CMSEXO20012 ; CERNEP2023064  
Search for resonances in events with photon and jet final states in protonproton collisions at $ \sqrt{s} = $ 13 TeV  
CMS Collaboration  
14 May 2023  
JHEP 12 (2023) 189  
Abstract: A search for resonances in events with the $ \gamma $+jet final state has been performed using protonproton collision data collected at $ \sqrt{s} = $ 13 TeV by the CMS experiment at the LHC. The total data analyzed correspond to an integrated luminosity of 138 fb$ ^{1} $. Models of excited quarks and quantum black holes are considered. Using a widejet reconstruction for the candidate jet, the $ \gamma $+jet invariant mass spectrum measured in data is examined for the presence of resonances over the standard model continuum background. The background is estimated by fitting this mass distribution with a functional form. The data exhibit no statistically significant deviations from the expected standard model background. Exclusion limits at 95% confidence level on the resonance mass and other parameters are set. Excited lightflavor quarks (excited bottom quarks) are excluded up to a mass of 6.0 (3.8) TeV. Quantum black hole production is excluded for masses up to 7.5 (5.2) TeV in the ArkaniHamedDimopoulosDvali (RandallSundrum) model. These lower mass bounds are the most stringent to date among those obtained in the $ \gamma $+jet final state.  
Links: eprint arXiv:2305.07998 [hepex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; 
Figures  
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Figure 1:
Illustrative Feynman diagrams for qg $ \to\gamma $+jet resonance signal models of q*, b* (left), and QBH production (right). 
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Figure 1a:
Illustrative Feynman diagram for qg $ \to\gamma $+jet resonance signal models of q*, b* production. 
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Figure 1b:
Illustrative Feynman diagram for qg $ \to\gamma $+jet resonance signal models of QBH production. 
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Figure 2:
Distributions of reconstructed $ \gamma $+jet invariant mass for the q* and b* signal models with resonance mass of 4 TeV, and for QBH from the ADD and RS1 models with $ M_\text{th}= $ 4 TeV. 
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Figure 3:
The product of the cross section and branching fraction, $ \sigma\mathcal{B} $, as a function of the resonance mass of q* or b* signals ($ M_{\mathrm{q}^{*}} $ or $ M_{\mathrm{b}^{*}} $) or the threshold mass of QBH signal models ($ M_\text{th} $). 
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Figure 4:
The product of acceptance and efficiency for the q* signal in the inclusive category and the b* signal in the b tag and 0b tag categories, for SM coupling $ f = $ 1.0 and for different resonance values (left), and the signal for the QBH (ADD/RS1) model in the inclusive category, for different $ M_\text{th} $ values (right), for the years 2016, 2017, and 2018. 
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Figure 4a:
The product of acceptance and efficiency for the q* signal in the inclusive category and the b* signal in the b tag and 0b tag categories, for SM coupling $ f = $ 1.0 and for different resonance values, for the years 2016, 2017, and 2018. 
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Figure 4b:
The product of acceptance and efficiency for the signal for the QBH (ADD/RS1) model in the inclusive category, for different $ M_\text{th} $ values, for the years 2016, 2017, and 2018. 
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Figure 5:
Fit to the $ \gamma $+jet invariant mass distribution in data with Eq. 2 for the "inclusive" category of q* and QBH after all selections. Simulations of the q* signal with a 2 TeV mass and coupling $ f = $ 1.0, the QBH ADD signal with $ M_\text{th}= $ 3 TeV, and the QBH RS1 signal with $ M_\text{th}= $ 4 TeV are also shown. The lower panel shows the difference between the data yield and the background prediction divided by the statistical uncertainty of the data. The green (inner) and yellow (outer) bands, respectively, represent the 68 and 95% confidence level statistical uncertainties in the fit. 
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Figure 6:
Fits to the $ \gamma $+jet invariant mass distributions in data with Eq. 2 for the b* selection for the b tag category (left) and 0b tag category (right). Simulations of b* signals are shown for mass values of 1.0 and 2.0 TeV and for $ f = $ 1.0. The lower panel shows the difference between the data yield and background prediction divided by the statistical uncertainty of the data. The green (inner) and yellow (outer) bands, respectively, represent the 68 and 95% confidence level statistical uncertainties in the fit. 
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Figure 6a:
Fits to the $ \gamma $+jet invariant mass distributions in data with Eq. 2 for the b* selection for the b tag category. Simulations of b* signals are shown for mass values of 1.0 and 2.0 TeV and for $ f = $ 1.0. The lower panel shows the difference between the data yield and background prediction divided by the statistical uncertainty of the data. The green (inner) and yellow (outer) bands, respectively, represent the 68 and 95% confidence level statistical uncertainties in the fit. 
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Figure 6b:
Fits to the $ \gamma $+jet invariant mass distributions in data with Eq. 2 for the b* selection for the 0b tag category. Simulations of b* signals are shown for mass values of 1.0 and 2.0 TeV and for $ f = $ 1.0. The lower panel shows the difference between the data yield and background prediction divided by the statistical uncertainty of the data. The green (inner) and yellow (outer) bands, respectively, represent the 68 and 95% confidence level statistical uncertainties in the fit. 
