A sample of 7253 K ± → π ± e + e - (γ) decay candidates with 1.0% background contamination has been collected by the NA48/2 experiment at the CERN SPS, which allowed a precise measurement of the decay properties. The branching ratio in the full kinematic range was measured to be BR = (3.11 ± 0.12) × 10 - 7, where the uncertainty includes also the model dependence. The shape of the form factor W (z), where z = (M e e / M K) 2, was parameterized according to several models, and, in particular, the slope δ of the linear form factor W (z) = W 0 (1 + δ z) was determined to be δ = 2.32 ± 0.18. A possible CP violating asymmetry of K + and K - decay widths was investigated, and a conservative upper limit of 2.1 × 10 - 2 at 90% CL was established.
|Original language||English (US)|
|Number of pages||9|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - Jun 29 2009|
ASJC Scopus subject areas
- Nuclear and High Energy Physics