New Results in Rare Allowed Muon and Pion Decays

Počanić, D.; Munyangabe, E.; Bychkov, M.; Alonzi, L. P.; Баранов, В. А.; Bertl, W.; Bystritsky, Yu. M.; Frlež, E.; Kalinnikov, V. A.; Khomutov, N. V.; Korenchenko, A. S.; Korenchenko, S.M.; Korolija, M.; Kozłowski, T.; Kravchuk, N. P.; Kuchinsky, N.A.; Lehman, M. C.; Mekterović, D.; Mzhavia, D.; Palladino, A.; Robmann, P.; Rozhdestvensky, A.M.; Supek, I.; Truöl, P.; Tsamalaidze, Z.; Schaaf, A. van der; VanDevender, B. A.; Velicheva, E. P.; Volnykh, V. P.

doi:10.1142/s2010194514604372

Cited by 9 publications

(19 citation statements)

References 18 publications

(12 reference statements)

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“…This measurement agrees with our theoretical prediction, and new precise results are expected to be published in the near future by the Meg and Pibeta collaborations [8,25].…”

Section: Numerical Resultssupporting

confidence: 90%

“…An improvement of their theoretical calculation down to a precision of O(1%) is desired [25]. Preliminary new measurements of the branching ratio µ → eγνν were presented recently by the Meg [25] and Pibeta [8] collaborations.…”

Section: Jhep07(2015)153mentioning

confidence: 99%

“…Radiative µ and τ leptonic decays, where an inner bremsstrahlung photon is measured, can be predicted with very high precision and provide an independent determination of the BMKS parameters as well as the possibility to extract new combinations like theη parameter [5][6][7]. A new preliminary measurement of the muonη was reported recently [8], while analyses are ongoing to determine theη and ξκ parameters of the τ [9,10]. Precise data on radiative τ leptonic decays also offer the opportunity to probe the electromagnetic properties of the τ and may allow to determine its anomalous magnetic moment which, in spite of its precise SM prediction [11], has never been measured [12][13][14].…”

Section: Introductionmentioning

confidence: 99%

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Radiative μ and τ leptonic decays at NLO

Fael¹,

Mercolli²,

Passera³

2015

J. High Energ. Phys.

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We present the differential rates and branching ratios of the radiative decays τ → lννγ, with l = e or µ, and µ → eννγ in the Standard Model at next-to-leading order. Radiative corrections are computed taking into account the full depencence on the mass m l of the final charged leptons, which is necessary for the correct determination of the branching ratios. Only partial agreement is found with previous calculations performed in the m l → 0 limit. Our results agree with the measurements of the branching ratios B(µ → eννγ) and B(τ → µννγ) for a minimum photon energy of 10 MeV in the µ and τ rest frames, respectively. Babar's recent precise measurement of the branching ratio B(τ → eννγ), for the same photon energy threshold, differs from our prediction by 3.5 standard deviations.

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“…This measurement agrees with our theoretical prediction, and new precise results are expected to be published in the near future by the Meg and Pibeta collaborations [8,25].…”

Section: Numerical Resultssupporting

confidence: 90%

Section: Jhep07(2015)153mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Radiative μ and τ leptonic decays at NLO

Fael¹,

Mercolli²,

Passera³

2015

J. High Energ. Phys.

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“…The best estimate reported in [23] is η = 0.057 ± 0.034. Contributions beyond the SM can be also searched for in RMDs [27,28,29]. In this case, deviations from the V-A structure of weak interactions should be observed in the electron and photon spectra and described by a parameter η that is zero in the SM [30,31,32].…”

Section: Searches For New Physics In Standard Muon Decaysmentioning

confidence: 99%

“…In this case, deviations from the V-A structure of weak interactions should be observed in the electron and photon spectra and described by a parameter η that is zero in the SM [30,31,32]. The best measurement [29] is currently η = 0.006 ± 0.017 (stat) ± 0.018 (syst).…”

