Model-independent view on the low-mass proton-antiproton enhancement

We present a simple interpretation of the recently observed near-threshold proton-antiproton enhancement. It is described by a set of low-energy parameters deduced from the analysis of NantiN experiments at LEAR. We predict a related effect in photoproduction reaction under study by CLAS collaboration.Comment: 10 pages, 2 figure

Distribution amplitudes and decay constants for (π,K,ρ,K∗)(\pi,K,\rho,K^*) mesons in light-front quark model

We present a calculation of the quark distribution amplitudes(DAs), the Gegenbauer moments, and decay constants for $\pi,\rho,K$ and $K^*$ mesons using the light-front quark model. While the quark DA for $\pi$ is somewhat broader than the asymptotic one, that for $\rho$ meson is very close to the asymptotic one. The quark DAs for $K$ and $K^*$ show asymmetric form due to the flavor SU(3)-symmetry breaking effect. The decay constants for the transversely polarized $\rho$ and $K^*$ mesons($f^T_\rho$ and $f^T_{K^*}$) as well as the longitudinally polarized ones($f_\rho$ and $f_{K^*}$) are also obtained. Our averaged values for $f^T_V/f_V$, i.e. $(f^T_\rho/f_\rho)_{\rm av}=0.78$ and $(f^T_{K^*}/f_{K^*})_{\rm av}=0.84$, are found to be consistent with other model predictions. Especially, our results for the decay constants are in a good agreement with the SU(6) symmetry relation, $f^T_{\rho(K^*)}=(f_{\pi(K)}+f_{\rho(K^*)})/2$.Comment: 12 pages, 6figure

Polarization effects in the reaction e++e−→ρ++ρ−e^++e^-\to \rho^+ +\rho^- and determination of the ρ−\rho - meson form factors in the time--like region

The electron positron annihilation reaction into four pion production has been studied, through the channel $e^++e^-\to \bar \rho+\rho$. The differential (and total) cross sections and various polarization observables for this reaction have been calculated in terms of the electromagnetic form factors of the corresponding $\gamma^*\rho\rho$ current. The elements of the spin--density matrix of the $\rho -$meson were also calculated. Numerical estimations have been done, with the help of phenomenological form factors obtained in the space--like region of the momentum transfer squared and analytically extended to the time-like region.Comment: 19 pages, 2 figures, to appear in Phys Rev

Electromagnetic Structure of the ρ\rho Meson in the Light-Front Quark Model

We investigate the elastic form factors of the rho meson in the light-front quark model(LFQM). With the phenomenologically accessible meson vertices including the one obtained by the Melosh transformation frequently used in the LFQM, we find that only the helicity $0\to 0$ matrix element of the plus current receives the zero-mode contribution. We quantify the zero-mode contribution in the helicity $0\to 0$ amplitude using the angular condition of spin-1 system. After taking care of the zero-mode issue, we obtain the magnetic($\mu$) and quadrupole($Q$) moments of the rho meson as $\mu=1.92$ and $Q=0.43$, respectively, in the LFQM consistent with the Melosh transformation and compare our results with other available theoretical predictions.Comment: 14pages, 5figure

The Lambda_b lifetime in the light front quark model

The enhancement of the Lambda_b decay width relative to B decay one due to the difference of Fermi motion effects in Lambda_b and B is calculated in the light--front quark model with the simplifying assumption that Lambda_b consists of the heavy quark and light scalar diquark. In order to explain the large deviation from unity in the experimental result for tau(Lambda_b)/tau(B), it is necessary that diquark be light and the ratio of the squares of the Lambda_b and B wave functions at the origin be \le 1.Comment: final journal version to appear in JETP Letter

Isoscalar short-range current in the deuteron induced by an intermediate dibaryon

A new model for short-range isoscalar currents in the deuteron and in the NN system is developed; it is based on the generation of an intermediate dibaryon which is the basic ingredient for the medium- and short-range NN interaction which was proposed recently by the present authors.This new current model can very well describe the experimental data for the three basic deuteron observables of isoscalar magnetic type, viz. the magnetic moment, the circular polarization of the photon in the $np\to d\gamma$ process at thermal neutron energies and the structure function B up to Q$^2$=60 fm$^{-2}$.Comment: LaTex, 22 pages with 8 figure