A compact frozen-spin trap for the search for the electric dipole moment of the muon

Adelmann, A. and Bainbridge, A. R. and Bailey, I. and Baldini, A. and Basnet, S. and Berger, N. and Bianco, L. and Calzolaio, C. and Caminada, L. and Cavoto, G. and Cei, F. and Chakraborty, R. and Barajas Chavez, C. and Chiappini, M. and Chislett, R. and Crivellin, A. and Dutsov, C. and Ebrahimi, A. and Francesconi, M. and Galli, L. and Gallucci, G. and Giovannozzi, M. and Goyal, H. and Grassi, M. and Gurgone, A. and Hesketh, G. and Hildebrandt, M. and Hoferichter, M. and Hoh, S. Y. and Höhl, D. and Hu, T. and Hume, T. and Jaeger, J. A. and Juknevicius, P. and Kästli, H. C. and Keshavarzi, A. and Khaw, K. S. and Kirch, K. and Kozlinskiy, A. and Lancaster, M. and Leonetti, F. and Märkisch, B. and Morvaj, L. and Papa, A. and Paraliev, M. and Pasciuto, D. and Price, J. and Renga, F. and Sakurai, M. and Sanz-Becerra, D. and Schmidt-Wellenburg, P. and Shang, Y. Z. and Takeuchi, Y. and Tegano, M. E. and Teubner, T. and Trillaud, F. and Uglietti, D. and Vasilkova, D. and Venturini, A. and Vitali, B. and Voena, C. and Vossebeld, J. and Wauters, F. and Wong, G. M. and Zeng, Y. (2025) A compact frozen-spin trap for the search for the electric dipole moment of the muon. European Physical Journal C: Particles and Fields, 85 (6): 622. ISSN 1434-6044

Abstract

Electric dipole moments (EDM) of fundamental particles inherently violate time-reversal (T) and the combined charge-conjugation and parity symmetry (CP). We aim to measure the EDM of the muon using the frozen-spin technique within a compact storage trap. This method exploits the high effective electric field, E≈165MV/m, experienced in the rest frame of the muon with a momentum of about 23MeV/c when it passes through a solenoidal magnetic field of |B→|=2.5T. In this paper, we outline the fundamental considerations for a muon EDM search and present a conceptual design for a demonstration experiment to be conducted at secondary muon beamlines of the Paul Scherrer Institute in Switzerland. In Phase I, with an anticipated data acquisition period of 200 days, the expected sensitivity to a muon EDM is σ(d)≤4E-21e·cm. In a subsequent phase, Phase II, we propose to improve the sensitivity to σ(d)≤6E-23e·cm using a dedicated instrument installed on a different beamline that produces muons of momentum 125 MeV/c.