# New Method for a Continuous Determination of the Spin Tune in Storage Rings and Implications for Precision Experiments

A new method to determine the spin tune was established and tested. In an ideal planar magnetic storage ring, the spin tune – defined as the number of spin precessions per turn – is given by ν_{s} = γG (γ is the Lorentz factor, G the gyromagnetic anomaly). At 970MeV/c, the deuteron spins coherently precess at a frequency of about 120kHz in COSY. The spin tune was deduced from the up-down asymmetry of deuteron-carbon scattering. In a time interval of 2.6s, the spin tune was determined with a precision of the order 10^{-8}, and to 1 x 10^{-10} for a continuous 100s accelerator cycle. This renders the new method a precision tool for accelerator physics; controlling the spin motion of particles to high precision is mandatory, in particular, for the measurement of electric dipole moments of charged particles in a storage ring.