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Register a new userA search for deeply bound kaonic nuclear states
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We have measured proton and neutron energy spectra by stopping negative kaons on liquid helium4. Two distinct peak structures were found on both spectra, which were assigned to the formation of new kinds of strange stribaryons. In this paper, we summarize both results.
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We review recent claims of the existence of deeply bound kaonic states in nuclei. Also we study in details the (K-,p) reaction on C12 with 1 GeV/c momentum kaon beam, based on which a deep kaon nucleus optical potential was claimed in [1]. In our Monte Carlo simulation of this reaction we include not only the quasi-elastic K- p scattering, as in [1], but also K- absorption by one and two nucleons followed by the decay of the hyperon in pi N, which can also produce strength in the region of interest. The final state interactions in terms of multiple scattering of the K-, p and all other primary particles on their way out of the nucleus is also considered. We will show that all these additional mechanisms allow us to explain the observed spectrum with a standard shallow kaon nucleus optical potential obtained in chiral models. [1] T. Kishimoto et al., Prog. Theor. Phys. 118, 181 (2007).
The search of nuclear bound states of anti-K in few-body nuclear systems such as K-pp, can be extended from the nuclear medium to the vacuum, using the glue-rich Y(1S) decays at B-factories. Here the possibility for such a measurement at the future SuperB factory is discussed.
Very recently, we have performed a couple of experiments, {it{KEK PS-E549/E570}}, for the detailed study of the strange tribaryon $S^0(3115)$ obtained in {it{KEK PS-E471}}. These experiments were performed to accumulate much higher statistics with improved experimental apparatusespecially for the better proton spectroscopy of the $^4$He({it{stopped K}}$^-$, {it{N}}) reaction. In contrast to the previous proton spectrum, no narrow ($sim$ 20 MeV) peak structure was found either in the inclusive $^4$He({it{stopped K}}$^-$, {it{p}}) or in the semi-inclusive $^4$He({it{stopped K}}$^-$, {it{p}}$X^pm$) reaction channel, which is equivalent to the previous $E471$ event trigger condition. Detailed analysis of the present data and simulation shows that the peak, corresponding to $S^0(3115)$, has been an experimental artifact. Present analysis does not exclude the possible existence of a much wider structure. To be sensitive to such structure and for better understanding of the non-mesonic $K^-$ absorption reaction channel, detailed analysis of the data is in progress.
Recent experiments studying the meson-nucleus interaction to extract meson-nucleus potentials are reviewed. The real part of the potentials quantifies whether the interaction is attractive or repulsive while the imaginary part describes the meson absorption in nuclei. The review is focused on mesons which are sufficiently long-lived to potentially form meson-nucleus quasi-bound states. The presentation is confined to meson production off nuclei in photon-, pion-, proton-, and light-ion induced reactions and heavy-ion collisions at energies near the production threshold. Tools to extract the potential parameters are presented. In most cases, the real part of the potential is determined by comparing measured meson momentum distributions or excitation functions with collision model or transport model calculations. The imaginary part is extracted from transparency ratio measurements. Results on $K^+, K^0, K^-, eta, eta^prime, omega$, and $phi$ mesons are presented and compared with theoretical predictions. The interaction of $K^+$ and $K^0$ mesons with nuclei is found to be weakly repulsive, while the $K^-, eta,eta^prime, omega$ and $phi$ meson-nucleus potentials are attractive, however, with widely different strengths. Because of meson absorption in the nuclear medium the imaginary parts of the meson-nucleus potentials are all negative, again with a large spread. An outlook on planned experiments in the charm sector is given. In view of the determined potential parameters, the criteria and chances for experimentally observing meson-nucleus quasi-bound states are discussed. The most promising candidates appear to be the $eta$ and $eta^prime$ mesons.
The mass of the {eta} meson is theoretically expected to be reduced at finite density, which indicates the existence of {eta}-nucleus bound states. To investigate these states, we perform missing-mass spectroscopy for the (p, d) reaction near the {eta} production threshold. The overview of the experimental situation is given and the current status is discussed.
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