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B τ → eνν + B τ → $_{µνν}$. The true yields N true i obtained from Eq. 2 are given in the third column of Table II. 

This normalization method requires a precise measurement of the number of { e, µ } events and a careful determination of the corresponding efficiency. Figure 9 shows a comparison of the invariant mass of the electron and muon system and the cosine of the angle between electron and muon, for real { e, µ } events and the sum of MC expectations. The MC reproduces the data reasonably well. The background fraction is estimated to be 5 . 9% using MC. After subtracting background, we obtain the number of { e, µ } events. 

Figure 10 shows the observed distributions of M ( πππ ), M ( Kππ ), M ( KKπ ), and M ( KKK ). The backgrounds are represented by the hatched and the gray histograms for the 

