Muon Decay Experiments

Abstract

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

ConstrainingCPT-even and Lorentz-violating nonminimal couplings with the electron magnetic and electric dipole moments

“…The magnitude of d e has been constrained with increasing precision [1,32,33], reaching the level |d e | ≤ …”

A relativistic quantum oscillator subject to a Coulomb-type potential induced by effects of the violation of the Lorentz symmetry

“…Theories that go beyond SM predict a small, but potentially measurable EDM (d e ≤ 10 −29 e · cm) [4]. Experimental measurements have been improved and reached the level d e ≈ 10 −31 e · cm [5][6][7][8][9]. Despite the great success of SM to give an overview of the microscopic processes through a field theory that unifies the weak and electromagnetic interactions, SM has some limitations.…”

Electrical and Optical Characteristics of an a-Si:H/c-Si Heterojunction Switch

“…where n = number of generations and U (1) ej , U (1) µj are the elements of the charged lepton current mixing matrix for light neutrinos ν j associated with the electron and the muon (see figures 1 and 2). The corresponding quantities with superscript (2) refer to heavy neutrinos N j .…”

“…There is a plethora of processes predicted by many extensions of the standard model, such as grand unification, supersymmetric theories etc, which violate the lepton family quantum numbers [1][2][3][4]. Among them the neutrinoless conversion of a bound muon to an electron,…”

“…On the other hand, the nuclear form factors, which describe the rates of process (1) have been computed employing various nuclear models [11][12][13][14][15][16]. In recent years some refinements of the quasiparticle random phase approximation (QRPA), which have been popular in evaluating successfully the nuclear transition matrix elements entering processes such as double beta decay (see e.g.…”