Search for the lepton flavour violating decay $$\mu ^+ \rightarrow \mathrm {e}^+ \gamma $$ μ + → e + γ with the full dataset of the MEG experiment

Self Cite

A search for lepton flavour violating decays of the Higgs boson in the µτ and eτ 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 B(H → µτ ) < 0.25% (0.25%) and B(H → eτ ) < 0.61% (0.37%), at 95% confidence level. These results are used to derive upper limits on the off-diagonal µτ and eτ Yukawa couplings √ |Y µτ | 2 + |Y τ µ | 2 < 1.43×10 −3 and |Y eτ | 2 + |Y τ e | 2 < 2.26×10 −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. The CMS collaboration 33 IntroductionThe discovery of the Higgs boson (H) at the CERN LHC [1][2][3] has stimulated further precision measurements of the properties of the new particle. A combined study of the 7 and 8 TeV data sets collected by the CMS and ATLAS collaborations shows consistency between the measured couplings of the Higgs boson and the standard model (SM) predictions [4]. However, the constraint on the branching fraction to non-SM decay modes derived from these measurements, B(non-SM) < 34% at 95% confidence level (CL), still allows for a significant contribution from exotic decays [4]. In this paper a search for lepton flavour violating (LFV) decays of the Higgs boson in the µτ and eτ channels is presented. These decays are forbidden in the SM but occur in many new physics scenarios. These include supersymmetric [5][6][7][8][9][10][11][12][13], composite Higgs [14,15], or Randall-Sundrum models [16][17][18], SM extensions with more than one Higgs boson doublet [19,20] or with flavour symmetries [21], and many other scenarios [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. The presence of LFV Higgs boson couplings would allow τ → µ and τ → e to proceed via a virtual Higgs boson [37,38]. Consequently the experimental limits on rare τ lepton -1 - JHEP06(2018)001decays, such as τ → eγ and τ → µγ [39], provide upper limits on B(H → µτ ) and B(H → eτ ) [40,41] of O(10%). Measurements of the electron and muon magnetic moments, and exclusion limits on the electric dipole moment of the electron also provide complementary constraints [42]. The LFV Higgs boson decay to µe is strongly constrained by the µ → eγ limit, B(H → eµ) < O(10 −9 ) [43].The CMS experiment published the first direct search for H → µτ [44], followed by searches for H → eτ and H → eµ decays [45], using proton-proton (pp) collision data corresponding to an integrated luminosity of 19.7 fb −1 at a centre-of-mass energy of 8 TeV.A small excess of data with respect to the SM background-only hypothesis at m H = 125 GeV was observed in the H → µτ channel, with a significance of 2.4 standard deviations (σ), and the bes...

Section: Jhep06(2018)001mentioning

confidence: 99%

mentioning

confidence: 99%

Search for lepton flavour violating decays of the Higgs boson to μτ and eτ in proton-proton collisions at $$ \sqrt{s}=13 $$ TeV

Sirunyan

Tumasyan

Adam

et al. 2018

Self Cite

“…In the muon sector, the upcoming Mu2e [17], DeeMe [18] and Comet [19] experiments will search for µ → e conversion of muons bounded to a nucleus, while Meg [20] and Mu3e [21] at PSI are dedicated to the SM forbidden decays µ → eγ and µ → eee, respectively.…”

Section: Jhep01(2017)084mentioning

confidence: 99%

Next-to-leading order prediction for the decay μ → e e + e − ν ν ¯ $$ \mu \to e\kern0.22em \left({e}^{+}{e}^{-}\right)\;\nu \kern0.2em \overline{\nu} $$

Fael

Greub

2017

We present the differential decay rates and the branching ratios of the muon decay with internal conversion, µ → e (e + e − ) νν, in the Standard Model at next-to-leading order (NLO) in the on-shell scheme. This rare decay mode of the muon is among the main sources of background to the search for µ → eee decay. We found that in the phase space region where the neutrino energies are small, and the three-electron momenta have a similar signature as in the µ → eee decay, the NLO corrections decrease the leading-order prediction by about 10 − 20% depending on the applied cut.

“…Since U as a 7 × 7 matrix is unitary this non-vanishing has to be compensated by the heavy states such that we find as well The branching ratio is defined with respect to the width of the muon Γ(µ → eνν) = m 5 µ G 2 F /192π 3 such that we find which are all far below the current bound BR(µ → eγ) < 4.2 × 10 −13 at 90% confidence level of the MEG experiment [49]. The branching ratios for other cLFV processes are similarly suppressed but their bounds are generally weaker.…”

Section: The Non-susy Partmentioning

confidence: 53%

A supersymmetric electroweak scale seesaw model

Chang

Cheung

Ishida

et al. 2017

In this paper we propose a novel supersymmetric inverse seesaw model which has only one additional Z 6 symmetry. The field content is minimal to get a viable neutrino spectrum at tree-level. Interestingly, the inverse seesaw scale in our model is related to the scale of electroweak symmetry breaking. Due to that origin we are less biased about hierarchies and discuss three different types of the inverse seesaw mechanism with different phenomenologies. We can successfully reproduce neutrino masses and mixing and our model is consistent with current bounds on neutrinoless double beta decay, non-unitarity of the PMNS matrix and charged lepton flavor violation.