Background suppression forμ→eγwith polarized muons

Abstract

A search for the lepton-flavor-violating ϩ →e ϩ ␥ decay using polarized muons is reexamined in terms of suppression of the serious background arising from an accidental coincidence between an e ϩ in the normal muon decay and a high energy photon in the radiative muon decay, ϩ →e ϩ ␥. It is found that a high energy photon in ϩ →e ϩ ␥ decay is preferentially emitted parallel to the muon spin direction, similarly to e ϩ in the normal muon decay. The selective measurements of either e ϩ 's or photons moving antiparallel to the muon spin direction would suppress the accidental background for ϩ →e ϩ ␥ with right-handed and left-handed e ϩ 's, respectively. ͓S0556-2821͑97͒50205-0͔ PACS number͑s͒: 13.35.Bv, 11.30.Fs, 13.88.ϩe 55

Charged Lepton Flavor Violation Experiments

“…This distribution may provide important information for helping to pin down the source of the LFV. Researchers have also proposed to reduce backgrounds by limiting the experimental acceptance, as the background positrons and γ rays have angular distributions with respect to the muon spin (26).…”

The MEG detector for μ +→e+ γ decay search

“…77; due Table 7 Trigger rates as a function of progressively applied selection criteria (γ -ray energy, relative e-γ timing and direction) at 3 × Fig. 76 Spectrum of E γ measured offline by the LXe detector, as obtained with the threshold at 45 MeV on the online measured γ -ray energy, superimposed to a lower-threshold one. The corresponding efficiency curve, resulting from the ratio of the two spectra, is also shown to limitations inherent in the DAQ (the digitiser read-out lasting ∼24 ms/event), the TC acceptance region is modified until the DAQ efficiency reaches the maximum allowed value.…”

Search for lepton flavor violating muon decay: latest result from MEG

“…The other is accidental overlaps of a high-energy positron from normal muon decay, µ + → e + ν e ν µ (Michel decay) with an uncorrelated high-energy gamma ray from RD, annihilation-in-flight of positron or bremsstrahlung. The rate of the accidental one can be written as [6], where R µ is instantaneous rate of muon beam; f e and f γ are positron and gamma ray background yield at signal region which are shown in Figure 1 and 2, respectively; ∆Θ eγ and ∆t eγ are resolutions of angle and timing measurements, respectively. At our muon rate of ∼ 3 × 10 7 /sec and with our detector resolutions, the accidental one becomes dominant.…”