Search

We have measured an inclusive missing-mass spectrum of the 12 C(K−, p) reaction over wide energy region at the kaon incident momentum of 1.8 GeV/c at J-PARC K1.8 beam line. This measurement was carried out as a by-product of a pilot run of J-PARC E05 experiment, which searched for the Ξ-hypernuclei via 12C(K−, K+) reaction. We have compared the observed missing-mass spectrum with a DWIA calculation to study the K-nucleus interaction. In this comparison, we have changed the depth of both real and imaginary parts of the optical potential between the K and nucleus. It is found that the observed spectrum is best reproduced by the calculation of the potential depth of V0 ∼ −80 MeV (real part) and W0 ∼ −40 MeV (imaginary part). On the other hand, we have observed a definitive excess around the deeply bound region BK ≳ 100 MeV. The excess cannot be explained by the any optical potential and quasi-free background reaction. It is well fitted with a Breit-Wigner function with a binding energy of 90 MeV and a width of 100 MeV, which can be interpreted as a deeply bound Λ(1405) nucleus.

For the full understanding of baryon-baryon interactions in flavor SU(3), the ΞN interaction is the last missing piece of information. So far, we have revealed the ΛN interaction to be attractive (UΛ ≈ 30 MeV), and ΣN interaction to be repulsive in the medium to heavy mass-number region. The ΛΛ bonding energy is weakly attractive. While we have a few experimental observations suggesting the ΞN interaction would be attractive, there still exist large theoretical ambiguities weather it is attractive or not. Experimental determinations on the existence of bound states of Ξ hypernuclei by observing bound-state peaks are strongly awaited. In this report, a new preliminary result on the missing-mass spectrum of a 12C(K−, K+) reaction, which strongly suggests the existence of Ξ-hypernuclear bound states, is presented.For the full understanding of baryon-baryon interactions in flavor SU(3), the ΞN interaction is the last missing piece of information. So far, we have revealed the ΛN interaction to be attractive (UΛ ≈ 30 MeV), and ΣN interaction to be repulsive in the medium to heavy mass-number region. The ΛΛ bonding energy is weakly attractive. While we have a few experimental observations suggesting the ΞN interaction would be attractive, there still exist large theoretical ambiguities weather it is attractive or not. Experimental determinations on the existence of bound states of Ξ hypernuclei by observing bound-state peaks are strongly awaited. In this report, a new preliminary result on the missing-mass spectrum of a 12C(K−, K+) reaction, which strongly suggests the existence of Ξ-hypernuclear bound states, is presented.

Experimental results from the J-PARC E13 experiments are summarized. A new experimental set up of E13 has established a platform for the future γ-ray hypernuclear spectroscopy at J-PARC using kaon beams. New γ rays are identified in HeΛ4 and FΛ19. The energy of 1.406 MeV for the HeΛ4(1+→0+) transition confirmed a sizable effect of Charge Symmetry Breaking (CSB) in ΛN interaction in the A=4 hypernuclear system. The identification of four γ rays in FΛ19 is made for the first time in sd shell hypernuclei. Especially, energy spacing of the ground state doublet is found to be 315.5 keV. A good agreement with two theoretical calculations suggests that the theoretical formalism used in p shell hypernuclei is also applicable to heavier hypernuclei. Lastly, an overview of the future J-PARC E63 experiment is given.