CMS-PAS-B2G-18-007

CMS-PAS-B2G-18-007
Search for new physics in events with collimated photons and gluons
CMS Collaboration
March 2019

Abstract: This letter reports the results of a search for physics beyond the standard model. The search is performed with events containing jets with substructure resulting from new particles decaying into a photon and two gluons. Jet substructure techniques are adapted to develop a new approach for photon identification in a dense hadronic environment. The proton-proton collision data analyzed were collected by the CMS experiment at $\sqrt{s}= $ 13 TeV during 2016 and correspond to an integrated luminosity of 35.9 fb$^{-1}$. No statistically significant excess is observed and the first cross section limits on processes yielding such events are set.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, PRL 123 (2019) 241801. The superseded preliminary plots can be found here.

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: The decay diagram for a gluino predicted by stealth SUSY. The S and $\tilde{S}$ states are predicted to have a small mass gap resulting in soft $\tilde{G}$ emissions. This analysis mainly explores cases where the mass difference between the $\tilde{g}$ and $\tilde{\chi}^{0}_{1}$ is large and results in a high momentum $\tilde{\chi}^{0}_{1}$ with the photon and the gluons merging into a single jet.
png pdf	Figure 2: Normalized distribution of the ${f_\gamma}$ variable. Simulated signal jets are denoted with the colored lines, each depicting a different mass of $\tilde{\chi}^{0}_{1}$ and $\tilde{g}$. The shaded area represents the QCD jets distribution. The black points present data. The jet distributions presented here are required to satisfy the loose photon-jet requirements.
png pdf	Figure 3: Signal region ${H_{\mathrm {T}}}$ distributions for the AK8 3 jet category (top row) and the 4+ AK8 category (bottom). Events with zero, one and two tight photon-jets are presented from left to right, present events with different number of tight photon-jets. The balck points denote the observed data ${H_{\mathrm {T}}}$ distributions. The magenta line with the gray band, presents the data based background estimation prediction while the other colored lines present expected single ${H_{\mathrm {T}}}$ distributions.
png pdf	Figure 3-a: Signal region ${H_{\mathrm {T}}}$ distributions for the AK8 3 jet category. Events with zero, one and two tight photon-jets are presented from left to right, present events with different number of tight photon-jets. The balck points denote the observed data ${H_{\mathrm {T}}}$ distributions. The magenta line with the gray band, presents the data based background estimation prediction while the other colored lines present expected single ${H_{\mathrm {T}}}$ distributions.
png pdf	Figure 3-b: Signal region ${H_{\mathrm {T}}}$ distributions for the 4+ AK8 category. Events with zero, one and two tight photon-jets are presented from left to right, present events with different number of tight photon-jets. The balck points denote the observed data ${H_{\mathrm {T}}}$ distributions. The magenta line with the gray band, presents the data based background estimation prediction while the other colored lines present expected single ${H_{\mathrm {T}}}$ distributions.
png pdf	Figure 4: The excluded mass parameter space for the gluino and neutralino masses. The region left of the red exclusion line is excluded. The black line defines the expected excluded area based on the data driven background estimation. The error on the observed limit corresponds to the cross section theoretical uncertainties. The color scale denoted the the upper limits on the cross section for pair production of $\tilde{g}$, for each mass point at the 95% confidence level. Exclusion in the low $\tilde{\chi}^{0}_{1}$ high $\tilde{g}$ mass region is a result of the implementation of substructure techniques.

Tables
png pdf	Table 1: Systematic uncertainties considered. The starred $\ast $ uncertainties are evaluated as shape uncertainties while the rest as uncertainties on the normalization. The magnitude of each uncertainty refers to the effect on signal event efficiencies.

Summary

To summarize, a search for superparticle production is presented, performed in events with two substructure rich jets composed of a photon and two gluons, using a pp collisions dataset collected by the CMS experiment and corresponding to an integrated luminosity of 35.9 fb$^{-1}$. This is the first search of its kind targeting the region of parameter space where photons from neutralino decays are not isolated. We use existing jet-substructure variables and novel techniques to identify the unusual jets. The total hadronic activity distributions of events are compared to distributions directly estimated from data. No statistically significant excess is observed above the SM expectation. We establish upper limits with 95% confidence level on gluino pair production cross section using a simplified stealth SUSY model. The excluded gluino masses extend up to 1.5-1.7 TeV depending on the neutralino mass with the highest exclusion set for neutralinos with a mass of about 200 GeV.

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