arXiv subjects

Sachiko Takeuchi

Publications and source records attributed to Sachiko Takeuchi.

At least 19 recordsLinked to original sources

arXiv2025

Strange pentaquarks with a hidden heavy quark-antiquark pair

The strange pentaquarks with hidden heavy quark pair ($q^3c\bar c$ and $q^3b \bar b$) are investigated by the coupled-channel quark cluster model. Two types of the $q^3$ color-octet configurations are found to provide the attraction, which makes bound states, sharp resonances, and cusps in the baryon meson scattering. A resonance appears at around 4500 MeV in the strange hidden charm sector. Such structures are more clearly seen in the hidden bottom systems.

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arXiv2025

Di-$J/\psi$ structures from the quark Pauli-blocking effect

The double-charmonium scattering states such as $J/\psi J/\psi$, $\eta_cJ/\psi$, and $\eta_c\eta_c$ are investigated by a simplified quark cluster model. It is found that the quark Pauli-principle over the $c\bar c c\bar c$ system causes a rapid increase and a node in the two-meson phase shifts. The increase is not large enough to be regarded as a resonance, but if it is seen experimentally, that is most likely the quark Pauli-blocking effect.

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arXiv2024

X(3872) revisited: the roles of OPEP and the quark degrees of freedom

The $X(3872)$ is investigated by employing the quark-hadron hybrid model, that consists of the $c\bar c$ core, $D^{(*)}\bar D{}^*$, $J/\psi\omega$, and $J/\psi\rho$ two-meson states. Due to the attraction from the $c\bar c$-$D\bar D{}^*$ coupling and from the OPEP tensor coupling, a very thin peak can appear at the $D^{0}\bar D{}^{*0}$ threshold. The energy of the corresponding pole of the scattering matrix is $E=(+0.06-0.14i)$ MeV, which is on the physical sheet and above the threshold, the same as the one of the poles from the LHCb data analysis.

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arXiv2024

The impact of quark many-body effects on exotic hadrons

We investigate the exotic hadrons consisting of two light quarks and two heavy antiquarks, $(q\bar Q)$-$(q\bar Q)$. The spin-dependent term between quarks is known to give an attraction to the $ud$ spin-0 component in the isospin-0 $u\bar c d\bar c$ system, $T_{cc}$. However, the said component also gets a repulsion from the partial Pauli-blocking. By the dynamical calculation with a simplified quark model, we discuss that the competition of the two effects leads to a shallow bound state for $T_{cc}$, which is preferred from the experiment, and a deep bound state for $T_{bb}$.

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arXiv2022

Rich structure of the hidden-charm pentaquarks near threshold regions

The recent abundant observations of pentaquarks and tetraquarks by high-energy accelerator facilities indicate the realization of the conjecture by Gell-Mann and Zweig, and by De Rujula, Georgi and Glashow [1-3]. We construct a coupled-channel model for the hidden-charm pentaquarks with strangeness whose quark content is $udsc \bar c$, $P_{cs}$, described as $ Λ_c \bar{D}_s^{(*)}, Ξ_c^{('*)} \bar{D}^{(*)}$ molecules coupled to the five-quark states. These molecules are formed by the suitable cooperation of heavy quark and chiral symmetries. We reproduce the experimental mass and quantum numbers $J^P$ of $P_{cs}(4338)$ for which LHCb has just announced the discovery. We make other predictions for new $P_{cs}$ states as molecular states near threshold regions that can be studied by LHCb.

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arXiv2022

Substructure of Multiquark Hadrons (Snowmass 2021 White Paper)

In recent years there has been a rapidly growing body of experimental evidence for existence of exotic, multiquark hadrons, i.e. mesons which contain additional quarks, beyond the usual quark-antiquark pair and baryons which consist of more than three quarks. In all cases with robust evidence they contain at least one heavy quark Q=c or b, the majority including two heavy quarks. Two key theoretical questions have been triggered by these discoveries: (a) how are quarks organized inside these multiquark states -- as compact objects with all quarks within one confinement volume, interacting via color forces, perhaps with an important role played by diquarks, or as deuteron-like hadronic molecules, bound by light-meson exchange? (b) what other multiquark states should we expect? The two questions are tightly intertwined. Each of the interpretations provides a natural explanation of parts of the data, but neither explains all of the data. It is quite possible that both kinds of structures appear in Nature. It may also be the case that certain states are superpositions of the compact and molecular configurations. This Whitepaper brings together contributions from many leading practitioners in the field, representing a wide spectrum of theoretical interpretations. We discuss the importance of future experimental and phenomenological work, which will lead to better understandingof multiquark phenomena in QCD.

