When a muon bound in an atom decays, there is a small probability that the daughter electron remains bound. That probability is evaluated. Surprisingly, a significant part of the rate is contributed by the negative energy component of the wave function, neglected in a previous study. A simple integral representation of the rate is presented. In the limit of close muon and electron masses, an analytic formula is derived.
Environmental effects on the muon lifetime are described. A general theorem on the cancellation of bound state phase space suppression and final state interaction enhancement is illustrated for muonium and muonic atoms. Lessons from those bound muon examples are applied to the b decay puzzle and apparent inconsistencies in K{e3} decay rates.
Theoretical aspects of kaon and muon decays are reviewed. In particular, three topics on kaon and muon decays, namely $K \to πν\barν$ processes, T violation in $K^+ \to π^0μ^+ ν$ decay and lepton flavor violation in muon decay are considered. Theoretical backgrounds and possible significance on new physics searches by these processes are discussed.
The first order QED corrections to the polarized muon decay spectrum are considered. The exact dependence on electron and muon masses is kept. Numerical results are presented.
Radiative muon and tau lepton decays are described within the model-independent approach with the help of generalized Michel parameters. The exact dependence on charged lepton masses is taken into account. The results are relevant for modern and future experiments on muon and tau lepton decays.
O(alpha^2 ln^2(m_mu/m_e)) QED corrections to the electron spectrum and angular distribution in muon decay are evaluated. Impact on the determination of Michel parameters is estimated. Current theoretical uncertainty in the muon decay distributions is discussed.
Muon pair production in exclusive radiative decays $χ_{cJ}\to J/ψμμ$, $χ_{bJ}\toΥμμ$ are considered. We present numerical values of the branching fractions and distributions over various kinematical variables.
Predictions for the muon decay spectrum are usually derived from the derivative-free Hamiltonian. However, it is not the most general form of the possible interactions. Additional simple terms with derivatives can be introduced. In this work the distortion of the standard energy and angular distribution of the electrons in polarized muon decay caused by these terms is presented.
We consider low-energy CPT-violating modifications in charged current weak interactions and analyze possible ramifications in muon and antimuon decays. We calculate the lifetime of muon and antimuon with these modifications, and from the result, put bounds on the CPT-violating parameters. Moreover, we elaborate on the muon and antimuon decay rate differentials in electron energy and spatial angle, which entail interesting phenomenological consequences presenting new ways to constrain CPT violation in charged lepton decays.
The radiative decay of muon-neutrinos in matter with a scheme of mass-degenerate neutrinos could be the common origin of the appearance of anti-electron-neutrinos at LSND and the disappearance of muons-neutrinos at SuperKamiokande. With the decay probability fixed by the LSND signal, the deficit of atmospheric neutrinos can be satisfactorily reproduced.
When a particle decays in an external field, the energy spectrum of the products is smeared. We derive an analytical expression for the shape function accounting for the motion of the decaying particle and the final state interactions. We apply our result to calculate the muonium decay spectrum and comment on applications to the muon bound in an atom.
We analyze allowed region of muon anomalous magnetic moment (muon $g-2$), satisfying lepton flavor violations, $Z$ boson decays, and collider physics, in a framework of multi-charged particles. Then we explore the typical size of the muon $g-2$, and discuss which modes dominantly affect muon $g-2$.
One-loop QED corrections to the differential width of radiative muon decay are considered. Results can be used to analyze high statistics data of modern and future experiments.
QED radiative corrections to polarized muon decay spectrum are considered. Leading and next--to--leading logarithmic approximations are used. Exponentiation of soft radiation is discussed. The present theoretical uncertainty of the spectrum description is estimated.
O(α^2 \ln(m_μ/m_e)) corrections to electron energy spectrum in muon decay are computed using perturbative fragmentation function approach. The magnitude of these corrections is comparable to anticipated precision of the TWIST experiment at TRIUMF where Michel parameters will be extracted from the measurement of the electron energy spectrum in muon decay.
We compute the dominant, logarithmically enhanced radiative corrections to the electron spectrum in the bound muon decay in the whole experimentally interesting range. The corrected spectrum fits well the TWIST results. The remaining theoretical error, dominated by the nuclear charge distribution, can be reduced in the muon-electron conversion searches by measuring the spectrum slightly below the New Physics signal window.
We investigate the muonic decay of a light Higgs boson, produced in weak boson fusion at future hadron colliders. We find that this decay mode would be observable at the CERN LHC only with an unreasonably large amount of data, while at a 200 TeV vLHC this process could be used to extract the muon Yukawa coupling to about the 10% level, or better if significant improvements in detector design can be achieved.
