arXiv subjects

H. Nagahiro

Publications and source records attributed to H. Nagahiro.

At least 19 recordsLinked to original sources

arXiv2026

Nature of the newly found $Ω(2109)$

We present model calculations to reveal the nature of the newly found $Ω^-(2109)$ by the BESIII Collaboration, and show that the state has a strong correlation with the $\bar K^*(892)Ξ$ system. Our study is based on solving scattering equations in a coupled channel approach, which involves $K^-Ξ^0$, $\bar K^0Ξ^-$, $K^{*-}Ξ^0$, and $\bar K^{*0}Ξ^-$. We obtain the lowest order amplitudes for different spin and isospin cases and find that an isoscalar state with spin-parity $1/2^-$ is generated with precisely the same mass as $Ω^-(2109)$. We do not find any state with total spin 3/2, nor do we find any state in the isovector sector. We determine correlation functions to encourage such an experimental study and confirm the nature of $Ω^-(2109)$.

hep-ph↗

arXiv2024

Intriguing aspects of light baryon resonances

We discuss that some light baryon resonances exhibit properties which cannot be described when attributing a three-valence quark structure to them. Besides pointing out the hadron resonances which clearly require description beyond the quark model, we focus on the third $s_{11},~ N^*$ state and its decay to final states consisting of the lightest hyperon resonances which have a partial width comparable to that for the decay to $πN$. Such properties of the mentioned nucleon resonance get manifested in the cross sections and other observables related to processes producing the lightest hyperon resonances. We show that all these findings arise from the strong association of the baryon resonances to the dynamics among the ground-state hadrons.

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arXiv2023

Excitation spectra of heavy baryons in a quark-diquark model with relativistic corrections

The excitation spectra of Λ_c and Λ_b baryons are investigated by using a quark-diquark model in which a single-heavy baryon is treated as the bound state of a heavy quark and a scalar diquark. We take two types of relativistic corrections into account for the quark-diquark potential. In the first type, we consider the one-gluon exchange between the heavy quark and one of the light quarks in the diquark. In the second, we consider the one-gluon exchange between a scalar particle and a heavy quark. We find that there is a large difference between two types of corrections due to different treatment of the internal color structure of the diquark. The relativistic corrections are important for the solution to the string tension puzzle, particularly, the Darwin term makes a large contribution.

hep-ph↗

arXiv2022

The decay of $N^*$(1895) to light hyperon resonances

In this talk I review the findings of our recent works where we have studied the decay of $N^*(1895)$ and the implications of such properties on the photoproduction of light hyperons. I discuss that meson-baryon interactions play an essential role in describing the nature of $N^*(1895)$ and report the details of our investigation of its decays to different meson-baryon systems and to final states involving $Λ(1405)$ and a proposed $Σ(1400)$. We find that the width of $N^*(1895)$ gets important contributions from the decay to light hyperon resonances. Such an information can be used to look for alternative processes to study $N^*(1895)$ in experimental data.

hep-ph↗

arXiv2020

Decay properties of $N^*(1895)$

The nature of nucleon resonances is still being debated, while much experimental data are accumulated. In this work, we focus on the negative parity resonance $N^*(1895)$ which is located in the scattering region of various meson-baryon coupled channels, and such dynamics can be crucial in understanding its properties. To test the relevance of such hadron dynamics, we investigate the decay properties of $N^*(1895)$ in detail. We examine how a two pole nature of $N^*(1895)$ is compatible with its observed decay properties. Moreover, we find that the resonance decays into final states involving $Λ(1405)$ and $Σ(1400)$, where the latter is not yet observed experimentally. Such decay processes can be useful to study the properties of the aforementioned hyperon resonances.

hep-ph↗

arXiv2020

Search for $η'$ bound nuclei in the $^{12}{\rm C}(γ,p)$ reaction with simultaneous detection of decay products

