) and a parton. The weights are the expected signal event fractions for each category, assuming a signal cross section equal to the 95% CL upper limit. Also shown is the same quantity from the background-only fits in each category (solid histogram), with statistical uncertainty (hatched), and from the signal normalized to the upper limit (dashed histogram). The lower panel shows the difference between the data and the background prediction divided by the statistical uncertainty of the background (solid red), and the same quantity for the signal (dashed).
png pdf	Figure 4: Observed upper limits on signal cross section, as a function of the ratio of the two resonance masses versus the first resonance mass, for a trijet resonance model with 3 gluons in the final state. The excluded regions from this search, optimized for the $G_{KK} \rightarrow \phi + g \rightarrow ggg$ decay, are compared with those obtained from a reinterpretation of the inclusive CMS dijet resonance search [1], sensitive to the $G_{KK} \rightarrow q\bar{q}$ decay.

Summary

In summary, a novel search for new high mass hadronic resonances, that decay to a parton and a second resonance, that in turn decays into a pair of partons, has been presented. This is the first dedicated search for trijet resonances at the LHC in events with a boosted dijet. No statistically significant excesses above the background predictions are observed. Results are interpreted in a warped extra dimension model where the first resonance is a Kaluza-Klein gluon, the second one is a radion, and the final state partons are all gluons. By exploring a novel experimental signature, we extend significantly the experimental exclusion of this benchmark model of new physics at the LHC.

References
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