scholarly journals Searching for the Muon Decay to Three Electrons with the Mu3e Experiment

Universe ◽  
2021 ◽  
Vol 7 (11) ◽  
pp. 420
Author(s):  
Cristina Martin Perez ◽  
Luigi Vigani
Keyword(s):  
Particle Physics ◽  
Branching Fractions ◽  
New Physics ◽  
Muon Decay ◽  
High Rate ◽  
Lepton Flavor ◽  
Electrons And Positrons ◽  
Pixel Sensors ◽  
Tracking Detector ◽  
Paul Scherrer

Mu3e is a dedicated experiment designed to find or exclude the charged lepton flavor violating μ→ eee decay at branching fractions above 10−16. The search is pursued in two operational phases: Phase I uses an existing beamline at the Paul Scherrer Institute (PSI), targeting a single event sensitivity of 2·10−15, while the ultimate sensitivity is reached in Phase II using a high intensity muon beamline under study at PSI. As the μ→ eee decay is heavily suppressed in the Standard Model of particle physics, the observation of such a signal would be an unambiguous indication of the existence of new physics. Achieving the desired sensitivity requires a high rate of muons (108 stopped muons per second) along with a detector with large kinematic acceptance and efficiency, able to reconstruct the low momentum of the decay electrons and positrons. To achieve this goal, the Mu3e experiment is mounted with an ultra thin tracking detector based on monolithic active pixel sensors for excellent momentum and vertex resolution, combined with scintillating fibers and tiles for precise timing measurements.

scholarly journals Probing new physics in semileptonic $$\Xi _{b}\rightarrow \Lambda (\Xi _{c})\tau ^{-}\bar{\nu }_{\tau }$$ decays

2019 ◽  
Vol 79 (10) ◽  
Author(s):  
Jiao Zhang ◽  
Xiuyun An ◽  
Ruirui Sun ◽  
Jianfeng Su
Keyword(s):  
Standard Model ◽  
B Meson ◽  
Branching Fraction ◽  
Branching Fractions ◽  
New Physics ◽  
Effective Theory ◽  
Tau Decays ◽  
Lepton Flavor ◽  
Measurement Results ◽  
Quark Level

Abstract Recently, several observed anomalies in semileptonic B meson decays have implied hints of lepton flavor universal violation. Motivated by these inspiring results, we study the baryon decays $$\Xi _{b}\rightarrow \Lambda (\Xi _{c})\tau ^{-}\bar{\nu }_{\tau }$$Ξb→Λ(Ξc)τ-ν¯τ which are mediated by $$b\rightarrow u(c)\tau ^{-}\bar{\nu }_{\tau }$$b→u(c)τ-ν¯τ transitions at quark level in the Standard Model and different New Physics scenarios. In the framework of the extended Standard Model on assuming a general effective theory, we constrain the Wilson coefficients of the NP operators using the experimental measurement results for the $$Br(B_{c}^+\rightarrow \tau ^+ \nu _{\tau })$$Br(Bc+→τ+ντ), $$R^{l}_{\pi }$$Rπl, $$R_{D^{(*)}}$$RD(∗), $$R_{J/\psi }$$RJ/ψ and $$F_{L}^{D^{*}}$$FLD∗ anomalies and investigate their New Physics effects on several observables relative to the $$\Xi _{b}\rightarrow \Lambda (\Xi _{c})\tau ^{-}\bar{\nu }_{\tau }$$Ξb→Λ(Ξc)τ-ν¯τ decays. We mention the differential branching fraction $${\text {d}}Br/{\text {d}}q^2$$dBr/dq2, the ratio of branching fractions $$R(q^2)$$R(q2), the lepton-side forward–backward asymmetry $$A_{FB}(q^2)$$AFB(q2), the longitudinal polarization $$P_{L}^{\Lambda (\Xi _{c})}(q^2)$$PLΛ(Ξc)(q2) of the daughter baryons $$\Lambda (\Xi _{c})$$Λ(Ξc) and $$P_{L}^{\tau }(q^2)$$PLτ(q2) of the $$\tau $$τ lepton, and the convexity parameter $$C_{F}(q^2)$$CF(q2).

scholarly journals The Search for μ+ → e+γ with 10–14 Sensitivity: The Upgrade of the MEG Experiment

Symmetry ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1591
Author(s):  
Alessandro M. Baldini ◽  
Vladimir Baranov ◽  
Michele Biasotti ◽  
Gianluigi Boca ◽  
Paolo W. Cattaneo ◽  
...  
Keyword(s):  
Particle Physics ◽  
Rate Capability ◽  
Muon Beam ◽  
Paul Scherrer Institute ◽  
Current Status ◽  
Elementary Particle Physics ◽  
Lepton Flavor ◽  
The Standard Model ◽  
Stringent Limit ◽  
Paul Scherrer

