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CMS-PAS-EXO-16-029

Search for low-mass pair-produced dijet resonances using jet substructure techniques in proton-proton collisions at $\sqrt{s}= $ 13 TeV

CMS Collaboration

November 2016

Abstract: Results from a search for paired boosted diquark resonances, using jet substructure techniques, are reported. This search uses data corresponding to an integrated luminosity of 2.7 fb$^{-1}$ from proton-proton collisions at a center-of-mass energy of $\sqrt{s}= $ 13 TeV, recorded by the CMS detector at the LHC in 2015. Limits at 95% confidence level are set on the production of top squarks decaying to two light quarks in the framework of R-parity violating supersymmetry. Top squarks with masses between 80 and 240 GeV are excluded.

Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures
png pdf	Figure 1: Direct pair production of stops decaying via the hadronic RPV coupling $\lambda _{312}''$ into two light quarks.
png pdf	Figure 2: Average pruned jet mass distribution shown for data (dots) and the total background prediction. The different background components are shown with different colors while the grey hashed band shows the total background uncertainty. On the bottom, ratio between data and background prediction, with the grey hashed band showing the total background uncertainty. The background uncertainties are described in Section 7 and summarized in Table 4. The shaded colored regions on the bottom indicate the expected top squark signal distributions shown for two different selected masses as they would appear in data.
png pdf	Figure 3: Observed and expected 95% CL upper limits on cross section vs. stop mass. The dashed pink line shows the NLO + NLL theoretical predictions for stop pair production.

Tables
png pdf	Table 1: Summary of variables used in the analysis and the corresponding optimized selection.
png pdf	Table 2: Definition of the regions A, B, C, D for the ABCD method.
png pdf	Table 3: Overview of the systematic uncertainties on the signal acceptance by source.
png pdf	Table 4: Overview of the systematic uncertainties on the background prediction by source.

Summary

A search has been performed for pair production of boosted resonances decaying to quarks giving a dijet signature from proton-proton collisions from the LHC at $\sqrt{s}=$ 13 TeV with the CMS detector. The distribution in the average pruned jet mass of selected events has been used to search for an excess compatible with a resonance signal above the SM background estimate. No significant deviation is found. Exclusion limits are set on the top squark pair production cross section with decays through the RPV SUSY coupling $\lambda^{''}_{\mathrm{312}}$ to light-flavor jets at 95% confidence level. We exclude stop masses between 80 GeV and 240 GeV.

Additional Figures
png pdf	Additional Figure 1: Trigger efficiency as a function of the total transverse hadronic energy ${H_{\mathrm {T}}}$ and the pruned jet mass measured in data.
png pdf	Additional Figure 2: MC distributions of kinematic variables used in the analysis shown for backgrounds and signal. Each variable is plotted with all selection criteria apart from that on the variable being shown. The distributions are normalized to unit area. (Top left) $\tau _{21}$ distribution for the leading ${p_{\mathrm {T}}}$ jet, (top right) $\tau _{21}$ distribution for the second leading ${p_{\mathrm {T}}}$ jet, (bottom left) mass asymmetry $M_{asym}$, (bottom right) $| \eta _{j1} - \eta _{j2} |$.
png pdf	Additional Figure 2-a: MC $\tau _{21}$ distribution for the leading ${p_{\mathrm {T}}}$ jet, shown for backgrounds and signal. The variable is plotted with all selection criteria apart from that on the variable being shown. The distribution is normalized to unit area.
png pdf	Additional Figure 2-b: MC $\tau _{21}$ distribution for the second leading ${p_{\mathrm {T}}}$ jet, shown for backgrounds and signal. The variable is plotted with all selection criteria apart from that on the variable being shown. The distribution is normalized to unit area.
png pdf	Additional Figure 2-c: MC mass asymmetry $M_{asym}$ distribution, shown for backgrounds and signal. The variable is plotted with all selection criteria apart from that on the variable being shown. The distribution is normalized to unit area.
png pdf	Additional Figure 2-d: MC $| \eta _{j1} - \eta _{j2} |$ distribution, shown for backgrounds and signal. The variable is plotted with all selection criteria apart from that on the variable being shown. The distribution is normalized to unit area.
png pdf	Additional Figure 3: Data/MC comparison of the average pruned jet mass distribution after the final selection is applied. Data is shown in dots while the different background MC components are stacked with different colors. The expected signal distributions at different stop masses are also shown (dashed lines). The QCD multijets background is ultimately not estimated from MC in this analysis, but using data as described in the text.
png pdf	Additional Figure 4: Transfer factor ratio (B/D) vs. averaged pruned jet mass, used in QCD multijets background estimate (ABCD), shown for data not corrected for resonant backgrounds (blue dots), data minus resonant background expectations from MC (red dots) and the sum of all the MC backgrounds (green crosses). Fits to the data (blue line), data minus resonant backgrounds (red line) and to the MC (blue solid line) with the sigmoid function: $ (p_0 + \exp( p_1 + p_2 x^3 ))^{-1} $ from 60 GeV to 350 GeV are also shown. Thin red dashed lines show the uncertainties from the fit to the data minus the resonant backgrounds.
png pdf	Additional Figure 5: Average pruned jet mass distribution demonstrating the closure of the ABCD QCD multijets background estimation. Red line: the sum of all SM MC backgrounds after applying the final analysis selection. On the bottom, the ratio between the two background predictions is shown, and the blue lines represents the level of closure found to be $\pm$10 % which is used as a systematic uncertainty on the yield of the ABCD background prediction.
png pdf	Additional Figure 6: Acceptance times efficiency vs. stop mass from the Monte Carlo simulation.
png pdf	Additional Figure 7: Signal mass distributions for various simulated stop masses probed in this analysis after applying the final analysis selection. These distributions are scaled to unit area.

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