arXiv subjects

M. A. Alberg

Publications and source records attributed to M. A. Alberg.

5 recordsLinked to original sources

arXiv1996

New approach to $^4$He charge distribution

We present a study of the $^4$He charge distribution based on realistic nucleonic wave functions and incorporation of the nucleon's quark substructure. The central depression of the proton point density seen in modern four-body calculations is too small by itself to lead to a correct description of the charge distribution. We utilize six-quark structures calculated in the Chromodielectric Model for N-N interactions, and we find a swelling of the proton charge distribution as the internucleon distance decreases. These charge distributions are combined with the $^4$He wave function using the Independent Pair Approximation and two-body distributions generated from Green's Function Monte Carlo calculations. We obtain a reasonably good fit to the experimental charge distribution without including meson exchange currents.

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arXiv1996

The "Hole" In He

The measurement and analysis of electron scattering from He-3 and He-4 by Sick and collaborators reported 20 years ago remains a matter of current interest. By unfolding the measured free-proton charge distribution, they deduced a depression in the central point nucleon density, which is not found in few-body calculations based on realistic potentials. We find that using wave functions from such calculations we can obtain good fits to the He charge distributions under the assumption that the proton charge size expands toward the center of the nucleus. The relationship to 6-quark Chromo-Dielectric Model calculations, is discussed. The expansion is larger than than the predictions of mean field bag calculations by others or our CDM calculations in the independent pair approximation. There is interest here in the search for a "smoking gun" signal of quark substructure.

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arXiv1993

A Quark Model of Lambdabar-Lambda Production of Pbar-P Interactions

A quark model which includes both scalar and vector contributions to the reaction mechanism (SV quark model) is used in a DWBA calculation of $\bar ΛΛ$ production in $\bar p p$ interractions. Total and differential cross-sections, polarizations, depolarizations, and spin-correlattion coefficients are computed for laboratory momenta from threshold to 1695 MeV/c. The free parameters of the calculation are the scalar and vector strengths, a quark cluster size parameter,and the parameters of the unknown $\bar ΛΛ$ potentials. Good agreement with experiment is found for constructive interference of the scalar and vector terms, and for $\bar ΛΛ$ potentials which differ from those 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 also better than that found in meson-exchange models. The recent suggestion[1] that measurement of the depolarization parameter $D_{nn}$ can be used to discriminatebetween meson-exchange and quark models is examined in detail. We conclude that a measurement of $D_{nn}$ will provide a test of which of these models, as presently constructed,is the more appropriate description of strangeness production in the $\bar p p \ rightarrow \bar ΛΛ$ reaction.

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arXiv1993

Semi-Classical Description of Antiproton Capture on Atomic Helium

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$^{++}\,\bar p$ or He$^{+}\,\bar p$], 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.

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arXiv1993

A Quark Model of Antilambda-Lambda Production in Pbar-P Interactions

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 $\bar p p \rightarrow \bar ΛΛ$ 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 $\bar ΛΛ$ interaction. Excellent agreement with experiment is found for a constructive interference of scalar and vector terms, and for a $\bar ΛΛ$ 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.

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