Models for differential cross section in neutron-proton scattering and their implications

Abstract

A few analytic exponential models of elastic differential cross section, constructed as purely phenomenological models, are proposed and tested. The models incorporate energy-dependent exponential slopes, power-law prefactors, and localized Gaussian modifications which are built to reproduce the observed dip region, supplemented in some cases by logarithmic $t$-dependent slopes. Simple additive sub-leading exponential contributions that represent charge conjugation and isospin roles are introduced in the models to increase applicability and quality of fit across elastic differential cross section data of $np$, $n\bar{p}$, $pp$, and $p\bar{p}$ elastic scattering. The models reproduce the characteristic features of the elastic scattering data such as the dip-bump structure, shrinkage of the forward peak, and controlled curvature that is localized around the dip. Parameters of the models are found by fitting the experimental data of elastic $np$ differential cross section in an energy range of $\sqrt{s}$ = 3.36 GeV to 26.02 GeV, across a momentum range of $0.065 \leq \mid t\mid \leq 5.341 \textrm{GeV}^{2}$. The parameter values and their ranges, obtained by $\chi^{2}$ minimization are found within their assumed expected bounds with the $np$ data fitting. The total cross section, the slope parameter, the interaction radius, the total elastic cross section, the inelastic cross section, the ratios $\sigma_{el}/\sigma_{tot}$, and $\sigma_{inel}/\sigma_{tot}$ are predicted by the models for the $np$ scattering at all the energies, which show accurate quantitative agreement with their reference values. The results show that the proposed models not only provide accurate quantitative description of $np$ elastic differential cross section but also yield estimates of the observables that are consistent with theoretical expectations from Regge phenomenology and high-energy scattering constraints.