Mary Alberg

Theory of kaonic atoms

Abstract A nonlocal energy-dependent self-consistent kaon-nucleus optical potential is derived for kaonic atoms. Energy level shifts and widths are calculated for several light nuclei, and the results are compared with experiment. The sensitivity of the results to changes in parameters of the nuclear matter distribution is studied. Nonlocality and off-energy-shell effects are examined. The optical potential is derived by means of a Brueckner-type many-body theory with the independent pair approximation for the kaon and the nucleon. The two-body interaction on which the optical potential depends is represented by separable potentials of the Yamaguchi form. Coupled channels ( K N and Σπ) are used for the I = 0 states, which are dominated by the Y 0 ∗ resonance, and only a single channel ( K N ) is used for the I = 1 state. Calculations are carried out in three levels of approximation of the nonlocal energy-dependent optical potential. In no approximation is the potential found to be proportional to the nuclear density. Indeed, the real part of the potential changes sign in the nuclear surface. Sensitivity of the results to variations in the nuclear matter distribution is investigated and found to be on the order of experimental error. Nonlocality and off-energy-shell effects are estimated to be at least as large as this error, so that these effects must be included if one wishes to extract information about the nuclear surface from the existing experimental data. The use of correct nucleon wavefunctions and binding energies is similarly found to be essential in the calculation.

The proton spin puzzle and depolarization in pp → ΛΛ

Abstract We point out that the measurement of target spin depolarization Dnn in the p p → Λ Λ reaction may test dynamical mechanisms invoked to explain the proton spin puzzle revealed by polarized deep-inelastic scattering experiments. In particular, models with negatively polarized s s pairs in the proton wave function predict Dnn 0.

Exact solutions to the Schrödinger equation for potentials with Coulomb and harmonic oscillator terms

Abstract Exact solutions to the Schrodinger equation for potentials containing Coulomb (∼1/ r ) plus harmonic oscillator (∼ r 2 ) terms are found, subject to constraints on the ratio of the strengths of the Coulomb and harmonic oscillator terms. The solutions have the simple form of a product of exponential and polynomial functions.

Semiclassical description of antiproton capture on atomic helium

A semiclassical, 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[sup 2+][ital [bar p]] or He[sup +][ital [bar 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 [Iwasaki [ital et] [ital al]., Phys. Rev. Lett. 67, 1246 (1991)].

Omega meson cloud and the proton's light anti-quark distributions

Abstract We use the meson cloud model of the nucleon to calculate distribution functions for ( d − u ) and d / u in the proton. Including the effect of the omega meson cloud, with a coupling constant gω2/4π≈8, allows a reasonably good description of the data.

Determination of flavor asymmetry for Σ± by the Drell-Yan process☆

Flavor asymmetries for the valence and sea quarks of the Σ± can be obtained from Drell-Yan experiments using charged hyperon beams on proton and deuteron targets. A large, measurable difference in sea quark asymmetries is predicted between SU(3) and pseudoscalar meson models. The latter predict that in Σ+, ud ≤ 12, whereas the former predict ud ≈ 43. Estimates of valence quark asymmetries based on quark models also show large deviations from SU(3) predictions, which should be measurable.

Parton distributions in the proton and pion

We use detailed balance for a hadron composed of quark and gluon Fock states to obtain parton distributions in the proton and pion on the basis of a simple statistical model.

A quark model of antilambda-lambda production in p̄p interactions

Abstract A quark model which includes both scalar and vector contributions to the reaction mechanism is used in a DWBA calculation of total and differential cross sections, polarizations, and spin-correlation coefficients for the reaction p p → Λ Λ at laboratory momenta from threshold to 1.92 GeV/ c . The free parameters of the calculation include the scalar and vector strengths, a quark-cluster size parameter, and six parameters in the unknown Λ Λ interaction. Excellent agreement with experiment is found for a constructive interference of scalar and vector terms, and for a Λ Λ potential which differs from that suggested by several authors on the basis of SU(3) arguments. The fit to the data is better than that obtained by other quark models, which use only scalar or vector annihilation terms. The agreement with experiment is as good as that found in meson-exchange models, which use more parameters than the present calculation.

Field-theory treatment of the pp→dπ+ reaction

Abstract A field-theoretic treatment of the pp→d π + reaction is presented. Qualitative agreement with the experimental total cross sections and angular distributions is obtained in a model which uses neither a fundamental cutoff in the π-nucleon interaction, nor a ρ-exchange between nucleons.

The quark distributions in the Σ+ hyperon

Abstract We use the meson could model and the Sullivan mechanism to estimate the sea flavor asymmetry in the Σ+ baryon and calculate the distribution functions of both sea and valence quarks. We find large deviations from SU(3).