0000000001018734
AUTHOR
Hiroshi Toki
Chiral unitary model for the kaonic atom
We study kaonic atoms over the periodic table using a kaon self-energy in the nuclear medium derived from the SU(3) chiral unitary model. This model is quite successful in reproducing the scattering amplitude of meson meson and the strangeness $S=\ensuremath{-}1$ meson baryon reactions. In particular the properties of the $\ensuremath{\Lambda}(1405)$ resonance are well reproduced. In the nuclear medium the properties of this resonance are appreciably modified, and consequently the kaon nucleon scattering amplitudes, leading to an attractive kaon nucleus self-energy for densities higher than ${\ensuremath{\rho}}_{0}/25.$ With this interaction we are able to reproduce shifts and widths of kao…
Sigma Exchange in the NN interaction within the chiral unitary approach
We study the nucleon-nucleon interaction in the isoscalar-scalar channel using t he chiral unitary approach. The $t$-matrix of the pion-pion scattering in this c hannel is summed up to all orders using the B-S equation. We find that the calcu lated results at long distances are close to those of the $\sigma$-exchange inte raction. In addition, there appears a shorter range repulsion in this channel.
Recent progress on the chiral unitary approach to meson meson and meson baryon interactions
We report on recent progress on the chiral unitary approach, analogous to the effective range expansion in Quantum Mechanics, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented. Results for the extension of these ideas to the meson baryon sector are discussed, together with applications to kaons in a nuclear medium and $K^-$ atoms.
Mass dependence of inclusive nuclear $\phi$ photoproduction
Based on a prior determination of the $\phi$ selfenergy in a nuclear medium we perform a theoretical study of inclusive $\phi$ photoproduction in nuclei, looking at the $A$ dependence of the cross sections for different $\phi$ momenta. We find sizeable reductions in the nuclear cross sections with respect to the elementary one, using a $\phi$ selfenergy which implies a width about six times the free one at normal nuclear density. The calculations are done to match the set up for an ongoing experiment at {\it SPring8/Osaka} which should provide valuable information on the renormalization of the $\phi$ properties in nuclei.
Chiral unitary theory: Application to nuclear problems
In this talk we briefly describe some basic elements of chiral perturbation theory, $\chi PT$, and how the implementation of unitarity and other novel elements lead to a better expansion of the $T$ matrix for meson meson and meson baryon interactions. Applications are then done to the $ \pi \pi $ interaction in nuclear matter in the scalar and vector channels, antikaons in nuclei and $K^-$ atoms, and how the $\phi$ meson properties are changed in a nuclear medium.
Radiative decay of rho(0) and phi mesons in a chiral unitary approach
We study the rho^0 and phi decays into pi^+ pi^- gamma, pi^0 pi^0 gamma and phi into pi^0 eta gamma using a chiral unitary approach to deal with the final state interaction of the M M system. The final state interaction modifies only moderately the large momenta tail of the photon spectrum of the rho^0 --> pi^+ pi^- gamma decay. In the case of phi decay the contribution to pi^+ pi^- gamma and pi^0 pi^0 gamma decay proceeds via kaonic loops and gives a distribution of pi pi invariant masses in which the f_0(980) resonance shows up with a very distinct peak. The spectrum found for phi --> pi^0 pi^0 gamma decay agrees with the recent experimental results obtained at Novosibirsk. The bran…
Relativistic density-dependent Hartree approach for finite nuclei.
We develop a relativistic density-dependent Hartree approach for finite nuclei, where the coupling constants of the relativistic Hartree Lagrangian are made density dependent and are obtained from the relativistic Brueckner-Hartree-Fock results of nuclear matter. The calculated results on binding energies and root mean square radii of {sup 16}O and {sup 40}Ca agree very well with experiment. The charge densities from electron scattering are also calculated and their dependence on the nucleon-nucleon interaction is discussed in relation with nuclear matter properties.
