Extracting Hypernuclear Properties from the (e, e′K+) Cross Section

Omar Benhar

doi:10.3390/particles4020018

Abstract

Experimental studies of hypernuclear dynamics, besides being essential for the understanding of strong interactions in the strange sector, have important astrophysical implications. The observation of neutron stars with masses exceeding two solar masses poses a serious challenge to the models of hyperon dynamics in dense nuclear matter, many of which predict a maximum mass incompatible with the data. In this paper, it is argued that valuable new insight can be gained from the forthcoming extension of the experimental studies of kaon electro production from nuclei to include the 208Pb(e,e′K+)Λ208Tl process. A comprehensive framework for the description of kaon electro production, based on factorization of the nuclear cross section and the formalism of the nuclear many-body theory, is outlined. This approach highlights the connection between the kaon production and proton knockout reactions, which will allow us to exploit the available 208Pb(e,e′p)207Tl data to achieve a largely model-independent analysis of the measured cross section.

Highlights

Experimental studies of the (e, e K+) reaction on nuclei have long been recognized as a valuable source of information on hypernuclear spectroscopy
The extensive program of measurements performed or approved at Jefferson Lab [1,2]—encompassing a variety of nuclear targets ranging from 6Li to 40Ca and 48Ca—has the potential to shed new light on the dynamics of strong interactions in the strange sector, addressing outstanding issues such as the isospin-dependence of hyperon-nucleon interactions and the role of three-body forces involving nucleons and hyperons
Because the appearance of hyperons is expected to become energetically favored in dense nuclear matter, these measurements have important implications for neutron star physics

Summary

Introduction

Experimental studies of the (e, e K+) reaction on nuclei have long been recognized as a valuable source of information on hypernuclear spectroscopy. The formalism exploiting factorization of the nuclear cross section is expected to be applicable in the impulse approximation regime, corresponding to momentum transfer such that the wavelength of the virtual photon, λ ∼ 1/|q|, is short compared to the average distance between nucleons in the target nucleus, dNN ∼ 1.5 fm Under these condition, which can be met at Jefferson Lab—hereafter JLab—the beam particles primarily interact with individual protons, the remaining A − 1 nucleons acting as spectators. The nuclear spectral functions have been extensively studied measuring the cross section of the (e, e p) reaction, in which the scattered electron and the knocked out nucleon are detected in coincidence The results of these experiments, carried out using a variety of nuclear targets, have unambiguously identified the states predicted by the shell model, at the same time highlighting the limitations of the mean-field approximation and the effects of nucleon–nucleon correlations [7,11,12]. Note that both the electron energy loss, ω, and the energy of the outgoing kaon, EK+ , are measured kinematical quantities

Kinematics

Nuclear and Hypernuclear Dynamics

Summary and Outlook