arXiv subjects

S. Hirenzaki

Publications and source records attributed to S. Hirenzaki.

At least 55 records · Page 3Linked to original sources

arXiv2008

Photo- and Electron-Production of Mesons on Nucleons and Nuclei

In these lectures I will show some results obtained with the chiral unitary approach applied to the photo and electroproduction of mesons. The results for photoproduction of $ηπ^0 p$ and $K^0 π^0 Σ^+$, together with related reactions will be shown, having with common denominator the excitation of the $Δ(1700)$ resonance which is one of those dynamically generated in the chiral unitary approach. Then I will show results obtained for the $e^+ e^- \to ϕf_0(980)$ reaction which reproduce the bulk of the data except for a pronounced peak, giving support to a new mesonic resonance, X(2175). Results will also be shown for the electromagnetic form factors of the $N^*(1535)$ resonance, also dynamically generated in this approach. Finally, I will show some results on the photoproduction of the $ω$ in nuclei, showing that present experimental results claiming a shift of the $ω$ mass in the medium are tied to a particular choice of background and are not conclusive. One the other hand, the same experimental results show unambiguously a huge increase of the $ω$ width in the nuclear medium.

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arXiv2008

Level crossing of particle-hole and mesonic modes in eta mesic nuclei

We study eta meson properties in the infinite nuclear matter and in atomic nuclei with an emphasis on effects of the eta coupling to N*(1535)--nucleon-hole modes. The N*(1535) resonance, which dominates the low-energy eta-nucleon scattering, can be seen as a chiral partner of the nucleon. The change of the chiral mass gap between the N* and the nucleon in a nuclear medium has an impact on the properties of the eta-nucleus system. If the N*-nucleon mass gap decreases with a density increase (chiral symmetry restoration) the calculations show the existence of the resonance state at the energy about 60 MeV and two bound eta-nucleus states with the binding energies about -80 MeV. These states can have strong effect on predicted cross sections of the ^12C (gamma,p) ^11B reaction with eta-meson production.

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arXiv2007

Photoproduction of $ω$ and $ω$ in the Nuclear Medium

We reanalyze data from ELSA on $ω$ production in nuclei, from where claims of a large shift of the mass were made earlier, which are tied to a certain election of the background in nuclei, very different in shape to the one on the proton. The reanalysis shows that the data demand a very large width of the $ω$ in the medium, with no need for a shift of the mass, for which the experiment is quite insensitive. We study possible $ω$ bound states in the nucleus and find that, even assuming a small width, they could not be observed with the present ELSA resolution. Finally we show that, due to the interplay of background and $ω$ signal, a two bump structure appears with the ELSA set up for the $(γ,p)$ reaction that should not be misidentified with a signal of a possible $ω$ bound state in the nucleus.

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arXiv2007

Neutrino-induced coherent pion production

We have investigated the neutrino induced coherent pion production reaction at the energies of interest for recent experiments like K2K and MiniBooNE. The model includes pion, nucleon and the Delta(1232) resonance. Medium effects in the production mechanism and the distortion of the pion wave function are taken into account. We find a strong reduction of the cross section due to these effects and also substantial modifications in the energy distributions of the final pion. The sensitivity of the results on the axial N-Delta coupling C5A(0) and the coherent fraction in neutral-current pi0 production are discussed.

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arXiv2007

Coherent pion production in neutrino-nucleus collisions

We have investigated the neutrino induced coherent pion production reaction at low and intermediate energies including pion, nucleon and Delta(1232) resonance. Medium effects in the production mechanism and the distortion of the pion wave function are included in the calculation. We find a strong reduction of the cross section due to these effects and also substantial modifications in the energy distributions of the final pion. The dependence on the atomic number is discussed.

