Detection of $\pi^+\pi^-$atoms with the DIRAC spectrometer at CERN

TL;DR

The DIRAC experiment at CERN aims to precisely measure the lifetime of $^+^-$ atoms to determine $$-scattering lengths difference, using detection of characteristic $^+^-$ pairs from atom break-up.

Contribution

First high-statistics data sample of $^+^-$ atoms obtained and methods developed to distinguish signal from background.

Findings

Successful detection of $^+^-$ atoms from p Ni interactions.

Development of background separation techniques.

Initial data demonstrating feasibility of lifetime measurement.

Abstract

The goal of the DIRAC experiment at CERN is to measure with high precision the lifetime of the $\pi^+\pi^-$ atom ($A_{2\pi}$), which is of order $3\times10^{-15}$ s, and thus to determine the s-wave $\pi\pi$-scattering lengths difference $|a_{0}-a_{2}|$. $A_{2\pi}$ atoms are detected through the characteristic features of $\pi^+\pi^-$ pairs from the atom break-up (ionization) in the target. We report on a first high statistics atomic data sample obtained from p Ni interactions at 24 GeV/$c$ proton momentum and present the methods to separate the signal from the background.