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S. Hirenzaki

Publications and source records attributed to S. Hirenzaki.

At least 73 records · Page 4Linked to original sources

Chiral loops and VMD in the V->PPgamma decays

We evaluate radiative decays of $ρ$ and $ω$ going to two neutral mesons, $π^{0} π^{0}$ and $π^{0} η$. We use the sequential vector decay mechanisms in addition to chiral loops and $ρ$-$ω$ mixing. The chiral loops are obtained using elements of $UχPT$ successfully applied in the study of meson-meson interactions up to 1.2 GeV. The chiral loops are found very important in the case of the $ρ\to π^{0} π^{0} γ$ decay and small in the other cases. A good agreement with present measurements of $ρ\to π^{0} π^{0} γ$ and $ω\to π^{0} π^{0}γ$ is obtained and predictions are made for the other decays where the rates obtained are rather small.

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Deeply bound pionic atoms from the $(γ,p)$ reaction in nuclei

We study the $(γ,p)$ reaction on $^{208}Pb$ leading to $^{207}Pb$ with a bound pion attached to it in the lowest 1s or 2p pionic levels. The reaction can be made recoilless to optimize the production cross section but we must choose a bit higher photon energy to overcome the Coulomb barrier in the proton emission. The cross sections obtained are easily measurable and can be larger than 50 per cent of the background from inclusive ($γ$,p). This makes it a clear case for the detection of the pionic atom signals, converting this reaction into a practical tool to produce deeply bound pionic atoms.

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Chiral unitary theory: application to nuclear problems

In this talk we briefly describe some basic elements of chiral perturbation theory, $χPT$, 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 $ ππ$ interaction in nuclear matter in the scalar and vector channels, antikaons in nuclei and $K^-$ atoms, and how the $ϕ$ meson properties are changed in a nuclear medium.

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Antikaons in nuclei and dense nuclear matter

We present recent progress on the properties of antikaons in nuclei and dense nuclear matter as obtained from two {\bar K}N interaction models: one based on the lowest-order meson-baryon chiral lagrangian and the other derived from a meson-exchange picture.

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Chiral Unitary Approach to the Kaon Nucleus Interaction and Kaonic Atoms

We review recent work on various topics related to the modification of kaon properties in nuclei. After a brief exposition of the kaon-nucleon and kaon-nucleus interaction, results from the application to kaonic atoms, renormalization of the f0 and a0 scalar resonances in nuclei and phi decay in the nucleus are shown.

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The phi --> pi^+ pi^- and phi radiative decays within a chiral unitary approach

We report on recent results on the decay of the phi into pi^+ pi^- and phi radiative decays into pi^0 pi^0 gamma and pi^0 eta gamma, which require the consideration of the final state interaction of a pair of mesons in a region inaccessible to Chiral Perturbation Theory. By using nonperturbative chiral unitary methods for the meson meson interaction we can obtain the corresponding decay widths and the results are compared with recent experimental data.

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Projectile $Δ$ and target-Roper excitation in the p (d, d')X reaction

In this paper we compare a model that contains the mechanisms of $Δ$ excitation in the projectile and Roper excitation in the target with experimental data from two (d, d') experiments on a proton target. The agreement of the theory with the experiment is fair for the data taken at T_d = 2.3 GeV. The $Δ$ excitation in the projectile is predicted close to the observed energy with the correct width. The theory, however, underpredicts by about 40% the cross sections measured at T_d = 1.6 GeV at angles where the cross section has fallen by about two orders of magnitude. The analysis done here allows to extract an approximate strength for the excitation of the Roper [N^*(1440)] excitation and a qualitative agreement with the theoretical predictions is also found.

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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 branching ratio for phi --> pi^0 eta gamma, dominated by the a_0(980), is also in agreement with recent Novosibirsk results.

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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.

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Photon Absorption on a Neutron-Proton Pair in 3He and 4He

We have developed a phenomenological quasi-deuteron model to describe photodisintegration reactions of $^3$He and $^4$He at intermediate photon energies, and compared the results with experimental data obtained by TAGX group in which contributions from photon absorption by $pn$ pair were selectively observed. The data can be reproduced reasonably well, however there still remain certain discrepancies between calculated results and data.

