We extend our recent study of dilepton invariant-mass spectra from the decays of ρ mesons produced by photon reactions off nuclei. We specifically focus on experimental spectra as recently measured by the CLAS Collaboration at the Thomas Jefferson National Accelerator Facility using carbon and iron nuclei. Building on our earlier work, we broaden our description to a larger set of observables to identify sensitivities to the medium effects predicted by microscopic calculations of the ρ spectral function. We compute mass spectra for several target nuclei and study the spectral shape as a function of the three-momentum of the outgoing lepton pair. We also compute the so-called nuclear transparency ratio, which provides an alternative means (and thus consistency check) of estimating the ρ width in the cold nuclear medium.

We reanalyze the dissociation process of the J/ψ by π and ρ mesons into D +D, D * +D, D +D * , and D * +D * within a meson exchange model. In addition to the dissociation mechanisms considered in the literature, we consider anomalous parity interactions, whose couplings are constrained by heavy quark spin symmetry and phenomenology. This opens new dissociation channels and adds new diagrams in the previously considered processes. Compared to the previous results, we find that these new additions have only a minor effect on the ρ + J/ψ total inelastic cross section, but reduce the one for π + J/ψ by about 50 % near the threshold.

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We study the photoproduction of K * (892) vector meson from both the charged and neutral reactions, γp → K * + Λ and γn → K * 0 Λ. The production mechanisms that we consider include t-channel K * , K, κ exchanges, s-channel nucleon diagram, and u-channel Λ, Σ, Σ * diagrams. These could constitute important backgrounds for future investigation of "missing" resonances that can be searched for especially in these reactions. The t-channel K meson exchange is found to dominate both reactions. The total and differential cross sections are presented together with some spin asymmetries.

Heavy baryon/meson ratios c /D 0 and b /B 0 in relativistic heavy ion collisions are studied in the quark coalescence model. For heavy baryons, we include production from coalescence of heavy quarks with free light quarks as well as with bounded light diquarks that might exist in the strongly coupled quark-gluon plasma produced in these collisions. Including the contribution from decays of heavy hadron resonances and also that due to fragmentation of heavy quarks that are left in the system after coalescence, the resulting c /D 0 and b /B 0 ratios in midrapidity (|y| 0.5) from central Au + Au collisions at √ s NN = 200 GeV are about a factor of five and ten, respectively, larger than those given by the thermal model, and about a factor of ten and twelve, respectively, larger than corresponding ratios in the PYTHIA model for pp collisions. These ratios are reduced by a factor of about 1.6 if there are no diquarks in the quark-gluon plasma. The transverse momentum dependence of the heavy baryon/meson ratios is found to be sensitive to the heavy quark mass, with the b /B 0 ratio being much flatter than the c /D 0 ratio. The latter peaks at the transverse momentum p T

The photoproduction reaction γN → KKΞ is investigated based on a relativistic meson-exchange model of hadronic interactions. The production amplitude is calculated in the tree-level approximation from relevant effective Lagrangians, whose (coupling constant) parameters are mostly fixed from the empirical data and/or quark models together with SU(3) symmetry considerations. Gauge invariance of the resulting amplitude is maintained by introducing the contact currents by extending the gauge-invariant approach of Haberzettl for one-meson photoproduction to two-meson photoproduction. The role of the intermediate low-lying hyperons and of the intermediate higher-mass hyperon resonances are analyzed in detail. In particular, the basic features of the production of Ξ − (1318) in γp → K + K + Ξ − and their possible manifestations in the forthcoming experimental data are discussed.

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