K  fake rates from D ⁰ →K -  + Vs D ⁰ →K ±  ∓ Sadia Khalil & Sheldon Stone EHEP Group Meeting Oct 2007

Objective Study the RICH efficiency and fake rates for kaons and pions. Method D 0 D 0 → K -  +, K   ± (CC is implied) Selection Criteria TagSide Signal Side <  E 1 < <  E 2 < <m bc1 < <m bc2 <1.87 For Trk 1, n  K ≥3 and for Trk 2 n  ≥3 For Trk 2, L K L  Tracks are within RICH solid angle } NoPID Charge of (K Tag ≠ K signal ) Charge of (K Tag = K signal ) Wrong Sign Rigth Sign

No PID

Kaon with RICH

Pion with RICH

Double ID

To ascertain the backgrounds we checked m bc (Kpi) Vs m bc (Kpi) plot The signal side is described with the RICH applied.

No PIDSingle K Single  Double ID K -  +, K   ± RSWSRSWSRSWSRSWS Result(600pb -1 ) The 2 events in WS-Double ID can be only from mixing as doubly Cabbibo decays are forbidden due to Bose-Einsitien statistics or they can be background. We subtract these 2 (actually RS) events from the other WS candidates. Efficiencies and Fake Rates ε K = 90.6 %, ε  = 97.4 % f K→  = (2.41± 0.52) % f  →K = (1.08± 0.34) %