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CMS-EXO-19-019 ; CERN-EP-2021-026
Search for resonant and nonresonant new phenomena in high-mass dilepton final states at $\sqrt{s} = $ 13 TeV
JHEP 07 (2021) 208
Abstract: A search is presented for physics beyond the standard model (SM) using electron or muon pairs with high invariant mass. A data set of proton-proton collisions collected by the CMS experiment at the LHC at $\sqrt{s} = $ 13 TeV from 2016 to 2018 corresponding to a total integrated luminosity of up to 140 fb$^{-1}$ is analyzed. No significant deviation is observed with respect to the SM background expectations. Upper limits are presented on the ratio of the product of the production cross section and the branching fraction to dileptons of a new narrow resonance to that of the Z boson. These provide the most stringent lower limits to date on the masses for various spin-1 particles, spin-2 gravitons in the Randall-Sundrum model, as well as spin-1 mediators between the SM and dark matter particles. Lower limits on the ultraviolet cutoff parameter are set both for four-fermion contact interactions and for the Arkani-Hamed, Dimopoulos, and Dvali model with large extra dimensions. Lepton flavor universality is tested at the TeV scale for the first time by comparing the dimuon and dielectron mass spectra. No significant deviation from the SM expectation of unity is observed.
Figures & Tables Summary Additional Figures References CMS Publications
Figures

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Figure 1:
Product of the acceptance and the efficiency for (left) dielectron and (right) dimuon pairs as a function of generated mass in simulated events. The DY samples are used to represent spin-1 particles, and RS graviton samples are used for spin-2 particles.

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Figure 1-a:
Product of the acceptance and the efficiency for dielectron pairs as a function of generated mass in simulated events. The DY samples are used to represent spin-1 particles, and RS graviton samples are used for spin-2 particles.

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Figure 1-b:
Product of the acceptance and the efficiency for dimuon pairs as a function of generated mass in simulated events. The DY samples are used to represent spin-1 particles, and RS graviton samples are used for spin-2 particles.

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Figure 2:
The invariant mass distribution of pairs of (left) electrons and (right) muons observed in data (black dots with statistical uncertainties) and expected from the SM processes (stacked histograms). For the dimuon channel, a prescaled trigger with a ${p_{\mathrm {T}}}$ threshold of 27 GeV was used to collect events in the normalization region (NR) with $ {m_{\mu \mu}} < $ 120 GeV. The corresponding offline threshold is 30 GeV. Events in the signal region (SR) corresponding to masses above 120 GeV are collected using an unprescaled single-muon trigger. The bin width gradually increases with mass. The ratios of the data yields after background subtraction to the expected background yields are shown in the lower plots. The blue shaded band represents the combined statistical and systematic uncertainties in the background. Signal contributions expected from simulated ${\mathrm {G}_\mathrm {KK}}$ and ${\mathrm{Z'} _\mathrm {SSM}}$ resonances with masses of 3.5 and 5 TeV, respectively, are shown.

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Figure 2-a:
The invariant mass distribution of pairs of electrons observed in data (black dots with statistical uncertainties) and expected from the SM processes (stacked histograms). The bin width gradually increases with mass. The ratios of the data yields after background subtraction to the expected background yields are shown in the lower plot. The blue shaded band represents the combined statistical and systematic uncertainties in the background. Signal contributions expected from simulated ${\mathrm {G}_\mathrm {KK}}$ and ${\mathrm{Z'} _\mathrm {SSM}}$ resonances with masses of 3.5 and 5 TeV, respectively, are shown.

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Figure 2-b:
The invariant mass distribution of pairs of electrons muons observed in data (black dots with statistical uncertainties) and expected from the SM processes (stacked histograms). A prescaled trigger with a ${p_{\mathrm {T}}}$ threshold of 27 GeV was used to collect events in the normalization region (NR) with $ {m_{\mu \mu}} < $ 120 GeV. The corresponding offline threshold is 30 GeV. Events in the signal region (SR) corresponding to masses above 120 GeV are collected using an unprescaled single-muon trigger. The bin width gradually increases with mass. The ratios of the data yields after background subtraction to the expected background yields are shown in the lower plot. The blue shaded band represents the combined statistical and systematic uncertainties in the background. Signal contributions expected from simulated ${\mathrm {G}_\mathrm {KK}}$ and ${\mathrm{Z'} _\mathrm {SSM}}$ resonances with masses of 3.5 and 5 TeV, respectively, are shown.

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Figure 3:
The invariant mass distribution of pairs of (upper) electrons and (lower) muons observed in data (black dots with statistical uncertainties) and expected from simulated SM processes (stacked histograms) for (left) $ \cos\theta ^\ast < $ 0 and (right) $ \cos\theta ^\ast \geq $ 0. The bin width gradually increases with mass. The ratios of the data yields after background subtraction to the expected background yields are shown in the lower plots. The blue band represents the combined statistical and systematic uncertainties in the background. The signal contributions expected from the constructive LL CI model with $\Lambda = $ 16 TeV are shown as dashed green lines.

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Figure 3-a:
The invariant mass distribution of pairs of electrons observed in data (black dots with statistical uncertainties) and expected from simulated SM processes (stacked histograms) for $ \cos\theta ^\ast < $ 0. The bin width gradually increases with mass. The ratios of the data yields after background subtraction to the expected background yields are shown in the lower plot. The blue band represents the combined statistical and systematic uncertainties in the background. The signal contribution expected from the constructive LL CI model with $\Lambda = $ 16 TeV is shown as a dashed green line.

