New precision measurement of the J / psi and psi-prime meson masses

A new high precision measurement of the J / ψ - and ψ ′-meson masses has been performed at the VEPP-4M collider using the KEDR detector. The resonant depolarization method has been employed for the absolute calibration of the beam energy. The following mass values have been obtained: M J/ψ =3096.917±0.010±0.007  MeV , M ψ′ =3686.111±0.025±0.009  MeV . The relative measurement accuracy has reached 4×10 −6 for J / ψ and 7×10 −6 for ψ ′, approximately 3 times better than in the previous precise experiments.