Experimental Observation of the Hypernuclei Beryllium -12 and HYDROGEN-7 Using the (negative Kaon, Positive Pion) Reaction at 715 Mev/c.

(, )Be and (, )H hypernuclear spectra have been measured in the A(K('-),(pi)('+))((SIGMA)('-) (A-1)) reaction using a 715 MeV/c incident momentum kaon beam, corresponding to 130 -150 meV/c momentum transfer, at the Brookhaven National Laboratory(('46,47)). The experiment was designed to verify the narrow structure and the level assignment in the recently reported KEK spectra in (, )Be and to measure the predicted spin orbit splitting between the (3/2('-),3/2) and (1/2('-),1/2) states in (' )H. The BNL LESBI beam line and the hypernuclear spectrometer were used to perform this experiment. The spectra were measured at two different reaction angles, 0 and 12 degrees, to investigate the momentum transfer dependence in order to help identify the spin of the possible states. A decay detector surrounded the target to provide a decay mode tag. Data were analyzed with and without this tag. By means of this decay detector and a proper Monte Carlo simulation, the data were separated into the two final state channels corresponding to (LAMDA) and (SIGMA)('-) particles. No narrow structure similar to the KEK data in the (, )Be spectra was observed and a different than expected momentum transfer has been seen. Thus the level structure assignment made by the KEK group is probably incorrect. The (, )H spectra did not follow the predicted level splitting and momentum transfer dependence. However, a similarity between the corresponding (SIGMA)- and (LAMDA) - hypernuclear spectra was found and is discussed. The decay mode tag enhances the hypernuclear structure with respect to the quasifree background for the (LAMDA) decay mode, due to a reduction of the quasifree background. The fact that the spectrum with the (LAMDA) decay mode tag retains all the information about the hypernuclear structure, while the spectrum with the (SIGMA) decay mode tag contains more quasifree background, shows the strong connection between (SIGMA) and (LAMDA) particles in final state, especially, near and above the (SIGMA) threshold. Therefore, a final state interaction mechanism is suggested and a rather simplified final state inter- action model is applied to calculate the hypernuclear spectrum. The results reproduce the enhancement near the (SIGMA) threshold as seen in the experimental data. The quasifree background can also be well. reproduced by allowing the (SIGMA) particle in the final state to be a non-interacting particle. ('46,47)Please see dissertation for references.