Lepton Flavour Violation Experiments

Table 5

Efficiencies, number of expected background and observed events and 90% C.L. BR upper limits (BR90) for 𝜏→3ℓ CLFV searches for BaBar and Belle (adapted from [119, 120]).

Mode	BaBar				Belle
	𝜖 (%)	𝑁bkg	𝑁obs	BR90	𝜖 (%)	𝑁bkg	𝑁obs	BR90
𝑒^−𝑒^+𝑒^−	8.6±0.2	0.12±0.02	0	2.9×10^−8	6.0	0.21±0.15	0	2.7×10^−8
𝜇^−𝑒^+𝑒^−	8.8±0.5	0.64±0.19	0	2.2×10^−8	9.3	0.04±0.04	0	1.8×10^−8
𝜇^+𝑒^−𝑒^−	12.7±0.7	0.34±0.12	0	1.8×10^−8	11.5	0.01±0.01	0	1.5×10^−8
𝑒^+𝜇^−𝜇^−	10.2±0.6	0.03±0.02	0	2.6×10^−8	10.1	0.02±0.02	0	1.7×10^−8
𝑒^−𝜇^+𝜇^−	6.4±0.4	0.54±0.14	0	3.2×10^−8	6.1	0.10±0.04	0	2.7×10^−8
𝜇^−𝜇^+𝜇^−	6.6±0.6	0.44±0.17	0	3.3×10^−8	7.6	0.13±0.06	0	2.1×10^−8