Spectroscopy of hypernuclei with stopped kaons

Pion momentum spectra from K- absorption at rest on various nuclear targets were measured by means of a magnetic spectrometer with wide momentum range (100 ∼ 300 MeV/c). The ground state of Σ- hypernucleus, if well bound with a narrow width, is expected to be populated in 12C(stopped K-, π+) inclusive (untagged) spectrum, but such a peak was not observed. The spectrum is compared with the DWIA calculations by Morimatsu and Yazaki, indicating that the depth of the nuclear potential of Σ- is shallower than 12 MeV, and that its imaginary part is larger than 5 MeV if the potential depth is about 10 MeV. In the 12C(stopped K-, π-) spectrum, the ground state ((p3/2)n-1(s1/2)Λ) and the excited states ((p3/2)n-1(p)Λ) of Λ12C were observed, and their formation probabilities were roughly in agreement with the results of DWIA calculations. In the π- spectra on 12C, 9Be, and 7Li targets a distinct peak was observed at 132.1 ± 0.7 MeV/c. It is ascribed to π- from the mesic decay of Λ4H; Λ4H → 4He π-. The formation probability of Λ4H on C, Be, or Li target is much larger than those of the discrete states of Λ12C via the direct (stopped K-, π-) reaction. (author)