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arXiv2021

Extension of the J-PARC Hadron Experimental Facility: Third White Paper

The J-PARC Hadron Experimental Facility was constructed with an aim to explore the origin and evolution of matter in the universe through the experiments with intense particle beams. In the past decade, many results on particle and nuclear physics have been obtained at the present facility. To expand the physics programs to unexplored regions never achieved, the extension project of the Hadron Experimental Facility has been extensively discussed. This white paper presents the physics of the extension of the Hadron Experimental Facility for resolving the issues in the fields of the strangeness nuclear physics, hadron physics, and flavor physics.

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arXiv2020

Heavy hadronic molecules with pion exchange and quark core couplings: a guide for practitioners

We discuss selected and important features of hadronic molecules as one of promising forms of exotic hadrons near thresholds. Using examples of $D \bar D^*$ systems such as $X(3872)$ and $Z_c$, emphasis is put on the roles of the one pion exchange interaction between them and their coupling to intrinsic quark states. Thus hadronic molecules emerge as admixtures of the dominant long-range hadron structure and short-range quark structure. For the pion exchange interaction, properties of the tensor force are analyzed in detail. More coupled channels supply more attractions, and heavier constituents suppress kinetic energies, providing more chances to form hadronic molecules of heavy hadrons. Throughout this article, we show details of basic ideas and methods.

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arXiv2020

$P_c$ pentaquarks with chiral tensor and quark dynamics

We investigate the hidden-charm pentaquarks as superpositions of $Λ_c \bar{D}^{(*)}$ and $Σ_c^{(*)} \bar{D}^{(*)}$ (isospin $I = 1/2$) meson-baryon channels coupled to a $uudc\bar{c}$ compact core by employing an interaction satisfying the heavy quark and chiral symmetries. Our model can consistently explain the masses and decay widths of $P_c^+(4312)$, $P_c^+(4440)$ and $P_c^+(4457)$ with the dominant components of $Σ_c \bar D$ and $Σ_c \bar D^\ast$ with spin parity assignments $J^P = 1/2^{-}, 3/2^{-}$ and $1/2^{-}$, respectively. We analyze basic properties of the $P_c$'s such as masses and decay widths, and find that the mass ordering is dominantly determined by the quark dynamics while the decay widths by the tensor force of the one-pion exchange.

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arXiv2018

Hidden-charm and bottom meson-baryon molecules coupled with five-quark states

In this paper, we investigate the hidden-charm pentaquarks as $\bar{D}^{(\ast)}Λ_{\rm c}$ and $\bar{D}^{(\ast)}Σ^{(\ast)}_{\rm c}$ molecules coupled to the five-quark states. Furthermore, we extend our calculations to the hidden-bottom sector. The coupling to the five-quark states is treated as the short range potential, where the relative strength for the meson-baryon channels is determined by the structure of the five-quark states. We found that resonant and/or bound states appear in both the charm and bottom sectors. The five-quark state potential turned out to be attractive and, for this reason, it plays an important role to produce these states. In the charm sector, we need the five-quark potential in addition to the pion exchange potential in producing bound and resonant states, whereas, in the bottom sector, the pion exchange interaction is strong enough to produce states. Thus, from this investigation, it emerges that the hidden-bottom pentaquarks are more likely to form than their hidden-charm counterparts; for this reason, we suggest that the experimentalists should look for states in the bottom sector.

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arXiv2016

The hidden charm pentaquarks are the hidden color-octet $uud$ baryons?

