Rare Muon Decay Research Articles

Improved muon decay simulation with McMule and Geant4

The physics programme of the MEG II experiment can be extended with the search for new invisible particles produced in rare muon decays. The hunt for such elusive signals requires accurate simulations to characterise the detector response and estimate the experimental sensitivity. This work presents an improved simulation of muon decay in MEG II, based on McMule and Geant4.

Search for lepton flavor violating decay at FASER

FASER is one of the promising experiments which search for long-lived particles beyond the Standard Model. In this paper, we consider charged lepton flavor violation (CLFV) via a light and weakly interacting boson and discuss the detectability by FASER. We focus on four types of CLFV interactions, i.e., the scalar-, pseudoscalar-, vector-, and dipole-type interaction, and calculate the sensitivity of FASER to each CLFV interaction. We show that, with the setup of FASER2, a wide region of the parameter space can be explored. Particularly, it is found that FASER2 has a sensitivity to very small coupling regions in which the rare muon decays, such as μ → eγ, cannot place bounds, and that there is a possibility to detect CLFV decays of the new light bosons.

Dynamical Minimal Flavour Violating inverse seesaw

The Inverse Seesaw mechanism is dynamically realised within the Minimal Lepton Flavour Violation context. Lepton number, whose breaking is spontaneously realised, is generalised to a global Abelian factor of the whole flavour symmetry, that also plays the role of the Peccei-Quinn symmetry. The associated Goldstone boson is a Majoraxion that solves the Strong CP problem and represents a Dark Matter candidate.Three distinct scenarios are identified in terms of flavour symmetry and transformation properties of the exotic neutral leptons that enrich the Standard Model spectrum. The associated phenomenology is studied, focusing on the deviations from unitarity of the PMNS mixing matrix. The strongest constraints arise from the determination of the number of active neutrinos through the invisible width of the Z, the comparison of the measured W boson mass with its prediction in terms of the Fermi constant from muon decay, and the null searches for the radiative rare muon decay and μ → e conversion in nuclei. The heavy neutral leptons may have masses of a few TeV, leaving open the possibility for a direct detection at future colliders.The impact of the recent measurement of the W mass at the CDF II detector has also been considered, which, in one of the scenarios, points to a sharp prediction for the masses of the heavy neutral leptons at about 2 − 3 TeV.

Fully differential NLO predictions for the rare muon decay

Using the automation program GoSam, fully differential NLO corrections were obtained for the rare decay of the muon $\mu\to e\nu\bar\nu ee$. This process is an important Standard Model background to searches of the Mu3e collaboration for lepton-flavour violation, as it becomes indistinguishable from the signal $\mu\to 3e$ if the neutrinos carry little energy. With our NLO program we are able to compute the branching ratio as well as custom-tailored observables for the experiment. With minor modifications, related decays of the tau can also be computed.

Study of Rare Muon Decay: with Polarized Muons

We studied the rare muon decay process ▪. This Standard Model process is the background with respect to the signal process ▪ which is predicted by many extensions of the SM. We show that the process ▪ could be suppressed by cuts on the total energy of charged leptons in the kinematic region where the signal of new physics such as ▪ is expected to appear. Also, we demonstrated that angular distributions of decay products in the process ▪ are sensitive to the muon polarization and could be used to distinguish the signal of new physics ▪ from the background process ▪.

SuperLFV: An SLHA tool for lepton flavor violating observables in supersymmetric models

