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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.
Authors:
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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

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., Bari, A. De, Gerone, M. De, 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, 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., and Yudin, Yu. V.. Muon polarization in the MEG experiment: predictions and measurements. United States: N. p., Web. doi:10.1140/epjc/s10052-016-4047-3.
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., Bari, A. De, Gerone, M. De, 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, 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, Yu. V.. Muon polarization in the MEG experiment: predictions and measurements. United States. doi:10.1140/epjc/s10052-016-4047-3.
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., Bari, A. De, Gerone, M. De, 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, 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., and Yudin, Yu. V.. 2016. "Muon polarization in the MEG experiment: predictions and measurements". United States. doi:10.1140/epjc/s10052-016-4047-3. https://www.osti.gov/servlets/purl/1361495.
@article{osti_1361495,
title = {Muon polarization in the MEG experiment: predictions and measurements},
author = {Baldini, A. M. and Bao, Y. and Baracchini, E. and Bemporad, C. and Berg, F. and Biasotti, M. and Boca, G. and Cattaneo, P. W. and Cavoto, G. and Cei, F. and Chiarello, G. and Chiri, C. and Bari, A. De and Gerone, M. De and D’Onofrio, A. and Dussoni, S. and Fujii, Y. and Galli, L. and Gatti, F. and Grancagnolo, F. and Grassi, M. and Graziosi, A. and Grigoriev, D. N. and Haruyama, T. and Hildebrandt, M. and Hodge, Z. and Ieki, K. and Ignatov, F. and Iwamoto, T. and Kaneko, D. and Kang, T. I. and Kettle, P. -R. and Khazin, B. I. and Khomutov, N. and Korenchenko, A. and Kravchuk, N. and Lim, G. M. A. and Mihara, S. and Molzon, W. and Mori, Toshinori and Mtchedlishvili, A. and Nakaura, S. and Nicolò, D. and Nishiguchi, H. and Nishimura, M. and Ogawa, S. and Ootani, W. and Panareo, M. and Papa, A. and Pepino, A. and Piredda, G. and Pizzigoni, G. and Popov, A. and Renga, F. and Ripiccini, E. and Ritt, S. and Rossella, M. and Rutar, G. and Sawada, R. and Sergiampietri, F. and Signorelli, G. and Tassielli, G. F. and Tenchini, F. and Uchiyama, Y. and Venturini, M. and Voena, C. and Yamamoto, A. and Yoshida, K. and You, Z. and Yudin, Yu. V.},
abstractNote = {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 Pμ=-1 by the Standard Model (SM) with massless neutrinos. We estimated our residual muon polarization to be Pμ= -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+$\bar{v}$μνeγ.},
doi = {10.1140/epjc/s10052-016-4047-3},
journal = {European Physical Journal. C, Particles and Fields},
number = 4,
volume = 76,
place = {United States},
year = {2016},
month = {4}
}