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Kazutaka Sudoh

Publications and source records attributed to Kazutaka Sudoh.

18 recordsLinked to original sources

Heavy Hadrons in Nuclear Matter

Current studies on heavy hadrons in nuclear medium are reviewed with a summary of the basic theoretical concepts of QCD, namely chiral symmetry, heavy quark spin symmetry, and the effective Lagrangian approach. The nuclear matter is an interesting place to study the properties of heavy hadrons from many different points of view. We emphasize the importance of the following topics: (i) charm/bottom hadron-nucleon interaction, (ii) structure of charm/bottom nuclei, and (iii) QCD vacuum properties and hadron modifications in nuclear medium. We pick up three different groups of heavy hadrons, quarkonia ($J/ψ$, $Υ$), heavy-light mesons ($D$/$\bar{D}$, $\bar{B}$/$B$) and heavy baryons ($Λ_{c}$, $Λ_{b}$). The modifications of those hadrons in nuclear matter provide us with important information to investigate the essential properties of heavy hadrons. We also give the discussions about the heavy hadrons, not only in nuclear matter with infinite volume, but also in atomic nuclei with finite baryon numbers, to serve future experiments.

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Kondo effect of $\bar{D}_{s}$ and $\bar{D}_{s}^{\ast}$ mesons in nuclear matter

We study the Kondo effect for $\bar{D}_{s}$ and $\bar{D}_{s}^{\ast}$ mesons as impurity particles in nuclear matter. The spin-exchange interaction between the $\bar{D}_{s}$ or $\bar{D}_{s}^{\ast}$ meson and the nucleon induces the enhancement of the effective coupling in the low-energy scattering in the infrared region, whose scale of singularity is given by the Kondo scale. We investigate the Kondo scale in the renormalization group equation at nucleon one-loop level. We furthermore study the ground state with the Kondo effect in the mean-field approach, and present that the Kondo scale is related to the mixing strength between the $\bar{D}_{s}$ or $\bar{D}_{s}^{\ast}$ meson and the nucleon in nuclear matter. We show the spectral function of the impurity when the Kondo effect occurs.

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Production of doubly charmed tetraquarks with exotic color configurations in electron-positron collisions

Structure and production of doubly charmed tetraquarks T_cc (cc ubar dbar) are studied from the viewpoint of color configurations. Based on the diquark correlation, the tetraquark T_cc with I(JP)=0(1+) is considered to be stable against strong decay. We discuss that the mixing probability of color antitriplet and sextet cc components in T_cc is suppressed by 1/m_c^2, so the two configurations are separately realized in the heavy quark limit. Utilizing the nonrelativistic QCD framework, we evaluate the production cross sections of T_cc in electron-positron collisions. The momentum dependence of the cross section of color antitriplet is found to be different from that of sextet, which can be used to discriminate the color structure of the T_cc states in experimental measurements.

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Exotic mesons with hidden bottom near thresholds

We study heavy hadron spectroscopy near open bottom thresholds. We employ B and B* mesons as effective degrees of freedom near the thresholds, and consider meson exchange potentials between them. All possible composite states which can be constructed from the B and B* mesons are studied up to the total angular momentum J = 0, 1, 2. We consider, as exotic states, isosinglet states with exotic (J,PC) quantum numbers and isotriplet states. We solve numerically the Schrodinger equation with channel-couplings for each state. The masses of twin resonances Zb(10608) and Zb(10653) recently found by Belle are reproduced. We predict several possible bound and/or resonant states in other channels for future experiments.

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Exotic mesons with double charm and bottom flavor

We study exotic mesons with double charm and bottom flavor, whose quark configuration is \bar{Q}\bar{Q}qq. This quark configuration has no annihilation process of quark and antiquark, and hence is a genuinely exotic states. We take a hadronic picture by considering the molecular states composed of a pair of heavy mesons, such as DD, DD* and D*D* for charm flavor, and BB, BB* and B*B* for bottom flavor. The interactions between heavy mesons are derived from the heavy quark effective theory. All molecular states are classified by I(J^P) quantum numbers, and are systematically studied up to the total angular momentum J \leq 2. By solving the coupled channel Schrodinger equations, due to the strong tensor force of one pion exchanging, we find bound and/or resonant states of various quantum numbers.

