Proton emission off nuclei induced by kaons in flight

TL;DR

This study models the (K-,p) reaction on nuclei at 1 GeV/c to evaluate the sensitivity of proton spectra to the kaon optical potential, concluding that the reaction is not suitable for determining the potential's depth due to limited sensitivity and additional process contributions.

Contribution

The paper introduces a comprehensive Monte Carlo simulation including multiple reaction mechanisms and final state interactions to analyze kaon-induced proton emission spectra.

Findings

The reaction is not sensitive enough to the kaon optical potential to determine its depth.

Additional processes significantly distort the proton spectra, complicating potential extraction.

The observed spectra can be explained with a shallow kaon optical potential consistent with chiral models.

Abstract

We study the (K-,p) reaction on nuclei with a 1 GeV/c momentum kaon beam, paying a special attention at the region of emitted protons having kinetic energy above 600 MeV, which was used to claim a deeply attractive kaon nucleus optical potential. Our model describes the nuclear reaction in the framework of a local density approach and the calculations are performed following two different procedures: one is based on a many-body method using the Lindhard function and the other one is based on a Monte Carlo simulation. While both procedures coincide when it comes to consider the contribution of kaon quasi-elastic scattering, the simulation method offers more flexibility since it allows us to account for other processes which also contribute to the proton spectra, such as K- absorption by one and two nucleons producing hyperons. The simulation also considers final state interactions in terms of multiple scattering of the K-, p and all other primary and secondary particles on their way out of the nucleus, as well as the weak decay of the produced hyperons into (pi N). We find that this kaon in-flight reaction is not well suited to determine the kaon optical potential due, essentially, to the limited sensitivity of the cross section to its strength, but also to unavoidable uncertainties in the contribution from other processes. We also simulate the experimental requirement of having, together with the energetic proton, at least one charged particle detected in the decay counter surrounding the target, and find that the shape of the original cross section is appreciably distorted. We conclude that the new mechanisms, not considered in the analysis of the original experiment, allow us to explain the observed spectrum with the shallow kaon nucleus optical potential obtained in chiral models.