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Figure 3-b:
The invariant mass distribution of pairs of electrons observed in data (black dots with statistical uncertainties) and expected from simulated SM processes (stacked histograms) for $ \cos\theta ^\ast \geq $ 0. The bin width gradually increases with mass. The ratios of the data yields after background subtraction to the expected background yields are shown in the lower plot. The blue band represents the combined statistical and systematic uncertainties in the background. The signal contribution expected from the constructive LL CI model with $\Lambda = $ 16 TeV is shown as a dashed green line.

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Figure 3-c:
The invariant mass distribution of pairs of muons observed in data (black dots with statistical uncertainties) and expected from simulated SM processes (stacked histograms) for $ \cos\theta ^\ast < $ 0. The bin width gradually increases with mass. The ratios of the data yields after background subtraction to the expected background yields are shown in the lower plot. The blue band represents the combined statistical and systematic uncertainties in the background. The signal contribution expected from the constructive LL CI model with $\Lambda = $ 16 TeV is shown as a dashed green line.

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Figure 3-d:
The invariant mass distribution of pairs of muons observed in data (black dots with statistical uncertainties) and expected from simulated SM processes (stacked histograms) for $ \cos\theta ^\ast \geq $ 0. The bin width gradually increases with mass. The ratios of the data yields after background subtraction to the expected background yields are shown in the lower plot. The blue band represents the combined statistical and systematic uncertainties in the background. The signal contribution expected from the constructive LL CI model with $\Lambda = $ 16 TeV is shown as a dashed green line.

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Figure 4:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of the production cross section and the branching fraction of a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for (top left) the dielectron channel, (top right) the dimuon channel, and (bottom) their combination. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Simulated predictions for the spin-1 ${\mathrm{Z'} _\mathrm {SSM}}$ and ${\mathrm{Z'} _\psi}$ resonances are shown for comparison.

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Figure 4-a:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of the production cross section and the branching fraction of a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for the dielectron channel. The shaded band corresponda to the 68 and 95% quantiles for the expected limits. Simulated predictions for the spin-1 ${\mathrm{Z'} _\mathrm {SSM}}$ and ${\mathrm{Z'} _\psi}$ resonances are shown for comparison.

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Figure 4-b:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of the production cross section and the branching fraction of a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for the dimuon channel. The shaded band corresponda to the 68 and 95% quantiles for the expected limits. Simulated predictions for the spin-1 ${\mathrm{Z'} _\mathrm {SSM}}$ and ${\mathrm{Z'} _\psi}$ resonances are shown for comparison.

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Figure 4-c:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-1 resonance with a width equal to 0.6% of the resonance mass, relative to the product of the production cross section and the branching fraction of a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for the combination of dielecton and dimuon channels. The shaded band corresponda to the 68 and 95% quantiles for the expected limits. Simulated predictions for the spin-1 ${\mathrm{Z'} _\mathrm {SSM}}$ and ${\mathrm{Z'} _\psi}$ resonances are shown for comparison.

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Figure 5:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-1 resonance, for widths equal to 0.6, 3, 5, and 10% of the resonance mass, relative to the product of the production cross section and the branching fraction for a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for (upper left) the dielectron channel, (upper right) the dimuon channel, and (lower) their combination. Theoretical predictions for the spin-1 ${\mathrm{Z'} _\mathrm {SSM}}$ and ${\mathrm{Z'} _\psi}$ resonances are also shown.

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Figure 5-a:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-1 resonance, for widths equal to 0.6, 3, 5, and 10% of the resonance mass, relative to the product of the production cross section and the branching fraction for a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for the dielectron channel. Theoretical predictions for the spin-1 ${\mathrm{Z'} _\mathrm {SSM}}$ and ${\mathrm{Z'} _\psi}$ resonances are also shown.

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Figure 5-b:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-1 resonance, for widths equal to 0.6, 3, 5, and 10% of the resonance mass, relative to the product of the production cross section and the branching fraction for a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for the dimuon channel. Theoretical predictions for the spin-1 ${\mathrm{Z'} _\mathrm {SSM}}$ and ${\mathrm{Z'} _\psi}$ resonances are also shown.

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Figure 5-c:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-1 resonance, for widths equal to 0.6, 3, 5, and 10% of the resonance mass, relative to the product of the production cross section and the branching fraction for a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for the combination of dielecton and dimuon channels. Theoretical predictions for the spin-1 ${\mathrm{Z'} _\mathrm {SSM}}$ and ${\mathrm{Z'} _\psi}$ resonances are also shown.

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Figure 6:
Lower limits in the $(c_{\mathrm{d}},c_{\mathrm{u}})$ plane obtained by recasting the combined limit at 95% CL on the Z' boson cross section for narrow resonances from dielectron and dimuon channels. For a given Z' boson mass, the cross section limit results in a solid thin black line. These lines are labeled with the relevant Z' boson masses. The closed contours representing the GSM, LRS, and E$_6$ model classes are composed of thick curve segments. Each point on a segment corresponds to a particular model, and the location of the point gives the mass limit on the relevant Z' boson. As indicated in the lower left legend, the curve segment styles correspond to ranges of the particular mixing angle, for each considered model. The lower right legend indicates constituents of each model class.

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Figure 7:
The observed local $p$-value for a given resonance mass hypothesis for (upper left) the dielectron channel, (upper right) the dimuon channel, and (lower) their combination, as a function of the dilepton invariant mass. The four different lines correspond to different signal width hypotheses.