We introduce SuperLFV, a numerical tool for calculating low-energy observables that exhibit charged lepton flavor violation (LFV) in the context of the minimal supersymmetric standard model (MSSM). As the Large Hadron Collider and MEG, a dedicated μ+→e+γ experiment, are presently acquiring data, there is need for tools that provide rapid discrimination of models that exhibit LFV. SuperLFVaccepts a spectrum file compliant with the SUSY Les Houches Accord (SLHA), containing the MSSM couplings and masses with complex phases at the supersymmetry breaking scale. In this manner, SuperLFVis compatible with but divorced from existing SLHA spectrum calculators that provide the low energy spectrum. Hence, input spectra are not confined to the LFV sources provided by established SLHA spectrum calculators. Input spectra may be generated by personal code or by hand, allowing for arbitrary models not supported by existing spectrum calculators. Program summaryProgram title: SuperLFVCatalogue identifier: AERD_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AERD_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 12508No. of bytes in distributed program, including test data, etc.: 1510093Distribution format: tar.gzProgramming language: Java.Computer: Any computer with a Java Virtual Machine.Operating system: Unix, including OS X; Linux, Windows.RAM: <1 GbClassification: 11.6.External routines: Apache Commons, JAMANature of problem:In the era of the Large Hadron Collider, the ability to automate rapid model discrimination is needed. Dedicated experimental searches for charged lepton flavor violation (LFV) are currently operational with next generation experiments on the horizon. Generically, extensions of the standard model, including supersymmetric models, will induce LFV, such as rare muon (tau) decay. No single tool should bear the burden of providing all conceivable calculations within a certain model. Hence, it is warranted that numerical tools interoperate together and be developed as independent components, each providing defined tasks.Solution method:The Supersymmetry Les Houches Accord (SLHA) provides a standardized protocol for the interoperation of tools that provide the calculation of mass spectra in supersymmetric models, the calculation of observables, and the calculation of event generation. SuperLFV is an SLHA compliant observables calculator, with a dedicated focus on lepton flavor violation.Running time:1 s on modern systems.

Performance of liquid xenon gamma ray detector for MEG

MEG experiment searches for a rare muon decay (μ+→e+γ) at PSI in Switzerland. A physics run to take large amount of data was started at the end of summer in 2008. MEG will have a sensitivity around predicted branching ratio by new theories beyond the standard model. In order to discriminate signal events from backgrounds, precise measurement of energy, emission angle and time is important. The gamma ray detector of the experiment is a scintillation detector utilizing 900 litters of liquid xenon and 846 photo-multiplier tubes. The photon yield of xenon is high and the decay time is fast. Because of these properties, the detector has good energy, position and time resolutions. The construction of the gamma ray detector was completed in 2007. The control of the transfer and purification system of xenon and the operation of the detector worked successfully. In 2008, calibration of the detector was done in one month by using gamma rays from neutral pion decays. During the calibration run, resolutions for energy, position and time were measured and calibration parameters for reconstruction algorithms were obtained. During the physics run, variation of light yield due to purification was observed. The variation was well monitored by using several light sources.

Rare muon decayμ+→e+e−e+νeν¯μ

An analytical expression for the spin-averaged amplitude squared of the rare muon decay $\mu^+ \to e^+e^-e^+\nu_e\bar{\nu_\mu}$ is calculated. Monte Carlo phase space simulation using the analytical expression for the amplitude has been used to get various differential distributions of charged leptons. The approximate analytical expression for the total energy spectrum of charged leptons near the end point is presented. The dependence of branching ratio on cuts in total energy of charged leptons is studied taking into account an experimental energy resolution. It is shown that the measured branching ratio is very sensitive to the energy resolution.

Liquid Xenon Detector for the MEG Experiment

The MEG experiment, which will search for a rare muon decay, μ + → e + γ , to explore supersymmetric grand unification, is currently being prepared at Paul Scherrer Institut, Switzerland. Its innovative detector system that enables orders of magnitude better sensitivity than previous experiments is under construction and is described here in some detail.

Liquid xenon gamma ray detector for MEG

The MEG experiment searches for the rare muon decay μ + → e + γ , which is forbidden in the standard model. The detection of this muon decay is a probe for new physics beyond the standard model. In order to improve the sensitivity of the experiment, a liquid xenon detector is used for measuring energy, position and time of gamma rays. The detector consists of 800 l of liquid xenon and 846 photo-multiplier tubes. We have performed beam tests and evaluated resolutions by using a prototype.

Lepton flavor violation in extra dimension models

Models involving large extra spatial dimension(s) have interesting predictions on lepton flavor violating processes. We consider some five-dimensional (5D) models which are related to neutrino mass generation or address the fermion masses hierarchy problem. We study the signatures in low energy experiments that can discriminate the different models. The focus is on muon-electron conversion in nuclei $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$ and $\ensuremath{\mu}\ensuremath{\rightarrow}3e$ processes and their $\ensuremath{\tau}$ counterparts. Their links with the active neutrino mass matrix are investigated. We show that in the models we discussed the branching ratio of $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$ like rare process is much smaller than the ones of $\ensuremath{\mu}\ensuremath{\rightarrow}3e$ like processes. This is in sharp contrast to most of the traditional wisdom based on four-dimensional (4D) gauge models. Moreover, some rare tau decays are more promising than the rare muon decays.

