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

2. M. Anzelc, DPF 2006 Parallel2 CKM & New Physics Tevatron B-factories New Physics? Upper-limit on Δm s limits large SM deviations

3. M. Anzelc, DPF 2006 Parallel3 Tevatron and DØ D0 CDF Main Injector p-bar source Booster Linac DØ Coverage: Muon system: |  | < 2 Silicon: up to |  | < 3 Fiber Tracker: |  | < 2 Where  = -ln(tan(θ/2)) Muon System

4. M. Anzelc, DPF 2006 Parallel4 Analysis Outline (Standard Procedure) Reconstruct decay products Determine flavor of B s at production and decay –Tells us if B s oscillated or not Measure B s decay length –Oscillation probabilities are function of decay length Other inputs include: K factors, sample composition, efficiencies, scale factors Fit for Δm d – verify procedure Fit for Δm s

5. M. Anzelc, DPF 2006 Parallel5 Tagging Events Opposite-side: uses decay lepton, jet charge Same-side: decay lepton charge gives decay flavor Reconstructed/Signal Side (decay flavor) Opposite Side (production flavor) Efficiency: Dilution: Tagging Power:

6. M. Anzelc, DPF 2006 Parallel6 Analysis Inputs Correct B s momentum using K factor Correct impact parameter uncertainty, σ IP –Tracking estimates σ IP  J/ψ pull distribution For correct σ IP  pull width=1, centered at 0 Fit to J/ψ pull distribution gives SF=1.0 for 78%, 1.8 for remainder

7. M. Anzelc, DPF 2006 Parallel7 OST Calibration with B d Amplitude Scan shows B d oscillations – at correct place  no lifetime bias – w/ correct ampl.  correct dilution calibration B d  XμD±(  φπ) NB s (φπ+μ) = 5601  102 Δm d = 0.506 ±0.020(stat.) ps -1 WA, Winter 2006: Δm d = 0.507 ± 0.004 ps -1

8. M. Anzelc, DPF 2006 Parallel8 DØ Result First upper-limit on Δm s : 17ps -1 < Δm s < 21ps -1 at the 90% confidence level PRL 97, 021802 (2006) DØ Published Result (B s →D s μ X, D s →φπ)

9. M. Anzelc, DPF 2006 Parallel9 DØ Result Tevatron B-factories New Physics? Excludes large Standard Model deviations at the 95% confidence level

10. M. Anzelc, DPF 2006 Parallel10 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

11. M. Anzelc, DPF 2006 Parallel11 Tagged B s Samples NB s (φπ+e) = 1012  62 –(Muon tagged) NB s (K*K+μ) = 2997  146 NB s (K s K+μ) = 593 ± 67 NB s (φπ+e) = 1012  62 –(Muon tagged) NB s (K*K+μ) = 2997  146 NB s (K s K+μ) = 593 ± 67 B s  D s e X D s  φπ D s  K*K B s  D s μ X Ds KsKDs KsK DØ RunII Preliminary

12. M. Anzelc, DPF 2006 Parallel12 Combined Result Using the same dataset and analysis as the published result (B s →D s μ X, D s →φπ) –Combination increases sensitivity by 2.4ps -1

13. M. Anzelc, DPF 2006 Parallel13 Same-side Tagging Quark fragmentation → B s (Kaon), B d (pion) Charge of Kaon  flavor of B s on signal side Developing same-side tag, using dE/dx Charge of this… …is used to determine this dE MeV p K π

14. M. Anzelc, DPF 2006 Parallel14 K-factor Studies Developing more sophisticated K factors Expected ~10% improvement Different μD s mass ranges

15. M. Anzelc, DPF 2006 Parallel15 Scale Factors 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 σ IP IP Uncertainty Scale Factor is p T dependent σ IP smaller for higher p T tracks Method developed at DELPHI

16. M. Anzelc, DPF 2006 Parallel16 Silicon: Layer0 Added inner silicon layer in May, radius = 1.6cm Expect ~30% increase in SV resolution

17. M. Anzelc, DPF 2006 Parallel17 Outlook Have added three semi-leptonic channels Have many improvements on the way, greatly increasing sensitivity Hardware improvement with Layer0 Additional luminosity in RunIIb

18. Backup Slides

19. M. Anzelc, DPF 2006 Parallel19 Results of the Lifetime Fit From a fit to signal and background region: Decay Mode c  Bs (  m)c  bkg (  m) Bs  Ds  X, Ds   404  9627  6 Bs  Ds e X, Ds   444  29645  18 Bs  Ds  X, Ds  K*K407  22549  10 Bs  Ds e X Ds   Ds  K*K Bs  Ds  X

20. M. Anzelc, DPF 2006 Parallel20