Ξ − atomic X-ray spectroscopy using a counter-emulsion hybrid method

Abstract

Ξ− atomic X-ray spectroscopy is one of the most useful methods for investigation of the Ξ-nucleus strong interaction. Since the X-ray energy is shifted and/or broadened due to the Ξ-nucleus strong interaction compared to those calculated from electromagnetic interaction alone, the measurement of the energy shift, ΔE, and the width, Γ, give us information on the Ξ-nucleus potential. A serious problem in the measurement is the significant background derived from in-flight Ξ− decay. A novel method of identifying stopped Ξ− events using the nuclear emulsion was developed to realize the first Ξ− atomic X-ray spectroscopy experiment as the J-PARC E07 experiment, which also aimed at searching for ΛΛ and Ξ− hypernuclei in the emulsion. The X-rays emitted from Ξ− Br and Ξ− Ag atoms were measured using germanium detectors. No clear peaks were observed in the obtained spectra. However, we succeeded in reducing the background to 1/170 by this method employing the coincidence measurements using the nuclear emulsion and X-ray detectors.