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Figure 7-a:
The observed local $p$-value for a given resonance mass hypothesis for the dielectron channel, (as a function of the dilepton invariant mass. The four different lines correspond to different signal width hypotheses.

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Figure 7-b:
The observed local $p$-value for a given resonance mass hypothesis for the dimuon channel, as a function of the dilepton invariant mass. The four different lines correspond to different signal width hypotheses.

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Figure 7-c:
The observed local $p$-value for a given resonance mass hypothesis for the combination of dielectron and dimuon channels, as a function of the dilepton invariant mass. The four different lines correspond to different signal width hypotheses.

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Figure 8:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-2 resonance, relative to the product of the production cross section and the branching fraction of a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for (upper left) the dielectron channel, (upper right) the dimuon channel, and (lower) their combination. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-2 resonances for widths equal to 0.01, 0.36, and 1.42 GeV corresponding to coupling parameters $k/\overline {M}_\mathrm {Pl}$ of 0.01, 0.05, and 0.10, respectively, are shown for comparison.

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Figure 8-a:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-2 resonance, relative to the product of the production cross section and the branching fraction of a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for the dielectron channel. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-2 resonances for widths equal to 0.01, 0.36, and 1.42 GeV corresponding to coupling parameters $k/\overline {M}_\mathrm {Pl}$ of 0.01, 0.05, and 0.10, respectively, are shown for comparison.

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Figure 8-b:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-2 resonance, relative to the product of the production cross section and the branching fraction of a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for the dimuon channel. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-2 resonances for widths equal to 0.01, 0.36, and 1.42 GeV corresponding to coupling parameters $k/\overline {M}_\mathrm {Pl}$ of 0.01, 0.05, and 0.10, respectively, are shown for comparison.

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Figure 8-c:
The upper limits at 95% CL on the product of the production cross section and the branching fraction for a spin-2 resonance, relative to the product of the production cross section and the branching fraction of a Z boson, multiplied by the theoretical value of $\sigma ({\mathrm{p}} {\mathrm{p}} \to \mathrm{Z} +\mathrm{X}\to \ell \ell +\mathrm{X})$ of 1928 pb, for the combination of the dielectron and dimuon channels. The shaded bands correspond to the 68 and 95% quantiles for the expected limits. Theoretical predictions for the spin-2 resonances for widths equal to 0.01, 0.36, and 1.42 GeV corresponding to coupling parameters $k/\overline {M}_\mathrm {Pl}$ of 0.01, 0.05, and 0.10, respectively, are shown for comparison.

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Figure 9:
Summary of upper limits at 95% CL on the masses of the DM particle, which is assumed to be a Dirac fermion, and its associated mediator, in a simplified model of DM production via a (left) vector or (right) axial-vector mediator. The parameter exclusion regions are obtained by comparing the limits on the product of the production cross section and the branching fraction for decay to a Z boson with the values obtained from calculations in the simplified model. For each combination of the DM particle and mediator mass values, the width of the mediator is taken into account in the limit calculation. The curves with the hatching represent the excluded regions. The solid gray curves, marked as "$\Omega h^{2} \ge $ 0.12'', correspond to parameter regions that reproduce the observed DM relic density in the universe [95,96,6,47], with the hatched area indicating the region where the DM relic abundance exceeds the observed value.

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Figure 9-a:
Summary of upper limits at 95% CL on the masses of the DM particle, which is assumed to be a Dirac fermion, and its associated mediator, in a simplified model of DM production via a vector mediator. The parameter exclusion regions are obtained by comparing the limits on the product of the production cross section and the branching fraction for decay to a Z boson with the values obtained from calculations in the simplified model. For each combination of the DM particle and mediator mass values, the width of the mediator is taken into account in the limit calculation. The curves with the hatching represent the excluded regions. The solid gray curves, marked as "$\Omega h^{2} \ge $ 0.12'', correspond to parameter regions that reproduce the observed DM relic density in the universe [95,96,6,47], with the hatched area indicating the region where the DM relic abundance exceeds the observed value.

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Figure 9-b:
Summary of upper limits at 95% CL on the masses of the DM particle, which is assumed to be a Dirac fermion, and its associated mediator, in a simplified model of DM production via an axial-vector mediator. The parameter exclusion regions are obtained by comparing the limits on the product of the production cross section and the branching fraction for decay to a Z boson with the values obtained from calculations in the simplified model. For each combination of the DM particle and mediator mass values, the width of the mediator is taken into account in the limit calculation. The curves with the hatching represent the excluded regions. The solid gray curves, marked as "$\Omega h^{2} \ge $ 0.12'', correspond to parameter regions that reproduce the observed DM relic density in the universe [95,96,6,47], with the hatched area indicating the region where the DM relic abundance exceeds the observed value.

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Figure 10:
Exclusion limits at 95% CL on the ultraviolet cutoff for (upper left) the dielectron channel, (upper right) the dimuon channel, and (lower) their combination, with $ {m_{\ell \ell}} > $ 1.8 TeV ($ {m_{\ell \ell}} > $ 1.9 TeV for 2016) in the GRW (first bin), Hewett (second bin), and HLZ conventions (third to seventh bin) for the ADD model. Signal model cross sections are calculated up to LO, and an NNLO correction factor of 1.3 is applied.

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Figure 10-a:
Exclusion limits at 95% CL on the ultraviolet cutoff for the dielectron channel, with $ {m_{\ell \ell}} > $ 1.8 TeV ($ {m_{\ell \ell}} > $ 1.9 TeV for 2016) in the GRW (first bin), Hewett (second bin), and HLZ conventions (third to seventh bin) for the ADD model. Signal model cross sections are calculated up to LO, and an NNLO correction factor of 1.3 is applied.

