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, Gianluca; 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.; Grassi, M.; Graziosi, A.; Grigoriev, D. N.; Haruyama, T.; Hildebrandt, M.; Hodge, Z.; Ieki, K.; Ignatov, F.; Iwamoto, T.; Kaneko, D.; Kang, T. I.; Kettle, P. R.; Khazin, B. I.; Khomutov, N.; Korenchenko, A.; Kravchuk, N.; Lim, G. M. A.; Mihara, S.; Molzon, W.; Mori, Toshinori; Mtchedlishvili, A.; Nakaura, S.; Nicolò, D.; Nishiguchi, H.; Nishimura, M.; Ogawa, S.; Ootani, W.; Panareo, M.; Papa, A.; Pepino, A.; Piredda, G.; Pizzigoni, G.; Popov, A.; Renga, F.; Ripiccini, Emanuele; Ritt, S.; Rossella, M.; Rutar, G.; Sawada, R.; Sergiampietri, F.; Signorelli, G.; Tassielli, G. F.; Tenchini, F.; Uchiyama, Y.; Venturini, M.; Voena, C.; Yamamoto, A.; Yoshida, K.; You, Z.; Yudin, Y. u. V.. - 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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