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Roper excitation in $\vec{p}+α\to \vec{p}+α+X$ reactions

We calculate differential cross sections and the spin transfer coefficient $D_{nn}$ in the $\vec{p}+α\to \vec{p}+α+π^0$ reaction for proton bombarding energies from 1 to 10 GeV and $π^0 - p$ invariant masses spanning the region of the N$^*$(1440) Roper resonance. Two processes -- $Δ$ excitation in the $α$-particle and Roper excitation in the proton -- are included in an effective reaction model which was shown previously to reproduce existing inclusive spectra. The present calculations demonstrate that these two contributions can be clearly distinguished via $D_{nn}$, even under kinematic conditions where cross sections alone exhibit no clear peak structure due to the excitation of the Roper.

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Proton Elastic Scattering and Neutron Distribution of Unstable Nuclei

We study theoretically how we can determine the neutron density distributions of unstable nuclei from proton elastic scattering. We apply the relativistic impulse model to study the sensitivities of the observables to the density distributionswhich are expressed in Woods-Saxon form. We find that the both radius and diffuseness of densities can be determined from restricted elastic scattering data in principle. We think this result is helpful to design future experiments.

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Formation of $η$-mesic Nuclei Using the Recoilless (d,$^3$He) Reaction

We propose to use the recoilless (d,$^3$He) reaction to produce $η$-mesic nuclei. This reaction has been used to observe deeply bound pionic states and proven to be powerful recently. We calculate $η$-mesic bound states in the nucleus using an optical potential and their formation cross section with the Green function method. Then, we carefully check the experimental feasibility. We find that $η$-mesic nuclei can be observed experimentally using the (d,$^3$He) reaction. We also mention the possibility to study the formation of $ω$-mesic nuclei.

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Neutron pick-up pion transfer reactions for the formation of deeply bound pionic atoms in $^{208}$Pb

We study $(n,d)$ and (d,$^3$He) reactions on $^{208}Pb$ leading to deeply bound pionic atoms with one neutron hole being left. We develop a theoretical model to calculate cross sections of deeply bound pionic atoms and quasi-elastic pion production. The results are compared with data which have been obtained so far. We show that the theoretical model describes the data of both reactions well.

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Nuclear Quadrupole Effects in Deeply Bound Pionic Atoms

We have studied nuclear quadrupole deformation effects in deeply bound pionic atoms theoretically. We have evaluated the level shifts and widths of the hyperfine components using the first order perturbation theory and compared them with the effects of neutron skin. We conclude that the nuclear quadrupole deformation effects for deeply bound $1s$ and $2p$ states are very difficult to observe and that the effects could be observed for $3d$ states. We also conclude that the deformation effects are sensitive to the parameters of the pion-nucleus optical potential.

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Formation of Deeply Bound 1s Pionic States in the $^{206}$Pb(d,$^3$He) Reaction

Recently, deeply bound pionic states were found experimentally in (d,$^3$He) reactions on $^{208}$Pb. The observed spectrum showed an excellent agreement with the DWIA calculation and the dominant peak was attributed to the pionic 2p state contribution. We studied theoretically $^{206}$Pb(d,$^3$He) reactions within the same model, and found that it is very likely to observe the pionic 1s state as an isolated peak in the $^{206}$Pb(d,$^3$He) reaction with feasible energy resolution and statistics.

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Theoretical Response to the Discovery of Deeply Bound Pionic States in 208Pb(d,3He) reactions

Recently, deeply bound pionic states were found experimentally in (d, $^3$He) reactions on $^{208}$Pb. They found an isolated peak structure in the bound region below the pion production threshold. We study theoretically these excitation functions in (d, $^3$He) reactions on $^{208}$Pb at T$_d$=600 MeV. We found very good agreement with the (d, $^3$He) excitation functions and could identify the underlying structures of the pionic states. We study the energy dependence of the (d, $^3$He) reactions and the change of the excitation functions with the incident energy.

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Isoscalar Roper Excitation in $p(α, α')$ Reactions in the $10 - 15$ $GeV$ Region

Recent experiments at Saturne at $4$ $GeV$ showed that the $(α,α')$ reaction on the proton shows two distinctive peaks, which were associated to $Δ$ projectile excitation and Roper target excitation. A subsequent theoretical analysis has shown that this picture is qualitatively correct but there are important interference effects between the two mechanisms. Futhermore, at this energy the ratio of strengths for the Roper and $Δ$ peak is about $1/4$. In the present paper we show that by going to the $10 - 15$ $GeV$ region the interference effects become negligible, the signal for the Roper excitation is increased by more than an order of magnitude and the ratio of cross sections at the peaks for Roper and $Δ$ excitation becomes of the order of unity, thus making this range of energies ideal for studies of isoscalar Roper excitation.

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