Radiative proton-antiproton annihilation and isospin mixing in protonium

A detailed analysis of the radiative $p\bar p$ annihilation is made in the framework of a two-step formalism, the $p\bar p$ annihilates into meson channels containing a vector meson with a subsequent conversion into a photon via the vector dominance model (VDM). Both steps are derived from the underlying quark model. First, branching ratios for radiative protonium annihilation are calculated and compared with data. Then, details of the isospin interference are studied for different models of the initial protonium state and also for different kinematical form factors. The isospin interference is shown to be uniquely connected to the $p\bar p - n\bar n$ mixing in the protonium state. Values of the interference terms directly deduced from data are consistent with theoretical expectations, indicating a dominant $p\bar p$ component for the $^1S_0$ and a sizable $n\bar n$ component for the $^3S_1$ protonium state. The analysis is extended to the $p\bar p \to \gamma \Phi$ transition, where the large observed branching ratio remains unexplained in the VDM approach.Comment: 34 pages, RevTeX, 2 figures, to appear in Phys. Rev. C; typos correcte

The exclusive rare decays B -> K l(bar) l and B_c -> D(D*) l(bar) l in a relativistic quark model

We study the exclusive rare decay B -> K l(bar) l. We calculate the relevant form factors within a relativistic constituent quark model, for the first time without employing the impulse approximation. The calculated form factors are used to evaluate differential decay rates and polarization observables. We present results on the q2-dependence of a set of observables with and without long-distance contributions. A similar analysis is done for the exclusive rare decays B_c -> D (D*) l(bar) l with special emphasis on the cascade decay B_c -> D* (-> D pi) l(bar) l. We derive a four-fold angular decay distribution for this process in terms of helicity amplitudes including lepton mass effects. The four-fold angular decay distribution allows to define a number of physical observables which are amenable to measurement. We compare our results with the results of other studies.Comment: 28 pages, 12 figure

The semileptonic decay Lambda_b -> Lambda_c + tau(-) + antinu_tau in the covariant confined quark model

Recently there has been much interest in the tauonic semileptonic meson decays B -> D + tau + nu_tau and B -> D* + tau + nu_tau where one has found larger rates than what is predicted by the Standard Model. We analyze the corresponding semileptonic baryon decays Lambda_b(0) -> Lambda_c(+) + tau(-) + antinu_tau with particular emphasis on the lepton helicity flip and scalar contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization of the daughter baryon Lambda_c(+) and the tau-lepton, and the lepton-side forward-backward asymmetries. The nonvanishing polarization of the daughter baryon Lambda_c(+) leads to hadron-side asymmetries in e.g. the decay Lambda_c(+) -> Lambda(0) + pi(+) and azimuthal correlations between the two final state decay planes which we specify. We provide numerical results on these observables using results of the covariant confined quark model. We find large lepton mass effects in the q2-spectra and in the polarization observables.Comment: 26 page

Weak decays of heavy hadron molecules involving the f0(980)

We study weak decays of the charm- and bottom-strange mesons Ds0*(2317), Ds1(2460), Bs0*(5725) and Bs1(5778) with f0(980) in the final state by assuming a hadronic molecule interpretation for their structures. Since in the proposed framework the initial and final states are occupied by hadronic molecules, the predictions for observables can provide a sensitive tool to further test the hadronic molecule structure in future experiments.Comment: 11 pages, 5 figures, accepted for publication in Phys. Rev.

phi-meson production in proton-antiproton annihilation

Apparent channel-dependent violations of the OZI rule in nucleon-antinucleon annihilation reactions are discussed in the presence of an intrinsic strangeness component in the nucleon. Admixture of strange-antistrange quark pairs in the nucleon wave function enables the direct coupling to the phi-meson in the annihilation channel without violating the OZI rule. Three forms are considered in this work for the strangeness content of the proton wave function, namely, the uud cluster with a strange-antistrange sea quark component, kaon-hyperon clusters based on a simple chiral quark model, and the pentaquark picture. Nonrelativistic quark model calculations reveal that the strangeness magnetic moment and the strangeness contribution to the proton spin from the first two models are consistent with recent experimental data. For the third model, the uuds subsystem with the configurations FS[31]F[211]S[22] and FS[31]F[31]S[22] leads to negative values for the strangeness magnetic moment and the strangeness contribution to the proton spin. With effective quark line diagrams incorporating the 3P0 quark model we give estimates for the branching ratios of the proton-antiproton annihilation reactions at rest to two mesons. Results for the branching ratios of phi-meson production from atomic proton-antiproton s-wave states are for the first and third model found to be strongly channel dependent, in good agreement with measured rates.Comment: 12 pages, 1 figur