The $I(J^P)={1\over 2}({1\over 2}^-)$, ${1\over 2}({3\over 2}^-)$, and ${1\over 2}({5\over 2}^-)$ $uudc\overline{c}$ pentaquarks are investigated by the quark cluster model. This model, which reproduces the mass spectra of the color-singlet $S$-wave $q^3$ baryons and $q\overline{q}$ mesons, also enables us to evaluate the quark interaction in the color-octet $uud$ configurations. It is shown that the color-octet isospin-${1\over 2}$ spin-${3\over 2}$ $uud$ configuration gains attraction. The $uudc\overline{c}$ states with this configuration have structures around the $Σ_c{}^{(*)}\overline{D}{}^{(*)}$ thresholds: one bound state, two resonances, and one large cusp are found. We argue that the negative parity pentaquark found by the LHCb experiments may be given by these structures.

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arXiv2016

The ccbar Pentaquarks by a Quark Model

Recent LHCb experiments have shown us that there are two resonances in the $J/ψp$ channel in the $Λ_b$ decay, whose spin and parity are most probably (3/2$^-$ 5/2$^+$). In this work, we investigate the $I(J^P)=1/2(1/2^-)$, $1/2(3/2^-)$, and $1/2(5/2^-)$ $uudc{\bar c}$ pentaquark states by employing the quark cluster model. It is found that the color-octet isospin-1/2 spin-3/2 $uud$ configuration gives an attraction to such five-quark systems. This configuration together with the color-octet $c{\bar c}$ pair gives structures around the $Σ_c^{(*)}{\bar D}{}^{(*)}$ thresholds: one bound state, two resonances, and one large cusp are found in the $uudc{\bar c}$ negative parity channels. We argue that these resonances and cusp may correspond to, or combine to form, the negative parity pentaquark peak observed by LHCb.

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arXiv2016

Radiative Decays of the $X(3872)$ in the Charmonium-Molecule Hybrid Picture

The X(3872) radiative decay is discussed by employing a two-meson multichannel model with the charmonium components, which explains many of the other observed features of X(3872). We have found that the ratio of the branching fractions of the X(3872) radiative decays, $R_γ=\text{Br}(X(3872)\rightarrowψ(2S)γ)$ / Br$(X(3872)\rightarrow J/ψγ)$, is 1.1 $\sim$ 3.4 if one assumes that the decay occurs only from the charmonium components. The invariant mass spectra of $cc^{bar}$($2P$)$\rightarrow J/ψγ$ and $cc^{bar}$($2P$)$\rightarrow ψ(2S) γ$ are also investigated. It is found that an enhancement appears at around $E\sim 3960$ MeV in the $ψ(2S) γ$ spectrum but not in the $J/ψγ$ spectrum. This corresponds to the missing $cc^{bar}$($2P$) pole which was predicted by the quark models but has not been observed due to the coupling to the $DD^{bar}$ states. We argue that the fluctuation seen in the experimental $ψ(2S) γ$ spectrum reported by LHCb may correspond to this $cc^{bar}$($2P$) pole.

hep-ph↗

arXiv2015

On the origin of the narrow peak and the isospin symmetry breaking of the $X$(3872)

The $X$(3872) formation and decay processes in the $B$-decay are investigated by a $c\bar c$-two-meson hybrid model. The two-meson state consists of the $D^0{\bar D}^*{}^0$, $D^+D^{*-}$, $J/ψρ$, and $J/ψω$ channels. The energy-dependent decay widths of the $ρ$ and $ω$ mesons are introduced. The $D$-${\bar D}^*$ interaction is taken to be consistent with a lack of the $B{\bar B}^*$ bound state. The coupling between the $D{\bar D}^*$ and $J/ψρ$ or the $D{\bar D}^*$ and $J/ψω$ channels is obtained from a quark model. The $c{\bar c}$-$D{\bar D}^*$ coupling is taken as a parameter to fit the $X$(3872) mass. The spectrum is calculated up to 4 GeV. It is found that very narrow $J/ψρ$ and $J/ψω$ peaks appear around the $D^0{\bar D}^*{}^0$ threshold. The size of the $J/ψπ^3$ peak we calculated is 1.29-2.38 times as large as that of the $J/ψπ^2$. The isospin symmetry breaking in the present model comes from the mass difference of the charged and neutral $D$ and $D^*$ mesons, which gives a sufficiently large isospin mixing to explain the experiments. It is also found that values of the ratios of the transfer strengths can give the information on the $X$(3872) mass or the size of the $c{\bar c}$-$D{\bar D}^*$ coupling.

