First measurement of the $π^+π^-$ atom lifetime

Abstract

The goal of the DIRAC experiment at CERN (PS212) is to measure the $π^+π^-$ atom lifetime with 10% precision. Such a measurement would yield a precision of 5% on the value of the $S$-wave $ππ$ scattering lengths combination $|a_0-a_2|$. Based on part of the collected data we present a first result on the lifetime, $τ=[2.91 ^{+0.49}_{-0.62}]\times 10^{-15}$ s, and discuss the major systematic errors. This lifetime corresponds to $|a_0-a_2|=0.264 ^{+0.033}_{-0.020} m_π^{-1}$.