Precise tests of low energy QCD from Ke4 decay properties

Batley, J. R.; 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.; Stoynev, S.; Zinchenko, A.; Monnier, E.; Swallow, E.; Winston, R.; Rubin, P.; Walker, A.; Baldini, Wander; COTTA RAMUSINO, Angelo; Dalpiaz, Pietro; Damiani, C.; Fiorini, Massimiliano; Gianoli, Alberto; Martini, M.; Petrucci, Ferruccio Carlo; Savrie', Mauro; Scarpa, M.; Wahl, H.; Bizzeti, A.; Calvetti, M.; Iacopini, E.; Lenti, M.; Ruggiero, G.; 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.; Cenci, P.; Imbergamo, E.; Nappi, A.; Pepe, M.; Petrucci, M. C.; Piccini, M.; Raggi, M.; Valdata Nappi, M.; Cerri, C.; Collazuol, G.; Costantini, F.; Dilella, L.; Doble, N.; Fantechi, R.; Fiorini, L.; Giudici, S.; Lamanna, G.; Mannelli, I.; Michetti, A.; Pierazzini, G.; Sozzi, M.; Venditti, S.; Bloch Devaux, B.; Cheshkov, C.; Chèze, J. B.; De Beer, M.; Derré, J.; Marel, G.; Mazzucato, E.; Peyaud, B.; Vallage, B.; Holder, M.; Ziolkowski, M.; Bifani, S.; Biino, C.; Cartiglia, N.; Clemencic, M.; Goy Lopez, S.; Marchetto, F.; Dibon, H.; Jeitler, M.; Markytan, M.; Mikulec, I.; Neuhofer, G.; Widhalm, L.

doi:10.1140/epjc/s10052-010-1480-6

We report results from the analysis of the K± → π + π −e± ν (Ke4) decay by the NA48/2 collaboration at the CERN SPS, based on the total statistics of 1.13 million decays collected in 2003–2004. The hadronic form factors in the S- and P-wave and their variation with energy are obtained. The phase difference between the S- and P-wave states of the ππ system is accurately measured and allows a precise determination of the a00 and a20, the I = 0 and I = 2 S-wave ππ scattering lengths. Combination of this result with the other NA48/2 measurement obtained in the study of decays brings an improved determination of a00 and the first precise experimental measurement of a20, providing a stringent test of Chiral Perturbation Theory predictions and lattice QCD calculations. Using constraints based on analyticity and chiral symmetry, even more precise values are obtained.