Measurement of K 0 μ 3 form factors NA 48 Collaboration

This paper reports on a new high precision measurement of the form factors of the KL → π μ νμ decay. The data sample of about 2.3×106 events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, λ ′ + = (20.5±2.2stat±2.4syst)×10, and a quadratic, λ ′′ + = (2.6± 0.9stat ± 1.0syst) × 10 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 λ0 = (9.5±1.1stat±0.8syst)×10. Using a linear fit our results were: λ+ = (26.7±0.6stat ±0.8syst)×10 and, λ0 = (11.7±0.7stat ±1.0syst)×10. A pole fit of the form factors yields: mV = (905 ± 9stat ± 17syst) MeV/c and mS = (1400 ± 46stat ± 53syst) MeV/c.