The NA48 collaboration in CERN has recently provided information through two independent measurements on combinations of so-called scattering lengths associated with the scattering of two pions. The experiment is based on CERN's highest-intensity proton beamline and uses a large and sophisticated detector. The first measurement by the NA48/2 experiment1 comes from a recently proposed idea due to Cabibbo2 to measure a 'cusp' in the invariant mass distribution of pions resulting from the decay of kaons. A cusp at an energy corresponding to in the number distribution of the neutral pion pair as a function of their invariant mass, manifests itself as an abrupt change in the derivative of the number distribution. It is a fine effect and can be seen onlyif the sample size of events that are analysed is very large. The event sample here is enormous and is based on about 27 million 'events' For units in which the mass of the charged pion is set to unity, they obtain for the combination of scattering lengths the value 0.264 +-0.015, an accurate measurement of what was a rather poorly measured experimental quantity.
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