scholarly journals Lepton flavour violation in rare $$\Lambda _b$$ decays

2021 ◽  
Vol 81 (8) ◽  
Author(s):  
Marzia Bordone ◽  
Muslem Rahimi ◽  
K. Keri Vos
Keyword(s):  
Branching Ratio ◽  
New Physics ◽  
Lepton Flavour Violation ◽  
Flavour Violation ◽  
Model Independent ◽  
First Time ◽  
Lepton Flavour

AbstractLepton flavour violation (LFV) naturally occurs in many new physics models, specifically in those explaining the B anomalies. While LFV has already been studied for mesonic decays, it is important to consider also baryonic decays mediated by the same quark transition. In this paper, we study LFV in the baryonic $$\Lambda _b \rightarrow \Lambda \ell _1 \ell _2$$ Λ b → Λ ℓ 1 ℓ 2 using for the first time a full basis of New Physics operators. We present expected bounds on the branching ratio in a model-independent framework and using two specific new physics models. Finally, we point out the interplay and orthogonality between the baryonic and mesonic LFV searches.

scholarly journals Lepton flavour violating $${\Lambda }_{{b}}$$ decays in non-universal $${Z}^{\prime }$$ model

2021 ◽  
Vol 81 (6) ◽  
Author(s):  
S. Biswas ◽  
P. Nayek ◽  
P. Maji ◽  
S. Sahoo
Keyword(s):  
Branching Ratio ◽  
New Physics ◽  
Prime Model ◽  
B Decays ◽  
Decay Distribution ◽  
Lepton Flavour Violation ◽  
Flavour Violation ◽  
Predicted Values ◽  
Lepton Flavour

AbstractMotivated by the recent LHCb results of lepton flavour violation on $$b\rightarrow s$$ b → s and $$b\rightarrow c$$ b → c transitions we study the lepton flavour violating (LFV) baryonic decays $${\Lambda }_{b}\rightarrow {\Lambda }l_{i}^{+}l_{j}^{-}$$ Λ b → Λ l i + l j - in non-universal $$Z^{\prime }$$ Z ′ model. We discuss the two-fold decay distribution of $${\Lambda }_{b}\rightarrow {\Lambda }l_{i}^{+}l_{j}^{-}$$ Λ b → Λ l i + l j - decays in terms of transversity amplitudes. From this distribution we study the differential branching ratio and lepton side forward-backward asymmetry in new physics (NP). The predicted values of the observables are very interesting and that might emboss the footprints of NP more aesthetically.

scholarly journals Search for Charged Lepton Flavour Violation at CMS

2018 ◽  
Vol 182 ◽  
pp. 02090
Author(s):  
Swagata Mukherjee
Keyword(s):  
Gauge Symmetry ◽  
Standard Model ◽  
Particle Physics ◽  
Charged Lepton ◽  
New Physics ◽  
Lepton Sector ◽  
Lepton Flavour Violation ◽  
The Standard Model ◽  
Flavour Violation ◽  
Lepton Flavour

Lepton flavour is a conserved quantity in the standard model of particle physics, but it does not follow from an underlying gauge symmetry. After the discovery of neutrino oscillation, it has been established that lepton flavour is not conserved in the neutral sector. Thus the lepton sector is an excellent place to look for New Physics, and in this perspective the Charged Lepton Flavour Violation is interesting. Various extensions of the standard model predict lepton flavour violating decays that can be observed at LHC. This report summarises several searches for lepton flavour violation with data collected by the CMS detector.

scholarly journals Towards a new generation of Charged Lepton Flavour Violation searches at the Paul Scherrer Institut: The MEG upgrade and the Mu3e experiment

2020 ◽  
Vol 234 ◽  
pp. 01011 ◽  
Author(s):  
Angela Papa
Keyword(s):  
Phase I ◽  
Charged Lepton ◽  
Branching Ratio ◽  
Muon Beam ◽  
Lepton Flavour Violation ◽  
The Status ◽  
Flavour Violation ◽  
Order Of Magnitude ◽  
Paul Scherrer ◽  
Lepton Flavour

