arXiv subjects

A. Hosaka

Publications and source records attributed to A. Hosaka.

At least 19 recordsLinked to original sources

arXiv2026

Nature of the newly found $\Omega(2109)$

We present model calculations to reveal the nature of the newly found $\Omega^-(2109)$ by the BESIII Collaboration, and show that the state has a strong correlation with the $\bar K^*(892)\Xi$ system. Our study is based on solving scattering equations in a coupled channel approach, which involves $K^-\Xi^0$, $\bar K^0\Xi^-$, $K^{*-}\Xi^0$, and $\bar K^{*0}\Xi^-$. 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 $\Omega^-(2109)$. 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 $\Omega^-(2109)$.

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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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arXiv2022

Exotic properties of N^*(1895) and its impact on photoproduction of light hyperons

In this work, we outline the findings of our recent study of the properties of $N^*(1895)$ and its consequential impacts on the cross sections of the photoproduction of $Λ(1405)$. Further, we discuss the possibility of the existence of an isovector state, with the mass similar to $Λ(1405)$, which we refer to as $Σ(1400)$. With the idea of motivating experimental investigations of $Σ(1400)$, we have studied its photoproduction process and determined the respective cross sections and polarization observables. We have studied also the coupling of $N^*(1895)$ to $KΣ(1400)$ and found that it gives an important contribution to the cross sections near the threshold. In the process, we have determined the branching ratios of the decay of $N^*(1895)$, to the final states involving $Λ(1405)$ and $Σ(1400)$, to be in the range of 6-7 MeV. Our findings can motivate consideration of alternative processes in partial wave analyses of experimental data, when studying the properties of $N^*(1895)$.

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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.

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arXiv2021

$P_c(4312)^+$ and $P_c(4337)^+$ as interfering $Σ_c\bar{D}$ and $Λ_c\bar{D}^{*}$ threshold cusps

The recent LHCb data on $B_s^0\to J/ψp\bar{p}$ revealed a new pentaquark-like $P_c(4337)^+$ structure, while finding no evidence for $P_c(4312)^+$ discovered earlier in $Λ_b^0\to J/ψp K^-$. Though puzzling, the data actually offer an important hint to understand the nature of the pentaquark candidates. We develop a model to analyze the $B_s^0\to J/ψp\bar{p}$ data. We find that a $Σ_c\bar{D}$ one-loop mechanism causes a threshold cusp that fits well the $P_c(4337)^+$ peak. Also, the $Σ_c\bar{D}$ and $Λ_c\bar{D}^{*}$ threshold cusps interfere with each other to reproduce an oscillating behavior in the proton helicity angle distribution. These results combined with our earlier analysis on $Λ_b^0\to J/ψp K^-$ indicate that $P_c(4312)^+$ and $P_c(4337)^+$ are created by different interference patterns between the $Σ_c\bar{D}$ and $Λ_c\bar{D}^{*}$ (anomalous) threshold cusps. The proposed scenario consistently explains why the $P_c(4312)^+$ and $P_c(4337)^+$ peaks appear in $Λ_b^0\to J/ψp K^-$ and $B_s^0\to J/ψp\bar{p}$, respectively, but not vice versa or both.

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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.

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arXiv2020

Stable double-heavy tetraquarks: spectrum and structure

Bound states of double-heavy tetraquarks are studied in a constituent quark model. Two bound states are found for isospin and spin-parity I(J^P ) = 0(1^+) in the bb\bar{u}\bar{d} channel. One is deeply bound and compact made of colored diquarks, while the other is shallow and extended as a BB^* molecule. The former agrees well with lattice QCD results. A systematic decrease in the binding energy is seen by replacing one of the heavy quarks to a lighter one. Altogether we find ten bound states. It is shown for the first time that hadrons with totally different natures emerge from a single Hamiltonian.

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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.

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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 $Λ_c^{*}(2765)$.