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Exotic nuclei with open heavy flavor mesons

We propose stable exotic nuclei bound with $\bar{D}$ and $B$ mesons with respecting heavy quark symmetry. We indicate that an approximate degeneracy of $\bar{D}$($B$) and $\bar{D}^{*}$($B^{*}$) mesons plays an important role, and discuss the stability of $\bar{D}N$ and $BN$ bound states. We find the binding energies 1.4 MeV and 9.4 MeV for each state in the $J^{P}=1/2^{-}$ with I=0 channel. We discuss also possible existence of exotic nuclei $\bar{D}NN$ and $BNN$.

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Is the Z^+(4430) a radially excited state of D_s?

We present the interpretation that the recently discovered Z^+(4430) by the Belle Collaboration can be a radial excitation of the cs-bar state. We give an explicit cs-bar candidate for this state by calculating the mass value in our semirelativistic quark potential model and also give a natural interpretation on the reason why the decay mode Z-> J/ψπ^+ has not yet been seen while Z-> ψ' πcan be seen.

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Study of Structure of the Mass Gap between Two Spin Multiplets

Studying our semirelativistic potential model and the numerical results, which succeeds in predicting and reproducing recently discovered higher resonances of $D$, $D_s$, $B$, and $B_s$, we find a simple expression for the mass gap between two spin multiplets of heavy-light mesons, $(0^-,1^-)$ and $(0^+,1^+)$. The mass gap between chiral partners defined by $ΔM=M(0^+)-M(0^-)$ and/or $M(1^+)-M(1^-)$ is given by $ΔM=M(0^+)-M(0^-)=M(1^+)-M(1^-)\approx Λ_{\rm Q}-m_q$ in the limit of heavy quark symmetry. We also study the case including $1/m_Q$ corrections.

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Structure of Mass Gap between Two Spin Multiplets

Studying our semirelativistic potential model and the numerical results, which succeeds in predicting and reproducing recently discovered higher resonances of $D$, $D_s$, $B$, and $B_s$, we find a simple expression for the mass gap between two spin multiplets of heavy-light mesons, $(0^-,1^-)$ and $(0^+,1^+)$. The mass gap between chiral partners defined by $ΔM=M(0^+)-M(0^-)$ and/or $M(1^+)-M(1^-)$ is given by $ΔM=M(0^+)-M(0^-)=M(1^+)-M(1^-)\approx Λ_{\rm Q}-m_q$ in the limit of heavy quark symmetry, and including $1/m_Q$ corrections, we have $ΔM\approx Λ_{\rm Q}-m_q+(1.28\times 10^{5}+4.26\times 10^{2}\cdot m_q)/m_Q$ with $Λ_{\rm Q}\approx 300$ MeV, a light quark mass $m_q$, and a heavy quark mass $m_Q$. This equation holds both for $D$ and $D_s$ heavy mesons. Our model calculations for the $B$ and $B_s$ also follow this formula.

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Radial Excitations of Heavy Mesons

Recent discovery of D_s states suggests existence of radial excitations. Our semirelativistic quark potential model succeeds in reproducing these staes within one to two percent of accuracy compared with the experiments, D_s0(2860) and D_s^*(2715), which are identified as 0^+ and 1^- radial excitations (n=2). We also present calculations of radial excitations for B/B_s heavy mesons. Relation between our formulation and the modified Goldberger-Treiman relation is also described.