The MEG experiment has recently set a new upper limit on the branching ratio of the µ+ → e+γ decay, ℬ(µ+ → e+γ) < 4.2 × 10−13 (at 90% confidence level) and un upgrade of the experiment (the MEGII experiment) is ongoing with the aim of improving the single event sensitivity (SES) by one order of magnitude with respect to the previous MEG experiment’s SES. The strong scientific motivation associated with the charged Lepton Flavour Violation (cLFV) searches pushes also towards searching for the complementary muon cLFV µ+ → e+e+e− decay with a completely new apparatus, the Mu3e experiment, aiming at a SES improved by at least three orders of magnitude with respect to the previous SINDRUM experiment’s SES (Mu3e phase I). An ultimate SES of few ×10−16 is foreseen requiring 109 µ/s (Mu3e phase II). Both experiments will be hosted at the Paul Scherrer Institut which currently delivers the most intense continuous low energy muon beam in the world up to few ×108 µ/s. The status of both the MEGII and Mu3e phase I experiments is given.

scholarly journals Experimental Review on Lepton Universality and Lepton Flavour Violation tests in B decays

2020 ◽  
Vol 234 ◽  
pp. 01004 ◽  
Author(s):  
P. de Simone
Keyword(s):  
Standard Model ◽  
Theoretical Models ◽  
New Physics ◽  
B Decays ◽  
Experimental Status ◽  
Lepton Flavour Violation ◽  
Lepton Universality ◽  
The Standard Model ◽  
Flavour Violation ◽  
Lepton Flavour

Tests of lepton flavour universality in B decays offer an excellent opportunity to test the Standard Model, and show hints of new physics in analyses performed by the LHCb, Belle and BaBar experiments. Several theoretical models proposed to explain possible violation of lepton flavour universality claim a connection with lepton flavour violation in B decays. These proceedings review the experimental status of the tests of lepton flavour universality and the searches of lepton flavour violation in B decays.

scholarly journals Completeness and complementarity for μ → eγ, μ → $$ e\overline{e}e $$ and μA → eA

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
S. Davidson
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Complementary Information ◽  
Weak Scale ◽  
Lepton Flavour Violation ◽  
Flavour Violation ◽  
Lepton Flavour

Abstract Lepton Flavour Violation (LFV) is New Physics that must occur, but is stringently constrained by experiments searching for μ ↔ e flavour change, such as μ → eγ, μ →$$ e\overline{e}e $$ e e ¯ e or μ → e conversion. However, in an Effective Field Theory(EFT) parametrisation, there are many more μ ↔ e operators than restrictive constraints, so determining operator coefficients from data is a remote dream. It is nonetheless interesting to learn about New Physics from data, so this manuscript introduces “observable-vectors” in the space of operator coefficients, which identify at any scale the combination of coefficients probed by the observable. These vectors have an overlap ≳ 10−3 with most of the coefficients, and are used to study whether μ → eγ, μ →$$ e\overline{e}e $$ e e ¯ e and μ → e conversion give complementary information about New Physics. The appendix gives updated sensitivities of these processes, (and a subset of τ → ℓ decays), to operator coefficients at the weak scale in the SMEFT and in the EFT below mW.

scholarly journals Z lepton flavour violation as a probe for new physics at future $$e^+e^-$$ colliders

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
Lorenzo Calibbi ◽  
Xabier Marcano ◽  
Joydeep Roy
Keyword(s):  
Field Theory ◽  
Effective Field Theory ◽  
New Physics ◽  
Effective Field ◽  
Low Energy ◽  
The Standard Model ◽  
Discovery Potential ◽  
Flavour Violation ◽  
Model Independent ◽  
Lepton Flavour

