Insight into CP Violation in Bs Decays at 5th International Workshop on CKM Unitary Triangle

1. 5th International Workshop on the CKM Unitary Triangle Rome, Italy, 9-13 September 2008 CP violation inBs→ff and Bs → K*0K*0 Yuehong Xie University of Edinburgh (on behalf of the LHCb collaboration)

2. Weak phases in Bs penguin decays W, ? u,c,t W, ? b b s + s Φ,K*0 u, c, t u, c, t s,d B0s B0s B0s Φ,K*0 s,d s s b s W , ? + tiny correction New particles can enter both mixing and decay diagrams To be measured in Bs→J/Yf Yuehong Xie

3. Observables • Polarization fractions: FL, F// and F┴ • CP asymmetries in each polarization f = L, //, ┴ • Simplified for null test of SM: assume no NP in b→s decay, then just like in Bs→J/Yf • Only one phase F to measure • F ≠ 0 indicates NP Yuehong Xie

4. Analysis method • Maximum likelihood fit • Likelihood function models mass, proper time and angular distributions of signal and background candidates • Bs invariant mass: separate signal and background • Angular variables: separate different polarization components • Time evolution: extract CP parameters. An example Signal background B mass Angles in helicity basis Yuehong Xie

5. SM predictions and measurements • SM expectations • Sf ≈ 0 and Cf ≈ 0 for f = L, // and ┴, or F ≈ 0 • BR(Bs→ff) ~ (10 - 40) x10-6 • BR(Bs→ K*0K*0) ~ 10 x10-6 • FL > F// and F// ≈ F┴, values vary due to large hadronic uncertainties • CDF measured BR in data • sample of 180 pb-1 • BR(Bs→ff) =(14+6-5±6)x10-6 • (PRL 95:031801, 2005) 4.7 s significance Yuehong Xie

6. LHCb selection of Bs→ ff • Simulated 100k signal events and 22M b-inclusive events • Pass standard L0 trigger, mainly hadron trigger • Pass HLT tracking and event selection • Suppress b-inclusive background using • K particle ID, Pt • f impact parameter, vertex quality, Pt and invariant mass • Bs vertex quality, pointing angle and invariant mass inclusive-b K+ Pt inclusive-b B vertex c2 inclusive-b f mass signal f mass Signal K+ Pt signal B vertex c2 Yuehong Xie

7. Bs→ ffevent yields • Final signal yield in 2 fb-1(1 nominal year): 3380 ± 450 in ±50 MeV Bs mass window based on central value of CDF BR measurement • Inclusive-b B/S < 1.6 @ 95% CL • Specific background study ongoing Core gaussian: fraction 91% s = 14 MeV Bs mass Yuehong Xie

8. Detector effects in simulation core st ~ 40 fs Time acceptance Angular resolution effect negligible cosq acceptance: ~ flat f Acceptance: ~ flat Yuehong Xie

9. Flavour tagging e-, m- Opposite side Qvertex ,QJet K- B0opposite D PV Bs0signal K- Same side K + K+ • Opposite side • High Pt leptons • K± from b → c → s • Vertex charge f f • Same side • Fragmentation K± accompanying Bs K+ K- Total tagging efficiency: 0.706 ± 0.008 Total tagging power: 0.119 ± 0.012 Equivalent average mistag rate: 0.294 • combining taggers • NN trained for each tagger • Final decision is made using NN outputs of all taggers • Categorized according to per event mistag rate Yuehong Xie

10. Toy Monte Carlo generation • Physics inputs • Widths: ΓL = 0.738, ΓH = 0.654 • Mass difference: Δms = 17.77 ps-1 • F// = 0.25 and F┴ = 0.25 • d1 = arg(A┴/A//) = 0, d2 = arg(A┴/A0) = p • Weak phase F = 0 • Experimental inputs • 3380 signal events with B/S=1 • Tagging efficiency 71% and mistag rate 30% • Single gaussian resolutions for mass and time • Time acceptance taken from simulation • Angular resolution and acceptance ignored • All background distributions taken from simulation Yuehong Xie

11. Fit results • Fit parameters: F//, F┴ , Nsig, Nbg, d1, d2 and F • 1000 toy experiments • Result: s(F) ≈ 0.125 with 2 fb-1 • This resolution only weakly depends on input values of F//, F┴, d1, d2 and F • Calibration methods are being developed to obtain knowledge of tagging performance, background distributions, resolution and acceptance effects in order to control systematics. Yuehong Xie

12. Bs→ K*0K*0 • Can be studied in direct analogy to Bs→ff • A method to combine Bs→ K*0K*0 and Bd→ K*0K*0 to extract hadronic parameters for SM prediction of CP asymmetries in Bs→ K*0K*0 ( PRL 100:031802, 2008 ) is also being studied • Events are selected in a similar way to Bs→ff with relatively tighter cuts • Signal yields with 2 fb-1 w/o considering trigger • 7.6k Bs→ K*0K*0 with B/S = 1 • 1.9k Bd→ K*0K*0 with B/S = 4 • Angular fit studied. Time dependent analysis to measure CP asymmetries is under way. Yuehong Xie

13. Angular fit of Bq→ K*0K*0 B mass • Do combined fit to separate Bs and Bd • Polynomial model of angular acceptance works well Fit curve Bs projection Bd projection Background projection cosq1 In 2 fb-1 (1 nominal year): s(FL(Bs)) =0.005, s(FL (Bd)) = 0.018 and s(BR(Bs)/BR(Bd) ) =0.59 Yuehong Xie

14. Conclusions • Bs→ff and Bs→ K*0K*0 provide a new window into CP violation in hadronic b → s penguins • Updated study shows LHCb can achieve a resolution of s(F) ≈ 0.125 in Bs→ff with 2 fb-1 (1 nominal year), making it an ideal place to search for the anticipated unexpected physics • Study of Bs→ K*0K*0 is progressing well in LHCb • LHCb is about to take over the penguin world! Yuehong Xie