The MEG experiment took data at the Paul Scherrer Institute in the years 2009–2013 to test the violation of the lepton flavor conservation law, which originates from an accidental symmetry that the Standard Model of elementary particle physics has, and published the most stringent limit on the charged lepton flavor violating decay μ+→e+γ: BR(μ+→e+γ) <4.2×10−13 at 90% confidence level. The MEG detector has been upgraded in order to reach a sensitivity of 6×10−14. The basic principle of MEG II is to achieve the highest possible sensitivity using the full muon beam intensity at the Paul Scherrer Institute (7×107 muons/s) with an upgraded detector. The main improvements are better rate capability of all sub-detectors and improved resolutions while keeping the same detector concept. In this paper, we present the current status of the preparation, integration and commissioning of the MEG II detector in the recent engineering runs.

scholarly journals COMET, an Experiment to Search for mu-e Conversion in a Nuclear Field

2018 ◽  
Vol 46 ◽  
pp. 1860065
Author(s):  
Hiroaki Natori
Keyword(s):  
Elementary Particle ◽  
Particle Physics ◽  
New Physics ◽  
Experimental Limit ◽  
Elementary Particle Physics ◽  
Lepton Flavor ◽  
Nuclear Field ◽  
Past Experiment ◽  
The Standard Model ◽  
Current Experimental Limit

Charged lepton flavor violating (CLFV) process is predicted to be out of experimental reach by the Standard Model of elementary particle physics (SM). However, many models of the new physics beyond the SM predicts that it is just below the current experimental limit. COMET searches for one of the CLFV process, mu-e conversion in a nuclear field, improving the sensitivity by a factor of approximately [Formula: see text] for Phase-I and [Formula: see text] for Phase-II experiment from a past experiment.

scholarly journals Search for lepton-flavor-violating tau-lepton decays to ℓγ at Belle

2021 ◽  
Vol 2021 (10) ◽  
Author(s):  
◽  
K. Uno ◽  
K. Hayasaka ◽  
K. Inami ◽  
I. Adachi ◽  
...  
Keyword(s):  
Standard Model ◽  
Charged Lepton ◽  
Branching Fractions ◽  
New Physics ◽  
Lepton Flavor Violation ◽  
Full Data ◽  
Lepton Flavor ◽  
Flavor Violation ◽  
The Standard Model ◽  
Lepton Decays

Abstract Charged lepton flavor violation is forbidden in the Standard Model but possible in several new physics scenarios. In many of these models, the radiative decays τ± → ℓ±γ (ℓ = e, μ) are predicted to have a sizeable probability, making them particularly interesting channels to search at various experiments. An updated search via τ± → ℓ±γ using full data of the Belle experiment, corresponding to an integrated luminosity of 988 fb−1, is reported for charged lepton flavor violation. No significant excess over background predictions from the Standard Model is observed, and the upper limits on the branching fractions, $$ \mathcal{B} $$ B (τ± → μ±γ) ≤ 4.2 × 10−8 and $$ \mathcal{B} $$ B (τ± → e±γ) ≤ 5.6 × 10−8, are set at 90% confidence level.

scholarly journals Status of the Mu2e experiment

2018 ◽  
Vol 179 ◽  
pp. 01003 ◽  
Author(s):  
S. Giovannella
Keyword(s):  
Charged Lepton ◽  
Rest Mass ◽  
Energetic Electron ◽  
High Energy ◽  
New Physics ◽  
Muon Decay ◽  
Negative Muon ◽  
Lepton Flavor ◽  
Current Limit ◽  
The Status

The Mu2e experiment at Fermilab searches for the charged-lepton flavor violating neutrino-less conversion of a negative muon into an electron in the field of an aluminum nucleus. The dynamics of such a process is well modelled by a two-body decay, resulting in a mono-energetic electron with an energy slightly below the muon rest mass. If no events are observed, in three years of running Mu2e will improve the current limit by four orders of magnitude. Such a charged lepton flavor-violating reaction probes new physics at a scale inaccessible with direct searches at either present or planned high energy colliders. The experiment both complements and extends the current search for muon decay to electron-photon at MEG and searches for new physics at the LHC. This paper focuses on the physics motivation, the design and the status of the experiment.

scholarly journals Anomalies in b→s Transitions and Dark Matter

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Avelino Vicente
Keyword(s):  
Dark Matter ◽  
Standard Model ◽  
Particle Physics ◽  
Branching Ratios ◽  
New Physics ◽  
Lhcb Collaboration ◽  
Lepton Flavor ◽  
The Standard Model ◽  
Predicted Values ◽  
The Universe

Since 2013, the LHCb collaboration has reported on the measurement of several observables associated with b→s transitions, finding various deviations from their predicted values in the Standard Model. These include a set of deviations in branching ratios and angular observables, as well as in the observables RK and RK⁎, specially built to test the possible violation of Lepton Flavor Universality. Even though these tantalizing hints are not conclusive yet, the b→s anomalies have gained considerable attention in the flavor community. Here we review new physics models that address these anomalies and explore their possible connection to the dark matter of the Universe. After discussing some of the ideas introduced in these works and classifying the proposed models, two selected examples are presented in detail in order to illustrate the potential interplay between these two areas of current particle physics.