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arXiv2019

$ωN$ scattering length from $ω$ photoproduction on the proton near the threshold

Photoproduction of the $ω$ meson on the proton has been experimentally studied near the threshold. The total cross sections are determined at incident energies ranging from 1.09 to 1.15 GeV. The 1/2 and 3/2 spin-averaged scattering length $a_{ωp}$ and effective range $r_{ωp}$ between the $ω$ meson and proton are estimated from the shape of the total cross section as a function of the incident photon energy: $a_{ωp} = \left(-0.97^{+0.16_{\rm stat}}_{-0.16_{\rm stat}}{}^{+0.03_{\rm syst}}_{-0.00_{\rm syst}}\right)+i \left(0.07^{+0.15_{\rm stat}}_{-0.14_{\rm stat}}{}^{+0.17_{\rm syst}}_{-0.09_{\rm syst}}\right)$ fm and $r_{ωp}=\left(+2.78^{+0.68_{\rm stat}}_{-0.54_{\rm stat}}{}^{+0.11_{\rm syst}}_{-0.13_{\rm syst}}\right)+i\left(-0.01^{+0.46_{\rm stat}}_{-0.50_{\rm stat}}{}^{+0.07_{\rm syst}}_{-0.00_{\rm syst}}\right)$ fm, resulting in a repulsive force. The real and imaginary parts for $a_{ωp}$ and $r_{ωp}$ are determined separately for the first time. A small $P$-wave contribution does not affect the obtained values.

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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 $Λ_c^*$.

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arXiv2018

Axial anomaly and hadronic properties in a nuclear medium

We investigate meson and nucleon dynamics at finite baryon density and temperature by coupling the nucleon field and the omega meson to the three-flavor linear sigma model and calculate hadronic properties around the nuclear liquid-gas transition. We apply the functional renormalization group method, and find that mesonic fluctuations increase the strength of the coefficient of the $U_A(1)$ breaking determinant operator as a function of the chiral condensate. As a consequence, we find that the actual value of the anomaly increases discontinuously at the first order nuclear liquid-gas transition. We calculate how mesonic masses and partial restoration of chiral symmetry are modified due to such an effect.

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arXiv2018

Differential cross section and photon-beam asymmetry for the gamma p -> pi- Delta++(1232) reaction at forward pi- angles for Egamma=1.5-2.95 GeV

Differential cross sections and photon-beam asymmetries for the gamma p -> pi- Delta++(1232) reaction have been measured for 0.7<cos(theta)<1 and Egamma=1.5-2.95 GeV at SPring-8/LEPS. The first-ever high statistics cross section data are obtained in this kinematical region, and the asymmetry data for 1.5<Egamma(GeV)<2.8 are obtained for the first time. This reaction has a unique feature for studying the production mechanisms of a pure $u\bar{u}$ quark pair in the final state from the proton. Although there is no distinct peak structure in the cross sections, a non-negligible excess over the theoretical predictions is observed at Egamma=1.5-1.8 GeV. The asymmetries are found to be negative in most of the present kinematical regions, suggesting the dominance of pi-exchange in the t-channel. The negative asymmetries at forward meson production angles are different from the asymmetries previously measured for the photoproduction reactions which produce a $d\bar{d}$ or an $s\bar{s}$ quark pair in the final state. Advanced theoretical models introducing nucleon resonances and additional unnatural parity exchanges are needed to reproduce the present data.

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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.

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arXiv2018

Differential cross section and photon beam asymmetry for the gamma p -> pi+ n reaction at forward pi+ angles at Egamma=1.5-2.95 GeV

Differential cross sections and photon beam asymmetries for the gamma p -> pi+ n reaction have been measured for 0.6<cos(theta)<1 and Egamma=1.5-2.95 GeV at SPring-8/LEPS. The cross sections monotonically decrease as the photon beam energy increases for 0.6<cos(theta)<0.9. However, the energy dependence of the cross sections for 0.9<cos(theta)<1 and Egamma=1.5-2.2 GeV (W=1.9-2.2 GeV) is different, which may be due to a nucleon or Delta resonance. The present cross sections agree well with the previous cross sections measured by other groups and show forward peaking, suggesting significant t-channel contributions in this kinematical region. The asymmetries are found to be positive, which can be explained by rho-exchange in the t-channel. Large positive asymmetries in the small |t| region, where the rho-exchange contribution becomes small, could be explained by introducing pi-exchange interference with the s-channel.

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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

Mesonic and nucleon fluctuation effects at finite baryon density

Mesonic and nucleon fluctuation effects are investigated in medium. We couple the nucleon field to the $2+1$ flavor meson model and investigate the finite temperature and density behavior of the system, in particular, the axial anomaly function. Somewhat contrary to earlier expectations we find that it tends to strengthen at finite density. At lower temperatures nucleon density fluctuations can cause a relative difference in the $U_A(1)$ axial anomaly of about $20\%$. This has important consequences on the mesonic spectra, especially on the $η-η'$ system, as we observe no drop in the $η'$ mass as a function of the baryochemical potential, irrespective of the temperature. Based on the details of chiral symmetry restoration, it is argued that there has to be a competition between underlying QCD effects of the anomaly and fluctuations of the low energy hadronic degrees of freedom, and the fate of the $U_A(1)$ coefficient should be decided by taking into account both effects simultaneously.

hep-ph↗

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.

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