AbstractIn this work we assess the potential of discovering new physics by searching for lepton-flavour-violating (LFV) decays of the Z boson, $$Z\rightarrow \ell _i \ell _j$$ Z → ℓ i ℓ j , at the proposed circular $$e^+e^-$$ e + e - colliders CEPC and FCC-ee. Both projects plan to run at the Z-pole as a “Tera Z factory”, i.e., collecting $${\mathcal {O}}\left( 10^{12} \right) $$ O 10 12 Z decays. In order to discuss the discovery potential in a model-independent way, we revisit the LFV Z decays in the context of the Standard Model effective field theory and study the indirect constraints from LFV $$\mu $$ μ and $$\tau $$ τ decays on the operators that can induce $$Z\rightarrow \ell _i \ell _j$$ Z → ℓ i ℓ j . We find that, while the $$Z\rightarrow \mu e$$ Z → μ e rates are beyond the expected sensitivities, a Tera Z factory is promising for $$Z\rightarrow \tau \ell $$ Z → τ ℓ decays, probing New Physics at the same level of future low-energy LFV observables.

scholarly journals Charged lepton flavour violation searches at the Paul Scherrer Institut: Status of the MEGII and Mu3e experiments

2018 ◽  
Vol 179 ◽  
pp. 01018
Author(s):  
Angela Papa
Keyword(s):  
Charged Lepton ◽  
Branching Ratio ◽  
Muon Beam ◽  
Single Event ◽  
Lepton Flavour Violation ◽  
The Status ◽  
Flavour Violation ◽  
Order Of Magnitude ◽  
Paul Scherrer ◽  
Lepton Flavour

The MEG experiment has recently set a new upper limit on the branching ratio of the μ+ → e+γ decay, B(μ+ → e+γ) < 4.2 × 10-13 (at 90% confidence level) and un upgrade of the experiment (the MEGII experiment) is ongoing with the aim of improving the single event sensitivity (SES) by one order of magnitude with respect to the previous MEG experiment’s SES. The strong scientific motivation associated with the charged Lepton Flavour Violation (cLFV) searches pushes also towards searching for the complementary muon cLFV μ+ → e+e+e- decay with the Mu3e experiment aiming at a SES improved by at least three orders of magnitude with respect to the previous SINDRUM experiment’s SES (phase I) up to an ultimate SES of few ×10-16. Both experiments will be hosted at the Paul Scherrer Institut which delivers the most intense continuous low energy muon beam in the world up to few ×108 μ/s. The status of both the MEGII and Mu3e experiments is given.

scholarly journals Disentangling QCD and new physics in D → πℓ+ℓ−

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Aoife Bharucha ◽  
Diogo Boito ◽  
Cédric Méaux
Keyword(s):  
Standard Model ◽  
Branching Ratio ◽  
Branching Ratios ◽  
New Physics ◽  
Operator Product ◽  
Beyond The Standard Model ◽  
Spectral Functions ◽  
The Standard Model ◽  
Model Independent ◽  
Weak Annihilation

Abstract In this paper we consider the decay D+ → π+ℓ+ℓ−, addressing in particular the resonance contributions as well as the relatively large contributions from the weak annihilation diagrams. For the weak annihilation diagrams we include known results from QCD factorisation at low q2 and at high q2, adapting the existing calculation for B decays in the Operator Product Expansion. The hadronic resonance contributions are obtained through a dispersion relation, modelling the spectral functions as towers of Regge-like resonances in each channel, as suggested by Shifman, imposing the partonic behaviour in the deep Euclidean. The parameters of the model are extracted using e+e− → (hadrons) and τ → (hadrons) + ντ data as well as the branching ratios for the resonant decays D+ → π+R(R → ℓ+ℓ−), with R = ρ, ω, and ϕ. We perform a thorough error analysis, and present our results for the Standard Model differential branching ratio as a function of q2. Focusing then on the observables FH and AFB, we consider the sensitivity of this channel to effects of physics beyond the Standard Model, both in a model independent way and for the case of leptoquarks.

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