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Figure 10-b:
Exclusion limits at 95% CL on the ultraviolet cutoff for the dimuon channel, with $ {m_{\ell \ell}} > $ 1.8 TeV ($ {m_{\ell \ell}} > $ 1.9 TeV for 2016) in the GRW (first bin), Hewett (second bin), and HLZ conventions (third to seventh bin) for the ADD model. Signal model cross sections are calculated up to LO, and an NNLO correction factor of 1.3 is applied.

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Figure 10-c:
Exclusion limits at 95% CL on the ultraviolet cutoff for the combination of dielectron and dimuon channels, with $ {m_{\ell \ell}} > $ 1.8 TeV ($ {m_{\ell \ell}} > $ 1.9 TeV for 2016) in the GRW (first bin), Hewett (second bin), and HLZ conventions (third to seventh bin) for the ADD model. Signal model cross sections are calculated up to LO, and an NNLO correction factor of 1.3 is applied.

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Figure 11:
Dilepton lower exclusion limits at 95% CL on the CI scale ($\Lambda $) for the eight CI models considered, for (upper left) the dielectron channel, (upper right) the dimuon channel, and (lower) their combination. The limits are obtained for $ {m_{\ell \ell}} > $ 400 GeV.

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Figure 11-a:
Dilepton lower exclusion limits at 95% CL on the CI scale ($\Lambda $) for the eight CI models considered, for the dielectron channel. The limits are obtained for $ {m_{\ell \ell}} > $ 400 GeV.

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Figure 11-b:
Dilepton lower exclusion limits at 95% CL on the CI scale ($\Lambda $) for the eight CI models considered, for the dimuon channel. The limits are obtained for $ {m_{\ell \ell}} > $ 400 GeV.

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Figure 11-c:
Dilepton lower exclusion limits at 95% CL on the CI scale ($\Lambda $) for the eight CI models considered, for the combination of dielectron and dimuon channels. The limits are obtained for $ {m_{\ell \ell}} > $ 400 GeV.

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Figure 12:
Ratio of the differential dilepton production cross section in the dimuon and dielectron channels ${R_{\mu^{+} {}\mu^{-} /\mathrm{e^{+}} {}\mathrm{e^{-}}}}$, as a function of ${m_{\ell \ell}}$ for (upper left) events with two barrel leptons, (upper right) at least one lepton in the endcaps, and (lower) their combination. The ratio is obtained after correcting the reconstructed mass spectra to particle level. The error bars include both statistical and systematic uncertainties.

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Figure 12-a:
Ratio of the differential dilepton production cross section in the dimuon and dielectron channels ${R_{\mu^{+} {}\mu^{-} /\mathrm{e^{+}} {}\mathrm{e^{-}}}}$, as a function of ${m_{\ell \ell}}$ for events with two barrel leptons. The ratio is obtained after correcting the reconstructed mass spectra to particle level. The error bars include both statistical and systematic uncertainties.

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Figure 12-b:
Ratio of the differential dilepton production cross section in the dimuon and dielectron channels ${R_{\mu^{+} {}\mu^{-} /\mathrm{e^{+}} {}\mathrm{e^{-}}}}$, as a function of ${m_{\ell \ell}}$ for events with at least one lepton in the endcaps. The ratio is obtained after correcting the reconstructed mass spectra to particle level. The error bars include both statistical and systematic uncertainties.

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Figure 12-c:
Ratio of the differential dilepton production cross section in the dimuon and dielectron channels ${R_{\mu^{+} {}\mu^{-} /\mathrm{e^{+}} {}\mathrm{e^{-}}}}$, as a function of ${m_{\ell \ell}}$ for all events. The ratio is obtained after correcting the reconstructed mass spectra to particle level. The error bars include both statistical and systematic uncertainties.
Tables

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Table 1:
Various benchmark models in the GSM [41], LRS [41], and $E_\text {6}$ [1,43] model classes, with their corresponding mixing angles, their branching fraction ($\mathcal {B}$) to dileptons, the $c_{\mathrm{u}}$, $c_{\mathrm{d}}$ parameters and their ratio, and the width-to-mass ratio of the associated Z' boson.

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Table 2:
Sources of systematic uncertainties considered in the search for resonant signals and their relative magnitude.

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Table 3:
Systematic uncertainties considered in the search for nonresonant signals. The relative impact of the uncertainties on the background yield estimates is shown for two dilepton invariant mass thresholds, 1 and 3 TeV. The uncertainty in the jet misidentification background has a negligible effect on the overall background estimate and is not listed.

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Table 4:
Observed and expected background yields for different mass ranges in the (upper) dielectron channel and (lower) dimuon channel. The sum of all background contributions is shown as well as a breakdown into the three main categories. The quoted uncertainties include both the statistical and the systematic components.

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Table 5:
The observed (Obs.) and expected (Exp.) 95% CL lower limits on the masses of spin-1 ${\mathrm{Z'} _\mathrm {SSM}}$ and ${\mathrm{Z'} _\psi}$ bosons, assuming a signal width of 0.6 (3.0)% of the resonance mass for ${\mathrm{Z'} _\psi}$ (${\mathrm{Z'} _\mathrm {SSM}}$).

