Search results for "Flavour violation"
showing 10 items of 10 documents
Search for heavy neutral lepton production in K+ decays to positrons
2020
A search for heavy neutral lepton ($N$) production in $K^+\to e^+N$ decays using the data sample collected by the NA62 experiment at CERN in 2017--2018 is reported. Upper limits of the extended neutrino mixing matrix element $|U_{e4}|^2$ are established at the level of $10^{-9}$ over most of the accessible heavy neutral lepton mass range 144--462 MeV/$c^2$, with the assumption that the lifetime exceeds 50 ns. These limits improve significantly upon those of previous production and decay searches. The $|U_{e4}|^2$ range favoured by Big Bang Nucleosynthesis is excluded up to a mass of about 340 MeV/$c^2$.
Neutrino transition magnetic moments within the non-standard neutrino-nucleus interactions
2015
Tensorial non-standard neutrino interactions are studied through a combined analysis of nuclear structure calculations and a sensitivity $\chi^2$-type of neutrino events expected to be measured at the COHERENT experiment, recently planned to operate at the Spallation Neutron Source (Oak Ridge). Potential sizeable predictions on transition neutrino magnetic moments and other electromagnetic parameters, such as neutrino milli-charges, are also addressed. The non-standard neutrino-nucleus processes, explored from nuclear physics perspectives within the context of quasi-particle random phase approximation, are exploited in order to estimate the expected number of events originating from vector …
Technical design of the phase I Mu3e experiment
2021
Nuclear instruments & methods in physics research / A 1014, 165679 (2021). doi:10.1016/j.nima.2021.165679
Impact of squark generation mixing on the search for squarks decaying into fermions at LHC
2010
We study the effect of squark generation mixing on squark production and decays at LHC in the Minimal Supersymmetric Standard Model (MSSM). We show that the effect can be very large despite the very strong constraints on quark flavour violation (QFV) from experimental data on B mesons. We find that the two lightest up-type squarks su_{1,2} can have large branching ratios for the decays into 'c-quark + neutralino_1' and 't-quark + neutralino_1' at the same time due to squark generation mixing, leading to QFV signals 'pp -> c bar{t} (t bar{c}) + missing-E_T + X' with a significant rate. The observation of this remarkable signature would provide a powerful test of supersymmetric QFV at LHC.…
Disentangling new physics contributions in lepton flavour violating τ decays
2016
Abstract The possibility to discriminate between different operators contributing to lepton flavour violating tau decays is discussed within an effective field theory framework. Correlations among decay rates in different channels as well as differential distributions in many-body decays are considered. Recent developments in the determination of the hadronic form factors for τ → l π π ( l = e , μ ) decays are incorporated in the analysis. The above issues are exemplified by considering a Higgs-like boson with lepton flavour violating couplings. Implications of the search for lepton flavour violating Higgs decays performed recently by the CMS collaboration are also discussed.
Flavour-violating charged lepton decays in seesaw-type models
1994
Analytic expressions of lepton-flavour- and lepton-number-violating decays of charged leptons are derived in the context of general $SU(2)_L\otimes U(1)_Y$ seesaw scenarios that are motivated by grand unified theories (GUT's) or superstring models, in which left-handed and/or right-handed neutral singlets are present. Possible constraints imposed by cosmology and low-energy data are briefly discussed. The violation of the decoupling theorem in flavour-dependent graphs due to the presence of heavy neutral leptons of Dirac or Majorana nature is emphasized. Numerical estimates reveal that the decays $\tau^-\to e^-e^-e^+$ or $\tau^-\to e^-\mu^-\mu^+$ can be as large as $\sim 10^{-6}$, which may…
Minimal Flavour Violation and Multi-Higgs Models
2010
We propose an extension of the hypothesis of Minimal Flavour Violation (MFV) to general multi-Higgs models without the assumption of Natural Flavour Conservation (NFC) in the Higgs sector. We study in detail under what conditions the neutral Higgs couplings are only functions of V-CKM and propose a MFV expansion for the neutral Higgs couplings to fermions
Working group report: Neutrino physics
2009
This is the report of the neutrino physics working group at WHEPP-X. We summarize the problems selected and discussed at the workshop and the papers which have resulted subsequently.
Search for lepton flavour violation in the e mu continuum with the ATLAS detector in root s=7 TeV pp collisions at the LHC
2012
This paper presents a search for the t-channel exchange of an R-parity violating scalar top quark ([~ over t] ) in the e[superscript ±]μ[superscript ∓] continuum using 2.1 fb[superscript −1] of data collected by the ATLAS detector in s√=7 TeV pp collisions at the Large Hadron Collider. Data are found to be consistent with the expectation from the Standard Model backgrounds. Limits on R-parity-violating couplings at 95 % C.L. are calculated as a function of the scalar top mass ( m[subscript bar over t]). The upper limits on the production cross section for pp→eμX, through the t-channel exchange of a scalar top quark, ranges from 170 fb for m[subscript ~ over t]=95 GeV to 30 fb for m[subscrip…
Searches for lepton number violating $K^+$ decays
2019
The NA62 experiment at CERN reports a search for the lepton number violating decays K+ -> pi(-)e(+)e(+) and K+ -> pi(-)mu(+)mu(+) using a data sample collected in 2017. No signals are observed, and upper limits on the branching fractions of these decays of 2.2 x 10(-10) and 4.2 x 10(-11) are obtained, respectively, at 90% confidence level. These upper limits improve on previously reported measurements by factors of 3 and 2, respectively.