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Title: Search for lepton flavour violating decays of heavy resonances and quantum black holes to an eμ pair in proton-proton collisions at √s = 8 TeV

Abstract

A search for narrow resonances decaying to an electron and a muon is presented. The $$\mathrm {e}$$ $${\mu }$$ mass spectrum is also investigated for non-resonant contributions from the production of quantum black holes (QBHs). The analysis is performed using data corresponding to an integrated luminosity of 19.7 $$~\text {fb}^\text {-1}$$ collected in proton-proton collisions at a centre-of-mass energy of 8 $$~\text {TeV}$$ with the CMS detector at the LHC. With no evidence for physics beyond the standard model in the invariant mass spectrum of selected $$\mathrm {e}\mu $$ pairs, upper limits are set at 95  $$\%$$ confidence level on the product of cross section and branching fraction for signals arising in theories with charged lepton flavour violation. In the search for narrow resonances, the resonant production of a $$\mathrm {\tau }$$ sneutrino in R-parity violating supersymmetry is considered. The $$\mathrm {\tau }$$ sneutrino is excluded for masses below 1.28 $$~\text {TeV}$$ for couplings $$\lambda _{132}=\lambda _{231}=\lambda '_{311}=0.01$$ , and below 2.30 $$~\text {TeV}$$ for $$\lambda _{132}=\lambda _{231}=0.07$$ and $$\lambda '_{311}=0.11$$ . These are the most stringent limits to date from direct searches at high-energy colliders. In addition, the resonance searches are interpreted in terms of a model with heavy partners of the $${\mathrm {Z}} $$ boson and the photon. In a framework of TeV-scale quantum gravity based on a renormalization of Newton’s constant, the search for non-resonant contributions to the $$\mathrm {e}$$ $${\mu }$$ mass spectrum excludes QBH production below a threshold mass $$M_{\mathrm {th}}$$ of 1.99 $$~\text {TeV}$$ . In models that invoke extra dimensions, the bounds range from 2.36 $$~\text {TeV}$$ for one extra dimension to 3.63 $$~\text {TeV}$$ for six extra dimensions. Furthermore, this is the first search for QBHs decaying into the $$\mathrm {e}$$ $${\mu }$$ final state.

Authors:
 [1]
  1. Yerevan Physics Inst. (YerPhI), Yerevan (Armenia). et al.
Publication Date:
Research Org.:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Argonne National Lab. (ANL), Argonne, IL (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
OSTI Identifier:
1256708
Report Number(s):
CMS-EXO-13-002; CERN-EP-2016-068; FERMILAB-PUB-16-203-CMS; arXiv:1604.05239
Journal ID: ISSN 1434-6044; 1448302
Grant/Contract Number:
AC02-07CH11359; AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
European Physical Journal. C, Particles and Fields
Additional Journal Information:
Journal Volume: 76; Journal Issue: 6; Journal ID: ISSN 1434-6044
Publisher:
Springer
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats

