Lifetime measurement of atoms consisting of pi+ and pi- mesons

TL;DR

This paper reports a precise lifetime measurement of pi+pi- atoms (A2pi), which tests chiral symmetry breaking in QCD by comparing experimental results with theoretical predictions of pion-pion scattering lengths.

Contribution

It presents a novel experimental approach to measure the lifetime of A2pi atoms with 10% precision, providing a model-independent way to determine the difference in scattering lengths.

Findings

Preliminary lifetime measurement results are presented.

The method enables a sensitive test of chiral symmetry breaking.

Data from Pt, Ni, and Ti targets support the measurement approach.

Abstract

The lifetime measurement of pi+pi- atoms (A2pi) with 10% precision provides in a model independent way the difference between the S-wave pion-pion scattering lengths for isospin 0 and 2, |a0 -a2|, with 5% accuracy. The scattering lengths a0 and a2 have been calculated in Chiral Perturbation Theory (ChPT) with a precision better than 2.5%. Therefore, such a measurement will be a sensitive check of the understanding of chiral symmetry breaking in QCD by giving an indication about the value of the quark condensate, an order parameter of QCD. The method of observation and lifetime measurement of A2pi are discussed. Data on A2pi production in Pt, Ni and Ti targets and preliminary results for the lifetime measurement are presented.