A critical analysis on deeply bound kaonic states in nuclei
We make a critical analysis on the theoretical calculations that lead to predictions of deeply bound kaonic states in nuclei. The model set-up, after dropping several important processes and channels, leads unavoidably to an unrealistic deep potential with a very small imaginary part. We review also the experimental results taken as reference for the claim of deeply bound kaons. We suggest that the peaks of the proton spectra come from $K^-$ absorption on a pair of nucleons, leaving the rest of the nucleons as spectators. Based on this conjecture we predict what would happen in other nuclei.
Critical view on the deeply boundK−ppsystem
We briefly review the situation around the claimed deeply bound ${K}^{\ensuremath{-}}$ states in different recent experiments and concentrate particularly on the state ${K}^{\ensuremath{-}}\mathit{pp}$ advocated by the FINUDA collaboration in nuclear ${K}^{\ensuremath{-}}$ absorption. We perform a theoretical simulation of the process and show that the peak in the $\ensuremath{\Lambda}p$ spectrum that was interpreted as a deep ${K}^{\ensuremath{-}}\mathit{pp}$ bound state corresponds mostly to the process ${K}^{\ensuremath{-}}pp\ensuremath{\rightarrow}\ensuremath{\Lambda}p$ followed by final-state interactions of the produced particles with the daughter nucleus.
Pion double charge exchange reactions leading to deeply bound double pionic atoms
We study theoretically pion double charge exchange reactions leading to double pionic atoms. The reaction cross-sections with two pions in the deeper bound pionic orbits in 208Pb are calculated with realistic pionic atom wave functions and distortion effects. The cross-sections are found to be d2σ/dEdΩ~10−3−10−4 µb/srMeV, which are only a small fraction of the double charge exchange background.
Quark mean field model for nucleons in nuclei
We propose the quark mean field model for nucleons in nuclei, where the meson mean fields created by other nucleons act on quarks in a nucleon and change the nucleon properties in nuclei. We take the constituent quark model for the nucleon, which naturally allows the direct coupling of pions and in turn other mesons as $\ensuremath{\sigma}$ and $\ensuremath{\omega}$ mesons. We find very good nuclear matter properties with the use of the nonlinear self-energy terms in the meson Lagrangian. We expect the spin-orbit splitting in finite nuclei to be large due to the large reduction of the nucleon mass, which is in agreement with experiment. The nucleon size increases by about 7% at the normal m…
Photoproduction of the Lambda(1405) on the proton and nuclei
We study the gamma p ---> K^+ Lambda(1405) reaction at energies close to threshold using a chiral unitary model where the resonance is generated dynamically from K^-p interaction with other channels constructed from the octets of baryons and mesons. Predictions are made for cross sections into several channels and it is shown that the detection of the K^+ is sufficient to determine the shape and strength of the Lambda(1405) resonance. The determination of the resonance properties in nuclei requires instead the detection of the resonance decay channels. Pauli blocking effects on the resonance, which have been shown to be very important for the resonance at rest in the nucleus, are irrelev…
PION DOUBLE CHARGE EXCHANGE REACTIONS LEADING TO DOUBLE PIONIC ATOMS
We study theoretically pion double charge exchange reactions leading to double pionic atoms. The reaction cross-sections with two pions in the deeper bound pionic orbits in 208Pb are calculated with realistic pionic atom wave functions and distortion effects. The cross-sections are found to be d2σ/dEdΩ~10−3−10−4 µ b/srMeV , which are only a small fraction of the double charge exchange background.
