We report the results from a study of a partial sample of ∼2.3×107K±→π±π0π0 decays recorded by the NA48/2 experiment at the CERN SPS, showing an anomaly in the π0π0 invariant mass (M00) distribution in the region around M00=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 π+π−→π0π0 in K±→π±π+π− decay [N. Cabibbo, Phys. Rev. Lett. 93 (2004) 121801]. It provides a precise determination of a0−a2, the difference between the ππ scattering lengths in the isospin I=0 and I=2 states. A best fit to a rescattering model [N. Cabibbo, G. Isidori, JHEP 0503 (2005) 21] corrected for isospin symmetry breaking gives (a0−a2)m+=0.268±0.010(stat)±0.004(syst), with additional external uncertainties of ±0.013 from branching ratio and theoretical uncertainties. If the correlation between a0 and a2 predicted by chiral symmetry is taken into account, this result becomes (a0−a2)m+=0.264±0.006(stat)±0.004(syst)±0.013(ext).

Observation of a cusp-like structure in the pi(0)pi(0) invariant mass distribution from K-+/-->pi(+/-)pi(0)pi(0) decay and determination of the pi pi 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; 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. DiLell; 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. - In: PHYSICS LETTERS. SECTION B. - ISSN 0370-2693. - STAMPA. - 633:(2006), pp. 173-182. [10.1016/j.physletb.2005.11.087]

Observation of a cusp-like structure in the pi(0)pi(0) invariant mass distribution from K-+/-->pi(+/-)pi(0)pi(0) decay and determination of the pi pi scattering lengths

CALVETTI, MARIO;CELEGHINI, ENRICO;IACOPINI, ENRICO;M. Lenti;
2006

Abstract

We report the results from a study of a partial sample of ∼2.3×107K±→π±π0π0 decays recorded by the NA48/2 experiment at the CERN SPS, showing an anomaly in the π0π0 invariant mass (M00) distribution in the region around M00=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 π+π−→π0π0 in K±→π±π+π− decay [N. Cabibbo, Phys. Rev. Lett. 93 (2004) 121801]. It provides a precise determination of a0−a2, the difference between the ππ scattering lengths in the isospin I=0 and I=2 states. A best fit to a rescattering model [N. Cabibbo, G. Isidori, JHEP 0503 (2005) 21] corrected for isospin symmetry breaking gives (a0−a2)m+=0.268±0.010(stat)±0.004(syst), with additional external uncertainties of ±0.013 from branching ratio and theoretical uncertainties. If the correlation between a0 and a2 predicted by chiral symmetry is taken into account, this result becomes (a0−a2)m+=0.264±0.006(stat)±0.004(syst)±0.013(ext).
2006
633
173
182
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. DiLell; 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
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