The K_S \to pi+/- e+ e- decay mode has been investigated using the data
collected in 2002 by the NA48/1 collaboration. With about 23k signal events and
59k K_L \to pi+ pi- pi0_D normalization decays, the K_S \to pi+ pi- e+ e-
branching ratio was determined. This result is also used to set an upper limit
on the presence of E1 direct emission in the decay amplitude. The CP-violating
asymmetry has been also measured.
We report on measurements of the rare decays K +/- \to pi+/- e+ e- and K+/-
\to pi+/- mu+ mu- . The full NA48/2 data set was analyzed, leading to more than
7200 reconstructed events in the electronic and more than 3000 events in the
muonic channel, the latter exceeding the total existing statistics by a factor
of four. For both channels the selected events are almost background-free. From
these events, we have determined the branching fraction and form factors of
K+/- \to pi+/- e+ e- using different theoretical models. Our results improve
the existing world averages significantly. In addition, we measured the CP
violating asymmetry between K+ and K- in this channel to be less than a few
percent.Comment: 4 pages, 1 figure, To appear in the proceedings of IX International
Conference on Hyperons, Charm and Beauty Hadrons (BEACH2010), Perugia, Italy,
21-26 June 201
