Abstract:
A simple partial wave amplitude analysis of $\overline{p}p \rightarrow K^-K^+$ has been performed for data in the range $p_{\rm lab}$ = 360 -- 1000 MeV/$c$. In this low momentum interval only partial wave amplitudes with $J$ equal to 0, 1 and 2 are needed to obtain a good fit to the experimental data. This maximal $J$ = 2 value is smaller than what is required for the data of the reaction $\overline{p}p \rightarrow \pi^-\pi^+$ in the same momentum interval.

Abstract:
Results for d$\sigma$/d$\Omega$ and $A_N$ in the reaction $\bar{p}p \rightarrow \pi^- \pi^+$ are predicted by a simple quark model. They are compared to recent experimental data from LEAR, as well as to previous predictions from nucleon-exchange models. At low energy the quark model does better than the nucleon-exchange models, but the overall comparison to experiment remains poor. In particular, the double-dip structure of the experimental $A_N$ data is only partly represented. This shortcoming of the simple quark model is traced back to a too small J=2 amplitude. This has interesting implications for the range of this specific annihilation process.

Abstract:
Within the quark model a generalization is proposed of the commonly used annihilation potential to describe antiproton-proton annihilation into two mesons, the so-called $^3P_0$ and $^3S_1$ mechanisms. This generalized potential treats the two mechanisms in a more symmetric way, has additional angular dependence, and results in an expanded set of selection rules.

Abstract:
A simple $\pi \pi$, $\bar{K}K$, and $\rho \rho$($\omega \omega$) fully coupled channel model is proposed to predict the isoscalar S-wave phase shifts and inelasticities for $\pi \pi$ scattering in the 1.0 to 2.0 GeV region. The S-matrix is required to exhibit poles corresponding to the established isoscalar J$^{\pi}$ = 0$^+$ resonances f$_0$(975), f$_0$(1400), and f$_0$(1710). A dominant feature of the experimental $\pi \pi$ inelasticity is the clear opening of the $\bar{K}K$ channel near 1 GeV, and the opening of another channel in the 1.4 - 1.5 GeV region. The success of our model in predicting this observed dramatic energy dependence indicates that the effect of multi-pion channels is adequately described by the $\pi \pi$ coupling to the $\bar{K}K$ channel, the $\rho \rho$(4$\pi$) and $\omega \omega$(6$\pi$) channels.

Abstract:
A simple partial wave amplitude analysis of $\overline{p}p \rightarrow \pi^- \pi^+$ has been performed for data in the range p$_{\sl lab}$ = 360 -- 1000 MeV/c. Remarkably few partial waves are required to fit the data, while the number of required $J$ values barely changes over this energy range. However, the resulting set of partial wave amplitudes is not unique. We discuss possible measurements with polarized beam and target which will severely restrict and help resolve the present analysis ambiguities. New data from the reaction $\overline{p}p \rightarrow \pi^0 \pi^0$ alone, are insufficient for that purpose.

Abstract:
A pi-pi, Kbar-K, and rho-rho(omega-omega) fully coupled channel model is used to predict the lowest isospin S, P, D, F-wave phase shifts and inelasticities for elastic pi-pi scattering from threshold to 2.0 GeV. As input the S-matrix is required to exhibit poles corresponding to the meson resonance table of the Particle Data Group. As expected, the pi-pi inelasticity is very strongly related to the opening of the Kbar-K channel near 1 GeV, and the opening of rho-rho(4pi) and omega-omega(6pi) channels in the 1.5 GeV region. The predictions of this model are compared to the various elastic pi-pi to pi-pi amplitudes, that were obtained from analyses of pi(-) p to pi(-) pi(+) n data. The role of the various resonances, in particular the glueball candidate f_0(1500) and the f_J(1710) is investigated.

Abstract:
Extraction of spin observables from vector meson photoproduction on a nucleon target is described. Starting from density matrix elements in the vector meson's rest frame, we transform to spin observables in the photon-nucleon c.m. frame. Several constraints on the transformed density matrix and on the spin observables follow from requiring that the angular distribution and the density matrix be positive definite. A set of constraints that are required in order to extract meaningful spin observables from forthcoming data are enunciated.

Abstract:
We present a new fit to the LEAR data on antiproton-proton -> pi^- pi^+ differential cross sections and analyzing powers motivated by relativistic considerations. Within a quark model describing this annihilation we argue, since the pions are highly energetic, that relativistic effects cannot be neglected. The intrinsic pion wave functions are Lorentz transformed to the center of mass frame. This change in quark geometry gives rise to additional angular dependence in the transition operators and results in a relative enhancement of higher J \ge 2 partial wave amplitudes. The fit to the data is improved significantly.

Abstract:
Quark model intrinsic wave functions of highly energetic pions in the reaction \bar pp->\pi^-\pi^+ are subjected to a relativistic treatment. The annihilation is described in a constituent quark model with A2 and R2 flavor-flux topology and the annihilated quark-antiquark pairs are in 3P_0 and 3S_1 states. We study the effects of pure Lorentz transformations on the antiquark and quark spatial wave functions and their respective spinors in the pion. The modified quark geometry of the pion has considerable impact on the angular dependence of the annihilation mechanisms.

Abstract:
We present a geometric interpretation of the so-called annihilation range in reactions of the type $\bar pp \to$ {\em two light mesons} based upon Lorentz effects in the highly relativistic final states ($\gamma=E_{\mathrm{cm}}/2mc^2\simeq 6.8-8.0$). Lorentz-boosted meson wave functions, within the framework of the constituent quark model, result in a richer angular dependence of the annihilation amplitudes and thus in higher partial wave contributions ($J>1$) than usually obtained. This approach sheds some light on what could be a "{\em short}" annihilation range and how it is influenced by the angular distribution of the final states.