Pion scattering lengths from NA48

TL;DR

This paper reports on the measurement of pion scattering lengths using the cusp effect observed in kaon decays by the NA48/2 experiment, providing experimental data aligned with Chiral Perturbation Theory predictions.

Contribution

It presents the first measurement of the pion scattering length difference from NA48 data using the cusp effect interpretation within Chiral Perturbation Theory.

Findings

Measured (a0 - a2)m(pi+) = 0.281 +/- 0.007 (stat) +/- 0.014 (syst) +/- 0.014 (extern)

Confirmed the cusp effect as a tool for scattering length determination

Provided experimental validation for theoretical predictions in low-energy QCD

Abstract

The anomaly (cusp) in the mass spectrum of two neutral pions from the three-pion decays of charged kaon has been observed in the NA48/2 experiment. Using the recently developed interpretation of this effect in terms of Chiral Perturbative Theory, the pion scattering parameters are measured. The preliminary result for the pion scattering length difference, based on the part of statistics, is (a0-a2)m(pi+) = 0.281 +/- 0.007 (stat) +/- 0.014(syst) +/- 0.014(extern).