Experimental Study of the Polarization and Magnetic Moment of the Antiproton

Asymmetries in double scattering of antiprotons of 1.6 BeV/c momentum in the 72-in. hydrogen bubble chamber have been investigated. Analysis of 200 events in which both scatterings occur in the angular region $6.3\le {\theta }_{\mathrm{lab}}\le 23.6°$ yielded a polarization $P=\left({{50}_{-13\mathrm{}}}^{+8\mathrm{}}\right)\%$, at an average angle ${\theta }_{\mathrm{lab}}=10\mathrm{}°$. The precession of the spin polarization vector in the magnetic field of the bubble chamber between two scatterings decreases the up-down asymmetries by an amount determined by the magnetic moment of the particle. A method for determination of the magnetic moment of the antiproton, using a three-dimensional likelihood function, is described as applied to the above sample of events. The value of the antiproton magnetic moment was determined to be ${\mu }_{\overline{p}}=-1.8\mathrm{}\pm 1.2$ nuclear magnetons.