Measurement of K^{0}_{\mu3} form factors

Abstract

This paper reports on a new high precision measurement of the form factors of the K_{L}\to π^{\pm} μ^{\mp} ν_μ decay. The data sample of about 2.3$\times 10^6$ events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, ${\lambda }_{+}^{{}^{\prime }}=(20.5\pm 2.2_{stat}\pm 2.4_{syst})\times 10^{-3}$, and a quadratic, ${\lambda }_{+}^{{}^{\prime \prime }}=(2.6\pm 0.9_{stat}\pm 1.0_{syst})\times 10^{-3}$ term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be ${\lambda }_0=(9.5\pm 1.1_{stat}\pm 0.8_{syst})\times 10^{-3}$. Using a linear fit our results were: ${\lambda }_{+}=(26.7\pm 0.6_{stat}\pm 0.8_{syst})\times 10^{-3}$ and, ${\lambda }_0=(11.7\pm 0.7_{stat}\pm 1.0_{syst})\times 10^{-3}$. A pole fit of the form factors yields: $m_V=(905\pm 9_{stat}\pm 17_{syst})$ MeV/c${}^2$ and $m_S=(1400\pm 46_{stat}\pm 53_{syst})$ MeV/c${}^2$.

22 pages 7 figures