A REVIEW OF RARE PION AND MUON DECAYS

After a decade of no measurements of pion and muon rare decays, PIBETA, a new experimental program is producing its first results. We report on a new experimental study of the pion beta decay, π+→π0e+ν, the πe2γ radiative decay, π+→e+νγ, and muon radiative decay, [Formula: see text]. The new results represent four- to six-fold improvements in precision over the previous measurements. Excellent agreement with Standard Model predictions is observed in all channels except for one kinematic region of the πe2γ radiative decay involving energetic photons and lower-energy positrons.

Non-neutrino physics working group summary

This summary covers the physics topics that could benefit from the unprecedented flux of muons produced at the front end of the future neutrino factory. A selection of such opportunities was presented at NuFact02 and their demands on beam properties were evaluated. This summary will survey the rare muon decay experiments and the high precision measurements that could benefit from higher fluxes as well as some of the new programmes that could use very large μ− fluxes. A number of technological developments relevant to the neutrino factories were also discussed.

Rare muon decays at the neutrino factories

New experiments (MEG, MECO) searching for the lepton-flavor violation signal in the muon decay are shown in relation to their ancestor experiments (MEGA, SINDRUM II). It will be also shown tha the neutrino factories and their technologies could be very useful for persuading the rare muon decay experiments further more. As an example, a project PRISM will be explained and the prospect to the rare muon decays and the neutrino factories are shown.

Search for lepton flavour violation at PSI and HERA

Present limits of lepton flavour violating processes mediated by the exchange of a leptoquark are presented. Data are taken from ep → ℓ X at HERA and rare muon decays.

Opportunity for magnetic field spatial‐time correlation research using a μSR^2‐method

The existence of an opportunity for research on the spatial‐time correlation of magnetic fields is demonstrated. A summation method for the time correlation function of μSR signals containing information about fluctuations of the muon polarization is proposed for use with an experimental installation in which the muon decay point is recorded. A description of the S.PNIP μSR2 installation, formerly used in experiments related to the search for rare muon decays, is also given.

Muon number violating processes in single particle extensions of the standard model

We study the one-loop induced muon number processes when the standard model is minimally extended to include a SU(2) singlet of a charged scalar h + and a neutral fermion N. We find that μ → ey is more sensitive for the former model whereas μ − e conversion in nuclei for the latter. Effects of a scalar leptoquark y 1 3 and a heavy vector fermion E −, which induce tree level rare muon decays, are also discussed.

Design and performance of modularized NaI(Tl) detectors with rectangular crystal elements: An array of 49 and the crystal box

An array of 49 NaI(Tl) modules each 20 inch in depth and 2.5 inch × 2.5 inch in cross section has been constructed and its properties, especially energy resolution, explored for positrons in the range 20 MeV – 18 GeV. A subsequent much larger detector, the Crystal Box, has also been constructed from 396 modules of the same cross section, but mostly 12 inch in depth, and operated as a γ-ray and positron detector in a search for rare muon decays. The calibration procedure used for the Crystal Box and its characteristic resolutions in energy, impact point and time are described.

Muon and pion decays, an electroweak case for EHF

The experimental status of rare muon decays is reviewed. Since the probably last round of those experiments at the present meson factories is being proposed now, any further progress is only possible with a new machine with higher muon flux, for which EHF is a good candidate. In the written version of the talk reference is made to recent review articles published elsewhere. As an example for a second generation experiment done with an instrument specifically designed for a rare muon decay experiment (SINDRUM) the first observation of the decay π→3e ν is reported

A progress report on recent rare muon decay experiments at the los alamos meson physics facility

A search has been performed for the decays μ → eee, μ → e γ, and μ → eγγ with a sensitivity in the branching ratios at the level of 10 −10. The experiment used a separated, 26 MeV/c μ + beam with an average intensity of 300kHz. A total of 2.2 × 10 11 muon decays were examined for the present result. The detector for the experiment Is the Crystal Box, which consists of a cylindrical drift chamber surrounded by 396 NaI(T1) crystals. A layer of scintillation counters in front of the crystals provided timing for electrons and a veto for photons. The energy resolution for electrons and photons is ≈6% (FWHM). The position resolution of the drift chamber is 350 μm leading to a vertex cut with a rejection of 10 3 for μ → eee. The timing resolution is ≈300 ps from the scintillators and ~1 ns from the crystals. No candidate for μ → eee has been found, yielding an upper limit for the branching ratio of B μ3e < 1.3 × 10 −10 (90% C.L.).