We have searched for a deeply bound kaonic state by using the FINUDA spectrometer installed at the e(+)e(-) collider DAPhiNE. Almost monochromatic K(-)'s produced through the decay of phi(1020) ...mesons are used to observe K(-) absorption reactions stopped on very thin nuclear targets. Taking this unique advantage, we have succeeded to detect a kaon-bound state K(-)pp through its two-body decay into a Lambda hyperon and a proton. The binding energy and the decay width are determined from the invariant-mass distribution as 115(+6)(-5)(stat)(+3)(-4)(syst) MeV and 67(+14)(-11)(stat)(+2)(-3)(syst) MeV, respectively.
We observed a distinct peak in the Λp invariant mass spectrum of He3(K−,Λp)n, well below mK+2mp, i.e., the mass threshold of the K− to be bound to two protons. By selecting a relatively large ...momentum-transfer region q=350∼650 MeV/c, one can kinematically separate the peak from the quasi-free process, K‾N→K‾N followed by the non-resonant absorption by the two spectator-nucleons K‾NN→ΛN. We found that the simplest fit to the observed peak gives us a Breit–Wigner pole position at BKpp=47±3(stat.)−6+3(sys.) MeV having a width ΓKpp=115±7(stat.)−20+10(sys.) MeV, and the S-wave Gaussian reaction form-factor parameter QKpp=381±14(stat.)−0+57(sys.) MeV/c, as a new form of the nuclear bound system with strangeness – “K−pp”.
K
¯
-nuclear bound systems, kaonic nuclei, have been widely discussed as products of the strongly attractive
K
¯
N
interaction in
I
=
0
channels. Recently, we demonstrated that kaonic nuclei can be ...produced via in-flight
(
K
-
,
N
)
reactions using the low-momentum DC kaon beam at the J-PARC E15 experiment. We observed the simplest kaonic nuclei,
K
-
p
p
, having a much deeper binding energy than normal nuclei. For further studies, we have proposed a series of experimental programs for the systematic investigation of light kaonic nuclei, from
K
¯
N
(
Λ
(
1405
)
) to
K
¯
N
N
N
N
. In the new experiment approved as J-PARC E80, we will measure the
K
¯
N
N
N
(
A
=
3
) system as a first step toward a comprehensive study.
An experiment to search for the
$K^{-}pp$
bound state was performed via the in-flight
^3{\rm He}(K^{-},n)$
reaction using
$5.3 \times 10^9$
kaons at 1 GeV/
$c$
at the J-PARC hadron experimental ...facility. In the semi-inclusive neutron missing-mass spectrum at
$\theta _{n}^{lab}=0^\circ$
, no significant peak was observed in the region corresponding to
$K^{-}pp$
binding energy larger than 80 MeV, where a bump structure has been reported in the
$\Lambda p$
final state in different reactions. Assuming the state to be isotropically decaying into
$\Lambda p$
, mass-dependent upper limits on the production cross section were determined to be 30–180, 70–250, and 100–270
$\mu$
b/sr, for the natural widths of 20, 60, and 100 MeV, respectively, at 95% confidence level.
The decay of Λ-hypernuclei without π emission, known as Non-Mesonic Weak Decay (NMWD), gives an effective tool to investigate ΔS=1 four-baryon interactions. It was theoretically suggested that the ...two-nucleon induced mechanism could play a substantial role in reproducing the observed NMWD decay rates and nucleon spectra, but at present no direct evidence of such a mechanism has been obtained. The FINUDA experiment, exploiting the possibility to detect both charged and neutral particles coming from the hypernucleus decay, has allowed us to deduce the relative weight of the two nucleon induced decay rate to the total NMWD rate. The value of Γ2N/ΓNMWD=0.21±0.07stat−0.02sys+0.03sys has been deduced, well consistent with the previous determinations.
The J-PARC E15 experiment will be performed to search for the simplest kaonic nuclear bound state, K¯NN, by the in-flight He3(K−,N) reaction. The exclusive measurement will be performed by a ...simultaneous measurement of the missing mass using the forward neutron or proton, and the invariant mass via the expected decay, e.g. K−pp→Λp→pπ−p. In this report, an overview of the experiment and an analysis of engineering runs performed in February and June are presented.
This Letter is concerned with the study of the Kstop−A→π±Σ∓A′ reaction in p-shell nuclei, i.e., 6,7Li, 9Be, 13C and 16O. The π±Σ∓/Kstop− emission rates are reported as a function of A. These rates ...are discussed in comparison with previous findings. The ratio π−Σ+/π+Σ− in p-shell nuclei is found to depart largely from that on hydrogen, which provides support for large in-medium effects possibly generated by the sub-threshold Λ(1405). The continuum momentum spectra of prompt pions and free sigmas are also discussed as well as the π±Σ∓ missing mass behavior and the link with the reaction mechanism. The apparatus used for the investigation is the FINUDA spectrometer operating at the DAΦNEϕ-factory (LNF-INFN, Italy).
We are planning to perform an experiment at J-PARC and produce new neutron-rich Λ hypernuclei by using the (
π
−
,
K
+
) reaction (J-PARC E10). As the first step, we are planning to produce
...hypernuclei with a
6
Li target. To conduct this experiment, we are developing new detectors, those are scintillating fiber tracker, and silicon strip detector, for high rate operation to aim at increasing beam intensity up to 10
7
/spill. As a result of beam test in Jun 2012, we are going to use high-rate beam at least 10
7
/spill.
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