Investigation of systematic errors and estimation of $\pi K$ atom lifetime

This note describes details of analysis of data sample collected by DIRAC experiment on Ni target in 2008-2010 in order to estimate lifetime of $\pi K$ atoms. Experimental results consists of six distinct data samples: both charge combinations ($\pi^+K^−$ and $K^+\pi^−$ atoms) obtained in dierent experimental conditions corresponding to each year of data-taking. Sources of systematic errors are analyzed, and estimations of systematic errors are presented. Taking into account both statistical and systematic uncertainties, the lifetime of $\pi K$ atoms is estimated by maximum likelihood method.