Observation of the Lowest $P$-Wave $b\overline{b}$ Bound States

In a continuing study of the spectroscopy of the $b\overline{b}$ bound quark systems the discovery of the lowest $P$-wave bound states by observation of photons from the decays $2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}\left(b\overline{b}\right)\to \gamma +1\mathrm{}{}_{}{}^3{}_{}{}^{}P_J^{}{}_{}{}^{}\left(b\overline{b}\right)$ and $1{}_{}{}^3{}_{}{}^{}P_J^{}{}_{}{}^{}\left(b\overline{b}\right)\to \gamma +1\mathrm{}{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}\left(b\overline{b}\right)$ is reported. The photons are observed as narrow enhancements in the inclusive photon spectrum from ${\Upsilon }^{\prime }$ decays. The center of gravity of the ${}_{}{}^3{}_{}{}^{}P_J^{}{}_{}{}^{}$ states (${\chi }_b$), the fine-structure splitting, and the branching ratios for the two transitions are given.