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| CMS-PAS-EXO-19-014 | ||
| Search for heavy resonances and quantum black holes in e$\mu$, e$\tau$, and $\mu\tau$ final states in proton-proton collisions at $\sqrt{s}= $ 13 TeV | ||
| CMS Collaboration | ||
| August 2021 | ||
| Abstract: A search is reported for heavy resonances and quantum black holes decaying into e$\mu$, e$\tau$, and $\mu\tau$ final states in proton-proton collisions recorded by the CMS experiment at the CERN LHC at $\sqrt{s}= $ 13 TeV, corresponding to an integrated luminosity of 137.1 fb$^{-1}$. No evidence is found for physics beyond the standard model in the dilepton invariant mass spectra, and upper limits are set at 95% confidence level on the products of the cross sections and branching fractions for various lepton-flavor violating signals. These include resonant $\tau$ sneutrino production in R-parity violating supersymmetric models, heavy Z' gauge bosons with lepton-flavor violating transitions, and non-resonant quantum black-hole production in models with extra spatial dimensions. In addition, model-independent limits are provided allowing the results to be interpreted in other models with the same final states and similar kinematic distributions. The results of these searches provide the best collider limits to date for the models considered. | ||
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Links:
CDS record (PDF) ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, Submitted to JHEP. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
Invariant mass distributions for the e$\mu $ channel (top), and collinear mass distributions for the e$ \tau $ (middle) and $\mu \tau $ (bottom) channels. In addition to the observed data (black points) and standard model expectation (filled histograms), expected signal distributions for three models are shown: the RPV SUSY model with $\lambda = \lambda ' = $ 0.01 and sneutrino mass of 1.6 TeV, a Z' boson with a mass of 1.6 TeV, and the QBH expectation for $n=$ 4 and a threshold mass of 1.6 TeV. |
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Figure 1-a:
Invariant mass distributions for the e$\mu $ channel (top), and collinear mass distributions for the e$ \tau $ (middle) and $\mu \tau $ (bottom) channels. In addition to the observed data (black points) and standard model expectation (filled histograms), expected signal distributions for three models are shown: the RPV SUSY model with $\lambda = \lambda ' = $ 0.01 and sneutrino mass of 1.6 TeV, a Z' boson with a mass of 1.6 TeV, and the QBH expectation for $n=$ 4 and a threshold mass of 1.6 TeV. |
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Figure 1-b:
Invariant mass distributions for the e$\mu $ channel (top), and collinear mass distributions for the e$ \tau $ (middle) and $\mu \tau $ (bottom) channels. In addition to the observed data (black points) and standard model expectation (filled histograms), expected signal distributions for three models are shown: the RPV SUSY model with $\lambda = \lambda ' = $ 0.01 and sneutrino mass of 1.6 TeV, a Z' boson with a mass of 1.6 TeV, and the QBH expectation for $n=$ 4 and a threshold mass of 1.6 TeV. |
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Figure 1-c:
Invariant mass distributions for the e$\mu $ channel (top), and collinear mass distributions for the e$ \tau $ (middle) and $\mu \tau $ (bottom) channels. In addition to the observed data (black points) and standard model expectation (filled histograms), expected signal distributions for three models are shown: the RPV SUSY model with $\lambda = \lambda ' = $ 0.01 and sneutrino mass of 1.6 TeV, a Z' boson with a mass of 1.6 TeV, and the QBH expectation for $n=$ 4 and a threshold mass of 1.6 TeV. |
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Figure 2:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section times branching fraction as a function of the tau sneutrino mass in an RPV SUSY model for the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 2-a:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section times branching fraction as a function of the tau sneutrino mass in an RPV SUSY model for the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 2-b:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section times branching fraction as a function of the tau sneutrino mass in an RPV SUSY model for the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 2-c:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section times branching fraction as a function of the tau sneutrino mass in an RPV SUSY model for the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 3:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section and branching fraction for a Z' boson with LFV decays, in the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 3-a:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section and branching fraction for a Z' boson with LFV decays, in the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 3-b:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section and branching fraction for a Z' boson with LFV decays, in the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 3-c:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section and branching fraction for a Z' boson with LFV decays, in the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 4:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section and branching fraction for quantum black hole production in an ADD model with $n=$ 4 extra dimensions, in the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 4-a:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section and branching fraction for quantum black hole production in an ADD model with $n=$ 4 extra dimensions, in the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 4-b:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section and branching fraction for quantum black hole production in an ADD model with $n=$ 4 extra dimensions, in the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 4-c:
