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Title: Muon polarization in the MEG experiment: predictions and measurements

The MEG experiment makes use of one of the world’s most intense low energy muon beams, in order to search for the lepton flavour violating process μ +→e +γ. We determined the residual beam polarization at the thin stopping target, by measuring the asymmetry of the angular distribution of Michel decay positrons as a function of energy. The initial muon beam polarization at the production is predicted to be P μ=-1 by the Standard Model (SM) with massless neutrinos. We estimated our residual muon polarization to be P μ= -0.86 ± 0.02 (stat) $$+0.05\atop{-0.06}$$ (syst) at the stopping target, which is consistent with the SM predictions when the depolarizing effects occurring during the muon production, propagation and moderation in the target are taken into account. The knowledge of beam polarization is of fundamental importance in order to model the background of our μ +→e +γ search induced by the muon radiative decay: μ +→e +$$\bar{v}$$ μν eγ.
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Publication Date:
Grant/Contract Number:
FG02-91ER40679; 200021_137738; RBFR08XWGN; RFBR 14-22-03071
Type:
Accepted Manuscript
Journal Name:
European Physical Journal. C, Particles and Fields
Additional Journal Information:
Journal Volume: 76; Journal Issue: 4; Journal ID: ISSN 1434-6044
Publisher:
Springer
Research Org:
Univ. of California, Irvine, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Contributing Orgs:
The MEG Collaboration
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
OSTI Identifier:
1361495