Measurement of the $\pi K$ atom lifetime and the $\pi K$ scattering length

TL;DR

This paper reports the first measurement of the $ ext{pi K}$ atom lifetime and derives the $ ext{pi K}$ scattering length, providing new experimental data for understanding strong interactions in meson systems.

Contribution

The study presents the first measurement of the $ ext{pi K}$ atom lifetime and extracts the $ ext{pi K}$ scattering length with high precision, advancing knowledge of meson interactions.

Findings

Measured $ ext{pi K}$ atom lifetime: $(5.5^{+5.0}_{-2.8}) imes 10^{-15}$ s.

Derived $ ext{pi K}$ scattering length: $|a_0^-| = (0.072^{+0.031}_{-0.020}) M_{ ext{pi}}^{-1}$.

Abstract

After having announced the statistically significant observation (5.6~$\sigma$) of the new exotic $\pi K$ atom, the DIRAC experiment at the CERN proton synchrotron presents the measurement of the corresponding atom lifetime, based on the full $\pi K$ data sample: $\tau = (5.5^{+5.0}_{-2.8}) \cdot 10^{-15}s$. By means of a precise relation ($<1\%$) between atom lifetime and scattering length, the following value for the S-wave isospin-odd $\pi K$ scattering length $a_0^{-}~=~\frac{1}{3}(a_{1/2}-a_{3/2})$ has been derived: $\left|a_0^-\right| = (0.072^{+0.031}_{-0.020}) M_{\pi}^{-1}$.