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.; Dâ€™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.; Nicolã², D.; Nishiguchi, H.; Nishimura, M.; Ogawa, S.; Ootani, W.; Panareo, M.; Papa, A.; Pepino, A.; Piredda, G.; Pizzigoni, G.; Popov, A.; Renga, F.; Ripiccini, E.; 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.

doi:10.1140/epjc/s10052-016-4047-3

The MEG experiment makes use of one of the worldâs most intense low energy muon beams, in order to search for the lepton flavour violating process Î¼+ â e+ Î³. 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 PÎ¼ = â1 by the StandardModel (SM) with massless neutrinos. We estimated our residual muon polarization to be (formula presented) 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 Î¼+ â e+ Î³ search induced by themuon radiative decay: (formula presented).

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.;Dâ€™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.;NicolÃ², D.;Nishiguchi, H.;Nishimura, M.;Ogawa, S.;Ootani, W.;Panareo, M.;Papa, A.;Pepino, A.;Piredda, G.;Pizzigoni, G.;Popov, A.;Renga, F.;Ripiccini, E.;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.

2016-01-01

Abstract

The MEG experiment makes use of one of the worldâs most intense low energy muon beams, in order to search for the lepton flavour violating process Î¼+ â e+ Î³. 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 PÎ¼ = â1 by the StandardModel (SM) with massless neutrinos. We estimated our residual muon polarization to be (formula presented) 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 Î¼+ â e+ Î³ search induced by themuon radiative decay: (formula presented).