Observation of a cusp-like structure in the π0π0 invariant mass distribution from K±→π±π0π0 decay and determination of the ππ scattering lengths

J.R. Batley, C. Lazzeroni, D.J. Munday, M.W. Slater, S.A. Wotton, R. Arcidiacono, G. Bocquet, N. Cabibbo, A. Ceccucci, D. Cundy, V. Falaleev, M. Fidecaro (+107 others)
2006 Physics Letters B  
We report the results from a study of ~23 Million K+- ==> pi+- pizero pizero decays recorded by the NA48/2 experiment at the CERN SPS, showing an anomaly in the pizero pizero invariant mass distribution in the region around 2m+, where m+ is the charged pion mass. This anomaly, never observed in previous experiments, can be interpreted as an effect due mainly to the final state charge exchange scattering process pi+ pi- ==> pizero pizero in K+- ==> pi+- pi+ pi- decay. It provides a precise
more » ... des a precise determination of a0 - a2, the difference between the pi-pi scattering lengths in the isospin I=0 and I=2 states.
doi:10.1016/j.physletb.2005.11.087 fatcat:s4b7j7rs2nfnxmtxzmrwcewhxu