Semi-Leptonic Bs Mixing at DØ

1. Semi-Leptonic BsMixing at DØ Meghan Anzelc Northwestern University On Behalf of the DØ Collaboration DPF 2006

2. B-factories Tevatron New Physics? CKM & New Physics Upper-limit on Δms limits large SM deviations M. Anzelc, DPF 2006 Parallel

3. Linac CDF Booster p-bar source Main Injector D0 Tevatron and DØ DØ Coverage: • Muon system: || < 2 • Silicon: up to || < 3 • Fiber Tracker: || < 2 Muon System M. Anzelc, DPF 2006 Parallel Where  = -ln(tan(θ/2))

4. Analysis Outline (Standard Procedure) • Reconstruct decay products • Determine flavor of Bs at production and decay • Tells us if Bs oscillated or not • Measure Bs decay length • Oscillation probabilities are function of decay length • Other inputs include: K factors, sample composition, efficiencies, scale factors • Fit for Δmd – verify procedure • Fit for Δms M. Anzelc, DPF 2006 Parallel

5. Opposite Side (production flavor) Reconstructed/Signal Side (decay flavor) Tagging Events • Opposite-side: uses decay lepton, jet charge • Same-side: decay lepton charge gives decay flavor Efficiency: Tagging Power: Dilution: M. Anzelc, DPF 2006 Parallel

6. Analysis Inputs • Correct Bs momentum using K factor • Correct impact parameter uncertainty, σIP • Tracking estimates σIP J/ψ pull distribution For correct σIP pull width=1, centered at 0 Fit to J/ψ pull distribution gives SF=1.0 for 78%, 1.8 for remainder M. Anzelc, DPF 2006 Parallel

7. OST Calibration with Bd • Amplitude Scan shows Bd oscillations • at correct place  no lifetime bias • w/ correct ampl.  correct dilution calibration BdXμD±(φπ) NBs(φπ+μ) = 5601 102 Δmd = 0.506 ±0.020(stat.) ps-1 WA, Winter 2006: Δmd = 0.507 ± 0.004 ps-1 M. Anzelc, DPF 2006 Parallel

8. DØ Result DØ Published Result (Bs→DsμX, Ds→φπ) First upper-limit on Δms: 17ps-1 < Δms < 21ps-1 at the 90% confidence level PRL 97, 021802 (2006) M. Anzelc, DPF 2006 Parallel

9. B-factories Tevatron New Physics? DØ Result Excludes large Standard Model deviations at the 95% confidence level M. Anzelc, DPF 2006 Parallel

10. Now to Improve… • Adding additional channels • Improvements at every analysis step • Flavor tagging and event selection • K factors • Resolution Scale Factors • Detector upgrade – additional silicon layer • Increased integrated luminosity M. Anzelc, DPF 2006 Parallel

11. Tagged Bs Samples NBs(φπ+e) = 1012  62 • (Muon tagged) NBs(K*K+μ) = 2997  146 NBs(KsK+μ) = 593 ± 67 BsDs e  X Ds φπ DØ RunII Preliminary BsDsμ X Ds K*K BsDsμ X Ds KsK M. Anzelc, DPF 2006 Parallel

12. Combined Result • Using the same dataset and analysis as the published result (Bs→DsμX, Ds→φπ) • Combination increases sensitivity by 2.4ps-1 M. Anzelc, DPF 2006 Parallel

13. dE MeV p Charge of this… …is used to determine this K π Same-side Tagging • Quark fragmentation → Bs (Kaon), Bd (pion) • Charge of Kaon  flavor of Bs on signal side • Developing same-side tag, using dE/dx M. Anzelc, DPF 2006 Parallel

14. K-factor Studies • Developing more sophisticated K factors • Expected ~10% improvement Different μDs mass ranges M. Anzelc, DPF 2006 Parallel

15. Scale Factors Method developed at DELPHI IP Uncertainty σIP smaller for higher pT tracks Scale Factor is pT dependent • Divide tracks into categories based on hits and cluster width • Fit estimated (pink & green) and true (blue, red error bars) impact parameter uncertainties • Ratio → Scale Factor • New event-by-event SF additional ~6.5% reduction in σIP M. Anzelc, DPF 2006 Parallel

16. Silicon: Layer0 • Added inner silicon layer in May, radius = 1.6cm • Expect ~30% increase in SV resolution M. Anzelc, DPF 2006 Parallel

17. Outlook • Have added three semi-leptonic channels • Have many improvements on the way, greatly increasing sensitivity • Hardware improvement with Layer0 • Additional luminosity in RunIIb M. Anzelc, DPF 2006 Parallel

18. Backup Slides

19. Results of the Lifetime Fit • From a fit to signal and background region: BsDs e n X BsDs mn X Ds fp Ds  K*K M. Anzelc, DPF 2006 Parallel

20. M. Anzelc, DPF 2006 Parallel