Search for ${}_{\mathrm{\Lambda }}^6$H hypernucleus by the ${}^6$Li$({\pi }^{-},K^{+})$ reaction at $p_{{\pi }^{-}}$ = 1.2 GeV/$c$

We have carried out an experiment to search for a neutron-rich hypernucleus, ${}_{\mathrm{\Lambda }}^6$H, by the ${}^6$Li(${\pi }^{-},K^{+}$) reaction at $p_{{\pi }^{-}}$ =1.2 GeV/$c$. The obtained missing mass spectrum with an estimated energy resolution of 3.2 MeV (FWHM) showed no peak structure corresponding to the ${}_{\mathrm{\Lambda }}^6$H hypernucleus neither below nor above the ${}_{\mathrm{\Lambda }}^4$H$+2n$ particle decay threshold. An upper limit of the production cross section for the bound ${}_{\mathrm{\Lambda }}^6$H hypernucleus was estimated to be 1.2 nb/sr at 90% confidence level.