Experimental Measurement of the Form Factors of the DecayKL0→π±e∓ν

We have analyzed 25 000 $K_{e3\mathrm{}}$ decays, reconstructed to the center of mass by measurement of the ${K_L}^0$ momentum from time of flight and measurement of the $\pi$ and $e$ momenta with a spark-chamber-magnet spectrometer. Using the linear parametrization of the vector form factor $f_{+}\left(q^2\right)=1+{\lambda }_{+}\left(\frac{q^2}{{m_{\pi }}^2}\right)$ we find ${\lambda }_{+}=0.0270\mathrm{}\pm 0.0028$. Upper limits for the scalar ($f_s$) and tensor ($f_t$) form factors at the 68% confidence level are $\frac{f_s}{f_{+}}<0.04\mathrm{}$, $\frac{f_t}{f_{+}}<0.23\mathrm{}$, corresponding to intensity ratios $\frac{I_s}{I_v}=0.3\%$ and $\frac{I_t}{I_v}<0.4\%$.