Manifestations of the rotation and gravity of the Earth in spin physics experiments

Abstract

An influence of the rotation and gravity of the Earth on the particle motion and the spin evolution is not negligible and it should be taken into account in spin physics experiments. The Earth rotation brings the Coriolis and centrifugal forces in the lab frame and also manifests in the additional rotation of the spin and in the change of the Maxwell electrodynamics. The change of the Maxwell electrodynamics due to the Earth gravity is much smaller and can be neglected. One of manifestations of the Earth rotation is the Sagnac effect. The electric and magnetic fields acting on the spin in the Earth’s rotating frame coincide with the corresponding fields determined in the inertial frame instantly accompanying a lab. The effective electric field governing the particle motion differs from the electric field in the instantly accompanying frame. Nevertheless, the difference between the conventional Lorentz force and the actual force in the Earth’s rotating frame vanishes on average in accelerators and storage rings due to the beam rotation. The Earth gravity manifests in additional forces acting on particles/nuclei and in additional torques acting on the spin. The additional forces are the Newton-like force and the reaction force provided by a focusing system. The additional torques are caused by the corresponding focusing field and by the geodetic effect. As a result, the Earth gravity leads to the additional spin rotation about the radial axis which may not be negligible in EDM experiments.