Detailed study of the K ± → π 0 π 0 e ± ν (K e4 00 ) decay properties
J.R. Batley (Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, U.K.); G. Kalmus (Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, U.K.); C. Lazzeroni (Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, U.K.); D.J. Munday (Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, U.K.); M.W. Slater (Cavendish Laboratory, University of Cambridge, Cambridge, CB3 0HE, U.K.); et al - Show all 122 authors
A sample of 65210 K ± → π 0 π 0 e ± ν (K e4 00 ) decay candidates with 1% background contamination has been collected in 2003-2004 by the NA48/2 collaboration at the CERN SPS. A study of the differential rate provides the first measurement of the hadronic form factor variation in the plane ( M ππ 2 , M eν 2 ) and brings evidence for a cusp-like structure in the distribution of the squared π 0 π 0 invariant mass around 4 m π + 2 $$ 4{m}_{\pi^{+}}^2 $$ . Exploiting a model independent description of this form factor, the branching ratio, inclusive of radiative decays, is obtained using the K ± → π 0 π 0 π ± decay mode as normalization. It is measured to be BR(K e4 00 ) = (2.552 ± 0.010 stat ± 0.010 syst ± 0.032 ext ) × 10 −5 , which improves the current world average precision by an order of magnitude while the 1.4% relative precision is dominated by the external uncertainty from the normalization mode. A comparison with the properties of the corresponding mode involving a π + π − pair (K e4 + − ) is also presented.