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arXiv2013

X(3872) as a hybrid state of the charmonium and the hadronic molecule

In order to understand the structure of the X(3872), the $c \bar c$ charmonium core state coupling to the $D^0 \bar D^{\ast 0}$ and $D^+ D^{\ast -}$ molecular states are studied. The strengths of the couplings between the charmonium state and the hadronic molecular states are determined so as to reproduce the observed mass of the the X(3872). The isospin symmetry breaking is introduced by the mass differences of the neutral and charged $D$ mesons. The obtained structure of the X(3872) is that about 7% is $\ccbar$ charmonium, 75% is the isoscalar $D \bar D^\ast$ molecule and 18% is the isovector $D \bar D^\ast$ molecule, which explains observed properties of the X(3872) well. The structure of the X(3872) we have obtained is not just a $D^0 \bar D^{ast 0}$ hadronic molecule nor the compact tetraquark state but the charmonium-hadronic molecule hybrid state.

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arXiv2011

Charmonium and meson-molecule hybrid tetraquarks - Vector meson width and the isospin breaking in the X(3872) decay

In the X(3872) decay, both of the J/ψππ and J/ψπππ branching fractions are observed experimentally, and their sizes are comparable to each other. In order to clarify the mechanism to cause such a large isospin violation, we investigate X(3872) employing a model of coupled-channel two-meson scattering with a ccbar core. The two-meson states consist of D0Dbar*0, D+Dbar*-, J/ψρ, and J/ψω. The effects of the ρ and ω meson width are also taken into account. We calculate the transfer strength from the ccbar core to the final two-meson states. It is found that very narrow J/ψρ and J/ψω peaks appear very close to the D0Dbar*0 threshold for a wide range of variation in the parameter sets. The size of the J/ψρ peak is almost the same as that of J/ψω, which is consistent with the experiments. The large width of the ρ meson makes the originally small isospin violation by about five times larger.

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arXiv2008

Lambda(1405) in a baryon-meson scattering with a bound state embedded in the continuum

We investigate Lambda(1405) as a resonance in a coupled channel baryon-meson scattering with a `bound state embedded in the continuum'(BSEC). This BSEC is introduced by hand, as a state not originated from simple baryon-meson systems. We assume it comes from the three-quark state. There appears a resonance in the Sigma pi scattering below the N Kbar threshold when the N Kbar channel is taken to be strongly attractive. It occurs without introducing a BSEC, just like the chiral unitary approach. When a BSEC is introduced, a resonance also appears with a weaker baryon-meson interaction. The corresponding peak also has a large width, and the N Kbar scattering length is reproduced well. The interaction whose channel dependence is the same as the one originated from the color-magnetic interaction, where no N Kbar attraction exists, also gives a broad peak like Lambda(1405) with help of a BSEC. It is found that the BSEC coupling which does not vanish at the zero momentum transfer give a larger width. In order to reproduce the observed N Kbar scattering length, introducing a BSEC seems preferable. In our calculation, a model gives an appropriate value when the BSEC contribution to the resonance is roughly half of that of the N Kbar in size.

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arXiv2007

Lambda(1405) as a Resonance in the Baryon-Meson Scattering Coupled to the q^3 State in a Quark Model

In order to describe Lambda(1405) as a resonance in the baryon-meson scattering, we have investigated q^3-q qbar scattering system with the flavor-singlet q^3 (0s)^2(0p) state (the Lambda^1 pole). The scattering is treated by the quark cluster model (QCM). The Lambda^1 pole is treated as a bound state embedded in the continuum. We found that the peak appears below the N Kbar threshold in the spin one half, isospin 0 channel even if the mass of the Lambda^1 pole is above the threshold. This peak disappears when the coupling to the Lambda^1 pole is switched off. To use the observed hadron mass in the kinetic part of QCM is also found to be important to reproduce a peak just below the N Kbar threshold.

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