New Method for a Continuous Determination of the Spin Tune in Storage Rings and Implications for Precision Experiments
AbstractA new method to determine the spin tune is described and tested. In an ideal planar magnetic ring, the
spin tune – defined as the number of spin precessions per turn – is given by νs = γ G (γ is the Lorentz factor,
G the gyromagnetic anomaly). At 970 MeV/c, the deuteron spins coherently precess at a frequency of
≈120 kHz in the Cooler Synchrotron COSY. The spin tune is deduced from the up-down asymmetry of
deuteron-carbon scattering. In a time interval of 2.6 s, the spin tune was determined with a precision of the
order 10-8 and to 1×10-10 for a continuous 100 s accelerator cycle. This renders the presented method
a new 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
D. Eversmann et al. (JEDI collaboration),
Physical Review Letters 115 (2015) 094801
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