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 angu- lar distribution of Michel decay positrons as a function of energy. The initial muon beam polarization at the production is predicted to be Pμ = −1 by the Standard Model (SM) with massless neutrinos. We estimated our residual muon polar- ization to be Pμ = −0.86 ± 0.02 (stat) +0.05 (syst) at the −0.06 stopping target, which is consistent with the SM predictions when the depolarizing effects occurring during the muon pro- duction, propagation and moderation in the target are taken into account. The knowledge of beam polarization is of fun- damental importance in order to model the background of our μ+ → e+γ search induced by the muon radiative decay: μ+→e+ν ̄μνeγ.
Muon polarization in the MEG experiment: Predictions and measurements / Baldini, A.M., Bao, Y., Baracchini, E., Bemporad, C., Berg, F., Biasotti, M., Boca, G., Cattaneo, P.W., Cavoto, G., Cei, F., Chiarello, G., Chiri, C., De Bari, A., De Gerone, M., D’Onofrio, A., Dussoni, S., Fujii, Y., Galli, L., Gatti, F., Grancagnolo, F., et al.. - In: THE EUROPEAN PHYSICAL JOURNAL. C, PARTICLES AND FIELDS. - ISSN 1434-6044. - 76:4(2016). [10.1140/epjc/s10052-016-4047-3]
Muon polarization in the MEG experiment: Predictions and measurements
CAVOTO, GianlucaMembro del Collaboration Group
;RIPICCINI, EMANUELEMembro del Collaboration Group
;Voena, C.;
2016
Abstract
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 angu- lar distribution of Michel decay positrons as a function of energy. The initial muon beam polarization at the production is predicted to be Pμ = −1 by the Standard Model (SM) with massless neutrinos. We estimated our residual muon polar- ization to be Pμ = −0.86 ± 0.02 (stat) +0.05 (syst) at the −0.06 stopping target, which is consistent with the SM predictions when the depolarizing effects occurring during the muon pro- duction, propagation and moderation in the target are taken into account. The knowledge of beam polarization is of fun- damental importance in order to model the background of our μ+ → e+γ search induced by the muon radiative decay: μ+→e+ν ̄μνeγ.| File | Dimensione | Formato | |
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