Observation of a cusp-like structure in the π0π 0 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, L. Gatignon, A. Gonidec, W. Kubischta, A. Norton, M. Patel, A. Peters, S. Balev, P. L. FrabettiE. 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

*Corresponding author for this work

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157 Scopus citations


We report the results from a study of a partial sample of ∼2.3×107 K±→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 a 0-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).

Original languageEnglish (US)
Pages (from-to)173-182
Number of pages10
JournalPhysics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
Issue number2-3
StatePublished - Feb 9 2006

ASJC Scopus subject areas

  • Nuclear and High Energy Physics

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