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CMS-EXO-19-004 ; CERN-EP-2019-229
Search for dijet resonances using events with three jets in proton-proton collisions at $\sqrt{s} = $ 13 TeV
Phys. Lett. B 805 (2020) 135448
Abstract: A search for a narrow resonance with a mass between 350 and 700 GeV, and decaying into a pair of jets, is performed using proton-proton collision events containing at least three jets. The data sample corresponds to an integrated luminosity of 18.3 fb$^{-1}$ recorded at $\sqrt{s} = $ 13 TeV with the CMS detector. Data are collected with a technique known as "data scouting", in which the events are reconstructed, selected, and recorded at a high rate in a compact form by the high-level trigger. The three-jet final state provides sensitivity to lower resonance masses than in previous searches using the data scouting technique. The spectrum of the dijet invariant mass, calculated from the two jets with the largest transverse momenta in the event, is used to search for a resonance. No significant excess over a smoothly falling background is found. Limits at 95% confidence level are set on the production cross section of a narrow dijet resonance. The corresponding upper limits on the coupling of a narrow vector resonance interacting only with quarks are between 0.10 and 0.15, depending on the resonance mass. These results represent the most stringent upper limits in the mass range between 350 and 450 GeV obtained with a search that is sensitive to the decay of the resonance into light-flavor quarks.
Figures & Tables Summary Additional Figures & Tables References CMS Publications
Figures

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Figure 1:
Dijet mass spectrum (points) compared to a fitted parameterization of the background (solid curve), where the fit is performed in the range 290 $ < {m_{\mathrm {jj}}} < $ 1000 GeV. The horizontal bars show the widths of each bin in dijet mass. The dashed lines represent the dijet mass distribution from 400, 550, and 700 GeV resonance signals expected to be excluded at 95% CL by this analysis. The lower panel shows the difference between the data and the fitted parametrization, divided by the statistical uncertainty of the data.

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Figure 2:
Upper limits at 95% CL on the product of the cross section, branching fraction, and acceptance as a function of resonance mass for a narrow vector resonance decaying into a pair of quark jets. The acceptance is calculated for the analysis selection, namely three wide jets with $ {p_{\mathrm {T}}} > $ 72 GeV and $ {| \eta |} < $ 2.5, and ${| \eta _1 - \eta _2 |} < $ 1.1. The observed limits (solid curve), expected limits (dashed curve) and their variation at the 1 and 2 standard deviation levels (shaded bands) are shown. The dashed-dotted curve shows the expected cross section times acceptance for a DM mediator (see text).

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Figure 3:
Upper limits at 95% CL on the universal quark coupling ${g'_{\mathrm{q}}}$ , as a function of resonance mass, for a narrow vector resonance that only couples to quarks. The observed limits (solid curve), expected limits (dashed curve) and their variation at the 1 and 2 standard deviation levels (shaded bands) are shown. The dashed-dotted curve shows the coupling strength for which the cross section for dijet production in this model is the same as for a DM mediator (see text).
Tables

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Table 1:
Acceptance for a vector resonance decaying into a dijet as a function of the resonance mass. The acceptance is calculated using signal simulations for the analysis selection, namely three wide jets with ${p_{\mathrm {T}}} > $ 72 GeV and ${| \eta |} < $ 2.5, and $ {| \eta _1 - \eta _2 |} < $ 1.1. The errors are dominated by the uncertainties in the parton shower modeling used in signal simulations.
Summary
A search for a narrow vector resonance of mass between 350 and 700 GeV decaying into two jets has been performed in events containing at least three jets using proton-proton collision data at $\sqrt{s} = $ 13 TeV at the LHC corresponding to an integrated luminosity of 18.3 fb$^{-1}$. The dijet mass distribution of the two leading jets is smooth, and there is no evidence for a resonance. Upper limits at 95% confidence level are set on the product of the cross section, branching fraction, and acceptance as a function of resonance mass. This search excludes a simplified model of interactions between quarks and dark matter particles of mass 1 GeV, where the interactions are mediated by a vector particle with mass between 350 and 700 GeV, for coupling strengths of ${g_{\mathrm{q}}} =$ 0.25 and ${g_{\text{DM}}} =$ 1. Upper limits between 0.10 and 0.15 are also set on the coupling to quarks ${g'_{\mathrm{q}}}$ for a vector particle interacting only with quarks. These results represent the most stringent upper limits in the mass range between 350 and 450 GeV obtained with a search that is sensitive to the decay of the resonance into light-flavor quarks.
Additional Figures

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Additional Figure 1:
Comparison of the dijet mass distribution of the nominal selection (black), control selection without correction (red), and control selection with correction (blue) for data (solid histograms) and a simulation of a signal from a resonance with a mass of 400 GeV (dashed histograms). The correction, applied as a function of the product of the two largest jet transverse momenta in the event, is obtained as the ratio of the numbers of events passing the signal selection to those passing the control selection. For ease of readability, the dijet mass distributions of the signal have been scaled by an arbitrary factor. The bottom plot shows the relative difference between the dijet mass distributions of the data from the control and nominal selections. The yield of the uncorrected control selection for data is 95.7% of the nominal selection. The overlap between the two data selections is about 35% of the nominal selection. The yield of the uncorrected control selection for signal simulation of a 400- GeV resonance is about 50% of the nominal selection.

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Additional Figure 2:
Upper limits at 95% CL on the universal quark coupling $g'_q$, as a function of resonance mass, for a narrow vector resonance that only couples to quarks [arXiv:1611.03568] compared with other inclusive searches for dijet resonances. The observed limits (solid curve), expected limits (dashed curve) and their variation at the 1 and 2 standard deviation levels (shaded bands) are shown. The colored lines are the 95% CL observed limits set by other inclusive searches for dijet resonances.
Additional Tables

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Additional Table 1:
Fraction of data and simulated signal events passing different stages of the analysis selection. The selection corresponding to each line includes the selection of the upper lines. Data are required to pass the trigger selection. The uncertainties quoted are statistical only.
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