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New Heavy-Light Mesons $Q\bar q$

We succeed in reproducing the $\ell=1$ $B$ mesons, $B_1(5720)$, $B_2^*(5745)$, and $B_{s2}^*(5839)$ that are recently reported by D0 and CDF, by using our semirelativistic quark potentila model, which also succeeded in predicting the mass spectra of the narrow $D_{sJ}$ as well as broad $D_0^*(0^+)$ and $D_1'(1^+)$ particles a couple of years ago. Mass of higher excited states ($\ell=1, 2$) of $B$ and $B_s$ mesons, which are not yet observed, is also predicted at the first order in $p/m_b$. We find the corresponding $B_{sJ}$ are below $BK/B^*K$ threshold and should have narrow decay widths contrary to most other predictions. Also already established states ($\ell=0$ and $\ell=1$) of $D$, $D_s$, $B$, and $B_s$ heavy mesons are simultaneously reproduced in good agreement with experimental data within one percent of accuracy. To calculate these $D/D_s$ and $B/B_s$ heavy mesons we use different values of strong coupling $α_s$ which conforms to a notion of running coupling.

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D Meson Production in Neutrino DIS and Polarized Strange Quark Distribution

Semi-inclusive $D / \Dbar$ meson productions in neutrino deep inelastic scattering are studied including ${\cal O}(α_s)$ corrections. Supposing a future neutrino factory, cross sections and spin asymmetries in polarized processes are calculated by using various parametrization models of polarized parton distribution functions. We suggest that $\Dbar$ production is promising to directly extract the strange quark distribution.

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Polarized Parton Distribution in Neutrino Induced Heavy Flavor Production

In order to examine polarized strange quark distribution, semi-inclusive $D/\Dbar$ production in neutrino deep inelastic scattering is studied including ${\cal O}(α_s)$ corrections. Cross section and spin asymmetry are calculated by using various parametrizations of polarized parton distribution functions. It is found that $\Dbar$ production is promising to directly extract the polarized strange sea.

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Lambda_c^+ production in polarized pp scattering and polarized gluon distribution

To extract information about the polarized gluon distribution, $\dg$, in the nucleons, we propose Lambda_c^+ productions in polarized pp scattering, p + \vec{p} \to \vec{Lambda_c^+} + X, which will be observed at RHIC experiment starting soon. For this process, we have calculated the spin correlation differential cross section, dΔσ/d\pt, and the spin correlation asymmetry defined by \A_ll \equiv [ d Δσ/ d \pt ] / [ d σ/ d\pt ]. We have found that the \A_ll is sensitive to the polarized gluon distribution in the nucleon and thus the process is promising for testing ΔG(x,Q^2).

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Charmed Hadron Production in Neutrino Reactions and Polarized s-quark Distribution

In order to obtain information about the polarized strange quark distribution, we studied the semi-inclusive $Λ_c / \barΛ_c$ production in neutrino and polarized proton collisions. We found that these reactions are effective to clearly extract the polarization of strange quark by measuring the spin correlation between the target proton and the produced $Λ_c / \barΛ_c$ baryon.

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Electroproduction of psi' and polarized gluon distribution in a proton

In order to get information about the polarized gluon distribution in a proton, we studied the electroproduction of ψ' in polarized electron and polarized proton collisions in the framework of the NRQCD factorization approach. The value of the cross section dΔσ/ dp_T^2 for color-octet mechanism is about 5 times larger than that for color-singlet one, and it might be another test of the color-octet model if the polarized gluon distribution Δg(x) is well known. Furthermore, we found that this reaction is quite effective for testing the model of gluon polarization by measuring the double spin asymmetry A_{LL} for the initial electron and proton. Though the shape of p_T^2 distribution of A_{LL} is quite similar for the production mechanism with color-octet and color-singlet, we can see a big difference in A_{LL} among various models of the polarized gluon distribution function Δg(x).

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Two-Spin Asymmetry for $ψ^{\prime}$ Photoproduction with Color-Octet Mechanism

We studied the photoproduction of $ψ^{\prime}$ in the forward regions in polarized $γp$ collisions at relevant HERA energies. We found that this reaction is very effective to test the color-octet mechanism which is based on the NRQCD factorization formalism. Furthermore we found that the value of the NRQCD matrix elements can be severely constrained by measuring the two-spin asymmetry, though the process depends on the polarized gluon distribution $Δg(x)$.

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