We point out that the measurement of target spin depolarization D nn in thepp →ΛΛ reaction may test dynamical mechanisms invoked to explain the proton spin puzzle revealed by polarized deep-inelastic scattering experiments. In particular, models with negatively polarizedss pairs in the proton wave function predict D nn < 0, whereas models with positively polarized gluons would predict D nn > 0.

We present a light-front determination of the pionic contribution to the nucleon self-energy, Σ(π), to second order in pion-baryon coupling constants that allows the pion-nucleon vertex function to be treated in a model-independent manner constrained by experiment. The pion mass μ dependence of Σ(π) is consistent with chiral perturbation theory results for small values of μ and is also linearly dependent on μ for larger values, in accord with the results of lattice QCD calculations. The derivative of Σ(π) with respect to μ(2) yields the dominant contribution to the pion content, which is consistent with the d[over ¯]-u[over ¯] difference observed experimentally in the violation of the Gottfried sum rule.

Determining the nonperturbative ss content of the nucleon has attracted considerable interest and been the subject of numerous experimental searches. These measurements used a variety of reactions and place important limits on the vector form factors observed in parity-violating (PV) elastic scattering and the parton distributions determined by deep inelastic scattering (DIS). In spite of this progress, attempts to relate information obtained from elastic and DIS experiments have been sparse. To ameliorate this situation, we develop an interpolating model using lightfront wave functions capable of computing both DIS and elastic observables. This framework is used to show that existing knowledge of DIS places significant restrictions on our wave functions. The result is that the predicted effects of nucleon strangeness on elastic observables are much smaller than those tolerated by direct fits to PV elastic scattering data alone. Using our model, we find −0.024 ≤ µs ≤ 0.035, and −0.137 ≤ ρ D s ≤ 0.081 for the strange contributions to the nucleon magnetic moment and charge radius. The model we develop also independently predicts the nucleon's strange spin content ∆s and scalar density N |ss|N , and for these we find agreement with previous determinations.2

A semi-classical, many-body atomic model incorporating a momentum-dependent Heisenberg core to stabilize atomic electrons is used to study antiproton capture on Helium. Details of the antiproton collisions leading to eventual capture are presented, including the energy and angular momentum states of incident antiprotons which result in capture via single or double electron ionization, i.e. into [He ++p or He +p ], and the distribution of energy and angular momentum states following the Auger cascade. These final states are discussed in light of recently reported, anomalously long-lived antiproton states observed in liquid He.Typeset Using REVTEX

We propose a flavor asymmetry in the light quark sea of Σ ± , which can be measured in Drell-Yan experiments using charged hyperon beams on proton and deuteron targets. Such a measurement would help to reinforce the presence of pseudoscalar mesons in a quark model of baryons.

We use the meson cloud model of the nucleon to calculate distribution functions for (d −ū) andd/ū in the proton. Including the effect of the omega meson cloud, with a coupling constant g 2 ω /4π ≈ 8, allows a reasonably good description of the data.

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