E1 Transitions from the Υ″ State and the Fine Structure of theχb′States

Using the CUSB-II detector at the Cornell Electron Storage Ring, we have made precision measurements of the electric dipole transition rates from Υ″ to${\mathrm{\chi }}_{\mathrm{b}}^{\prime }$, which are in excellent agreement with theory. The fine-structure splitting is found to beM(${\mathrm{\chi }}_{\mathrm{b}2\mathrm{}}^{\prime }$)-M(${\mathrm{\chi }}_{\mathrm{b}1\mathrm{}}^{\prime }$=13.5±0.4±0.5 MeV and(${\mathrm{\chi }}_{\mathrm{b}1\mathrm{}}^{\prime }$)-M(${\mathrm{\chi }}_{\mathrm{b}0\mathrm{}}^{\prime }$)=23.2±0.7±0.7 MeV, leading to a ratioR=0.584±0.024±0.02. The fine structure measures the relative contributions of the spin-orbit interaction a=9.5±0.2±0.1 MeV and tensor interaction b=2.3±0.1±0.1 MeV. We also find that the long-range confining potential transforms as a Lorentz scalar.© 1991 The American Physical Society