New upper limit for μ− → e+ conversion

Backenstoss, G.; Kowald, W.; Wuest, James D.; Seiler, H.; Seiler, M.; Simons, L. M.

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

Cited by 19 publications

(9 citation statements)

References 4 publications

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“…Experimentally, no very detailed sensitivity studies exist at this stage for µ −e + conversion. Although new backgrounds such as protons [21] and pions [22] may apear, we can nevertheless expect sensitivity levels to be at least similar to those on µ − -e − conversion [20,22,24], with some previous limits being nearly identical for both processes [20,23]. Such studies can and should be done with existing resources.…”

Section: Discussionmentioning

confidence: 89%

“…While µ − -e − conversion is dominated by its coherent conversion [44], this may be very different for the CLNFV µ − -e + conversion, where several states can be excited and the resulting positrons will therefore have a more involved spectrum [22]. Past measurements of µ − -e + conversion [20][21][22][23][24][25], the last one being SINDRUM II [26], assumed that this process is completely mediated through the giant dipole resonance (GDR). SINDRUM II used a Ti target and assumed a Breit-Wigner shape to fit the GDR with 20 MeV excitation energy and 20 MeV width.…”

Section: Formalismmentioning

confidence: 99%

“…Thus, with sensitivities not identical but at least similar to those on µ − -e − conversion, we can also expect an improvement on the bounds on µ − -e + conversion by several orders of magnitude within the coming years. This CLNFV conversion has been targeted in previous experiments [20][21][22][23][24][25][26], however, nowadays most of this expertise seems to be "lost", and it is worth reconsidering µ − -e + conversion in the light of the newest technology.…”

Section: Introductionmentioning

confidence: 99%

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μ − – e + conversion in upcoming LFV experiments

2017

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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, in fact is a promising alternative possibility 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. *

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Section: Discussionmentioning

confidence: 89%

Section: Formalismmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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μ − – e + conversion in upcoming LFV experiments

2017

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“…Pa rasiti ca lly, in a jl --e-conversion ex periment jl -e+ conversion (161) ca n also be observed, although wi th smaller sensitivity because this process ca n leave the nucleus in a highly excited state leading to lower energy positrons. Alternatively, measu ri ng the yi eld ofthe residual nucleus by radiochemical methods (120) gi ves a branching ra ti o limit only for the more or less coherent fra ction of the reaction wi th the residual nucleus excited below the particle thresholds. In jl--e + conversion, lepton number conservation is violated in additive schemes by two units.…”

Section: Thementioning

confidence: 99%

Muon Decay Experiments

Engfer¹,

Walter²

1986

Annu. Rev. Nucl. Part. Sci.

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ENGFER & WALTER ning of a systematic search for the decay Jl � ey (instead of Jl.-07 ev) (5), which would have identifi ed the me son (we use the muon's symbol Jl here) . as a le pton. A little later , in 1948, Steinberger (6) found that the electron produced in Jl decay was not monoenergetic and suggested that the muon decays into neutral me son + electron + neutrino, very much like nuclear beta decay. The electron spectrum was calculated by Michel (7), with the determining quantity being the Michel shape parameter p. The history of the experimental determination of p then is characterized by a monotonic rise of this quantity fr om zero to its pre sent value of 3/4. The experimental problem can be recognized fr om the fa ct that a spectrum with p = 0, � = ° can be fi tted almost equally well by p = 3/4, � = 13 %, where � is the FWHM of the re solution function of the measuring device . This strong correlation thus require s extremely good kn owledge of the resolution function .One year after the discovery of parity violation, Feynman & Gell-Mann (8) in their famous 1958 paper on the universal current-current interaction sugge sted that weak interactions take place through the exchange of charged intermediate ve ctor bosons. No neutral bosons were introduced because of the apparent absence of the decays p,+ -> e+e+eand K + -> n+vv, which otherwise would have been induced at the tree level. On the other hand, Feinberg (9) showed that Jl -> ey was possible at a br anching ratio B/l�ey = (a /24n)N2 � 10-4, where N is a number of order unity depending on the anomalous magnetic moment of the charged inter mediate vector boson. Thi s result was in disagreement with the experi mental upper limit se t by Lokanathan & Steinberger (10) of B/l�ey < 2 X 10-5 and could only be reconciled with the brute for ce proposal by Nishijima (1 1), Schwinger (12), and later Bludman (13), Oneda & Pati (14) of the existence of two different species of neutrinos with their associated muon-like and electron -like lepton numbers. By postulating the conservation of these se parate lepton numbers, Jl .-07 ey etc was completely for bidden. To te st this hypothesis directly Pontecorvo (15) and in dependently Schwartz (16) pr oposed to scatter ne utrinos fr om n decay on nuclei to see if they could produce electron s. The expe riment was done by Danby et al (17) with the result that electron production was suppre ssed by at least a factor of a hundred . Me anwhile the upper limit for Jl -> ey was constantly lowered to B/l�ey < 2.2 x 10-8 (18). Muon number appar ently was a conserved quantity and the interest in these processes was ge tting very low (19).Rumors about a finite Jl--+ ey signal possibly seen at SIN, the increasing succe ss ofthe Glashow-Salam-Weinberg model of electroweak interacti ons (20--22), and the hope that physics beyond the standard model could also be de scribed by gauge the orie s suddenly revived the interest in this "new

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“…These phenomena have been explored mostly through 0νββ decay [10], which corresponds to the LNV process in the ee sector. LNV processes in other sectors also have been searched with muon-to-positron conversion µ − + N (A, Z) → e + + N (A, Z − 2) [11][12][13][14][15][16][17] and rare Kaon decays such as K + → µ + µ + π − [18][19][20][21], while their experimental limits are far behind that of 0νββ decay, as shown in Table. I.…”

Section: Introductionmentioning

confidence: 99%

Future experimental improvement for the search of lepton-number-violating processes in the eμ sector

et al. 2017

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The conservation of lepton flavor and total lepton number are no longer guaranteed in the Standard Model after the discovery of neutrino oscillations. µ − + N (A, Z) → e + + N (A, Z − 2) conversion in a muonic atom is one of the most promising channels to investigate the lepton number violation processes, and measurement of the µ − − e + conversion is planned in future µ − − e − conversion experiments with a muonic atom in a muon-stopping target. This letter discusses experimental strategies to maximize the sensitivity of the µ − − e + conversion experiment by introducing the new requirement of the mass relation of M (A, Z − 2) < M (A, Z − 1), where M (A, Z) is the mass of the muon-stopping target nucleus, to eliminate the backgrounds from radiative muon capture. The sensitivity of the µ − − e + conversion is expected to be improved by four orders of magnitude in forthcoming experiments using a proper target nucleus that satisfies the mass relation. The most promising isotopes found are 40 Ca and 32 S.

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New upper limit for μ− → e+ conversion

Cited by 19 publications

References 4 publications

μ − – e + conversion in upcoming LFV experiments

μ − – e + conversion in upcoming LFV experiments

Muon Decay Experiments

Future experimental improvement for the search of lepton-number-violating processes in the eμ sector

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