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arXiv2007

Formation of Deeply Bound Kaonic Atoms in (K^-,N) Reactions

We study theoretically the (K^-,N) reactions for the formation of the deeply bound kaonic atoms, which were predicted to be quasi--stable with narrow widths, using the Green function method. We consider various cases with different target nuclei and energies systematically and find the clear signals in the theoretical spectra for all cases considered in this article. The signals show very interesting structures, such as the $RESONANCE DIP$ instead of the resonance peak. We discuss the origins of the interesting structures and possibilities to get new information on the existence of the kaonic nuclei from the spectra of the atomic state formations.

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arXiv2007

Charged current neutrino induced coherent pion production

We analyze the neutrino induced charged current coherent pion production at the energies of interest for recent experiments like K2K and MiniBooNE. Medium effects in the production mechanism and the distortion of the pion wave function, obtained solving the Klein Gordon equation with a microscopic optical potential, are included in the calculation. We find a strong reduction of the cross section due to these effects and also substantial modifications of the energy distributions of the final lepton and pion.

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arXiv2006

Study of possible ωbound states in nuclei with the (γ,p) reaction

We perform calculations for ωproduction in nuclei by means of the (γ,p) reaction for photon energies and proton angles suited to running and future experiments in present Laboratories. For some cases of possible ωoptical potentials we find clear peaks which could be observable provided a good resolution in the ωenergy is available. We also study the inclusive production of π^0 γin nuclei around the ωenergy and find a double hump structure for the energy spectra, with a peak around a π^0 γenergy of m_ω-100 MeV, which could easily be misidentified by a signal of a bound ωstate in nuclei, while it is due to a different scaling of the uncorrelated π^0 γproduction and ωproduction with subsequent π^0 γdecay.

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arXiv2006

In--Flight ($K^-,p$) Reactions for the Formation of Kaonic Atoms and Kaonic Nuclei in Green function method

We study theoretically the kaonic atom and kaonic nucleus formations in the in--flight ($K^-,p$) reactions using the Green function method, which is suited to evaluate formation rates both of stable and unstable bound systems. We consider $^{12}$C and $^{16}$O as the targets and calculate the spectra of the ($K^-,p$) reactions. We conclude that a no peak structure due to kaonic nucleus formation is expected in the reaction spectra calculated with the chiral unitary kaon--nucleus optical potential. In the spectra with the phenomenological deep kaon--nucleus potential, we may have possibilities to observe some structures due to kaonic nucleus states. For all cases, we have peaks due to the kaonic atom formations in the reaction spectra.

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arXiv2005

Formation of mesic nuclei by (γ,p) reactions

We present a theoretical study on formation rates of ηand ωmeson-nucleus systems induced by (γ,p) reactions on nuclear targets at ideal recoilless condition. We find that the smaller distortion effect in the (γ,p) reaction enables us to investigate properties of the mesons created deeply inside nucleus more clearly. We also consider excitation of scalar-isoscalar (σ) mode in nucleus in order to investigate spectral enhancement around two-pion threshold caused by partial restoration of chiral symmetry. We conclude that valuable information of meson-nucleus interactions can be extracted from global structure of the missing mass spectra in the (γ,p) reaction.

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arXiv2005

Residual interaction effects on deeply bound pionic states in Sn and Pb isotopes

We have studied the residual interaction effects theoretically on the deeply bound pionic states in Pb and Sn isotopes. We need to evaluate the residual interaction effects carefully in order to deduce the nuclear medium effects for pion properties, which are believed to provide valuable information on nuclear chiral dynamics. The s- and p-wave $π-N$ interactions are used for the pion-nucleon residual interactions. We show that the complex energy shifts are around [(10-20)+i(2-7)]keV for 1s states in Sn, which should be taken into account in the analyses of the high precision data of deeply bound pionic $1s$ states in Sn isotopes.

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arXiv2005

Production of $Θ^+$ Hypernuclei with the $(K^+,π^+)$ reaction

We present results on the production of bound states of $Θ^+$ in nuclei using the $(K^+,π^+)$ reaction. By taking into account the states obtained within a wide range of strength of the $Θ^+$ nucleus optical potential, plus the possibility to replace different nucleons of the nucleus, we obtain an excitation spectra with clearly differentiated peaks. The magnitude of the calculated cross sections is well within reachable range.

