Selected Studies of Elastic and Radiative Two Body Decays of Charmonium.

Running at the Stanford Linear Accelerator Center's e('+)e('-) colliding beam machine SPEAR, the MARK III, a general purpose magnetic spectrometer, has collected 2.7 x 10('6) produced J/(psi)'s during the spring of 1982 and the spring of 1983. The electro- magnetic decays of the J/(psi) have been studied. New results are presented on the decay J/(psi)(--->)(pi)('+)(pi)('-), J/(psi)(-- ->)K('+)K('-) as well as the first observation of the decay J/(psi)(--->)K(,S)K(,L). Branching ratios are measured to be (1.60 (+OR-) .25) x 10('-4), (2.28 (+OR-) .42) x 10('-4) and (1.01 (+OR-) .20) x 10('-4), respectively. This implies the electromagnetic form. factors are then (VBAR)F(,(pi)('(+OR-)))(VBAR)('2) = (.87 (+OR-) .2) x 10('-2), (VBAR)F(,K('(+OR-)))(VBAR)('2) = (1.4 (+OR-) .4) x 10('-2) and (VBAR)F(,K('0))(VBAR)('2) = (.64 (+OR-) .16) x 10('-2). In the mode J/(psi)(--->)(gamma)(mu)('+)(mu)(' -), the QED prediction is found to match the data quite well, and limits are set on the product branching ratio BR(J/(psi)(--->)(gamma)(xi)(2.2)) (.) BR((xi)(2.2)(--->)(mu)('+)(mu)(' -)) < 8.3 x 10('-6) at the 90% C.L. Also presented are results on the decay J/(psi)(--->)pp with a branching ratio measured to be (1.91 (+OR-) .16) x 10('-3). The angular distribution is found to vary as 1 + (.56 (+OR-) .14)cos('2)(theta). The decay channel J/(psi)( --->)(gamma)pp has been studied. The inclusive branching ratio for J/(psi)(--->)(gamma)pp is found to be BR(J/(psi)( --->)(gamma)pp) = (4.89 (+OR-) .49) x 10('-4). Also seen is the decay J/(psi)(--->)(gamma)(eta)(,c)(--->)(gamma)pp and a product branching ratio is found to be BR(J/(psi)( --->)(eta)(,c)) (.) BR((eta)(,c)(--->)pp) = (1.4 (+OR-) .7) x 10('-5). Lastly, limits are set for the non-observation of the decay J/(psi)(--->)(gamma)(xi)(2.2)(--->)(gamma)pp with a product branching ratio BR(J/(psi)(--->)(gamma)(xi)(2.2)) (.) BR((xi)(2.2)(--->)pp) < 2.0 x 10('-5).