Few-Body Aspects of the Near Threshold Pseudoscalar Meson Production

Paweł Moskal

doi:10.1007/s00601-014-0854-y

Abstract

During the last decade large samples of data have been collected on the production of the ground-state pseudoscalar mesons in collisions of proton or deuteron beam with hydrogen or deuterium target. These measurements have been performed in the vicinity of the kinematical threshold for meson production where only a few partial waves in both initial and final state are expected to contribute to the production process. This simplifies significantly the interpretation of the data, yet still appears to be challenging due to the three or four particle final state systems with a complex hadronic potential. We review experiments and phenomenology of the near threshold production of the ground-state mesons in the few-body final states as for example: nucleus-meson and nucleon-nucleon-meson, and report on the status of the search of the mesic-nuclei (a meson-nucleus bound states). Experimental advantages of measurements close to the kinematical threshold are discussed, and general features of the production mechanism of the η and η′ mesons in the nucleon-nucleon collisions are presented emphasising results of measurements of spin and isospin dependence of the production cross sections.

Highlights

The organisers encouraged the author to summarize the threshold meson production studies conducted so far
We will concentrate on the η and η mesons and the report will be restricted to the hadronic processes whereas for the photo-production the interested reader is referred e.g. to [1]
The η and η mesons are short lived and it is unfeasible to accomplish out of them a beam or target, and their interaction with other hadrons cannot be investigated in the standard way via scattering experiments

Summary

Introduction

The organisers encouraged the author to summarize the threshold meson production studies conducted so far. The η and η mesons are short lived and it is unfeasible to accomplish out of them a beam or target, and their interaction with other hadrons cannot be investigated in the standard way via scattering experiments Production of these mesons close to the kinematical threshold with low relative velocities to nucleons gives a chance to study their interaction with nucleons which may manifest itself as structures in a meson-nucleon invariant mass. A precise quantitative determination of their contributions is important especially for the studies of the meson nucleon interaction This is because influence of the meson-nucleon interactions on the cross sections distributions is small and may be easly burdened by the effects caused by the higher partial waves. The author is not aware of any plans of measurements of the spin observables for the η meson production in the collissions of nucleons

Experimental Advantages of the Threshold Meson Production

Threshold Production of the η-Nucelon–Nucleon and η -Nucleon–Nucleon Systems