Chiral SU(3) Bethe Salpeter Model: Extension to SU(6) and SU(8) Spin-Flavor Symmetries
Consistent SU(6) and SU(8) spin-flavor extensions of the SU(3) flavor Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian are constructed, which incorporate vector meson degrees of freedom. In the charmless sector, the on-shell approximation to the Bethe-Salpeter (BS) approach successfully reproduces previous SU(3) WT results for the lowest-lying s--wave negative parity baryon resonances. It also provides some information on the dynamics of heavier ones and of the lightest d-wave negative parity resonances, as e.g. the Lambda(1520). For charmed baryons the scheme is consistent with heavy quark symmetry, and our preliminary results in the strangeness-less charm C=+1 sector describe the mai…
Test of phi renormalization in nuclei through phi photoproduction
We propose an experimental procedure to find out the medium modifications of the $\phi$ meson. The reaction is inclusive $\phi$ photoproduction in nuclei, looking for $K^+ K^-$ pairs from the $\phi$ decay with total momentum smaller than 100-150 $MeV/c$, which are made possible at energies of present laboratories from center of mass $\phi$ backward production and the help of Fermi motion. We have conducted a many body calculation of the mass distribution of the $\phi$ adapted to the experimental set up of a recent JLAB experiment where the backwards $\phi$ photoproduction has been measured. Using recent results for the in medium properties of the $\phi$, we find that the width of the invari…
Radiative production of the Λ(1405) resonance in K− collisions on protons and nuclei
We have carried a theoretical study of the K^- p\to M B \gamma reaction with M B = K^-p, \bar{K}^0 n, \pi^- \Sigma^+, \pi^+ \Sigma^-, \pi^0 \Sigma^0, \pi^0 \Lambda, for K^- lab. momenta between 200 and 500 MeV/c, using a chiral unitary approach for the strong K^-p interaction with its coupled channels. The \Lambda(1405) resonance, which is generated dynamically in this approach, shows up clearly in the d\sigma/dM_I spectrum, providing new tests for chiral symmetry and the unitary approach, as well as information regarding the nature of the resonance. The photon detection alone, summing all channels, is shown to reproduce quite accurately the strength and shape of the \Lambda(1405) resonance…
Photoproduction of meson and baryon resonances in a chiral unitary approach
By means of a coupled channel non-perturbative unitary approach, it is possible to extend the strong constrains of Chiral Perturbation Theory to higher energies. In particular, it is possible to reproduce the lowest lying resonances in meson-meson scattering up to 1.2 GeV using the parameters of the O(p^2) and O(p^4) Chiral Lagrangian. The meson baryon sector can also be tackled along similar lines. We report on an update of these results showing some examples of photon induced reactions where the techniques have been recently applied.
SU(3) Chiral approach to meson and baryon dynamics
We report on recent progress on the chiral unitary approach, which is shown to have a much larger convergence radius than ordinary chiral perturbation theory, allowing one to reproduce data for meson meson interaction up to 1.2 GeV and meson baryon interaction up to the first baryonic resonances. Applications to physical processes so far unsuited for a standard chiral perturbative approach are presented, concretely the K^- p\to\Lambda(1405)\gamma reaction and the N^\ast (1535)N^\ast(1535)\pi and \eta couplings.
Double-delta production in the gamma-d-]pn-pi(+)pi(-) reaction
We have studied the gamma d ---> Delta++ Delta- reaction which requires the collaboration of the two nucleons in deuteron. By means of a model previously developed for the gamma p ----> p pi+ pi- reaction, the two body exchange currents leading to double delta creation are derived. A fair agreement is obtained with a recent experiment, but more precise measurements and the extension to higher photon energies look advisable in order to see the limits of the present theoretical approach
Photon induced Lambda (1520) production and the role of the K* exchange
We study the photon induced Lambda(1520) production in the effective Lagrangian method near threshold, E_��^{LAB}<2 GeV, and in the quark-gluon string model at higher energies 3 GeV < E_��^{LAB} < 5 GeV. In particular, we study the role of the K^* exchange for the production of Lambda(1520) within the SU(6) Weinberg-Tomozowa chiral unitary model proposed in Phys. Rev. D74 (2006) 034025. The coupling of the Lambda(1520) resonance to the N \bar K^* pair, which is dynamically generated, turns out to be relatively small and, thus, the K exchange mechanism dominates the reaction. In the higher energy region, where experimental data are available, the quark-gluon string mechanism with th…
Recent developments in chiral dynamics of hadrons and hadrons in a nuclear medium
In this talk I present recent developments in chiral dynamics of hadrons and hadrons in a medium addressing the following points: interaction of the octet of pseudoscalar mesons with the octet of baryons of the nucleon, showing recent experimental evidence on the existence of two $\Lambda(1405)$ states, the interaction of the octet of pseudoscalar mesons with the decuplet of baryons of the $\Delta$, with particular emphasis on the $\Lambda(1520)$ resonance, dynamically generated by this interaction. Then I review the interaction of kaons in a nuclear medium and briefly discuss the situation around the claims of deeply bound states in nuclei. The large renormalization of the $\Lambda(1520)$ …
Further considerations concerning claims for deeply bound kaon atoms
We briefly review the experiments of KEK and FINUDA, that claim evidence for deeply bound kaon states, from the perspective of recent theoretical papers and experiments that provide an alternative explanation of the peaks seen. At the same time we rebate recent criticisms raised against our theoretical results.
