Evidence for an exotic S=+1 baryon resonance at a mass of 1540 MeV

摘要

A new baryon resonance with manifestly exotic strangeness quantum number S = +1 was first observed from the LEPS detector at the SPring-8 facility in Japan. The photoproduction reaction γn → K~-Θ~+ was measured, where the neutron is bound in a ~(12)C nucleus and the Θ~+ is the new name of this resonance. The existence of the Θ~+ was inferred by observing a peak in the missing mass spectrum of the K~-, with the requirement of a coincident K~+ in the detector from the decay of the Θ~+. The mass of the resonance is 1.54 ± 0.01 GeV and a width of <25 MeV.