We measured missing mass spectrum of the $^{12}{\rm C}(γ,p)$ reaction for the first time in coincidence with potential decay products from $η'$ bound nuclei. We tagged an ($η+p$) pair associated with the $η'N\toηN$ process in a nucleus. After applying kinematical selections to reduce backgrounds, no signal events were observed in the bound-state region. An upper limit of the signal cross section in the opening angle $\cosθ^{ηp}_{lab}<-0.9$ was obtained to be 2.2 nb/sr at the 90$\%$ confidence level. It is compared with theoretical cross sections, whose normalization ambiguity is suppressed by measuring a quasifree $η'$ production rate. Our results indicate a small branching fraction of the $η'N\toηN$ process and/or a shallow $η'$-nucleus potential.

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arXiv2020

Roper-like resonances with various flavor contents and their two-pion emission decays

We study the three-body decay of the newly observed bottom baryon $Λ_b^*(6072)$ by LHCb; $Λ_b^*(6072) \to Λ_b ππ$. Its mass about 500 MeV above the ground state $Λ_b$ and a broad width imply that the state could be an analogue of the Roper resonance of the nucleon $N(1440)$. In terms of sequential processes going through $Σ_b$ and $Σ_b^*$, we find that the observed invariant mass distribution is reproduced assuming its spin and parity $J^P = 1/2^+$. We discuss that the ratio of the two sequential processes and angular correlation of two pions are useful for the determination of spin and parity. We suggest further studies for the Roper resonance analogue in various flavor contents, raising an interesting and important question in baryon spectroscopy.

hep-ph↗

arXiv2020

Three-body decay of $Λ_c^{*} (2765)$ and determination of its spin-parity

We study three-body decays of $Λ_c^{*}(2765) \to Λ_c^+π^+π^-$ by using effective Lagrangians in a non-relativistic framework. We consider the sequential decays through $Σ_c(2455)π$ and $Σ_c^*(2520)π$ in intermediate states which are dominant contributions. The coupling constants in the effective Lagrangians are computed in the quark model. We demonstrate that the ratio $R= Γ(Λ_c^*\toΣ_c^*(2520)π)/Γ(Λ_c^*\to Σ_c(2455)π)$ and angular correlations are sensitive to the spin and parity of $Λ_c^{*}(2765)$. Thus, the measurement of these observables in experimental facilities such as Belle and LHCb can provide useful constraints to determine the spin and parity of $Λ_c^{*}(2765)$.

hep-ph↗

arXiv2018

Three-Body Decay of $Λ_c^{}(2595)$ and $Λ_c^{}(2625)$ with the Inclusion of Direct Two-Pion Coupling

We investigate the three-body decays of $Λ_c^*(2595)$ and $Λ_c^*(2625)$ into $Λ_c ππ$ by including a direct process going through the two-pion coupling of $Λ_c^*Λ_c ππ$ in addition to the sequential processes going through $Σ_c(2455)$ and $Σ_c^*(2520)$. The strength of the direct coupling is related to that of the Yukawa coupling by the chiral partner structure between $Λ_c$'s and $Σ_c$'s, while the strength of the Yukawa coupling is estimated by the quark model. It is found that the direct process gives a considerable contribution especially in the decay of $Λ_c^*(2625)$. A clear indication of the direct process is seen in an asymmetric pattern in the angular correlation between the two pions. We discuss the usefulness of the detailed analysis of the decays for the study of the structure of $Λ_c^*$.

hep-ph↗

arXiv2018

Spectroscopy of pionic atoms in $\mathbf{{}^{122}{\textbf Sn}({\textit d},{}^3{\textbf He})}$ reaction and angular dependence of the formation cross sections

