High statistic measurement of the K−→π0e−ν decay form-factors

Abstract The decay K − → π 0 e − ν is studied using in-flight decays detected with the “ISTRA+” spectrometer. About 920K events are collected for the analysis. The λ + slope parameter of the decay form-factor f + ( t ) in the linear approximation (average slope) is measured: λ + lin =0.02774±0.00047(stat)±0.00032(syst). The quadratic contribution to the form-factor was estimated to be λ ′ + =0.00084±0.00027(stat)±0.00031(syst). The linear slope, which has a meaning of df + ( t )/ dt | t =0 for this fit, is λ + =0.02324±0.00152(stat)±0.00032(syst). The limits on possible tensor and scalar couplings are derived: f T / f + (0)=−0.012±0.021(stat)±0.011(syst), f S / f + (0)=−0.0037 +0.0066 −0.0056 (stat)±0.0041(syst).