Recent experimental results in Σ hypernuclei

This paper reports on the status of narrow Σ hypernuclear states below and above Σ threshold. We have measured (K-,π±) spectra from 4He, 6Li and 9Be at pK=600 MeV/c with reasonable energy resolution and high statistics. The (K-, π±) spectra from 6Li and 9Be show no evidence of any narrow structure above the Σ threshold, and hence rule out such previously claimed narrow states in this region. The 4He(K -,π-) spectrum clearly shows a peak below the Σ+ production threshold, confirming the existence of a bound state of Σ4He, which was reported in the 4He(Stopped K-,π-) reaction. As in the case of stopped kaons, no such peak was found in the 4He(K-,π+) spectrum. Quantitatively reliable parameters for this level have been established. (orig.)