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Table 6:
The observed and expected 95% CL lower limits on the masses of spin-2 resonances for widths equal to 0.01, 0.36, and 1.42 GeV, corresponding to coupling parameters $k/\overline {M}_\mathrm {Pl}$ of 0.01, 0.05, and 0.10.

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Table 7:
Exclusion limits at 95% CL for the electron and muon channels, and their combination, for various parameter conventions of the ADD model. Signal model cross sections are calculated up to LO and the NNLO correction factor of 1.3 is applied. For each of the model parameters, the observed limit is shown first, followed by the expected limit in parentheses.
Summary
A search for resonant and nonresonant new phenomena in the dilepton invariant mass spectrum in proton-proton collisions at $\sqrt{s} = $ 13 TeV corresponding to an integrated luminosity of up to 140 fb$^{-1}$ has been presented. High-mass dielectron and dimuon events were reconstructed and selected with algorithms optimized for electrons and muons with high transverse momenta. Standard model (SM) backgrounds were primarily estimated from simulation, with the dominant Drell-Yan background corrected to the highest order calculations available, including the contribution from photon-induced processes. When searching for resonant signals, the background normalizations were obtained from sidebands in the data, while for non-resonant signals, the background was normalized to the data in a control region around the Z boson peak. No significant deviation from SM expectation is observed.

Upper limits are set on the ratio of the product of the production cross section and the branching fraction in a dilepton channel of a new resonance with an intrinsic width of up to 10% to that of the SM Z boson at 95% confidence level. The limits are interpreted in the context of a sequential SM (SSM) and a superstring-inspired model that predict spin-1 resonances. Lower mass limits of 5.15 (4.56) TeV are set in the $\mathrm{Z}'_{\text{SSM}}$ ($\mathrm{Z}'_{\psi}$) models. The observed limit on narrow spin-1 resonances is translated into limits on generalized couplings of the Z' to up and down quarks in several classes of new physics models. For spin-2 graviton resonances in the Randall-Sundrum model of extra dimensions, lower limits on the graviton mass of 2.47-4.78 TeV are set for values of the coupling parameter $k/\overline{M}_{\mathrm{Pl}}$ between 0.01 and 0.1. The lower mass limits for spin-1 and spin-2 resonances are the most stringent to date.

For spin-1 resonances that act as a mediator between SM particles and dark matter (DM), exclusion limits are set in the mass plane of the mediator and DM particles. For large values of $m_{\mathrm{DM}}$, mediator masses below 1.92 (4.64) TeV are excluded in a model where the mediator is a vector (axial vector) with small (large) coupling to leptons. For $m_{\mathrm{DM}} = $ 0, these limits are reduced to 1.04 and 3.41 TeV, respectively.

Two models of nonresonant signatures have been considered. In case of a four-fermion contact interaction, lower limits on the ultraviolet cutoff parameter $\Lambda$ range from 23.8 to 36.4 TeV depending on the helicity structure of the interaction and the sign of its interference with the SM Drell-Yan background. In the Arkani-Hamed, Dimopoulos, and Dvali model of large extra dimensions, lower limits on the ultraviolet cutoff ranging from 5.9 to 8.9 TeV are set, depending on the parameter convention.

For the first time in this kind of analysis, the dimuon and dielectron invariant mass spectra are corrected for the detector effects and compared at the TeV scale. No significant deviation from lepton flavor universality is observed.
Additional Figures

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Additional Figure 1:
Invariant mass resolution for dielectron pairs as obtained from simulated DY samples as a function of generated mass. The resolution for events with two electrons in the barrel (one electron in the barrel and one in the endcaps) is shown as a black line (dashed red line).

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Additional Figure 2:
Invariant mass resolution for dimuon pairs as obtained from simulated DY samples as a function of generated mass. The resolution for events with two muons in the barrel (at least one muon in the endcaps) is shown as a black line (dashed red line).

