Nucleon-Meson Coupling Constants and Form Factors in the Quark Model

We demonstrate the calculation of the coupling constants and form factors required by effective hadron lagrangians using the quark model. These relations follow from equating expressions for strong transition amplitudes in the two approaches. As examples we derive the NNm nucleon-meson coupling constants and form factors for m = pi, eta, eta', sigma, a_0, omega and rho, using harmonic oscillator quark model meson and baryon wavefunctions and the 3P0 decay model; this is a first step towards deriving a quark-based model of the NN force at all separations. This technique should be useful in the application of effective lagrangians to processes in which the lack of data precludes the direct determination of coupling constants and form factors from experiment.Comment: 7 pages, 4 figures, 1 tabl

Y(2175): Distinguish Hybrid State from Higher Quarkonium

The possibility of Y(2175) as a $2{^3D_1}$ $s\bar{s}$ meson is studied. We study the decay of $2{^3D_1}$ $s\bar{s}$ from both the $^3P_0$ model and the flux tube model, and the results are similar in the two models. We show that the decay patterns of $1^{--}$ strangeonium hybrid and $2{^3D_1}$ $s\bar{s}$ are very different. The experimental search of the decay modes $KK$, $K^{*}K^{*}$, $K(1460)K$, $h_1(1380)\eta$ is suggested to distinguish the two pictures. Measuring the $K^{*}K^{*}$ partial width ratios is crucial to discriminate the $2{^3D_1}$ from the $3{^3S_1}$ $s\bar{s}$ assignment.Comment: 13 pages, 8 figure

The decay of the observed JPC=1−+J^{PC}=1^{-+} (1400) and JPC=1−+J^{PC}=1^{-+}(1600) hybrid candidates

We study the possible interpretation of the two exotic resonances $J^{PC}= 1^{-+}$ at 1400 and 1600 MeV, claimed to be observed by BNL, decaying respectively into $\eta\pi$, $\eta'\pi$, $f_{1}\pi$ and $\rho\pi$. These objects are interpreted as hybrid mesons, in the quark-gluon constituent model using a chromoharmonic confining potentiel. The quantum numbers $J^{PC}I^{G} = 1^{-+} 1^{-}$ can be considered in a constituent model as an hybrid meson ($q \bar q g$). The lowest $J^{PC}= 1^{-+}$states may be built in two ways : $l_{g}$=1 (gluon-excited) corresponding to an angular momentum between the gluon and ($q \bar q$) system, while $l_{q \bar q}=1$ (quarks-excited) corresponds to an angular momentum between $q$ and $\bar q$. For the gluon-excited mode $1^{-+}$ hybrids, we find the decay dominated by the $b_{1}\pi$ channel, and by the $\rho \pi$ channel for the quark-excited mode. In our model, neither the quark-excited nor the gluon-excited $1^{-+}$ (1400 MeV) hybrids can decay into $\eta\pi$ and $\eta'\pi$, in contradiction with experiment. Hence, the 1400 MeV resonance seems unlikely to be an hybrid state. The $1^{-+}$ (1600 MeV) gluon-excited hybrid is predicted with too large a total decay width, to be considered as an hybrid candidate. On the contrary the quark-excited mode has a total decay width around 165 MeV, with a $\rho \pi$ preferred decay channel, in agreement with BNL. Our conclusion is that {\it{this resonance may be considered as a hybrid meson in the quark-excited mode}}Comment: 13 pages, 1 figur

Distinguishing Among Strong Decay Models

Two competing models for strong hadronic decays, the $^3P_0$ and $^3S_1$ models, are currently in use. Attempts to rule out one or the other have been hindered by a poor understanding of final state interactions and by ambiguities in the treatment of relativistic effects. In this article we study meson decays in both models, focussing on certain amplitude ratios for which the relativistic uncertainties largely cancel out (notably the $S/D$ ratios in $b_1\rightarrow\pi\omega$ and $a_1\rightarrow\pi\rho$), and using a Quark Born Formalism to estimate the final state interactions. We find that the $^3P_0$ model is strongly favoured. In addition, we predict a $P/F$ amplitude ratio of $1.6\pm .2$ for the decay $\pi_2\rightarrow\pi\rho$. We also study the parameter-dependence of some individual amplitudes (as opposed to amplitude ratios), in an attempt to identify a ``best'' version of the $^3P_0$ model.Comment: 20 pages, uuencoded postscript file with 7 figures, MIT-CTP-2295; CMU-HEP94-1

Scaling of the 3P0 strength in heavy meson strong decays

The phenomenological 3P0 decay model has been extensively applied to calculate meson strong decays. The strength \gamma\ of the decay interaction is regarded as a free flavor independent constant and is fitted to the data. We calculate through the 3P0 model the total strong decay widths of the mesons which belong to charmed, charmed-strange, hidden charm and hidden bottom sectors. The wave function of the mesons involved in the strong decays are given by a constituent quark model that describes well the meson phenomenology from the light to the heavy quark sector. A global fit of the experimental data shows that, contrarily to the usual wisdom, the \gamma\ depends on the reduced mass of the quark-antiquark pair in the decaying meson. With this scale-dependent strength \gamma, we are able to predict the decay width of orbitally excited B mesons not included in the fit.Comment: 7 pages, 5 tables, 2 figure

D mesons in matter and the in-medium properties of charmonium

We study the changes in the partial decay widths of excited charmonium states into $D \bar{D}$, when the D meson mass decreases in nuclear matter, taking the internal structure of the hadrons into account. Calculations within the 3P0 model for $\psi(3686)$ and $\psi(3770)$ imply that naive estimates of the in-medium widths based only on phase space are grossly exaggerated. Due to nodes in the wave functions, these states may even become narrow at high densities, if the D meson mass is decreased by about 200 MeV. For the $\chi$ states, we generally expect stronger modifications of the widths. The relevance of the $\chi$ widths for $J/\psi$ suppression in heavy ion collision is discussed. These phenomena could be explored in experiments at the future accelerator facility at GSI.Comment: 12 pages, 3 figures; allowed for two independent oscillator parameters for the charmonium states and D mesons, results are not significantly modified and conclusions remains unaltere

J/Psi mass shift in nuclear matter

The $J/\Psi$ mass shift in cold nuclear matter is computed using an effective Lagrangian approach. The mass shift is computed by evaluating $D$ and $D^*$ meson loop contributions to the $J/\Psi$ self-energy employing medium-modified meson masses. The modification of the $D$ and $D^*$ masses in nuclear matter is obtained using the quark-meson coupling model. The loop integrals are regularized with dipole form factors and the sensitivity of the results to the values of form-factor cutoff masses is investigated. The $J/\Psi$ mass shift arising from the modification of the $D$ and $D^*$ loops at normal nuclear matter density is found to range from -16 MeV to -24 MeV under a wide variation of values of the cutoff masses. Experimental perspectives for the formation of a bound state of $J/\Psi$ to a nucleus are investigated.Comment: 9 pages, latex file, 6 figures. Version published in Phys. Lett.