A Fisher discriminant selection for $Bd \to K^{*0} \mu+ \mu-$ at LHCb

The decay $Bd \to K^{*0} \mu+ \mu-$ proceeds via a flavour changing neutral current and is sensitive to new physics. Previous studies have used a cut-based selection to isolate the signal. In the present note a selection based on a Fisher discriminant is presented. The total selection efficiency is estimated to be 1.08 +- 0.01 % (assuming a trigger efficiency of 87%). The signal yield is then expected to be 6200 -1500 +1700 events/2fb-1 integrated luminosity with a background of 1550 +- 310 events, giving a background-to-signal ratio 0.25 +- 0.08. Peaking backgrounds from $Bs \to \phi \mu+ \mu-$ and $Bd \to J\psi K{*^0}$ have been identified. These are each suppressed to less than 100 events/2fb-1 by using suitable vetos on the relevant invariant masses. The remaining background is dominated by candidates in which three particles from one B hadron decay are combined with a particle selected from another B decay, and candidates in which at least 30% of the hits used for reconstructing a particle do not come from the same simulated particle.