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Additional Figure 3:
Distribution of $\cos\theta ^\ast $ in dimuon events for invariant masses above 2000 GeV as obtained from DY and signal simulation. The DY background is shown in black. The signal MC samples contain the DY contribution to model interference between signal and background. Four CI signals with $\Lambda = $ 24 TeV and constructive interference are shown, differing by the helicity configuration of the interaction. The left-left model shown in red, the left-right and right-left model in blue, and the right-right model in orange. An ADD sample with $\Lambda _{\mathrm {T}} = $ 6 TeV is shown in cyan.
References
1 A. Leike The phenomenology of extra neutral gauge bosons PR 317 (1999) 143 hep-ph/9805494
2 P. Langacker The physics of heavy Z' gauge bosons Rev. Mod. Phys. 81 (2009) 1199 0801.1345
3 N. Arkani-Hamed, S. Dimopoulos, and G. Dvali The hierarchy problem and new dimensions at a millimeter PLB 429 (1998) 263 hep-ph/9803315
4 N. Arkani-Hamed, S. Dimopoulos, and G. Dvali Phenomenology, astrophysics and cosmology of theories with sub-millimeter dimensions and TeV scale quantum gravity PRD 59 (1999) 086004 hep-ph/9807344
5 L. Randall and R. Sundrum A large mass hierarchy from a small extra dimension PRL 83 (1999) 3370 hep-ph/9905221
6 Planck Collaboration Planck 2015 results. XIII. Cosmological parameters Astron. Astrophys. 594 (2016) A13 1502.01589
7 LHC New Physics Working Group Collaboration Simplified models for LHC new physics searches JPG 39 (2012) 105005 1105.2838
8 E. Eichten, I. Hinchliffe, K. Lane, and C. Quigg Supercollider physics Rev. Mod. Phys. 56 (1984) 579
9 E. Eichten, K. Lane, and M. Peskin New tests for quark and lepton substructure PRL 50 (1983) 811
10 LHCb Collaboration Test of lepton universality with $ b^{0} \rightarrow k^{*0}\ell^{+}\ell^{-} $ decays JHEP 08 (2017) 055 1705.05802
11 LHCb Collaboration Search for lepton-universality violation in $ B^+\to K^+\ell^+\ell^- $ decays PRL 122 (2019) 191801 1903.09252
12 S. Bifani, S. Descotes-Genon, A. Romero Vidal, and M.-H. Schune Review of lepton universality tests in $ b $ decays JPG 46 (2019) 023001 1809.06229
13 D. Be\vcirević, N. Ko\vsnik, O. Sumensari, and R. Zukanovich Funchal Palatable leptoquark scenarios for lepton flavor violation in exclusive $ b\to s\ell_1\ell_2 $ modes JHEP 11 (2016) 035 1608.07583
14 A. Greljo and D. Marzocca High-$ p_{\mathrm{T}} $ dilepton tails and flavor physics EPJC 77 (2017) 548 1704.09015
15 CMS Collaboration Search for resonances in the dilepton mass distribution in $ {\mathrm{p}}{\mathrm{p}} $ collisions at $ \sqrt{s}= $ 7 TeV JHEP 05 (2011) 093 CMS-EXO-10-013
1103.0981
16 CMS Collaboration Search for narrow resonances in dilepton mass spectra in $ {\mathrm{p}}{\mathrm{p}} $ collisions at $ \sqrt{s}= $ 7 TeV PLB 714 (2012) 158 CMS-EXO-11-019
1206.1849
17 CMS Collaboration Search for heavy narrow dilepton resonances in $ {\mathrm{p}}{\mathrm{p}} $ collisions at $ \sqrt{s}= $ 7 TeV and $ \sqrt{s}= $ 8 TeV PLB 720 (2013) 63 CMS-EXO-12-015
1212.6175
18 CMS Collaboration Search for physics beyond the standard model in dilepton mass spectra in proton-proton collisions at $ \sqrt{s}= $ 8 TeV JHEP 04 (2015) 025 CMS-EXO-12-061
1412.6302
19 CMS Collaboration Search for narrow resonances in dilepton mass spectra in proton-proton collisions at $ \sqrt{s} = $ 13 TeV and combination with 8 TeV data PLB 768 (2017) 57 CMS-EXO-15-005
1609.05391
20 CMS Collaboration Search for high-mass resonances in dilepton final states in proton-proton collisions at $ \sqrt{s}= $ 13 TeV JHEP 06 (2018) 120 CMS-EXO-16-047
1803.06292
21 ATLAS Collaboration Search for high mass dilepton resonances in $ {\mathrm{p}}{\mathrm{p}} $ collisions at $ \sqrt{s}= $ 7 TeV with the ATLAS experiment PLB 700 (2011) 163 1103.6218
22 ATLAS Collaboration Search for high-mass resonances decaying to dilepton final states in $ {\mathrm{p}}{\mathrm{p}} $ collisions at $ \sqrt{s} = $ 7 TeV with the ATLAS detector JHEP 11 (2012) 138 1209.2535
23 ATLAS Collaboration Search for high-mass dilepton resonances in pp collisions at $ \sqrt{s}= $ 8 TeV with the ATLAS detector PRD 90 (2014) 052005 1405.4123
24 ATLAS Collaboration Search for new high-mass phenomena in the dilepton final state using 36.1 fb$ ^{-1} $ of proton-proton collision data at $ \sqrt{s} = $ 13 TeV with the ATLAS detector JHEP 10 (2017) 182 1707.02424
25 ATLAS Collaboration Search for high-mass dilepton resonances using 139 fb$ ^{-1} $ of $ pp $ collision data collected at $ \sqrt{s}= $ 13 TeV with the ATLAS detector PLB 796 (2019) 68 1903.06248
26 ATLAS Collaboration Constraints on mediator-based dark matter and scalar dark energy models using $ \sqrt{s} = 13 TeV pp $ collision data collected by the ATLAS detector JHEP 05 (2019) 142 1903.01400
27 CMS Collaboration Search for contact interactions and large extra dimensions in the dilepton mass spectra from proton-proton collisions at $ \sqrt{s} = $ 13 TeV JHEP 04 (2019) 114 CMS-EXO-17-025
1812.10443
