Abstract
To search for an S= -1 di-baryonic state which decays to $\Lambda p$, the $ {\rm{}^3He}(K^-,\Lambda p)n_{missing}$ reaction was studied at 1.0 GeV/$c$. Unobserved neutrons were kinematically identified from the missing mass $M_X$ of the $ {\rm{}^3He}(K^-,\Lambda p)X$ reaction in order to have a large acceptance for the $\Lambda pn$ final state. The observed $\Lambda p n$ events, distributed widely over the kinematically allowed region of the Dalitz plot, establish that the major component comes from a three nucleon absorption process. A concentration of events at a specific neutron kinetic energy was observed in a region of low momentum transfer to the $\Lambda p$. To account for the observed peak structure, the simplest S-wave pole was assumed to exist in the reaction channel, having Breit-Wigner form in energy and with a Gaussian form-factor. A minimum $\chi^2$ method was applied to deduce its mass $M_X\ =$ 2355 $ ^{+ 6}_{ - 8}$ (stat.) $ \pm 12$ (syst.) MeV/c$^2$, and decay-width $\Gamma_X\ = $ 110 $ ^{+ 19}_{ - 17}$ (stat.) $ \pm 27$ (syst.) MeV/c$^2$, respectively. The form factor parameter $Q_X \sim$ 400 MeV/$c$ implies that the range of interaction is about 0.5
Highlights
The K N interaction is known to be strongly attractive from low-energy scattering data [1] and X-ray spectroscopy of kaonic atoms [2]
We present a study of the K − + 3He reaction at pK − = 1 GeV/c focusing on the p invariant mass spectrum, in particular on the pn final state for the May 2013 data
Where Minv. p is the invariant mass of p, q p is the momentum transfer of the reaction (q p = |p + pp|), MX is the energy, X is the decay width, and Q X is the form factor parameter of the pole
Summary
The K N interaction is known to be strongly attractive from low-energy scattering data [1] and X-ray spectroscopy of kaonic atoms [2]. Observation of a kaonic nuclear bound state would provide definitive information on the K N interaction in the sub-threshold region, as well as the nature of (1405). Both theoretical and experimental advances have been made in the last decade. All calculations predict the existence of a bound state. There are many reports on observed peak structure ∼100 MeV below the K N N production threshold. The FINUDA group reported a peak structure in the back-to-back p invariant mass spectra via the stopped kaon reaction on 6Li, 7Li, and 12C targets [14] with binding energy (B.E.) 115+−65 MeV and width (
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