We study effects of unparticle physics on muon g-2 and LFV tau decay processes. LFV interactions between the Standard Model sector and unparticles can explain the difference of experimental value of muon g-2 from the Standard Model prediction. While the same couplings generate LFV tau decay, we found that LFV coupling can be of O(0.1 ... 1) without conflict with experimental bounds of LFV tau decay if the scaling dimension of unparticle operator d_{U} > 1.6.
The calculation of the transverse muon polarization in $K^+ \to μ^+ νγ$ decay due to the final state interaction up to $O(p^6)$ CHPT level has been carried out. It is shown that $O(p^6)$ corrections to the observable is much less than $O(p^4)$ contribution.
Predictions are presented for the oscillation phase in neutrino oscillations following pion decay at rest and in flight, muon decay and nuclear $β-$decay at rest as well as for muon oscillations following pion decay at rest and in flight. The neutrino oscillation phases found disagree with the conventionally used value: $ϕ_{12} = Δm^2 L/(2P)$. The same oscillation phase is found for neutrino and muon oscillations following pion decay at rest. Shortcomings of previous treatments of the quantum mechanics of neutrino oscillations are commented on.
We have examined the decay $K^0_L \to π^0 μ^+ μ^-$ in which the branching ratio, the muon energy asymmetry and the muon decay asymmetry could be measured. In particular, we find that within the Standard Model the longitudinal polarization ($P_L$) of the muon is proportional to the direct CP violating amplitude. On the other hand the energy asymmetry and the out-of-plane polarization ($P_N$) depend on both indirect and direct CP violating amplitudes. Although the branching ratio is small and difficult to measure because of background, the asymmetries could be large $\cal{O}$(1) in the Standard …
We have performed a global analysis of muon decay measurements to establish model-independent limits on the space-time structure of the muon decay matrix element. We find limits on the scalar, vector and tensor coupling of right- and left-handed muons to right- and left-handed electrons. The limits on those terms that involve the decay of right-handed muons to left-handed electrons are more restrictive than in previous global analyses, while the limits on the other non-standard model interactions are comparable. The value of the Michel parameter eta found in the global analysis is -0.0036 \pm …
We consider the impact of O(alpha^2) hadronic corrections to the energy spectrum of the decay electron in muon decay. We find that the correction can be described, within good approximation, by a linear function in the electron energy. Explicit expressions for the form factors needed in an approach based on dispersion integrals are given.
The muon transverse polarization in the $K^+ \to μ^+ νγ$ process induced by the electromagnetic final state interaction is calculated in the framework of Standard Model. It is shown that one loop contributions lead to a nonvanihing muon transverse polarization. The value of the muon transverse polarization averaged over the kinematical region of $E_γ\geq 20$ MeV is equal to $5.63 \times 10^{-4}$.
Recently Georgi has discussed the possible existence of `Unparticles' describable by operators having non-integral scaling dimensions. With the interaction of these with the Standard Model (SM) particles being constrained only by gauge and Lorentz symmetries, it affords a new source for lepton flavour violation. Current and future muon decay experiments are shown to be very sensitive to such scenarios.
The progress in the evaluation of the muon decay lifetime is reviewed. The electroweak bosonic corrections are given together with the respective shift of the W boson mass. After inclusion of the recently corrected fermionic contributions, this requires an updated fitting formula for the prediction of MW.
The Majorana nature of neutrinos can be detected by the precise measurement of muon decay. This possibility comes from the presence of charged Higgs boson interaction for Majorana neutrinos. We study the effects of the neutrino Yukawa interaction via charged Higgs bosons in muon decay processes such as $μ\to eν\barν$ and $μ\to eγ$. The Higgs triplet model with small vacuum expectation value is of special importance whose neutrino Yukawa coupling can affect significantly muon decays. External neutrino lines in the Feynman diagrams of $μ\to eν\barν$ can be crossed because of its Majorana nature.…
Quantum chromodynamics (QCD) effects in the semileptonic decay b -> c l nu are evaluated to the second order in the coupling constant, O(alpha_s^2), and to several orders in the expansion in quark masses, m_c/m_b. Corrections are calculated for the total decay rate as well as for the first two moments of the lepton energy and the hadron system energy distributions. Applied to the muon decay, they decrease its predicted rate by -0.43 ppm.
We present an analysis of the two-loop amplitude of the muon decay in the Standard Model (SM) using algebraic renormalization techniques. In addition, we discuss a manifestly BRST invariant IR regulator for the photon within the SM.
The leptons are viewed as composite objects, exhibiting anomalous magnetic moments and anomalous flavor-changing transition moments. The decay $μ\to e γ$ is expected to occur with a branching ratio of the same order as the present experimental limit.
We calculate the transverse muon polarization in the decay $K^{\pm}\toπ^0μ^{\pm}ν$ induced by the electromagnetic two-photon final-state interaction. For the central part of the Dalitz plot the typical value of this polarization is about $4\times 10^{-6}$.
