CMS-PAS-EXO-16-001

CMS-PAS-EXO-16-001
Search for high-mass resonances and quantum black holes in the $\mathrm{e}\mu$ final state in proton-proton collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
April 2016

Abstract: A search for heavy resonances decaying into $\mathrm{e}\mu$ final states has been performed using an integrated luminosity of 2.7 fb$^{-1}$ of 13 TeV proton-proton collision data recorded with the CMS detector at the LHC. No evidence for physics beyond the Standard Model is observed in the invariant mass spectrum of selected $\mathrm{e}\mu$ pairs. Upper limits at 95% CL are set on the cross section times branching ratio of different signal benchmark models foreseeing lepton flavour violation in interactions involving charged leptons. Scenarios of resonant $\tau$ sneutrino production in R-parity violating supersymmetry are excluded for masses below 1.0 TeV for couplings $\lambda_{132}=\lambda_{231}=\lambda'_{311}= $ 0.01 and below 3.3 TeV for $\lambda_{132}=\lambda_{231}=\lambda'_{311}= $ 0.2 . The observed invariant mass spectrum is also interpreted in terms of the non-resonant signal of Quantum Black Hole (QBH) production in models with extra dimensions. The observed exclusion limits range from 2.5 TeV for one extra dimension to 4.5 TeV for six extra dimensions.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures	Summary	Additional Figures	References	CMS Publications

Figures
png pdf	Figure 1-a: a: The invariant mass distribution of selected $\mathrm{e}\mu$ pairs. The black points with error bars represent data and the stacked histograms represent the expectations from SM processes. The combined statistical and systematic uncertainty is labeled total uncertainty. b: The cumulative distribution of the invariant mass of selected $\mathrm{e}\mu$ pairs, where all events above the mass value on the $x$ axis are summed up.
png pdf	Figure 1-b: a: The invariant mass distribution of selected $\mathrm{e}\mu$ pairs. The black points with error bars represent data and the stacked histograms represent the expectations from SM processes. The combined statistical and systematic uncertainty is labeled total uncertainty. b: The cumulative distribution of the invariant mass of selected $\mathrm{e}\mu$ pairs, where all events above the mass value on the $x$ axis are summed up.
png pdf	Figure 2-a: a: 95% CL upper limit on the signal cross section times branching fraction for the RPV $\tau $ sneutrino signal as a function of the mass of the resonance. b: 95% CL limit contours for the RPV $\tau $ sneutrino signal in the ($M_{\tilde{\nu _{\tau }}},\lambda _{311}'$) parameter plane.
png pdf	Figure 2-b: a: 95% CL upper limit on the signal cross section times branching fraction for the RPV $\tau $ sneutrino signal as a function of the mass of the resonance. b: 95% CL limit contours for the RPV $\tau $ sneutrino signal in the ($M_{\tilde{\nu _{\tau }}},\lambda _{311}'$) parameter plane.
png pdf	Figure 3: 95% CL upper limit on the signal cross section times branching fraction for the QBH signal as a function of the threshold mass.

Summary

A search for heavy resonances decaying into an $\mathrm{e}\mu$ pair has been carried out using 2.7 fb$^{-1}$ of proton-proton collision data recorded with the CMS detector at the LHC at a centre-of-mass energy of 13 TeV. Agreement between the data and the SM expectation is observed. We set limits on the resonant production of $\tau$ sneutrinos in RPV SUSY with subsequent decay into an $\mathrm{e}\mu$ pair. For couplings $\lambda_{132}=\lambda_{231}=\lambda_{311}'= $ 0.01 we exclude a $\tau$ sneutrino LSP for masses below 1.0 TeV, for couplings $\lambda_{132}=\lambda_{231}=\lambda_{311}'= $ 0.1 we exclude masses below 2.7 TeV and for couplings $\lambda_{132}=\lambda_{231}=\lambda_{311}'= $ 0.2 we exclude masses below 3.3 TeV. The corresponding expected limits are 1.0 TeV, 2.7 TeV and 3.3 TeV. We set lower bounds on the mass thresholds for the production of quantum black holes with subsequent decay into an $\mathrm{e}\mu$ pair in models with one to six extra dimensions, assuming the threshold mass to be at the Planck scale, ranging from $M_{\rm th} =$ 2.5 TeV ($n= $ 1 ) to 4.5 TeV ($n= $ 6 ).

Additional Figures
png	Additional Figure 1: Event display of the highest mass $ \mathrm{e}\mu$ pair (1635 GeV) recorded in 2015 in the $rz$-plane.
png	Additional Figure 2: Event display of the highest mass $ \mathrm{e}\mu$ pair (1635 GeV) recorded in 2015 in the $r\phi$-plane.
png	Additional Figure 3: Event display of the highest mass $ \mathrm{e}\mu$ pair (1635 GeV) recorded in 2015.

References
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