Detailed discussion of a linear electric field frequency shift induced in confined gases by a magnetic field gradient: Implications for neutron electric-dipole-moment experiments

Abstract

The search for particle electric dipole moments (EDM) is one of the best places to look for physics beyond the Standard Model of electroweak interaction because the size of time reversal violation predicted by the Standard Model is incompatible with present ideas concerning the creation of the Baryon-Antibaryon asymmetry. As the sensitivity of these EDM searches increases more subtle systematic effects become important. We develop a general analytical approach to describe a systematic effect recently observed in an electric dipole moment experiment using stored particles[2]. Our approach is based on the relationship between the systematic frequency shift and the velocity autocorrelation function of the resonating particles. Our results, when applied to wellknown limiting forms of the correlation function, are in good agreement with both the limiting cases studied in recent work that employed a numerical/heuristic analysis. Our general approach explains some of the surprising results observed in that work and displays the rich behavior of the shift for intermediate frequencies, which has not been studied previously. In an appendix we give a new derivation of Egelstaf's theorem which we used in our study of the Diffusion theory (low frequency) limit of the effect.

Spin relaxation and linear-in-electric-field frequency shift in an arbitrary, time-independent magnetic field

“…Of particular concern in searches for electric dipole moments are effects that are linearly proportional to the electric field E. These may mimic effects expected for an electric dipole moment, thereby creating a ''false EDM.'' As shown by Lamoreaux and Golub [15], the linear-in-electricfield frequency shift for spins in a confined volume is given by the expression…”

“…In Ref. [15], the frequency shift is formulated in terms of the velocity autocorrelations, and one of the limiting cases discussed is the diffusion approximation in a rectangular cell with a uniform magnetic field gradient. We employ a slightly modified approach to calculate this limit in an arbitrary magnetic field.…”

Ultra-sensitive magnetometry based on free precession of nuclear spins

“…Furthermore, due to a geometric phase effect [34], particles trapped in electric and magnetic fields accumulate a phase shift, which is linear in E and thus cannot be distinguished from a true EDM effect. As a consequence, the magnetometer has to operate in an E-field free region and thus in a separate volume than the ultra cold neutrons (UCN) unless interparticle-collisions suppress these correlated effects [35]. The use of 3 He as a magnetometer has already been proposed in 1984 by Ramsey [36].…”

Plans for a Neutron EDM Experiment at SNS

“…• study of the neutron storage time in an acrylic cell coated with deuterated polystyrene • study of dielectric properties of superfluid helium [15] • theoretical and experimental study of the possible systematic effects due to the interference between the motional magnetic field effects and the gradient of the B 0 field [16,17] • modeling and prototyping of various coils • study of the neutron beam line [18] The R&D and the design will continue through calendar year 2007. The construction is expected to start subsequently.…”