1. A Method to measure  + /   detection efficiency asymmetry at LHCb Liming Zhang 08/15/07

2. 2 Idea Partially reconstruct D  +   s  D 0, D 0  K S 0  +   without   => partial yield Combine   to fully reconstruct D 0 => full yield full/partial yield => absolute  efficiency Br(b  D* + X) = (17.3  2.0)% Br(D* +  D 0  K S 0 (  +      +   ) = (1.36  0.09)%

3. 3 MC Samples 491 k signal MC B 0  D*   +, D*  to this channel 680 k inclusive b MC 766 k inclusive b biased MC

4. 4 Signal MC M(K S  + )  m = M(K S  +  + )  M(K S  + ) M(K S  + ) in [1.5, 1.7] GeV M(K S  + ) in [1.0, 1.3] GeV Reconstructed Distributions Only consider this region here

5. 5 Optimization of Selection Criteria Maximize Figure of Merit FOM = S/sqrt(S+B) on inclusive b MC S: signal yield in this inclusive b MC, predicted by using efficiency from signal MC B: background yield scaled from  m sideband of this inclusive b MC The signal region:  m<15 MeV Sideband region: [50, 150] MeV  m background distribution Sideband region Signal region

6. 6 K S 0 reconstruction K S  DD (2/3) (only used here) K S  LL (1/3) Daughters IP significance > 2 Daughters track fit    Vertex    Pt > 1 GeV/c Proper time/life time > 0.17 Vr>21 mm Vz  [150, 2330] mm Mass window  17 MeV

7. 7 Distributions of K S 0 purity 80%  ~ 10 MeV > 21 mm >0.17 [150,2330] mm  17 MeV Signal Background

8. 8 Selection Criteria Prompt  + from D 0 : –PID –IP significance > 5 –Pt > 700 MeV Signal Background

9. 9 Selection Criteria slow  s + : –IP significance > 1 –Pt > 220 MeV Signal Background

10. 10 Selection Criteria D 0 vertex    D* vertex    Multiply candidates selection –Same D0 combines with several slow pion –Choose the one which has the best D* vertex   –B/S reduced from 2.0 to 1.7 Not helpful from cuts on IP significance, flight distance (significance) etc.

11. 11 Results of partial reconstruction Efficiency (before Trigger) –  = N REC /N GEN   GEN = 1656/391k  20% = (0.85  0.02)  10  3 Annual yield (before Trigger) –S = 2fb  1  500  b  2  (17.3  2.0)%  (1.36  0.09)%  (0.85  0.02)  10  3 = (4.0  0.3)  10 6 Signal from bb inclusive MC data –Expect 31 –29 found –Fit gives 33  9 –B/N ~ 1.7

12. 12 TO DO To check background sources and further suppress background level if possible Trigger efficiency To fully reconstruct D 0 by combining   with partially reconstructed candidate To find efficiency of    and give the prediction of stat. error on detection asymmetry from this method