Abstract: | We report results from a new measurement of the Ke4 decay K±→π+π-e±ν by the NA48/2 collaboration at the CERN SPS, based on a partial sample of more than 670 000 Ke4 decays in both charged modes collected in 2003. The form factors of the hadronic current (F,G,H) and ππ phase difference
(δ=δs-δp) have been measured in ten independent bins of the ππ mass spectrum to investigate their variation. A sizeable acceptance
at large ππ mass, a low background and a very good resolution contribute to an improved experimental accuracy, a factor two
better than in the previous measurement, when extracting the ππ scattering lengths a0
0 and a0
2. Under the assumption of isospin symmetry and using numerical solutions of the Roy equations, the following values are obtained
in the plane (a0
0,a0
2): a0
0=0.233±0.016stat±0.007syst,a0
2=-0.0471±0.011stat±0.004syst. The presence of potentially large isospin effects is also considered and will allow comparison
with precise predictions from Chiral Perturbation Theory.
PACS 13.20.Eb; 13.75.Lb |