Determination of the S-wave pi pi scattering lengths from a study of K+- -> pi+- pi0 pi0 decays

Understand

We report the results from a study of the full sample of ~ 6.031 10^7 K+- -> pi+- pi0 pi0 decays recorded by the NA48/2 experiment at the CERN SPS.

• As first observed in this experiment, the pi0 pi0 invariant mass M00 distribution shows a cusp-like anomaly in the region around M00 = 2m+, where m+ is the charged pion mass.
• This anomaly has been interpreted as an effect due mainly to the final state charge exchange scattering process pi+ pi- -> p0 p0 in K+- -> pi+- pi+ pi- decay.
• Fits to the M00 distribution using two different theoretical formulations provide the presently most precise determination of (a0 - a2), the difference between the pi pi S-wave scattering lengths in the isospin I=0 and I=2 states.