We present the concept of a compact storage ring of less than 0.5 m orbit radius to search for the electric dipole moment of the muon (d µ ) by adapting the "frozen spin" method. At existing muon facilities a statistics limited sensitivity of d µ ∼ 5 × 10 −23 e cm can be achieved within one year of data taking. Reaching this precision would demonstrate the viability of this novel technique to directly search for charged particle EDMs and already test a number of Standard Model extensions. At a future, high-power muon facility a statistical reach of d µ ∼ 5 × 10 −25 e cm seems realistic with this setup.Key words: Electric and magnetic moments, Muons, Storage rings PACS: 13.40. Em, 14.60.Ef, 29.20.Dh
MotivationThe observed matter-antimatter asymmetry of the Universe is not accounted for by the known extent of CP violation present in the Standard Model (SM) of particle physics. The search for permanent electric dipole moments (EDM) of fundamental particles is regarded as one of the most promising avenues for finding manifestations of additional CP violation, see, e.g., [1]. As these EDMs violate time reversal invariance (T) and parity (P), they also violate CP, if CPT invariance is assumed. Various systems have been under investigation for a long time with limits becoming more and more restrictive, often challenging models beyond the SM. Of particular interest are the searches for the EDM of the neutron [2], the electron [3] and the 199 Hg atom [4].