Excited Hyperon of Mass 1680 MeV

Abstract

We have analyzed 370 000 pictures taken in the 30-inch hydrogen bubble chamber exposed to the 5.5-GeV/c separated K~ beam 1 at the Argonne zero-gradient synchrotron (ZGS). Light particle contamination in the beam was £5% when calculated from a r scan of the film. A Cerenkov counter operated during the exposure indicated the same high purity. About 5000 two-prong events with an associated A decay have been found. After kinematic analysis, these yielded 328 fits to the final state A77 + TT"" and 89 fits to 2°77 + 7r~.When more than one hypothesis produced a fit to a given event, a x 2 probability cut was used to exclude all fits having a probability 5 times less than that for the best fit. After this selection, all events fitting the hypothesis ATT + 77~ with a \ 2 probability >1% were classified as ATT + TT~ events. Of the remaining events, all those fitting the Z°Tf + 7r~ hypothesis with a X 2 probability >1% were classified as £°7r + 77~" events. These criteria yield a rather pure sample of the four-constraint AIT + IT~ final state. 2 The two-constraint fits to S°7r + 7r"~ have some (unknown) contamination from the A7T + ir~n° events, but this uncertainty is not important for the present results. Because of the high-beam purity, contamination due to events originating from pions can be neglected. 3 The Dalitz plot and the mass-squared projection for the events classified as ATI + IT~ are shown in Fig.

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