New upper limit for μ− → e+ conversion

doi:10.1016/0370-2693(80)90495-5

Physics Letters B

Volume 95, Issue 2, 22 September 1980, Pages 318-322

https://doi.org/10.1016/0370-2693(80)90495-5 Get rights and content

Abstract

An upper limit for μ⁻ → e⁺ conversion has been established by searching for specific decay properties of the expected final state nucleus. We obtain $R_{coh} = (μ^{−} +^{127} I → e^{+}^{127} Sb^{∗})/(μ^{−} → v_{μ}) < 3 × 10^{−10}$ with 90% c.l.

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Cited by (18)

μ−–e+ conversion in upcoming LFV experiments
2017, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
We present an illustrative discussion of the physics potential of $μ^{-}$ – $e^{+}$ conversion. We point out that this process, although much less frequently studied than the related but much more popular processes of $μ^{-}$ – $e^{-}$ conversion and neutrinoless double beta decay, may in fact be a promising alternative to detect both lepton flavour and number violation. However, for this goal to be reached, a combined effort of experiments and theory, both in nuclear and particle physics, is necessary to advance. The aim of this paper is to be an “appetiser” to trigger such an initiative.
Transition matrix elements for the exotic double-charge exchange μ- → e+ conversion in 27Al
2006, Nuclear Physics A
The lepton and lepton flavor violating process of the muon-to-positron conversion in ²⁷Al is studied with emphasis on mechanisms mediated by heavy neutrinos. We investigate two such cases: (i) the mode which involves only nucleons in the nucleus (nuclear mode) and (ii) the mode mediated by pions (1-pion and 2-pions in flight between the interacting nucleons). The nuclear wave functions for the initial state of ²⁷Al and all accessible final states of ²⁷Na are obtained in the framework of 1s–0d shell model employing the well-known Wildenthal realistic interaction. The total strength is calculated by summing over all excited states up to the energy $E_{x} = 25 MeV$ . We found that the contributions from the 1-pion and nuclear mode are about eight times smaller than the 2-pion mode.
The exotic double-charge exchange μ- → e+ conversion in nuclei
2002, Nuclear Physics A
The formalism for the neutrinoless (μ⁻,e⁺) conversion is investigated in detail and the relevant nuclear matrix elements for light intermediate neutrinos in the case of ²⁷Al(μ⁻,e⁺)²⁷Na are calculated. The nucleus ²⁷Al is going to be used as a stopping target in the MECO experiment at Brookhaven, one of the most sensitive probes expected to reach a sensitivity in the branching ratio of the order 10⁻¹⁶ within the next few years. The relevant transition operators are constructed utilizing a variety of mechanisms present in current gauge theories, with emphasis on the intermediate neutrinos, both light and heavy, and heavy SUSY particles. The nuclear wave functions, both for the initial state and all excited final states are obtained in the framework of 1s–0d shell model employing the well-known and tested Wildenthal realistic interaction. In the case of the light intermediate neutrinos the transition rates to all excited final states up to 25 MeV in energy are calculated. We find that the imaginary part of the amplitude is dominant. The total rate is calculated by summing over all these partial transition strengths. We also find that the rate due to the real part of the amplitude is much smaller than the corresponding quantity found previously by the closure approximation.
The Neutrino mass and family, Lepton and Baryon number non-conservation in gauge theories
1986, Physics Reports
Study of the lepton-violating (μ-, e+) reaction in modern gauge theories
1983, Nuclear Physics, Section B
The lepton-violating (μ⁻, e⁺) reaction has been studiedin the context of modern gauge theories. Both left-handed and right-left symmetric models have been examined. Special attention has been paid to the following mechanisms: (i) those mediated by massive neutrinos (light or heavy); (ii) those accompanied by massless or light physical Higgs particles (majoron); (iii) those involving more intermediate Higgs particles, e.g. singly charged isosinglets (Zee model) and doubly charged isotriplets; (iv) right-handed currents. The formalism has been applied to the experimentally interesting process $μ^{−} +^{58} Ni →^{58} Fe(gs) + e^{+}$ . The branching ratio is computed using realistic nuclear wave functions. It is found to be ≲10⁻²⁷ in all models, i.e. too small to be measurable in the foreseeable future. The branching ratio for the (μ⁻, e⁺) reaction to all nuclear states is estimated to be ≲10⁻²⁰, i.e. beyond the goals of planned experiments.
Systematic analysis of lepton family number violating processes in the framework of local gauge theories
1983, Nuclear Physics, Section B
General unified electroweak gauge theories with neutral lepton mixing are reexamined with regard to processes that change lepton family numbers L_f. The most general allowed mass sectors of models based on SU(2) × U(1) and SU(2)_L × SU(2)_R × U(1) are studied and the consequences for L_f changing processes such as μ → eγ, ν_f′ → ν_f + γ are worked out. We discuss models that break individual lepton family numbers but still conserve total lepton number L, as well as models in which L is broken too.

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^☆: We thank Dr. A. Wyttenbach for valuable discussions in the early stage of the experiment. This work was supported by the Swiss National Science Foundation.

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Physics Letters B

Abstract

References (9)

Phys. Lett.

SIN Newsletter

Phys. Rev.

Cited by (18)

μ<sup>−</sup>–e<sup>+</sup> conversion in upcoming LFV experiments

Transition matrix elements for the exotic double-charge exchange μ<sup>-</sup> → e<sup>+</sup> conversion in <sup>27</sup>Al

The exotic double-charge exchange μ<sup>-</sup> → e<sup>+</sup> conversion in nuclei

The Neutrino mass and family, Lepton and Baryon number non-conservation in gauge theories

Study of the lepton-violating (μ<sup>-</sup>, e<sup>+</sup>) reaction in modern gauge theories

Systematic analysis of lepton family number violating processes in the framework of local gauge theories

New upper limit for μ− → e+ conversion☆

Abstract

Phys. Lett.

SIN Newsletter

Phys. Rev.

New upper limit for μ⁻ → e⁺ conversion☆