The average multiplicity is calculated with the formula
B(B → φX) = 1 2N BB B(φ → K + K − ) 16 i=1 N φ B,i ε i ,(1)
where N φ B,i is the number of φ mesons in momentum bin i found in the **data** and assumed to come from B mesons. This number is obtained by performing the background fit to the on-resonance **data** samples after subtracting the off-resonance **data** samples, scaled to the on-resonance luminosity. The efficiency ε = ε 2T ε K + ε K − is the product of the reconstruction efficiency and the kaon identification efficiencies for each track. The quantity N BB is the number of BB events in the **data** sample, which is measured to be N BB = (18.7 ± 0.2) × 10 6 using a technique described elsewhere [10].