Resonant depolarization technique at VEPP-4M in Novosibirsk

Due to the Sokolov–Ternov natural radiative mechanism, the electron–positron storage rings feature a unique possibility of creating spin polarization of circulating beams. The resulting transverse polarization of particles is mainly used to precisely calibrate the beam energy by measuring the spin precession frequency using the resonant depolarization technique (RD). RD is considered the most accurate method for instantaneous determination of particle energy. To date, RD has been applied in several laboratories around the world to measure the mass of various particles. The best result was obtained in experiments at BINP (Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences) on the VEPP-4M collider with the KEDR detector, in which the masses of narrow resonances of J/ψ and ψ (2S) were measured with a world-record accuracy of 10^-6 . We describe the principles and technical details of application of the resonant depolarization at the VEPP-4M collider. Experimental results are presented for various conditions of measuring the spin precession frequency by this method. The experience gained allows us to discuss possible features of RD application at future Higgs and Electroweak e^+e^- Factories from the projects FCC-ee and CEPC.