28 CMS Collaboration Search for physics beyond the standard model in high-mass diphoton events from proton-proton collisions at $ \sqrt{s}= $ 13 TeV PRD 98 (2018) 092001 CMS-EXO-17-017
1809.00327
29 CMS Collaboration Search for new physics in dijet angular distributions using proton-proton collisions at $ \sqrt{s}= $ 13 TeV and constraints on dark matter and other models EPJC 78 (2018) 789 CMS-EXO-16-046
1803.08030
30 ATLAS Collaboration Search for new phenomena in dijet events using 37 fb$ ^{-1} $ of $ pp $ collision data collected at $ \sqrt{s}= $ 13 TeV with the ATLAS detector PRD 96 (2017) 052004 1703.09127
31 ATLAS Collaboration Search for contact interactions and large extra dimensions in the dilepton channel using proton-proton collisions at $ \sqrt{s}= $ 8 TeV with the ATLAS detector EPJC 74 (2014) 3134 1407.2410
32 ATLAS Collaboration Search for new non-resonant phenomena in high-mass dilepton final states with the ATLAS detector JHEP 11 (2020) 005 2006.12946
33 CMS Collaboration CMS Luminosity Measurements for the 2016 Data Taking Period CMS-PAS-LUM-17-001 CMS-PAS-LUM-17-001
34 CMS Collaboration CMS luminosity measurement for the 2017 data-taking period at $ \sqrt{s} = $ 13 TeV CMS-PAS-LUM-17-004 CMS-PAS-LUM-17-004
35 CMS Collaboration CMS luminosity measurement for the 2018 data-taking period at $ \sqrt{s} = $ 13 TeV CMS-PAS-LUM-18-002 CMS-PAS-LUM-18-002
36 J. C. Collins and D. E. Soper Angular distribution of dileptons in high-energy hadron collisions PRD 16 (1977) 2219
37 CMS Collaboration HEPDATA record for this analysis to be released
38 CMS Collaboration CMS technical design report for the pixel detector upgrade CDS
39 CMS Collaboration The CMS experiment at the CERN LHC JINST 3 (2008) S08004 CMS-00-001
40 CMS Collaboration The CMS trigger system JINST 12 (2017) P01020 CMS-TRG-12-001
1609.02366
41 E. Accomando et al. Z' physics with early LHC data PRD 83 (2011) 075012 1010.6058
42 G. Altarelli, B. Mele, and M. Ruiz-Altaba Searching for new heavy vector bosons in $ {\mathrm{p}}\mathrm{\bar{p}} $ colliders Z. Phys. C 45 (1989) 109
43 J. L. Hewett and T. G. Rizzo Low-energy phenomenology of superstring-inspired E$ _6 $ models PR 183 (1989) 193
44 E. Accomando et al. Z' at the LHC: Interference and finite width effects in Drell-Yan JHEP 10 (2013) 153 1304.6700
45 M. S. Carena, A. Daleo, B. A. Dobrescu, and T. M. P. Tait Z' gauge bosons at the Tevatron PRD 70 (2004) 093009 hep-ph/0408098
46 L. Randall and R. Sundrum An alternative to compactification PRL 83 (1999) 4690 hep-th/9906064
47 A. Albert et al. Recommendations of the LHC Dark Matter Working Group: Comparing LHC searches for dark matter mediators in visible and invisible decay channels and calculations of the thermal relic density Phys. Dark Univ. 26 (2019) 100377 1703.05703
48 M. Backović et al. Higher-order QCD predictions for dark matter production at the LHC in simplified models with $ s $ channel mediators EPJC 75 (2015) 482 1508.05327
49 G. F. Giudice, R. Rattazzi, and J. D. Wells Quantum gravity and extra dimensions at high-energy colliders NPB 544 (1999) 3 hep-ph/9811291
50 J. L. Hewett Indirect collider signals for extra dimensions PRL 82 (1999) 4765 hep-ph/9811356
51 T. Han, J. D. Lykken, and R.-J. Zhang Kaluza--Klein states from large extra dimensions PRD 59 (1999) 105006 hep-ph/9811350
52 P. Nason A new method for combining NLO QCD with shower Monte Carlo algorithms JHEP 11 (2004) 040 hep-ph/0409146
53 S. Frixione, P. Nason, and C. Oleari Matching NLO QCD computations with parton shower simulations: the POWHEG method JHEP 11 (2007) 070 0709.2092
54 S. Alioli, P. Nason, C. Oleari, and E. Re A general framework for implementing NLO calculations in shower Monte Carlo programs: the POWHEG BOX JHEP 06 (2010) 043 1002.2581
55 S. Alioli, P. Nason, C. Oleari, and E. Re NLO vector-boson production matched with shower in POWHEG JHEP 07 (2008) 060 0805.4802
56 S. Frixione, P. Nason, and G. Ridolfi A positive-weight next-to-leading-order Monte Carlo for heavy flavour hadroproduction JHEP 09 (2007) 126 0707.3088
57 E. Re Single-top Wt-channel production matched with parton showers using the POWHEG method EPJC 71 (2011) 1547 1009.2450
58 M. R. Whalley, D. Bourilkov, and R. C. Group The Les Houches accord PDFs (LHAPDF) and LHAGLUE in HERA and the LHC: A Workshop on the implications of HERA for LHC physics. Proceedings, Part B 2005 hep-ph/0508110
59 D. Bourilkov, R. C. Group, and M. R. Whalley LHAPDF: PDF use from the Tevatron to the LHC in TeV4LHC Workshop - 4th meeting Batavia, Illinois, October 20-22, 2005 (2006) hep-ph/0605240
60 A. Buckley et al. LHAPDF6: parton density access in the LHC precision era EPJC 75 (2015) 132 1412.7420
61 NNPDF Collaboration Parton distributions for the LHC Run II JHEP 04 (2015) 040 1410.8849
62 NNPDF Collaboration Parton distributions from high-precision collider data EPJC 77 (2017) 663 1706.00428
63 T. Sjostrand et al. An Introduction to PYTHIA 8.2 CPC 191 (2015) 159 1410.3012
