positive muon
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The part-per-million measurement of the positive muon lifetime and determination of the Fermi constant by the MuLan experiment at the Paul Scherrer Institute is reviewed. The experiment used an innovative, time-structured, surface muon beam and a near-4\piπ, finely-segmented, plastic scintillator positron detector. Two in-vacuum muon stopping targets were used: a ferromagnetic foil with a large internal magnetic field, and a quartz crystal in a moderate external magnetic field. The experiment acquired a dataset of 1.6 \times 10^{12}1.6×1012 positive muon decays and obtained a muon lifetime \tau_{\mu} = 2\, 196\, 980.3(2.2)τμ=2196980.3(2.2)~ps (1.0~ppm) and Fermi constant G_F = 1.166\, 378\, 7(6) \times 10^{-5}F=1.1663787(6)×10−5 GeV^{-2}−2 (0.5~ppm). The thirty-fold improvement in \tau_{\mu}τμ has proven valuable for precision measurements in nuclear muon capture and the commensurate improvement in G_FF has proven valuable for precision tests of the standard model.

Positive muon is a spin half elementary particle lies in the second generation leptons in standard model of particles. It has been used as a sensitive magnetic (spin) probe for study of life and materials. Due to its special characteristics – 100% polarization and asymmetric decay to positron, it provides information about local electronic and spin states of material in which it stops. The asymmetry, relaxation of muon and its charge states in materials provide information about the interested phenomena. For life sciences study, muon can probe the dynamics of electron, proton, ions, H, O2, reaction dynamics, catalytic processes, concentration of molecules, magnetic behaviors, etc. in the biosamples. Here, the applications of positive muon to understand the life related phenomena are reviewed.

<p>Spin relaxation of muonium (Mu) observed in molecular oxygen (O₂) dissolved in water shows characteristic behaviour which enables us to detect O₂ in aqueous solution of albumin, serum and haemoglobin (Hb). These results suggest development of a new method using positive muon to measure oxygen level in biological systems which can be applied for diagnosis and treatment of cancer.</p><p><strong>Journal of Nepal Physical Society</strong><br />Volume 4, Issue 1, February 2017, Page: 7-10</p>