A New Measurement of Kaonic Hydrogen X rays

TL;DR

This paper reports the most precise measurements of the energy-level shift and width of kaonic hydrogen's 1s state, providing critical data for understanding low-energy antikaon-nucleon interactions and testing QCD predictions.

Contribution

It presents the first high-precision measurements of kaonic hydrogen X-ray spectra using advanced silicon drift detectors at DAΦNE, offering new constraints for low-energy QCD models.

Findings

Measured shift: -283 ± 36 ± 6 eV

Measured width: 541 ± 89 ± 22 eV

Provides constraints for theoretical models of ar K N interaction

Abstract

The $\bar{K}N$ system at threshold is a sensitive testing ground for low energy QCD, especially for the explicit chiral symmetry breaking. Therefore, we have measured the $K$-series x rays of kaonic hydrogen atoms at the DA$\Phi$NE electron-positron collider of Laboratori Nazionali di Frascati, and have determined the most precise values of the strong-interaction energy-level shift and width of the $1s$ atomic state. As x-ray detectors, we used large-area silicon drift detectors having excellent energy and timing resolution, which were developed especially for the SIDDHARTA experiment. The shift and width were determined to be $\epsilon_{1s} = -283 \pm 36 \pm 6 {(syst)}$ eV and $\Gamma_{1s} = 541 \pm 89 {(stat)} \pm 22 {(syst)}$ eV, respectively. The new values will provide vital constraints on the theoretical description of the low-energy $\bar{K}N$ interaction.