\(D=\frac{\varepsilon_{L0}\varepsilon_{L1}\varepsilon_S}{\varepsilon_{L0}^\prime\varepsilon_{L1}^{\prime}\varepsilon_S^\prime}\cdot\frac{N_e}{N_{\mu}}\)
where \prime (denominator) corresponds to efficiencies of \(B\to KJ/\psi(ee)\) selections.
The problem is MC doesn’t model data well, so one have to apply reweighting to MC before calculating the efficiencies. 
so the generic procedure is 
unfortunately reweighting doesn't work well (potential discrepancies on other features) and one have to fix the simulation on deeper level.

Proposed solution

So the hypothesis is that incorrect MC simulation comes from improper simulation of \(\pi\) coming from the primary vertex that overlap with signal traces at the ECAL. the obvious test to falsify this hypothesis is to