In a previous paper, we showed that the decay rate of a muon is only slightly affected by the presence of a circularly polarized laser and we gave an analytic expression for the correction. In this paper, we present the analytical result for the case of a linearly polarized laser. Again the effect of the laser is small.
We investigate the change in the decay rate of a muon caused by embedding it in the field of a laser. A previous paper found that the change could be large, as much as an order of magnitude. We find the more intuitive result that the change is small and give analytic expressions for the small corrections.
We consider the O(alpha^2) hadronic corrections to the energy spectrum of the decay electron in muon decay. We find that the correction can be described, within good approximation, by a linear function in the electron energy. Explicit expressions for the form factors needed in an approach based on dispersion integrals are given.
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, Pi(+) -> Pi(0) e(+) Nu, the Pi(e2 gamma) radiative decay, Pi(+) -> e(+) Nu Gamma, and muon radiative decay, Mu -> e Nu Gamma. 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 Pi(e2 gamma) radiative decay involving energetic photons and…
A search for the lepton-flavor violating $μ^{+}\rightarrow e^{+}γ$ decay using polarized muons is revisited in terms of suppression of the serious background arising from an accidental coincidence between a $e^{+}$ in the normal muon decay and a high energy photon in the radiative muon decay, $μ^{+} \rightarrow e^{+} ν\overlineν γ$. It is found that a high energy photon in $μ^{+} \rightarrow e^{+} ν\overlineν γ$ decay is preferentially emitted parallel to the muon spin direction, similarly to $e^{+}$ in the normal muon decay. The selective measurements of either $e^{+}$s or photons moving anti…
The angular asymmetry in decays of polarized muons and tau leptons is discussed. Both the standard $V-A$ Fermi model and the general parameterization via Michel parameters are considered. Numerical importance of contributions suppressed by charged lepton mass ratio is underlined. Contribution of the second order QED correction is estimated in the leading logarithm approximation.
We have noted that the electron spectrum of muon decay in the leading logarithmic approximation calculated in two lowest orders of the perturbation theory in the paper of Berman (1958), can be reproduced by the parton language. This fact permits one to generalize the result to all orders of the perturbation theory using the structure function method.
We consider massive Dirac electron antineutrino to be observed in the muon decay, $μ^{-} \rightarrow e^- +\barν_{e} + ν_μ$, at rest in the LAB reference frame. A computation of $\barν_{e}$ differential direct spectral shape and angular distribution was performed. This has resulted in transverse component of the neutrino polarization emerging from the nonstandard S, T sector of the Lorentz structure in the Fermi leptonic charged weak interaction. The calculation is based on empirical values of the coupling parameters.
We derive model-independent constraints on chirality-changing terms in the muon decay Lagrangian using limits on neutrino mass. We consider all dimension-six operators invariant under the gauge symmetry of the Standard Model which contribute to either a Dirac neutrino mass or muon decay. Taking an upper limit on neutrino mass of 1 eV, we derive limits on the contributions of chirality-changing operators to the Michel parameters four orders of magnitude tighter than the current experimental constraints. We also identify two operators which, due to their flavor structure, are not constrained by …
The recent real time KARMEN anomaly for the electron neutrino counting rates (obtained from stopped muon decays) is analyzed by employing a neutrino flavor rotation model in which the muon neutrino is in a superposition of only two mass eigenstates. On the basis of experimental electron neutrino counting oscillations, we find a neutrino mass splitting $|m_2^2-m_1^2|=(0.22\pm 0.02)(eV/c^2)^2$ and a flavor rotation angle $ϕ=0.34\pm 0.10$, both within a 95% confidence interval.
Recently, $O(α^3)$ corrections to the muon decay rate and $O(α_s^3)$ to heavy quark decays have been determined by Fael, Schönwald, and Steinhauser. This is the first such perturbative improvement of these important quantities in more than two decades. We reveal and explain a symmetry pattern in these new corrections, and confirm the most technically difficult parts of their evaluation.
The accurate knowledge of the $\barν_e (ν_μ)$ beam produced in $μ^-$ decays and the absence of $ν_e (\barν_μ)$ contamination, make a future muon storage ring the ideal place to look for $\numunue$ ($\numubarnuebar$) oscillations. Using a detector capable of electron and muon identification with charge discrimination (e.g., the presently running NOMAD experiment), good sensitivities to $\numunue (\numubarnuebar)$ oscillations could be achieved. With the CERN-PS as a proton driver for a muon storage ring of the kind envisaged for a $μ$-collider, the LSND claim would be confirmed or disproved in …
We study the feasibility of performing a $ν_μ$ disappearance long-baseline experiment using a neutrino beam coming from muon decays. The advantage of such a technique with respect to the production of neutrino beams from pions is that in a muon decay both muon and electron neutrinos are produced in the same quantity. In case of $ν_μ\toν_{τ,s}$ oscillations, the $ν_e$ charged current (CC) events can be used as a control sample, to predict in situ the $ν_μ$ rates, thus reducing the systematics due to the knowledge of the neutrino flux, which is the main source of uncertainties for disappearance …
We perform a quantitative analysis of the decays of $cc\bar c\bar c$ tetraquarks with $J^{PC}=0^{++}, 2^{++}$ into 4 muons and into hidden- and open-charm mesons and estimate, for the first time, the fully charmed tetraquark decay width. The calculated cross section upper limit is $\sim 40$ fb for the 4 muons channel, and $\sim 28$ nb for the $D^{(*)} \bar D^{(*)} \to eμ$ channel. On the basis of our results, with the present sensitivity LHCb should detect both signals, for $0^{++}$ and $2^{++}$ fully-charmed tetraquarks.
