Measurement of the mass splittings between the bb̄χb,J(1P) states

We present new measurements of photon energies and branching fractions for the radiative transitions {Upsilon}(2S){r_arrow}{gamma}{chi}{sub b(J=0,1,2)}(1P). The masses of the {chi}{sub b} states are determined from the measured radiative photon energies. The ratio of mass splittings between the {chi}{sub b} substates, r{equivalent_to}(M{sub J=2}{minus}M{sub J=1})/(M{sub J=1}{minus}M{sub J=0}), with M the {chi}{sub b} mass, provides information on the nature of the b{bar b} confining potential. We find r(1P)=0.542{plus_minus}0.022{plus_minus}0.024. This value is somewhat lower than the previous world average, but more consistent with the theoretical expectation that r(1P){lt}r(2P); i.e., that this mass splitting ratio is smaller for the {chi}{sub b}(1P) states than for the {chi}{sub b}(2P) states. {copyright} {ital 1999} {ital The American Physical Society}