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

• DOI: 10.1016/j.physletb.2005.11.087
• Publication Date: 2005-12-15T20:38:49Z
• Authors: 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; L. Gatignon; A. Gonidec; W. Kubischta; A. Norton; M. Patel; A. Peters; S. Balev; P.L. Frabetti; E. Goudzovski; P. Hristov; V. Kekelidze; V. Kozhuharov; L. Litov; D. Madigozhin; E. Marinova; N. Molokanova; I. Polenkevich; Yu. Potrebenikov; S. Stoynev; A. Zinchenko; E. Monnier; E. Swallow; R. Winston; P. Rubin; A. Walker; W. Baldini; A. Cotta Ramusino; P. Dalpiaz; C. Damiani; M. Fiorini; A. Gianoli; M. Martini; F. Petrucci; M. Savrié; M. Scarpa; H. Wahl; A. Bizzeti; M. Calvetti; E. Celeghini; E. Iacopini; M. Lenti; F. Martelli; G. Ruggiero; M. Veltri; M. Behler; K. Eppard; K. Kleinknecht; P. Marouelli; L. Masetti; U. Moosbrugger; C. Morales Morales; B. Renk; M. Wache; R. Wanke; A. Winhart; D. Coward; A. Dabrowski; T. Fonseca Martin; M. Shieh; M. Szleper; M. Velasco; M.D. Wood; G. Anzivino; P. Cenci; E. Imbergamo; M. Pepe; M.C. Petrucci; M. Piccini; M. Raggi; M. Valdata-Nappi; C. Cerri; G. Collazuol; F. Costantini; L. DiLella; N. Doble; R. Fantechi; L. Fiorini; S. Giudici; G. Lamanna; I. Mannelli; A. Michetti; G. Pierazzini; M. Sozzi; B. Bloch-Devaux; C. Cheshkov; J.B. Chèze; M. De Beer; J. Derré; G. Marel; E. Mazzucato; B. Peyaud; B. Vallage; M. Holder; A. Maier; M. Ziolkowski; S. Bifani; C. Biino; N. Cartiglia; M. Clemencic; S. Goy Lopez; F. Marchetto; H. Dibon; M. Jeitler; M. Markytan; I. Mikulec; G. Neuhofer; L. Widhalm
• Keywords: simmetria chirale; scattering lengths; Nuclear and High Energy Physics; High Energy Physics - Experiment (hep-ex); Pion scattering length; Charged Kaon Decay; Chiral Perturbation Theory; Dalitz Plot; Cusp Structure; pion-pion scattering length; k mesons; pion pion scattering; invariant mass; 0103 physical sciences; FOS: Physical sciences; 01 natural sciences; mesone K; decadimento; cusp; lunghezza di scattering; High Energy Physics - Experiment

We report the results from a study of ~23 Million K+- ==> pi+- pizero decays recorded by NA48/2 experiment at CERN SPS, showing an anomaly in invariant mass distribution region around 2m+, where m+ is charged pion mass. This anomaly, never observed previous experiments, can be interpreted as effect due mainly to final state charge exchange scattering process pi+ pi- decay. It provides precise determination a0 - a2, difference between pi-pi lengths isospin I=0 and I=2 states.