Khachatryan, Vardan. Search for lepton flavour violating decays of heavy resonances and quantum black holes to an eμ pair in proton-proton collisions at √s = 8 TeV. United States: N. p., 2016. Web. doi:10.1140/epjc/s10052-016-4149-y.
Khachatryan, Vardan. Search for lepton flavour violating decays of heavy resonances and quantum black holes to an eμ pair in proton-proton collisions at √s = 8 TeV. United States. doi:10.1140/epjc/s10052-016-4149-y.
Khachatryan, Vardan. 2016. "Search for lepton flavour violating decays of heavy resonances and quantum black holes to an eμ pair in proton-proton collisions at √s = 8 TeV". United States. doi:10.1140/epjc/s10052-016-4149-y. https://www.osti.gov/servlets/purl/1256708.
@article{osti_1256708,
title = {Search for lepton flavour violating decays of heavy resonances and quantum black holes to an eμ pair in proton-proton collisions at √s = 8 TeV},
author = {Khachatryan, Vardan},
abstractNote = {A search for narrow resonances decaying to an electron and a muon is presented. The $\mathrm {e}$ ${\mu }$ mass spectrum is also investigated for non-resonant contributions from the production of quantum black holes (QBHs). The analysis is performed using data corresponding to an integrated luminosity of 19.7 $~\text {fb}^\text {-1}$ collected in proton-proton collisions at a centre-of-mass energy of 8 $~\text {TeV}$ with the CMS detector at the LHC. With no evidence for physics beyond the standard model in the invariant mass spectrum of selected $\mathrm {e}\mu $ pairs, upper limits are set at 95  $\%$ confidence level on the product of cross section and branching fraction for signals arising in theories with charged lepton flavour violation. In the search for narrow resonances, the resonant production of a $\mathrm {\tau }$ sneutrino in R-parity violating supersymmetry is considered. The $\mathrm {\tau }$ sneutrino is excluded for masses below 1.28 $~\text {TeV}$ for couplings $\lambda _{132}=\lambda _{231}=\lambda '_{311}=0.01$ , and below 2.30 $~\text {TeV}$ for $\lambda _{132}=\lambda _{231}=0.07$ and $\lambda '_{311}=0.11$ . These are the most stringent limits to date from direct searches at high-energy colliders. In addition, the resonance searches are interpreted in terms of a model with heavy partners of the ${\mathrm {Z}} $ boson and the photon. In a framework of TeV-scale quantum gravity based on a renormalization of Newton’s constant, the search for non-resonant contributions to the $\mathrm {e}$ ${\mu }$ mass spectrum excludes QBH production below a threshold mass $M_{\mathrm {th}}$ of 1.99 $~\text {TeV}$ . In models that invoke extra dimensions, the bounds range from 2.36 $~\text {TeV}$ for one extra dimension to 3.63 $~\text {TeV}$ for six extra dimensions. Furthermore, this is the first search for QBHs decaying into the $\mathrm {e}$ ${\mu }$ final state.},
doi = {10.1140/epjc/s10052-016-4149-y},
journal = {European Physical Journal. C, Particles and Fields},
number = 6,
volume = 76,
place = {United States},
year = 2016,
month = 6
}