Section: Searches For New Physics In Standard Muon Decaysmentioning

confidence: 99%

Experimental searches for muon decays beyond the Standard Model

Renga

2019

Reviews in Physics

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The study of muon properties and decays played a crucial role in the early years of particle physics and contributed over decades to build and consolidate the Standard Model. At present, searches for muon decays beyond the Standard Model are performed by exploiting intense beams of muons, and plans exist to upgrade the present facilities or build new ones, which would open new prospects for the quest of new physics in this sector. In this paper I review the present status of the search for muon decays beyond the Standard Model, with a special attention to the most conventional muon lepton flavor violation experiments, but also considering more exotic scenarios and future outlooks. Experimental techniques for muon decay studiesAs already mentioned, the muon was discovered and firstly studied in the cosmic ray radiation. A significative step forward in the study of its properties and decay modes was performed when pion beam became available in the years 1950s. Pions can be stopped in a target and the muons produced in their decays can be studied. Finally, the first muon beams were delivered in the years 1970s.Muon beams are usually produced starting from a proton beam impinging on a target and producing pions. Pions decaying in the target itself produce muons that can be collected and transported by a beam line toward the experimental areas where the detectors are installed. The most intense continuous muon beams in the world [10,11] are currently delivered at the Paul Scherrer Institut (PSI), in Villigen (CH). A 2 mA current of protons of 590 MeV kinetic energy from the PSI Ring Cyclotron hits two different graphite targets where, in total, ∼ 18% of the protons are stopped, the rest being preserved to serve a downstream neutron spallation source. The two targets serve different beam lines. In order to get an intense, pure and monoenergetic muon beam, particles with momentum p ∼ 28 MeV/c are selected, corresponding to muons emitted by pions decaying at rest. It happens when the pion decays right on the surface of the production target (surface muons). The beam can be further purified by selecting particles with a given velocity (and hence a given mass) by means of a Wien filter, a superposition of orthogonal electric (E) and magnetic (B) fields through which only particles with the desired velocity v = E/B go straight, while others are removed by collimators. Beams with up to a few 10 8 surface muons per second can be currently delivered at PSI.In the Ring Cyclotron at PSI protons travel in bunches with a repetition rate of about 50 MHz. The pion lifetime (∼ 26 ns) is large enough to spoil the time structure of the beam and make a practically continuous muon beam. For some applications, pulsed beams are instead necessary. For instance, the Delivery Ring at Fermilab (Batavia, USA) used for the Mu2e experiment [12] provides protons in bunches separated in time by 1695 ns. They hit a target and produce muons that mostly arrive to the experimental apparatus within a few hundred ns. After about 700 ns and before the nex...

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Five-body leptonic decays of muon and tau leptons

Flores-Tlalpa

Castro

Roig

2016

J. High Energ. Phys.

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Abstract:We study the five-body decays µ − → e − e + e − ν µνe and τ − → ℓ − ℓ ′+ ℓ ′− ν τνℓ for ℓ, ℓ ′ = e, µ within the Standard Model (SM) and in a general effective field theory description of the weak interactions at low energies. We compute the branching ratios and compare our results with two previous -mutually discrepan -SM calculations. By assuming a general structure for the weak currents we derive the expressions for the energy and angular distributions of the three charged leptons when the decaying lepton is polarized, which will be useful in precise tests of the weak charged current at Belle II. In these decays, leptonic T-odd correlations in triple products of spin and momentawhich may signal time reversal violation in the leptonic sector -are suppressed by the tiny neutrino masses. Therefore, a measurement of such T-violating observables would be associated to neutrinoless lepton flavor violating (LFV) decays, where this effect is not extremely suppressed. We also study the backgrounds that the SM five-lepton lepton decays constitute to searches of LFV L − → ℓ − ℓ ′+ ℓ ′− decays. Searches at high values of the invariant mass of the ℓ ′+ ℓ ′− pair look the most convenient way to overcome the background.

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New Results in Rare Allowed Muon and Pion Decays

Cited by 9 publications

References 18 publications

Radiative μ and τ leptonic decays at NLO

Radiative μ and τ leptonic decays at NLO

Experimental searches for muon decays beyond the Standard Model

Five-body leptonic decays of muon and tau leptons

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