Speaker
Description
Recently, we conducted a kaonic nuclear-bound state search experiment using a K
−
beam
(1 GeV/c) bombarding a 3He target. We succeeded in observing a kaonic nuclear quasi-bound
state,“K−pp”, via a nucleon knockout reaction, K−N → K ̄n′, followed by the decay K ̄NN → Λp
(2NK ̄A) in the two-nucleon K ̄ absorption process, resulting in the final state Λp + n′. The result
−
cay width of about 100 MeV. From the Λp decay, the isospin of the system is determined to be
IK ̄NN = 1/2. The momentum transfer distribution of the Λp system is very broad, implying that
−
decay process of the K ̄NN via one-nucleon K ̄ absorption (1NK ̄A: K ̄N → πY ), and B) by searching
for the K ̄NNN bound state through the Λd invariant mass study of the Λd + n′ final state with
shows that the ”K pp” binding energy is about 40 MeV below the binding threshold, with a de-
the size of the ”K
We extended our study on the kaonic nuclear-bound state in two ways: A) by studying the mesonic
pp” system might be very compact [1, 2].
a K− beam (1 GeV/c) bombarding a 4He target. The aim of A) is to understand why the decay −
width of “K pp” is about twice as broad as that of Λ(1405) (∼ 50 MeV), which is assumed to be
a molecule-like hadronic cluster composed of a K ̄ meson and a nucleon, i.e., Λ(1405) ≡ K ̄N, as
introduced by R.H.Dalitz et.al.[3]. The result shows that the K ̄NN → πYN decay is dominant
(1NK ̄A ≫ 2NK ̄A) and that the πΣN to πΛN ratio is about 1:1, indicating that the IK ̄N = 1 channel
absorption channel is approximately equal to the IK ̄N = 0 channel. The result also suggests that
there is a hint of the ”K ̄0nn” bound state, a charge mirror state of “K−pp”, existing in the π−Λp −′
invariant mass spectrum of the π Λp + p final state.
In the Λd invariant mass study B), the two-dimensional preliminary spectrum of the Λd invari-
ant mass and the momentum transfer to Λd (mΛd,qΛd) shows an almost identical distribution to (mΛp , qΛp ), indicating the presence of K ̄NNN , decaying to Λd. If this is another kaonic nuclear- bound state, then the isospin, spin-parity is fixed to be I(JP ) = 0(1/2−).
In this talk, we’ll describe these two new results on kaonic nuclear-bound states and discuss the prospects of studying the molecule-like hadronic cluster with strangeness.