64 CMS Collaboration Event generator tunes obtained from underlying event and multiparton scattering measurements EPJC 76 (2016) 155 CMS-GEN-14-001
1512.00815
65 CMS Collaboration Extraction and validation of a new set of CMS PYTHIA8 tunes from underlying-event measurements EPJC 80 (2020) 4 CMS-GEN-17-001
1903.12179
66 Y. Li and F. Petriello Combining QCD and electroweak corrections to dilepton production in FEWZ PRD 86 (2012) 094034 1208.5967
67 A. Manohar, P. Nason, G. P. Salam, and G. Zanderighi How bright is the proton? A precise determination of the photon parton distribution function PRL 117 (2016) 242002 1607.04266
68 J. Butterworth et al. PDF4LHC recommendations for LHC Run II JPG 43 (2016) 023001 1510.03865
69 D. Bourilkov Photon-induced background for dilepton searches and measurements in pp collisions at 13 TeV 1606.00523
70 D. Bourilkov Exploring the LHC landscape with dileptons 1609.08994
71 M. Czakon and A. Mitov Top++: a program for the calculation of the top-pair cross-section at hadron colliders CPC 185 (2014) 2930 1112.5675
72 N. Kidonakis Two-loop soft anomalous dimensions for single top quark associated production with a W$ ^{-} $ or H$ ^{-} $ PRD 82 (2010) 054018 1005.4451
73 J. Alwall et al. The automated computation of tree-level and next-to-leading order differential cross sections and their matching to parton shower simulations JHEP 07 (2014) 079 1405.0301
74 R. Boughezal et al. Color-singlet production at NNLO in MCFM EPJC 77 (2016) 7 1605.08011
75 J. M. Campbell, R. K. Ellis, and W. T. Giele A multi-threaded version of MCFM EPJC 75 (2015) 246 1503.06182
76 J. M. Campbell, R. K. Ellis, and C. Williams Vector boson pair production at the LHC JHEP 07 (2011) 018 1105.0020
77 J. M. Campbell and R. K. Ellis Update on vector boson pair production at hadron colliders PRD 60 (1999) 113006 hep-ph/9905386
78 T. Ahmed et al. NNLO QCD corrections to the Drell--Yan cross section in models of TeV-scale gravity EPJC 77 (2017) 22 1606.08454
79 CMS Collaboration Performance of the CMS Level-1 trigger in proton-proton collisions at $ \sqrt{s} = $ 13 TeV JINST 15 (2020) P10017 CMS-TRG-17-001
2006.10165
80 GEANT4 Collaboration GEANT4--a simulation toolkit NIMA 506 (2003) 250
81 CMS Collaboration Performance of electron reconstruction and selection with the CMS detector in proton-proton collisions at $ \sqrt{s}= $ 8 TeV JINST 10 (2015) P06005 CMS-EGM-13-001
1502.02701
82 CMS Collaboration Electron and photon reconstruction and identification with the CMS experiment at the CERN LHC Submitted to JINST CMS-EGM-17-001
2012.06888
83 CMS Collaboration Performance of the CMS muon trigger system in proton-proton collisions at $ \sqrt{s} = $ 13 TeV Submitted to JINST CMS-MUO-19-001
2102.04790
84 CMS Collaboration Performance of CMS muon reconstruction in $ {\mathrm{p}}{\mathrm{p}} $ collision events at $ \sqrt{s} = $ 7 TeV JINST 7 (2012) P10002 CMS-MUO-10-004
1206.4071
85 CMS Collaboration Performance of the reconstruction and identification of high-momentum muons in proton-proton collisions at $ \sqrt{s} = $ 13 TeV JINST 15 (2020) P02027 CMS-MUO-17-001
1912.03516
86 CMS Collaboration Measurement of the inelastic proton-proton cross section at $ \sqrt{s}= $ 13 TeV JHEP 07 (2018) 161 CMS-FSQ-15-005
1802.02613
87 Particle Data Group, P. A. Zyla et al. Review of particle physics Prog. Theor. Exp. Phys
88 The ATLAS Collaboration, The CMS Collaboration, The LHC Higgs Combination Group Procedure for the LHC Higgs boson search combination in Summer 2011 CMS-NOTE-2011-005
89 L. Moneta et al. The RooStats project in 13th International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT2010) SISSA, 2010 1009.1003
90 M. J. Oreglia A study of the reactions $\psi' \to \gamma\gamma \psi$ PhD thesis, Stanford University, 1980 SLAC Report SLAC-R-236, see A
91 BaBar Collaboration Study of $ B \to X\gamma $ decays and determination of $ |V_{td}/V_{ts}| $ PRD 82 (2010) 051101 1005.4087
92 CMS Collaboration Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC PLB 716 (2012) 30 CMS-HIG-12-028
1207.7235
93 J. Alwall et al. Computing decay rates for new physics theories with FeynRules and MadGraph5_aMCatNLO CPC 197 (2015) 312 1402.1178
94 ATLAS Collaboration Dark matter summary plots for s-channel mediators ATL-PHYS-PUB-2020-021, CERN
95 M. Backović et al. MadDM: New dark matter tool in the LHC era AIP Conf. Proc. 1743 (2016) 060001 1509.03683
96 M. Backović, K. Kong, and M. McCaskey MadDM v.1.0: Computation of dark matter relic abundance using MadGraph5 Phys. Dark Univ. 5-6 (2014) 18 1308.4955
97 E. Adelberger et al. Torsion balance experiments: A low-energy frontier of particle physics Prog. Part. NP 62 (2009) 102
98 S. Hannestad and G. G. Raffelt Supernova and neutron star limits on large extra dimensions reexamined PRD 67 (2003) 125008 hep-ph/0304029
99 T. Adye Unfolding algorithms and tests using RooUnfold in Proceedings, PHYSTAT 2011 workshop on statistical issues related to discovery claims in search experiments and unfolding, p. 313 2011 1105.1160
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