Experimental program of the Super-FRS Collaboration at FAIR and developments of related instrumentation
The physics program at the super-conducting fragment separator (Super-FRS) at FAIR, being operated in a multiple-stage, high-resolution spectrometer mode, is discussed. The Super-FRS will produce, separate and transport radioactive beams at high energies up to 1.5 AGeV, and it can be also used as a stand-alone experimental device together with ancillary detectors. Various combinations of the magnetic sections of the Super-FRS can be operated in dispersive, achromatic or dispersion-matched spectrometer ion-optical modes, which allow measurements of momentum distributions of secondary-reaction products with high resolution and precision. A number of unique experiments in atomic, nuclear and h…
A theoretical view on bound antikaon-nuclear states
We present an overview of the latest theoretical studies on the antikaon properties in the nuclear medium, in connection with the recent experimental claims of very deeply bound antikaon-nuclear states. We argue that proper many-body formulations using modern realistic antikaon-nucleon interactions are not able to generate such systems. Instead, a simple two-nucleon antikaon absorption mechanism where the remaining nucleus acts as spectator explains the peak in the semi-inclusive proton momentum spectrum, observed on a 4He target at KEK (but later not confirmed in an inclusive experiment) and on a 6Li target at FINUDA. This signal is clearly seen in another FINUDA experiment measuring the i…
Critical view on the deeply bound K- pp system
We briefly review the situation around the claimed deeply bound K^- states in different recent experiments and concentrate particularly on the state K^- pp advocated by the FINUDA collaboration in nuclear K^- absorption. We perform a theoretical simulation of the process and show that the peak in the Lambda p spectrum that was interpreted as a deep K^- pp bound state corresponds mostly to the process K^- p p --> Lambda p followed by final state interactions of the produced particles with the daughter nucleus.
Photoproduction of scalar mesons on protons and nuclei
We study the photoproduction of scalar mesons close to the threshold of f_0(980) and a_0(980) using a unitary chiral model. Peaks for both resonances show up in the invariant mass distributions of pairs of pseudoscalar mesons. A discussion is made on the photoproduction of these resonances in nuclei, which can shed light on their nature, a subject of continuous debate.
The antikaon–nucleus interaction and alternative views to deeply bound antikaonic nuclear systems
Abstract We present an overview of the latest theoretical studies on the antikaon properties in the nuclear medium, in connection with the recent experimental claims of very deeply bound antikaon nuclear states. We argue that proper many-body formulations using modern realistic antikaon–nucleon interactions are not able to generate such systems. Instead, a simple two-nucleon antikaon absorption mechanism where the remaining nucleus acts as spectator explains the enhancement observed in semi-inclusive proton momentum spectra, seen as a bump in the KEK PS-E549 experiment on a 4 He target or as a peak in the FINUDA experiment on a 6 Li target. This signal is clearly visible in another FINUDA e…