Search for a baryon of positive strangeness

Abstract

A search has been made for a baryon of strangeness +1 (the Z+) in the mass range from 940 to 1440 MeV/c2. Three production modes have been considered: K+ + p → Z+ + π+, K+ + p → Z+ + π+ + π0, π+ + d → Z+ +\(\overline {K^0 } \) + p. Candidates for the first two reactions came from a 2.26 GeV/c K+p bubble chamber experiment and were of two types: all 2-prong events in which one track decayed in the chamber and a sample of nondecaying 2-prongs in which there was no apparent neutral production (as determined by the momentum balance at the production vertex). The associated production events were taken from π+d exposures at 1.2 and 2.8 GeV/c. In all cases the data are consistent with the absence of a Z+, although kinematic ambiguities of various types prevent an absolute statement. In the K+-initiated reactions, the production cross-sections are less thean 1 μb for the 2-body production of the decaying Z+, less than 3 μb for the 3-body production of the decaying Z+, and less than 25 μb for a Z+ which does not have a visible decay (with reasonable assumptions on the ambiguities). The associated production cross-section for a Z+ is less than 18 μb.