In this article two-loop QED corrections to the muon decay and corrections of order $α_s^2$ to the semileptonic decay of the bottom quark are considered. We compute the imaginary part of the four-loop diagrams contributing to the corresponding fermion propagator in the limit of small external momentum. The on-shell condition is obtained with the help of a conformal mapping and Padé approximation. Via this method we confirm the existing results by an independent calculation.
Combining neutrino oscillations at T2K or T2HK with antineutrinos oscillations from muon decay at rest (DAR) allows a determination of the leptonic CP-violating phase delta. The degeneracies of this phase with theta13 and theta23 are broken and delta can be reliably distinguished from 180-delta. We present the sensitivity to delta of T2(H)K together with a muon DAR experiment using Super-K as a near detector and Hyper-K at the Tochibora site as a far detector.
Using the automation program GoSam, fully differential NLO corrections were obtained for the rare decay of the muon $μ\to eν\barνee$. 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 $μ\to 3e$ 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.
Significant deviations from the Standard Model are observed in semileptonic charged and neutral-current B-decays, the muon magnetic moment, and the extraction of the Cabibbo angle. We propose that these deviations point towards a coherent pattern of New Physics effects induced by two scalar mediators, a leptoquark $S_1$ and a charged singlet $ϕ^+$. While $S_1$ can provide solutions to charged-current $B$-decays and the muon magnetic moment, and $ϕ^+$ can accommodate the Cabibbo-angle anomaly independently, their one-loop level synergy can also address neutral-current $B$-decays. This framework…
In this paper, we analyze the polarized muon decay at rest (PMDaR) and elastic neutrino-electron scattering (ENES) admitting the non-standard V+A interaction in addition to standard V-A interaction. Considerations are made for Dirac massive muon neutrino and electron antineutrino. Moreover, muon neutrinos are transversely polarized. It means that the outgoing muon-neutrino beam is a mixture of the left- and right-chirality muon neutrinos and has a fixed direction of transverse spin polarization with respect to production plane. We show that the angle-energy distribution of muon neutrinos conta…
In this paper the charged Higgs signal through the decay to a pair of muon and neutrino (H -> mu nu) is analyzed. The analysis attempts to estimate the amount of muonic signal of the charged Higgs at LHC at a center of mass energy of 14 TeV. The signal process is the top quark pair production with one of the top quarks decaying to a charged Higgs (non SM anomalous top quark decay) and the other decaying to a W boson which is assumed to decay hadronically to two light jets. Due to the small branching ratio of charged Higgs decay to muon, results are quoted for data corresponding to an integrate…
The disagreement between the standard model prediction and the experimental measurement of muon anomalous magnetic moment can be alleviated by invoking an additional particle which is either a vector boson ($X_1$) or a scalar ($X_0$). This new particle, with the mass $m_X \lesssim 2 m_μ$, can be searched for in the decay $J/ψ\to μ^- μ^+ X$, where $X$ is missing. Our numerical study shows that the search is quite feasible at the BESIII experiment in the parameter space allowed by muon $g-2$ measurements.
Particle oscillations following neutrino production processes are analysed within Feynman's path amplitude formulation of quantum mechanics. Consideration of the temporal sequence of production and detection events reveals an important contribution to the oscillation phase from the space-time propagator of the decaying source particle. Formulae are derived for spatial neutrino oscillations following pion decay (at rest and in flight), muon decay and nuclear $β$-decay at rest, as well as for similar muon oscillations after pion decay at rest and in flight. In all cases studied, the neutrino osc…
We study the observability of the $\tautau$ decay mode of a Higgs boson produced in the $s$-channel at a muon collider. We find that the spin correlations of the $\tautau$ in $τ\to πν_τ, ρν_τ$ decays are discriminative between the Higgs boson signal and the Standard Model background. Observation of the predicted distinctive distribution can confirm the spin-0 nature of the Higgs resonance. The relative coupling strength of the Higgs boson to $b$ and $τ$ can also be experimentally determined.
