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Spin precession of channeled particles in bent crystals has been observed for the first time. Polarized I"*" were channeled using bent Si crystals. These crystals provided an effective magnetic field of 45 T which resulted in a measured spin precession of 60° ±17°. This agrees with the prediction of 62° ± 2° using the world average of Z"*" magnetic moment measurements. This new technique gives a I"*" magnetic moment of (2.40 ± 0.46 ± 0.40)/X7v, where the quoted uncertainties are statistical and systematic, respectively. We see no evidence of depolarization in the channeling process. PACS numbers: 13.40.Fn, 14.20.Jn, 61.80.MkChanneling of high-energy particles in bent crystals has been observed in the momentum range [1-5] of 1.7-800 GeV/c. This technique has already found applications [3][4][5] in the deflection of high-energy beams. Another possibly important application of channeling is the precession of the spin of a polarized particle. This may allow the measurement of magnetic moments in distances of only a few cm. The lifetimes [6] of baryons containing charm quarks are so short that they travel only a few centimeters even at the highest available accelerator energies. Because of these short lifetimes, classical spin precession techniques using conventional magnets would produce negligibly small spin precession angles.It was pointed out by Baryshevskii [7] and Pondrom [8] that the magnetic moments of particles should precess if they were channeled in a bent crystal. The detailed precession theory has been developed by Lyuboshits [9] and Kim [10]. In a curved crystal the electrostatic field of the atomic planes deflecting the particle transforms into a magnetic field in the particle's rest frame. Thus the spin precession angle ^ is [9]

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