Determination of the S-wave pi pi scattering lengths from a study of K(+/-) -> pi(+/-)pi(0)pi(0) decays

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

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

We report the results from a study of the full sample of similar to 6.031 x 10(7) K(+/-) -> pi(+/-)pi(0)pi(0) decays recorded by the NA48/2 experiment at the CERN SPS. As first observed in this experiment, the pi(0)pi(0) invariant mass (M(00)) distribution shows a cusp-like anomaly in the region around M(00) = 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(-) -> pi(0)pi(0) in K(+/-) -> pi(+/-)pi(+)pi(-) decay. Fits to the M(00) distribution using two different theoretical formulations provide the presently most precise determination of a(0) - a(2), 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 a(2).