Intense Slow Muon Physics

Abstract

Physics programs with slow muons at a neutrino factory are described. Emphasis is given to the muon trio, the muon g − 2 anomalous magnetic moment, the muon electric dipole moment (EDM) and charged lepton mixing (CLM). In particular, a future muon source with high-intensity and high-luminosity, PRISM, developed at Osaka University is described. Muon TrioAn overview (but not comprehensive) list of intense slow muon physics programs at a future neutrino factory, ranging from particle physics, nuclear physics to applications, is given in Table 1, where programs are categorized into three groups, (1) precision measurements, (2) search for rare processes, and (3) application.Among the particle physics programs with muons [1], very important are (a) precision measurement of the muon g − 2 anomalous magnetic moment, (b) search for T-odd muon electric dipole moment (EDM), and (c) search for charged lepton mixing (CLM) 1 . I call them "the muon trio". They are significantly important to search for new physics, and also closely related one another in some cases of new physics, such as supersymmetry (SUSY). From this reason, I would focus on "the muon trio" hereafter.The goals of next generation experiments on the muon trio might be given as follows. The physics motivation of the muon trio should be robust for next decade. In the following, the physics cases are discussed for two possible cases on LHC, namely whether LHC finds SUSY (Case I) or does not (Case II).1 It is lepton flavor violation for charged leptons. Case I: LHC finds SUSY.It is known that all the muon trio has significant contributions from SUSY, if SUSY particles exist in the LHC mass range. In this case, studies of the muon trio would focus on SUSY. In SUSY models, SUSY contributions can be presented by a slepton mass matrix, given in Eq. (1).The SUSY contributions to the muon g − 2, muon EDM, and muon CLM are a real part of the diagonal element m 2 µμ , an imaginary part of the same diagonal element m 2 µμ , and an off-diagonal element ∆m 2 µẽ or ∆m 2 eμ , respectively. Therefore, determination of these three SUSY contributions would enable us to study the slepton mass matrix and therefore SUSY (soft) breaking. In the following, the SUSY contributions for each of the muon trio can be described. Muon g − 2The E821 at Brookhaven National Laboratory (BNL) carried out precision measurements of the anomalous g − 2 magnetic moments of µ + and µ − . Their combined result is [2] a µ = g − 2 2 = 11659208(6)×10 −10 (0.5ppm) (2)There is a difficulty in estimation of the standard model (SM) value of the muon g − 2, since the hadronic contribution has a large uncertainty,