Expected (black dashed line) and observed (black solid line) 95% CL upper limits on the product of cross section and branching fraction for quantum black hole production in an ADD model with $n=$ 4 extra dimensions, in the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
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Figure 5:
Upper limits at 95% CL on the RPV SUSY model in the plane of sneutrino mass and $\lambda '$ coupling, for four values of $\lambda $ couplings. The regions to the left of and above the limits are excluded. The top plot corresponds to the e$ \mu $ channel, while the bottom left and right plot show the e$ \tau $ and $\mu \tau $ channels, respectively. |
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Figure 5-a:
Upper limits at 95% CL on the RPV SUSY model in the plane of sneutrino mass and $\lambda '$ coupling, for four values of $\lambda $ couplings. The regions to the left of and above the limits are excluded. The top plot corresponds to the e$ \mu $ channel, while the bottom left and right plot show the e$ \tau $ and $\mu \tau $ channels, respectively. |
png pdf |
Figure 5-b:
Upper limits at 95% CL on the RPV SUSY model in the plane of sneutrino mass and $\lambda '$ coupling, for four values of $\lambda $ couplings. The regions to the left of and above the limits are excluded. The top plot corresponds to the e$ \mu $ channel, while the bottom left and right plot show the e$ \tau $ and $\mu \tau $ channels, respectively. |
png pdf |
Figure 5-c:
Upper limits at 95% CL on the RPV SUSY model in the plane of sneutrino mass and $\lambda '$ coupling, for four values of $\lambda $ couplings. The regions to the left of and above the limits are excluded. The top plot corresponds to the e$ \mu $ channel, while the bottom left and right plot show the e$ \tau $ and $\mu \tau $ channels, respectively. |
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Figure 6:
Model independent upper limits at 95% CL on the product of cross section, branching fraction, acceptance, and efficiency are shown. Observed (expected) limits are shown in black solid (dashed) lines for the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
png pdf |
Figure 6-a:
Model independent upper limits at 95% CL on the product of cross section, branching fraction, acceptance, and efficiency are shown. Observed (expected) limits are shown in black solid (dashed) lines for the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
png pdf |
Figure 6-b:
Model independent upper limits at 95% CL on the product of cross section, branching fraction, acceptance, and efficiency are shown. Observed (expected) limits are shown in black solid (dashed) lines for the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
png pdf |
Figure 6-c:
Model independent upper limits at 95% CL on the product of cross section, branching fraction, acceptance, and efficiency are shown. Observed (expected) limits are shown in black solid (dashed) lines for the e$ \mu $ (top), e$ \tau $ (bottom left), and $\mu \tau $ (bottom right) channels. The shaded bands represent the one and two standard deviation (s.d.) uncertainties. |
| Tables | |
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Table 1:
The observed and expected (in brackets) 95% CL lower mass limits on RPV SUSY, Z', and QBH signals for the e$ \mu $, e$ \tau $, and $\mu \tau $ channels. |
| Summary |
| A search for heavy particles decaying into e$\mu$, e$\tau$, or $\mu\tau$ final states is conducted using 137.1 fb$^{-1}$ of proton-proton collision data at $\sqrt{s}=13$ TeV recorded by the CMS detector at the LHC. The data are consistent with the standard model predictions, and lower limits at 95% confidence level are set on the mass of a supersymmetric $\tau$ sneutrino with R-parity-violating couplings $\lambda = \lambda' = $ 0.1 at 4.2 (e$\mu$ channel), 3.7 (e$\tau$), and 3.6 TeV ($\mu\tau$), respectively; on the mass of a Z' vector boson with lepton-flavor violating couplings at 5.0 (e$\mu$), 4.3 (e$\tau$), and 4.1 TeV ($\mu\tau$), respectively; and on the threshold mass for quantum black hole production in the context of the Arkani-Hamed-Dimopoulos-Dvali model with four extra dimensions at 5.6 (e$\mu$), 5.2 (e$\tau$), and 5.0 TeV ($\mu\tau$). In addition, model-independent limits are provided allowing the results to be interpreted in other models with the same final states and similar kinematic distributions. Limits in the e$\tau$ and $\mu\tau$ final states as well as model-independent limits are reported by CMS for the first time, and all results of this search are currently the best limits from the LHC in the considered models. |
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Compact Muon Solenoid LHC, CERN |
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