Testing LFV measuring the ratio [formula omitted] between the Branching Ratio of [formula omitted] and [formula omitted] in NA48/2 experiment: Measurement and Perspectives

Abstract

The measurement of the ratio R K = Br [ K ± → e ± ν ( γ ) ] / Br [ K ± → μ ± ν ( γ ) ] between the Branching Ratios of K ± → e ± ν ( γ ) and K → μ ± ν ( γ ) decays is a sensitive test of lepton universality and new physics. This ratio is predicted by the Standard Model with high precision [M. Finkemeier, Phys. Lett. B 387 (1996) 391, hep-ph/9505434 ], while its present measurement accuracy is limited by the lack of a statistically proportionate sample of K ± → e ± ν ( γ ) decays [A.R. Clark et al., Phys. Rev. Lett. 29 (1972) 1274] [K.S. Heard et al., Phys. Lett. B 55 (1975) 324] [K.S. Heard et al., Phys. Lett. B 60 (1976) 302]. The NA48/2 experiment [J.R. Batley et al., CERN/SPSC 2000-003 (2000)], located at CERN SPS accelerator, collected two different data sets of Kaon leptonic decays. The former sample has been collected in 2003 data taking and the latter in 2004 data taking. After the description of the most relevant features of the data collected in 2003 and 2004, a preliminary result based on 2003 data set will be presented: R K = ( 2.416 ± 0.043 ( stat ) ± 0.024 ( syst ) ) ⋅ 10 −5 Future perspectives to improve the measurement precision are also discussed.