Speaker
Description
The possible existence of deeply-bound $\bar K$-nuclear bound states
has been widely discussed as a consequence of the strongly attractive
$\bar K N$ interaction in I = 0 channels.
The investigation of those exotic states will provide unique information
of the $\bar K N$ interaction below the threshold, which is still not
fully understood up to date.
Furthermore, the grate interest of those exotic states is that they
might form high-density nuclear matter where the chiral symmetry is
expected to be restored.
Among the $\bar K$-nuclear bound states, the $\bar K NN$ system with $I
= 1/2$ and $J^{P} = 0^-$ (symbolically denoted as $K^-pp$'') is of
special interest because it is the lightest $S = -1$ $\bar K$ nucleus.
Many theoretical works agree on the existence of the bound state,
however, the binding energies and the decay widths are scattered.
Experimentally, there are several reports on observation of a$K^-pp$'' candidate with the binding energy of around 100 MeV.
On the other hand, several groups concluded that the reactions
can be understood without the inclusion of a bound state.
To clarify whether or not the $K^-pp$'' bound state exists, we
performed an exclusive measurement of the $^3$He$(K^-, \Lambda p)n$
reaction at 1.0 GeV/$c$ at J-PARC (J-PARC E15 xperiment).
In the experiment, we observed a distinct peak in the $\Lambda p$
invariant-mass spectrum well below the mass threshold of $K^- + p + p$,
of which the simplest and natural interpretation is a kaonic-nuclear
bound-state$K^-pp$''.
The obtained binding energy and the width are $47 \pm 3 ({\rm stat.})
^{+3}_{-6}({\rm syst.})$ MeV/$c^2$ and $115 \pm 7 ({\rm stat.})
^{+10}_{-20}({\rm syst.}) $MeV/$c^2$, respectively.
This result is experimentally solid as against the previously reported
results.
In addition, we observed $\Lambda(1405)pn$ final state in $K^-$ $+$
$^3$He reactions by reconstructing $\pi^{\mp}\Sigma^{\pm}pn$ events,
which is of special importance to understand the production mechanism of
the ``$K^-pp$'' state such as theoretically predicted $\Lambda(1405) N
\to \bar KNN$ doorway process.
We will discuss the possible existence of the $K^-pp$'' state from
both aspects of production and decay:$K^-pp$'' and $\Lambda(1405)p$
production, and $\Lambda p$ non-mesonic and $(\pi \Sigma)^{0} p$ mesonic
decay, respectively.
| Early Consideration | No |
|---|---|
| Graduate Student | No |