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arXiv2004

Precision spectroscopy of pionic 1s states of Sn nuclei and evidence for partial restoration of chiral symmetry in the nuclear medium

Deeply bound 1s states of $π^-$ in $^{115,119,123}$Sn were preferentially observed using the Sn($d$,$^3$He) pion-transfer reaction under the recoil-free condition. The 1s binding energies and widths were precisely determined, and were used to deduce the isovector parameter of the s-wave pion-nucleus potential to be $b_1 =-0.115\pm 0.007 ~m_π^{-1}$. The observed enhancement of $|b_1|$ over the free $πN$ value ($b_1^{\rm free}/b_1 = 0.78 \pm 0.05$) indicates a reduction of the chiral order parameter, $f^{*}_π (ρ)^2/f_π^2 \approx 0.64$, at the normal nuclear density, $ρ= ρ_0$.

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arXiv2003

eta-Nucleus interactions and in-medium properties of N*(1535) in chiral models

The properties of eta-nucleus interaction and their experimental consequences are investigated with eta-nucleus optical potentials obtained by postulating the N*(1535) dominance for eta-N system. The N*(1535) properties in nuclear medium are evaluated by two kinds of chiral effective models based on distinct pictures of N*(1535). We find that these two models provide qualitatively different optical potentials of the eta meson, reflecting the in-medium properties of N*(1535) in these models. In order to compare these models in physical observables, we calculate spectra of (d,3He) reactions for the eta mesic nucleus formation with various kinds of target nuclei. We show that the (d,3He) spectra obtained in these models are significantly different and are expected to be distinguishable in experiments.

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arXiv2003

Pionic Atom Formation in Halo Nuclei by (d,3He) Reactions

We investigate the formation cross sections of the deeply bound pionic atoms on halo nuclei theoretically. We consider one-neutron pick-up (d,3He) reaction for the pionic atom formation and find that the formation rate is significantly increased by the existence of the halo neutron with long tail of the wave function. This enhancement is expected to increase the experimental feasibility for the formation of the deeply bound pionic states on beta-unstable nuclei.

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arXiv2002

Medium effects to the N(1535) resonance and eta mesic nuclei

The structure of eta-nucleus bound systems (eta mesic nuclei) is investigated as one of the tools to study in-medium properties of the N(1535) (N*) resonance. We show that, as a general consequence, the eta-nucleus potential has a repulsive core at the nuclear center with an attractive part at the nuclear surface, if sufficient reduction of the mass difference of N and N* stems from the in-medium effects to N*. The (d,3He) spectra are evaluated for the formation of these bound states to investigate the experimental feasibility.

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arXiv2002

Medium effects to N(1535) resonance and eta mesic nuclei

The structure of eta-nucleus bound systems (eta mesic nuclei) is investigated as one of the tools to study in-medium properties of the N(1535) (N^*) resonance by using the chiral doublet model to incorporate the medium effects of the N^* resonance in a chiral symmetric way. We find that the shape and the depth of the eta-nucleus optical potential are strongly affected by the in-medium properties of the N^* and the nucleon. Especially, as a general feature of the potential, the existence of a repulsive core of the eta-nucleus potential at the nuclear center with an attractive part at the nuclear surface is concluded. We calculate the level structure of bound states in this 'central-repulsive and surface-attractive' optical potential and find that the level structure is sensitive to the in-medium properties of the N^*. The (d,3He) spectra are also evaluated for the formation of these bound states to investigate the experimental feasibility. We also make comments on the possible existence of halo-like eta states in beta-unstable halo nuclei.

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arXiv2002

Formation of sigma Mesic Nuclei in (d,t) and (d,^3He) Reactions

We explore the possibility to observe an enhanced 2pi correlation in the scalar iso-scalar (sigma) channel in nuclei by (d,t) and (d,^3He) reactions to obtain new information on the partial restoration of chiral symmetry in the nuclear medium. The sensitivity of the reaction spectra on the change of the chiral condensate in the nuclear medium is examined.

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