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Register a new userPentaquark components in low-lying baryon resonances
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We study pentaquark states of both light $q^4bar q$ and hidden heavy $q^3 Qbar Q$ (q = u,d,s quark in SU(3) flavor symmetry; Q = c, b quark) systems with a general group theory approach in the constituent quark model, and the spectrum of light baryon resonances in the ansatz that the $l=1$ baryon states may consist of the $q^3$ as well as $q^4bar q$ pentaquark component. The model is fitted to ground state baryons and light baryon resonances which are believed to be normal three-quark states. The work reveals that the $N(1535)1/2^{-}$ and $N(1520)3/2^-$ may consist of a large $q^4bar q$ component while the $N(1895)1/2^{-}$ and $N(1875)3/2^-$ are respectively their partners, and the $N^+(1685)$ might be a $q^4bar q$ state. By the way, a new set of color-spin-flavor-spatial wave function for $q^3 Qbar Q$ systems in the compact pentaquark picture are constructed systematically for studying hidden charm pentaquark states.
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$P_c$ resonances are studied in the approach of quark model and group theory. It is found that there are totally 17 possible pentaquark states with the quark contents $q^3Q bar Q$ ($q$ are $u$ and $d$ quarks; $Q$ is $c$ quark) in the compact pentaquark picture, where the hidden heavy pentaquark states may take the color singlet-singlet ($[111]_{{qqq}}otimes [111]_{{c bar c}}$) and color octet-octet ($[21]_{{qqq}}otimes [21]_{{c bar c}}$) configurations. The partial decay widths of hidden heavy pentaquark states are calculated for all possible decay channels. The results show that the $pJ/psi$ is the dominant decay channel for both the spin $3/2$ and $1/2$ pentaquark states, and indicate that the $P_c(4440)$ may not be a compact pentaquark state while $P_c(4312)$ and $P_c(4457)$ could be the spin-$frac{1}{2}$ and spin-$frac{3}{2}$ pentaquark states, respectively.
The pentaquark component is included in the proton wave functions to study phi meson production proton-antiproton annihilation reactions. With all possible configurations of the uuds subsystem proposed for describing the strangeness spin and magnetic moment of the proton, we estimate the branching ratios of the annihilation reactions at rest proton-antiproton to phi + X (X=pi, eta, rho, omega) from atomic proton-antiproton S- and P-wave states by using effective quark line diagrams incorporating the 3P0 model. The best agreement of theoretical prediction with the experimental data is found when the pentaquark configuration of the proton wave function takes the flavor-spin symmetry, [4]_FS [22]_F [22]_S.
We use a consistent SU(6) extension of the meson-baryon chiral Lagrangian within a coupled channel unitary approach in order to calculate the T-matrix for meson-baryon scattering in s-wave. The building blocks of the scheme are the pion and nucleon octets, the rho nonet and the Delta decuplet. We identify poles in this unitary T-matrix and interpret them as resonances. We study here the non exotic sectors with strangeness S=0,-1,-2,-3 and spin J=1/2, 3/2 and 5/2. Many of the poles generated can be associated with known N, Delta, Sigma, Lambda and Xi resonances with negative parity. We show that most of the low-lying three and four star odd parity baryon resonances with spin 1/2 and 3/2 can be related to multiplets of the spin-flavor symmetry group SU(6). This study allows us to predict the spin-parity of the Xi(1620), Xi(1690), Xi(1950), Xi(2250), Omega(2250) and Omega(2380) resonances, which have not been determined experimentally yet.
We study the magnetic moments of the octet, low-lying charm, and low-lying bottom baryons with nonzero light quarks in symmetric nuclear matter. This is the first study of estimating the medium modifications of magnetic moments for these low-lying charm and bottom baryons.
The branching ratio and other observables for the rare flavour-changing neutral current decay bar B_d^0 -> bar K*0 (-> K- pi+) e+ e- are studied below the bar{c} c threshold. The total amplitude for this decay includes the term coming from the standard model effective Hamiltonian and the term generated by the processes bar B_d^0 -> bar K*0 (-> K- pi+) V with intermediate low-lying vector resonances V = rho(770), omega(782), phi(1020) decaying into the e+ e- pair. The resonance contribution to the branching ratio, polarization fractions of the K* meson and coefficients in the angular distribution is calculated. The influence of the resonances on the integrated observables in the region of electron-positron invariant mass up to 1 GeV is studied in view of the planned measurements of the photon polarization at the LHCb.
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