Determination of the S-wave π π scattering lengths from a study of K ±→π ± π 0 π 0 decays

J R Batley,J Derré,U Moosbrugger,G Ruggiero,V Kekelidze,B Bloch-Devaux,E Goudzovski,D Cundy,M Sozzi,R Wanke,A Gonidec,A Bizzeti,F Petrucci,A Peters,M Holder,M Raggi,P Dalpiaz,G Pierazzini,A Ceccucci,A Norton,L Widhalm,M Scarpa,M Ziolkowski,M Patel,B Peyaud,W Kubischta,A Michetti,A J Culling,E Iacopini,I Polenkevich,B Vallage,C Damiani,M Savrié,M De Beer,G Collazuol,G Anzivino,D Madigozhin,C Biino,P Marouelli,V Falaleev,G Bocquet,M Martini,T Fonseca Martin,I Mannelli,M W Slater,A Gianoli,M Lenti,M Clemencic,G Lamanna,M Piccini,H Dibon,H Wahl,K Eppard,M Fiorini,M Markytan,C Morales Morales,G Marel,L Litov,A Maier,C Lazzeroni,M Velasco,R Winston,W Baldini,A Cotta Ramusino,D Coward,K Kleinknecht,V Kozhuharov,M Szleper,B Renk,A Dabrowski,P Rubin,S Stoynev,M Calvetti,G Kalmus,L Masetti,F Marchetto,E Marinova,M C Petrucci,R Fantechi,S Giudici,A Winhart,S Balev,L Fiorini,P L Frabetti,Yu Potrebenikov,S Bifani,A Nappi,E Monnier,N Cabibbo,M Shieh,C Cheshkov,L Gatignon,L Dilella,M Veltri,I Mikulec,P Hristov,M Wache,E Imbergamo,F Costantini,N Doble,G Neuhofer,N Molokanova,S Venditti,S A Wotton,M Fidecaro,P Cenci,R Arcidiacono,C Cerri,A Walker,E Mazzucato,M Jeitler,N Cartiglia,M Behler,A Zinchenko,Max Wood ,J.b Chèze ,D.j Munday ,E C Swallow ,S Goy Lopez ,M Pepé ,M Valdata‐Nappi

doi:10.1140/epjc/s10052-009-1171-3

Abstract

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. Higher-order pi pi rescattering terms, included in the two formulations, allow also an independent, though less precise, determination of a2.

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