Nuclear Charge Asymmetry Research Articles

Two-pion exchange contributions to nuclear charge asymmetry.

In a nonrelativistic formalism we derive a charge-symmetry-breaking (CSB) two-pion exchange interaction ${\mathit{V}}_{\mathit{nn}}$(2\ensuremath{\pi})-${\mathit{V}}_{\mathit{pp}}$(2\ensuremath{\pi}), which includes both CSB vertex corrections and the CSB effect of propagators arising from the mass differences of the intermediate baryons in different charge states. While the former are small, the latter gives a contribution of the sign and scale comparable to the experimental difference in the effective range parameters and the binding energy difference between $^{3}\mathrm{H}$ and $^{3}\mathrm{He}$. \textcopyright{} 1996 The American Physical Society.

Nuclear Charge Asymmetry and Charge Dependence and theH3-He3Binding-Energy Difference

Nuclear Charge Asymmetry and Charge Dependence and the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">He</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>Binding-Energy Difference

Nuclear charge asymmetry and charge dependence and the 3H-3He binding-energy difference.

We solve a set of Faddeev equations for some realistic two-nucleon potentials, taking into account the two-pion-exchange three-nucleon interaction, the Coulomb interaction, and the charge-independence- and charge-symmetry-breaking (CIB and CSB) interactions. After 32 case studies, we find a very good linear relationship between $^{3}\mathrm{H}$ and $^{3}\mathrm{He}$ binding energies, from which we deduce a model-independent value for the Coulomb energy difference (648\ifmmode\pm\else\textpm\fi{}4 keV for the finite-size protons) and the CIB and CSB nuclear effects. With other small effects, these effects reasonably account for the $^{3}\mathrm{\ensuremath{-}}^{3}$he binding-energy difference.

Rho - omega mixing in nuclear charge asymmetry.

The particle physics input to the NN charge asymmetric potential due to \ensuremath{\rho}-\ensuremath{\omega} mixing is updated. The calculated changes in scattering lengths \ensuremath{\Vert}${a}_{\mathrm{nn}\mathrm{\ensuremath{\Vert}}\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\Vert}}{a}_{\mathrm{pp}\mathrm{\ensuremath{\Vert}}\mathrm{\ensuremath{\sim}}1.3\ifmmode\pm\else\textpm\fi{}0.2}}$ fm are in good agreement with experiment (\ensuremath{\sim}1.4\ifmmode\pm\else\textpm\fi{}0.8 fm), as are the contributions to the binding energy difference in the A=3 mirror nuclei.

Role ofπ0η′mixing in nuclear charge asymmetry

We show that if all aspects of semi-strong and electromagnetic particle mixing are properly taken into account, the result is that the ..pi../sup 0/eta and ..pi../sup 0/eta' contributions to charge asymmetry of the nucleon force do not substantially modify the charge asymmetric NN scattering lengths due to ..pi../sup 0/eta mixing alone, and the ..pi../sup 0/eta' effect is approx.(1/3) the (already small) ..pi../sup 0/eta contribution to the /sup 3/He-/sup 3/H mass difference.

Nuclear charge asymmetry in the a = 3 nuclei

The nuclear charge asymmetry in the A = 3 system is determined by making a perturbative estimate of the direct electromagnetic (e.m.) contribution to the 3He- 3H binding energy difference. All local e.m. contributions are estimated in an almost model-independent way using experimental charge form factors and the relation exploited previously by Fabre de la Ripelle and Friar only for the contribution of the static Coulomb interaction. Model-dependent wave functions are used for the contribution of the small non-local terms of the e.m. interaction and the proton-neutron mass difference. Only 81 ± 29 keV of the experimental binding-energy difference has to be attributed to nuclear charge asymmetry, an amount smaller than previous estimates. The nearly model-independent method is used to estimate the contribution of some two-body charge asymmetric potentials, both theoretical and phenomenological, to the binding-energy difference.

Charge asymmetry and charge dependence of two-nucleon scattering

The electromagnetic (EM) contributions to nucleon-nucleon scattering are subtracted from the experimental scattering length in the 1S0 partial wave. The resulting nuclear proton-proton scattering length depends strongly on the unknown nuclear potential at small distances. The comparison between proton-proton and neutron-neutron data is therefore ambiguous. The amount of nuclear charge asymmetry in the 1S0 scattering length cannot be established. In contrast, the difference between the experimental proton-neutron and neutron-neutron 1S0 scattering lengths yields a quantitative estimate for the charge dependence of the nucleon-nucleon interaction, not invalidated by the subtraction of EM effects. A constraint on the parametrisation of the nuclear potential at small relative distances arising from nonrelativistic quantum mechanics is given.