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Figure 7:
The expected (dashed) and observed (solid) 95% CL upper limits on the product of the cross section and branching fraction, as functions of q* mass, for coupling strength $ f= $ 1.0 (upper left), $ f= $ 0.5 (upper right), and $ f= $ 0.1 (lower). The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit, respectively. The limits are compared with the theoretical predictions for q* production for the corresponding coupling strengths. 
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Figure 7a:
The expected (dashed) and observed (solid) 95% CL upper limits on the product of the cross section and branching fraction, as functions of q* mass, for coupling strength $ f= $ 1.0. The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit, respectively. The limits are compared with the theoretical predictions for q* production for the corresponding coupling strengths. 
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Figure 7b:
The expected (dashed) and observed (solid) 95% CL upper limits on the product of the cross section and branching fraction, as functions of q* mass, for coupling strength $ f= $ 0.5. The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit, respectively. The limits are compared with the theoretical predictions for q* production for the corresponding coupling strengths. 
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Figure 7c:
The expected (dashed) and observed (solid) 95% CL upper limits on the product of the cross section and branching fraction, as functions of q* mass, for coupling strength $ f= $ 0.1. The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit, respectively. The limits are compared with the theoretical predictions for q* production for the corresponding coupling strengths. 
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Figure 8:
The expected (dashed) and observed (solid) 95% CL upper limits on the product of the cross section and branching fraction, as functions of b* mass, for coupling strength $ f= $ 1.0 (upper left), $ f= $ 0.5 (upper right), and $ f= $ 0.1 (lower). The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit, respectively. The limits are compared with the theoretical predictions for b* production for the corresponding coupling strengths. For coupling $ f= $ 1.0, the limits are compared for b* production by gauge interactions (red), contact interactions (violet), and total b* signal by the addition of these two production modes. 
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Figure 8a:
The expected (dashed) and observed (solid) 95% CL upper limits on the product of the cross section and branching fraction, as functions of b* mass, for coupling strength $ f= $ 1.0. The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit, respectively. The limits are compared with the theoretical predictions for b* production for the corresponding coupling strengths. For this coupling, the limits are compared for b* production by gauge interactions (red), contact interactions (violet), and total b* signal by the addition of these two production modes. 
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Figure 8b:
The expected (dashed) and observed (solid) 95% CL upper limits on the product of the cross section and branching fraction, as functions of b* mass, for coupling strength $ f= $ 0.5. The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit, respectively. The limits are compared with the theoretical predictions for b* production for the corresponding coupling strengths. 
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Figure 8c:
The expected (dashed) and observed (solid) 95% CL upper limits on the product of the cross section and branching fraction, as functions of b* mass, for coupling strength $ f= $ 0.1. The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit, respectively. The limits are compared with the theoretical predictions for b* production for the corresponding coupling strengths. 
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Figure 9:
The expected (dashed) and observed (solid) 95% CL upper limit on the product of the cross section and branching fraction as a function of the minimum black hole mass for the ADD ($ n= $ 6) and RS1 ($ n= $ 1) models on the left and right, respectively. The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit. The limits are compared with the theoretical predictions for QBH production for ADD ($ n= $ 6) and RS1 ($ n= $ 1) models. 
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Figure 9a:
The expected (dashed) and observed (solid) 95% CL upper limit on the product of the cross section and branching fraction as a function of the minimum black hole mass for the ADD ($ n= $ 6) model.The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit. The limits are compared with the theoretical predictions for QBH production for the ADD ($ n= $ 6) model. 
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Figure 9b:
The expected (dashed) and observed (solid) 95% CL upper limit on the product of the cross section and branching fraction as a function of the minimum black hole mass for the RS1 ($ n= $ 1) model.The green (inner) and yellow (outer) bands correspond to 1 and 2 standard deviation uncertainties in the expected limit. The limits are compared with the theoretical predictions for QBH production for the RS1 ($ n= $ 1) model. 
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Figure 10:
The expected and observed 95% CL exclusion mass limit variation with the SM couplings for the excited q* and b* signal models. 
Tables  
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Table 1:
Systematic uncertainties in the signal yields for the mass range analyzed. 
Summary 
A search for resonances in the $ \gamma $+jet final state has been performed using protonproton collision data at $ \sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 138 fb$ ^{1} $. Compared to previous searches in this final state, this analysis features improved b jet tagging efficiency and signal mass resolution, as well as a significantly larger data set. The results are compared with standard model extensions postulating excited quarks, excited b quarks, and quantum black holes. For the coupling strength $ f = $ 1.0, the observed (expected) lower mass bounds on the excited lightflavor quarks and excited bottom quarks from gauge interactions are estimated to be 6.0 (6.0) and 2.2 (2.3) TeV, respectively. For the same coupling strength, the observed lower mass bounds on the excited bottom quarks extends to 3.8 TeV, when the production mode from contact interactions is also considered. For quantum black hole production, observed exclusion limits are estimated to be 7.5 and 5.2 TeV for the ArkaniHamedDimopoulosDvali and the RandallSundrum models with 6 and 1 extra dimensions, respectively. These lower mass bounds are extended compared to previous results by 0.40.8 TeV [13,16] and are the most stringent to date among those obtained in the $ \gamma $+jet final state. 
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