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  • A search for narrow resonances decaying to an electron and a muon is presented. The eμ mass spectrum is also investigated for non-resonant contributions from the production of quantum black holes (QBHs). The analysis is performed using data corresponding to an integrated luminosity of 19.7 fb -1 collected in proton-proton collisions at a centre-of-mass energy of 8 TeV with the CMS detector at the LHC. With no evidence for physics beyond the standard model in the invariant mass spectrum of selected eμ pairs, upper limits are set at 95 % confidence level on the product of cross section and branching fractionmore » for signals arising in theories with charged lepton flavour violation. In the search for narrow resonances, the resonant production of τ sneutrino in R-parity violating supersymmetry is considered. The τ sneutrino is excluded for masses below 1.28 TeV for couplings λ 132 = λ 231 = λ 311 ' = 0.01 , and below 2.30 TeV for λ 132 = λ 231 = 0.07 and λ 311 ' = 0.11. These are the most stringent limits to date from direct searches at high-energy colliders. In addition, the resonance searches are interpreted in terms of a model with heavy partners of the Z boson and the photon. In a framework of TeV-scale quantum gravity based on a renormalization of Newton’s constant, the search for non-resonant contributions to the eμ mass spectrum excludes QBH production below a threshold mass M th of 1.99 TeV. In models that invoke extra dimensions, the bounds range from 2.36 TeV for one extra dimension to 3.63 TeV for six extra dimensions. This is the first search for QBHs decaying into the eμ final state.« less
  • A search is reported for heavy resonances decaying into emore » $$\mu$$ 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 35.9 fb$$^{-1}$$. The search focuses on resonance masses above 200 GeV. With no evidence found for physics beyond the standard model in the e$$\mu$$ mass spectrum, upper limits are set at 95% confidence level on the product of the cross section and branching fraction for this lepton-flavor violating signal. Based on these results, resonant $$\tau$$ sneutrino production in R-parity violating supersymmetric models is excluded for masses below 1.7 TeV, for couplings $$\lambda_{132}=\lambda_{231}=\lambda'_{311}=0.01$$. Heavy Z$'$ gauge bosons with lepton-flavor violating transitions are excluded for masses up to 4.4 TeV. The e$$\mu$$ mass spectrum is also interpreted in terms of non-resonant contributions from quantum black-hole production in models with one to six extra spatial dimensions, and lower mass limits are found between 3.6 and 5.6 TeV. In all interpretations used in this analysis, the results of this search improve previous limits by about 1 TeV. These limits correspond to the most sensitive values obtained at colliders.« less
  • A direct search for lepton flavour violating decays of the Higgs boson (H) in the H→eτ and H→eμ channels is described. The data sample used in the search was collected in proton–proton collisions atmore » $$\sqrt s=$$ 8 TeV with the CMS detector at the LHC and corresponds to an integrated luminosity of 19.7 fb ₋1 . No evidence is found for lepton flavour violating decays in either final state. Upper limits on the branching fractions, B(H→eτ)<0.69% and B(H→eμ)<0.035%, are set at the 95% confidence level. The constraint set on B(H→eτ) is an order of magnitude more stringent than the existing indirect limits. Finally, the limits are used to constrain the corresponding flavour violating Yukawa couplings, absent in the standard model.« less
  • A search for lepton flavour violating decays of the Higgs boson in themore » $$\mu\tau$$ and e$$\tau$$ decay modes is presented. The search is based on a data set corresponding to an integrated luminosity of 35.9 fb$$^{-1}$$ of proton-proton collisions collected with the CMS detector in 2016, at a centre-of-mass energy of 13 TeV. No significant excess over the standard model expectation is observed. The observed (expected) upper limits on the lepton flavour violating branching fractions of the Higgs boson are $$\mathcal{B}$$(H$$\to\mu\tau$$) < 0.25% (0.25%) and $$\mathcal{B}$$(H$$\to$$e$$\tau$$) < 0.61% (0.37%), at 95% confidence level. These results are used to derive upper limits on the off-diagonal $$\mu\tau$$ and e$$\tau$$ Yukawa couplings $$\sqrt{|{Y_{\mu\tau}}|^{2}+|{Y_{\tau\mu}}|^{2}}<1.43\times 10^{-3}$$ and $$\sqrt{|{Y_{\mathrm{e}\tau}}|^{2}+|{Y_{\tau\mathrm{e}}}|^{2}}<2.26\times 10^{-3}$$ at 95% confidence level. The limits on the lepton flavour violating branching fractions of the Higgs boson and on the associated Yukawa couplings are the most stringent to date.« less
  • Our search for resonances and quantum black holes is performed using the dijet mass spectra measured in proton-proton collisions at √s=8 TeV with the CMS detector at the LHC. The data set corresponds to an integrated luminosity of 19.7 fb -1. In a search for narrow resonances that couple to quark-quark, quark-gluon, or gluon-gluon pairs, model-independent upper limits, at 95% confidence level, are obtained on the production cross section of resonances, with masses above 1.2 TeV. When interpreted in the context of specific models the limits exclude string resonances with masses below 5.0 TeV; excited quarks below 3.5 TeV; scalarmore » diquarks below 4.7 TeV; W' bosons below 1.9 TeV or between 2.0 and 2.2 TeV; Z' bosons below 1.7 TeV; and Randall-Sundrum gravitons below 1.6 TeV. A separate search is conducted for narrow resonances that decay to final states including b quarks. Furthermore, the first exclusion limit is set for excited b quarks, with a lower mass limit between 1.2 and 1.6 TeV depending on their decay properties. Searches are also carried out for wide resonances, assuming for the first time width-to-mass ratios up to 30%, and for quantum black holes with a range of model parameters. The wide resonance search excludes axigluons and colorons with mass below 3.6 TeV, and color-octet scalars with mass below 2.5 TeV. Lower bounds between 5.0 and 6.3 TeV are set on the masses of quantum black holes.« less
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