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Register a new userphi-meson production in proton-antiproton annihilation
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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.
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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.
This report reviews the achievements of the Crystal Barrel experiment at the Low Energy Antiproton Ring (LEAR) at CERN. During seven years of operation Crystal Barrel has collected very large statistical samples in pbarp annihilation, especially at rest and with emphasis on final states with high neutral multiplicity. The measured rates for annihilation into various two-body channels and for electromagnetic processes have been used to test simple models for the annihilation mechanism based on the quark internal structure of hadrons. From three-body annihilations three scalar mesons, a0(1450), f0(1370) and f0(1500) have been established in various decay modes. One of them, f0(1500), may be identified with the expected ground state scalar glueball.
The production of phi mesons in Au+Au collisions at RHIC and their propagation in a hot and dense nuclear medium is studied within the microscopic quark-gluon string model. The inverse slope parameter of the transverse mass distribution agrees well with that extracted from the STAR data, while the absolute yield of phi is underestimated by a factor 2. It appears that the fusion of strings alone cannot increase the phi yield either. Less than 30% of detectable phis experience elastic scattering, this rate is insufficient for the full thermalization of phi. The directed flow of phi at |y|<2 demonstrates strong antiflow behavior, whereas its elliptic flow rises up to about 3.5% in the same rapidity interval. As a function of transverse momentum it rises linearly with increasing p_t, in agreement with the STAR data, and saturates at p_t > 2 GeV/c.
In this work we study the e^{+}e^{-}tophi K^{+}K^{-} reaction. The leading order electromagnetic contributions to this process involve the gamma*phi K^{+}K^{-} vertex function with a highly virtual photon. We calculate this function at low energies using Rchi PT supplemented with the anomalous term for the VVP interactions. Tree level contributions involve the kaon form factors and the K*K transition form factors. We improve this result, valid for low photon virtualities, replacing the lowest order terms in the kaon form factors and K*K transition form factors by the form factors as obtained in Uchi PT in the former case and the ones extracted from recent data on e^{+}e^{-}to KK* in the latter case. We calculate rescattering effects which involve meson-meson amplitudes. The corresponding result is improved using the unitarized meson-meson amplitudes containing the scalar poles instead of the lowest order terms. Using the BABAR value for BR(Xto phi f_{0})Gamma (Xto e^{+} e^{-}), we calculate the contribution from intermediate X(2175). A good description of data is obtained in the case of destructive interference between this contribution and the previous ones, but more accurate data on the isovector K*K transition form factor is required in order to exclude contributions from an intermediate isovector resonance to e^{+}e^{-}to phi K^{+}K^{-} around 2.2 GeV.
The results of the microscopic transport calculations of $bar p$-nucleus interactions within a GiBUU model are presented. The dominating mechanism of hyperon production is the strangeness exchange processes $bar K N to Y pi$ and $bar K N to Xi K$. The calculated rapidity spectra of $Xi$ hyperons are significantly shifted to forward rapidities with respect to the spectra of $S=-1$ hyperons. We argue that this shift should be a sensitive test for the possible exotic mechanisms of $bar p$-nucleus annihilation. The production of the double $Lambda$-hypernuclei by $Xi^-$ interaction with a secondary target is calculated.
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