We observed the atomic $1s$ and $2p$ states of $π^-$ bound to ${}^{121}{\rm Sn}$ nuclei as distinct peak structures in the missing mass spectra of the ${}^{122}{\rm Sn}(d,{}^3{\rm He})$ nuclear reaction. A very intense deuteron beam and a spectrometer with a large angular acceptance let us achieve potential of discovery, which includes capability of determining the angle-dependent cross sections with high statistics. The $2p$ state in a Sn nucleus was observed for the first time. The binding energies and widths of the pionic states are determined and found to be consistent with previous experimental results of other Sn isotopes. The spectrum is measured at finite reaction angles for the first time. The formation cross sections at the reaction angles between 0 and $2^\circ$ are determined. The observed reaction-angle dependence of each state is reproduced by theoretical calculations. However, the quantitative comparison with our high-precision data reveals a significant discrepancy between the measured and calculated formation cross sections of the pionic $1s$ state.

nucl-ex↗

arXiv2018

Constraining the optical potential in the search for eta-mesic 4He

A consistent description of the $ d d \rightarrow$ $^{4}\hspace{-0.03cm}\mbox{He} η$ and $ d d \rightarrow$ ($^4$He$η$)$_{bound} \rightarrow X $ cross sections was recently proposed with a broad range of real ($V_{0}$) and imaginary (W0), $η$-$^4$He optical potential parameters leading to a good agreement with the d d -> 4He eta data. Here we compare the predictions of the model below the $η$ production threshold, with the WASA-at-COSY excitation functions for the dd -> 3He N pi reactions to put stronger constraints on (V0, W0). The allowed parameter space (with |V_0| < \sim 60 MeV and |W_0| < \sim 7 MeV estimated at 90% CL ) excludes most optical model predictions of eta-4He nuclei except for some loosely bound narrow states.

nucl-ex↗

arXiv2018

Why $Ξ(1690)$ and $Ξ(2120)$ are so narrow?

The $Ξ$ baryons are expected to be naturally narrower as compared to their nonstrange and strange counterparts since they have only one light quark and, thus, their decay involves producing either a light meson and doubly strange baryon or both meson and baryon with strangeness which involves, relatively, more energy. In fact, some $Ξ$'s have full widths of the order of even 10-20 MeV when, in principle, they have a large phase space to decay to some open channels. Such is the case of $Ξ(1690)$, for which the width has been found to be of the order of 10 MeV in the latest {\it BABAR} and BELLE data. In this manuscript we study why some $Ξ$'s are so narrow. Based on a coupled channel calculation of the pseudoscalar meson-baryon and vector meson-baryon systems with chiral and hidden local symmetry Lagrangians, we find that the answer lies in the intricate hadron dynamics. We find that the known mass, width, spin-parity and branching ratios of $Ξ(1690)$ can be naturally explained in terms of coupled channel meson-baryon dynamics. We find another narrow resonance which can be related to $Ξ(2120)$. We also look for exotic states $Ξ^{+}$ and $Ξ^{--}$ but find none. In addition we provide the cross sections for $ \bar K Λ, \bar K Σ\rightarrow πΞ$ which can be useful for understanding the enhanced yield of $Ξ$ reported in recent studies of heavy ion collisions.

nucl-th↗

arXiv2018

Missing-mass spectroscopy of the ${}^{12}{\rm C}(p,d)$ reaction near the $η^\prime$-meson production threshold

Excitation-energy spectra of $^{11}$C nuclei near the $η^\prime$-meson production threshold have been measured by missing-mass spectroscopy using the $^{12}$C($p$,$d$) reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce $η^\prime$ meson bound states in $^{11}$C nuclei. Deuterons emitted at $0^\circ$ in the reaction have been momentum-analyzed by the fragment separator (FRS) used as a high-resolution spectrometer. No distinct structure due to the formation of $η^\prime$-mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of $η^\prime$-mesic states are determined, and thereby a constraint imposed on the $η^\prime$-nucleus interaction is discussed.