scholarly journals The Mu3e experiment at PSI

2019 ◽  
Author(s):  
Alessandro Bravar
Keyword(s):  
Time Resolution ◽  
Muon Beam ◽  
Muon Decay ◽  
Lepton Flavor Violation ◽  
Lepton Flavor ◽  
Flavor Violation ◽  
Pixel Sensors ◽  
The World ◽  
Large Acceptance ◽  
Scintillating Fibers

Mu3e will search for charged Lepton Flavor Violation in the neutrinoless muon decay \mu^+ \rightarrow e^+ e^- e^+μ+→e+e−e+ with a sensitivity down to 10^{-16}10−16 (90% C.L.) using the world most intense continuous muon beam at PSI. This search requires a large acceptance detector capable of coping with rates of up to 2 \times 10^92×109 stopped muons per second with excellent momentum, spatial, and time resolution. The Mu3e detector is based on thin monolithic active silicon pixel sensors for tracking in conjunction with scintillating fibers and tiles for timing measurements. The Mu3e apparatus is under constructions and first data is expected in 2020.

scholarly journals Multimessenger Probes for New Physics in Light of A. Sakharov’s Legacy in Cosmoparticle Physics

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 222
Author(s):  
Maxim Khlopov
Keyword(s):  
Standard Model ◽  
Particle Physics ◽  
New Physics ◽  
Physical Models ◽  
Beyond The Standard Model ◽  
Fundamental Relationship ◽  
Relationship Of ◽  
The Universe ◽  
Selection Of

A.D. Sakharov’s legacy in now standard model of the Universe is not reduced to baryosynthesis but extends to the foundation of cosmoparticle physics, which studies the fundamental relationship of cosmology and particle physics. Development of cosmoparticle physics involves cross-disciplinary physical, astrophysical and cosmological studies of physics Beyond the Standard model (BSM) of elementary particles. To probe physical models for inflation, baryosynthesis and dark matter cosmoparticle physics pays special attention to model dependent messengers of the corresponding models, making their tests possible. Positive evidence for such exotic phenomena as nuclear interacting dark atoms, primordial black holes or antimatter globular cluster in our galaxy would provide the selection of viable BSM models determination of their parameters.

scholarly journals Study of Rare Mesonic Decays Involving Di-Neutrinos in Their Final State

2018 ◽  
Vol 2018 ◽  
pp. 1-20
Author(s):  
Azeem Mir ◽  
Farida Tahir ◽  
Shakeel Mahmood ◽  
Shi- Hai Dong
Keyword(s):  
Branching Fractions ◽  
New Physics ◽  
Supersymmetric Model ◽  
Final State ◽  
Yukawa Couplings ◽  
Leptonic Decays ◽  
Pseudoscalar Mesons ◽  
Theoretical Predictions ◽  
Minimal Supersymmetric Model

We have studied phenomenological implication of R-parity violating (Rp) Minimal Supersymmetric Model (MSSM) via analyses of pure leptonic (M→νν¯) and semileptonic decays of pseudoscalar mesons (M→Xνν¯). These analyses involve comparison between theoretical predictions made by Rp MSSM and the Standard Model (SM) with the experimental results like branching fractions (Br) of the said process. We have found, in general, that Rp contribution dominates over the SM contribution, i.e., by a factor of 10 for the pure leptonic decays of KL,S and by 102 and 104 in case of Bs and Bd, respectively. Furthermore, the limits obtained on Rp Yukawa couplings (λαkβ′λαkγ′⁎) by using Br  (M→Xνν¯) are used to calculate Br  (M→νν¯). This demonstrates the role of Rp MSSM as a viable model for the study of new physics contribution in rare decays at places like Super B factories, KOTO (J-PARC) and NA62 at CERN.

scholarly journals Infrared renormalons in collider processes

2021 ◽  
Author(s):  
Silvia Ferrario Ravasio
Keyword(s):  
Top Quark ◽  
Particle Physics ◽  
Theoretical Calculations ◽  
Accurate Determination ◽  
New Physics ◽  
Operator Product ◽  
Power Correction ◽  
Collider Phenomenology ◽  
Power Corrections ◽  
Decay Products

AbstractPrecise theoretical predictions are a key ingredient for an accurate determination of the structure of the Lagrangian of particle physics, including its free parameters, which summarizes our understanding of the fundamental interactions among particles. Furthermore, due to the absence of clear new-physics signals, precise theoretical calculations are required to pin down possible subtle deviations from the Standard Model predictions. The error associated with such calculations must be scrutinized, as non-perturbative power corrections, dubbed infrared renormalons, can limit the ultimate precision of truncated perturbative expansions in quantum chromodynamics. In this review, we focus on linear power corrections that can arise in certain kinematic distributions relevant for collider phenomenology where an operator product expansion is missing, e.g. those obtained from the top-quark decay products, shape observables and the transverse momentum of massive gauge bosons. Only the last one is found to be free from such corrections, while the mass of the system comprising the top decay products has a larger power correction if the perturbative expansion is expressed in terms of a short-distance mass instead of the pole mass. A proper modelization of non-perturbative corrections is crucial in the context of shape observables to obtain reliable strong coupling constant extractions.

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