1. 1 The use of control channels in the analysis of the B s  μ + μ - decay Tuesday Meeting, 2 June 2009

2. 2 Introduction Interest of the Bs  μμ  Very Rare decay: FCNC, helicity suppress  SM prediction:  Current limit of Tevatron: @ 90% CL  An indirect search of NP BR sensible to Higgs sector Search at LHCb  ~330 events /fb -1 in LHCb for SM BR  Clear signal but large background!  A “simple” analysis? 10 -7 2x10 -8 5x10 -9 SUSY- NUHM arXiv:0709.0098

3. 3 processes Main background: bb  μμ (dimuon)

4. 4 Selection  Remove obvious background  Similar between signal and control channels L0+HLT Stripping Selection

5. 5 Trigger  Main trigger: dimuon (from L0 to HLT2)  Robust triggers: single muon, muon+track L0+HLT Stripping Selection Trigger efficiency: L0 HLT1HLT2 Total efficiency: Acceptance selection Trigger

6. 6 Analysis strategy 3 Likelihoods:  Geometrical Likelihood (GL) Combine geometrical variables DOCA(μ,μ), minIPS(μ,μ), IP(B s ), τ(B s ), Isolation(μ,μ)  Invariant mass  PID Likelihood: IsMuon boolean variable Sensitive Region (SR)  GL>0.5 & mass window ± 60 MeV  10 signal, 90 +70 -40 bkg events Mass(μμ): signal (points) GL: dimuon bkg, signal GLMassμ-misID IP ~ 17 μmσ~ 22 MeV0.5% 1 fb -1

7. 7 Analysis performance Exclusion & Observation  Different distribution of signal and background events in SR  CLs (“modified frequestist”) method Bins in GL, mass: 2x5 bins Exclusion: CLs+b/CLb<0.9; Evidence (3σ) 1-CLb<0.027; Observation (5σ) BR excluded 90% CLBR evidence (squared) and observed (starts) Uncertainty bar

8. 8 Analysis performance (@ 8TeV) Exclusion & Observation  Exclusion: surpass Tevatron at 0.2 fb -1  Evidence (3σ), ~ 4 fb -1 BR excluded 90% CLBR evidence (squared) and observed (starts)

9. 9 Use of the control channels Confidence!  Use of the control channels to calibrate the relevant distributions and compute the efficiency ratios  Crosschecks Calibration:  GL, mass, μPID distribution for signal, background Normalization  Ratios of efficiencies 13% error! B→KπReconstruction Selection Trigger μID B + →J/Ψ K + TriggerReconstruction Selection B→hh B s →KK J/Ψ

10. 10 GL calibration Background  Sidebands: uncorrelated mass, GL  MC stats: 5 pb -1  50 pb -1 Signal  Use MC GL “operator”  Calibrate with B  hh  B  hh bias by trigger TIS B  hh  σ ~6%  B  μμ affected by trigger GL: B  hh (sel and triggered) GL: B  hh TIS Selection +trigger Dimuon μ+track μ GL: B  μμ 0.1 fb -1

11. 11 Mass calibration Background  Interpolate from sidebands Signal  Use B s  KK  PID modifies σ  σ vs PID cut in B  hh Simultaneous fit B, B s Mass dimuon bkg Mass: dot Bs  μμ, Bs  KK: dashed PID, line corrected line

12. 12 PID calibration μ-PID calibration  In MC use of the IsMuon variable Hits in FoI vs P  In data use of DLL Distance of μ-hits to extrapolation  Calibration “μ” from the J/Ψ J/Ψ 1.7 M/pb -1 Mip in the Calorimeter TIS Non-μ from Λ  pπ 10 4 M/pb -1 J/Ψ selection DLL = log (P μ ) – log(P non-μ ) Λ selection

13. 13 B  hh normalization: exclusive B  Kπ B  hh normalization  Exclusive decay B  Kπ  Similar sel, rec efficiencies  Different trigger Exclusive B  Kπ  Full fit of the B  hh contributions  Counting of exclusive decays vs PID At high purity: Fraction in B  hh vs PID cut MC 0.1 fb -1

14. 14 Ratio of reconstruction efficiencies Reconstruction efficiencies  Use MC: add track in event  Ratio of 2-bodies/3 ~ 3/4  Selection and trigger eff ratio ~1 Ratios 4/3, 3/2 vs B P, and double ratio MC 0.1 fb -1

15. 15 Total trigger efficiency Trigger efficiency  TIS efficiency from high stats channel ε TIS @HLT1 vs B PT 0.1 fb -1 MC B PT (Gev) B  Kπ Selection trigger weighted Distributions before trigger!

16. 16 Bs  μμ trigger efficiency, ratios of trigger efficiencies Bs  μμ total eff  Use B  hh weighted by ε TIS  Emulate muon triggers Use B +  J/Ψ(μμ)K + μ-trigger: vs max μ PT Di-μ trigger: vs min μ PT μ trigger efficiency vs max μ PT di-μ trigger efficiency vs min μ PT 0.1 fb -1 MC 0.1 fb -1

17. 17 Conclusions B s  μμ search  An opportunity to find indirectly NP at LHCb!  LHCb will surpass in exclusion CDF&D0 with 0.2fb -1  Relevant NP region can be excluded with 2-4 fb -1 Analysis  3 likelihoods: Geometrical (GL), mass, μPID  Normalize to B +  J/ΨK + (same trigger, diff sel, rec) or B  hh (same sel and rec, different trigger) Confidence (at 0.1 fb -1 ): use control channels  Method to calibrate GL, mass, using B  hh  Method to measure: Ratio of reconstruction eff., using B +  J/ΨK +, B  J/ΨK* Ratio of trigger eff., using B  hh, and emulating the muon trigger Use of TIS events (B  hh)  Main systematic error: Hadronization factor 13%

18. 18 Back-ups

19. 19 backgrounds

20. 20 Signal and background in SR

21. 21 Observation: limitation due to uncertainty

22. 22 Robust analysis

23. 23 crosscheck of selection efficiencies When real data is available we will need to compare each of the selection variables distributions for signal and control channel candidates, to asses if the ratio behaves as expected.

24. 24 Mass calibration

25. 25 TIS and TOS