nucl-ex↗

arXiv2017

Understanding the properties of $Ξ(1690)$ and $Ξ(2120)$

In this manuscript we discuss the results of our recent study on $Ξ$ resonances. We have studied meson-baryon interaction with strangeness $-2$ by solving scattering equations in a coupled channel approach and found that the dynamics gives rise to the development of two poles in the complex plane close to the real axis. The corresponding narrow states have isospin half and spin half in one case and spin 3/2 in the other case. We find that the properties of the isospin and spin 1/2 state are strikingly similar to $Ξ(1690)$, while the state with spin 3/2 can be related to $Ξ(2120)$. We find that our results on $Ξ(1690)$ are in good agreement with the data available from the BELLE and BABAR Collaborations. Our formalism consists of treating pseudoscalar-baryon and vector-baryon channels on an equal footing. Since the thresholds of such channels are distributed over a relatively larger energy range, we obtain all interaction kernels needed to solve the Bethe-Salpeter equation without resorting to any nonrelativistic approximation even though the amplitudes are calculated at low energies.

hep-ph↗

arXiv2017

$η$-nucleus interaction from the $d+d$ reaction around the $η$ production threshold

The $η$ mesic nucleus is considered to be one of the interesting exotic many body systems and has been studied since 1980's theoretically and experimentally. Recently, the formation of the $η$ mesic nucleus in the fusion reactions of the light nuclei such as $d + d \rightarrow (η+ α) \rightarrow X$ has been proposed and the experiments have been performed by WASA-at-COSY. We develop a theoretical model to evaluate the formation rate of the $η$ mesic nucleus in the fusion reactions and show the calculated results. We find that the $η$ bound states could be observed in the reactions in cases with the strong attractive and small absorptive $η$-nucleus interactions. We compare our results with existing data of the $d + d \rightarrow η+ α$ and the $d + d \rightarrow {^3 \rm He} + N + π$ reactions. We find that the analyses by our theoretical model with the existing data can provide new information on the $η$-nucleus interaction.

nucl-th↗

arXiv2017

Three-Body Decay of $Λ_c^{} (2595)$ and $Λ_c^{} (2625)$ with Consideration of $Σ_c(2455)π$ and $Σ_c^*(2520)π$ in Intermediate States

Three-body decay of charmed baryons $Λ^*_c(2595)$ and $Λ^*_c(2625)$ into $Λ_c ππ$ are studied with effective Lagrangians in which the coupling constants are extracted from the non-relativistic quark model. We take into account sequential processes going through $Σ_c (2455)$ and $Σ^*_c (2520)$ in intermediate states. The total decay widths are sensitive to the coupling of $Λ^*_c$ with $Σ_c π$ open channel and to $Σ^*_c π$ closed channel. We find that $Λ_c^*(2595)$ and $Λ_c^*(2625)$ with $λ$ mode assignment can explain nicely the experimental data. We also show invariant mass distributions of $Λ_c^*(2595)$ and $Λ_c^*(2625)$ decays which are significantly different for various quark configurations.

hep-ph↗

arXiv2016

Measurement of excitation spectra in the ${}^{12}$C$(p,d)$ reaction near the $η'$ emission threshold

Excitation spectra of $^{11}$C were measured in the $^{12}$C$(p,d)$ reaction near the $η'$ emission threshold. A proton beam extracted from the synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinged on a carbon target. The momenta of deuterons emitted at 0 degrees were precisely measured with the fragment separator FRS operated as a spectrometer. In contrast to theoretical predictions on the possible existence of deeply bound $η'$ mesic states in carbon nuclei, no distinct structures were observed associated with the formation of bound states. The spectra were analyzed to set stringent constraints on the formation cross section and on the hitherto barely-known $η'$-nucleus interaction.

nucl-ex↗

arXiv2016

Formation of eta'(958) Meson Bound States by the 6Li(gamma,d) reaction

We have investigated the 6Li(gamma,d) reaction theoretically for the formation of the eta'(958) mesic nucleus close to the recoilless kinematics. We have developed the theoretical formula and reported the quantitative results of the formation spectra for various cases in this article. We have found that the formation cross sections are reduced by the effects of the fragile deuteron form factor.

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