Missing-mass spectroscopy with the ${}^6$Li($\ddot{I}{€}^{-},K^{+}$)X reaction to search for ${}_{\hat{I}}^6›$H

Abstract

We searched for the bound state of the neutron-rich $\hat{I}›$-hypernucleus ${}_{\hat{I}}^6›$H, using the ${}^6$Li($\ddot{I}{€}^{-},K^{+}$)X double charge-exchange reaction at a $\ddot{I}{€}^{-}$ beam momentum of 1.2 GeV/c at J-PARC. A total of $1.4\times 10^{12}$ $\ddot{I}{€}^{-}$ was driven onto a ${}^6$Li target of 3.5-g/$\mathrm{c}{\mathrm{m}}^2$ thickness. No event was observed below the bound threshold, i.e., the mass of ${}_{\hat{I}}^4›$H + 2n, in the missing-mass spectrum of the ${}^6$Li($\ddot{I}{€}^{-},K^{+}$)X reaction in the $2^{\circ }$ < $\hat{I}{¸}_{\ddot{I}€K}$ < $20^{\circ }$ angular range. Furthermore, no event was found up to 2.8 MeV/$c^2$ above the bound threshold. We obtained the the double-differential cross section spectra of the ${}^6$Li($\ddot{I}{€}^{-},K^{+}$)X reaction in the angular range of $2^{\circ }$ < $\hat{I}{¸}_{\ddot{I}€K}$ < $14^{\circ }$. An upper limit of 0.56 nb/sr (90% C.L.) was obtained for the production cross section of the ${}_{\hat{I}}^6›$H hypernucleus bound state. In addition, not only the bound state region, but also the $\hat{I}›$ continuum region and part of the $\hat{I}{\pounds }^{-}$ quasi-free production region of the ${}^6$Li($\ddot{I}{€}^{-},K^{+}$)X reaction, were obtained with high statistics. The present missing-mass spectrum will facilitate the investigation of the $\hat{I}{\pounds }^{-}$-nucleus optical potential for $\hat{I}{\pounds }^{-}$-${}^5$He through spectrum shape analysis.

24 pages, 17 figures