Search for B s oscillations at D  Constraining the CKM matrix Large uncertainty Precise measurement of V td  properly constrain the CKM matrix yield info on strength of CP-violation V td can be measured via rare kaon decay mixing in the B system but large QCD effects dominate the extraction of V td Neutral B meson transition from particle to anti-particle state, and vice-versa Weak eigenstates  mass eigenstates Caused by higher order flavor changing weak interactions:  m q = m(B o heavy ) - m(B o light )  m q  |V tb V tq | 2 Mixing parameters x q =  m q /  q and y q =   q /  q where q=d,s First oscillations observed at ARGUS (’87) in the B d system  signaled a large top quark mass (later verified by CDF and DØ) What is mixing ?  consider ratio from Lattice QCD  m d has been precisely measured: the world average is  a direct measurement of  m s +  m d (current value) + V ts (relatively well known)  V td Central Scintillator Forward Mini- drift chamb’s Forward Scint Shielding Tracking: Solenoid,Silicon,Fiber Tracker,Preshowers New Electronics,Trigger,DAQ Calorimeter Central PDTs Large production cross-section All B species, including B s, B c,  b Rich B Physics program at DØ benefits from : Large muon acceptance: |  | < 2 Forward tracking coverage: |  | < 1.7 (tracking), |  | < 3 (silicon) Robust muon trigger A typical oscillation analysis involves: – Selection of final states suitable for the study Tagging the meson flavor at decay time (final state) Tagging the meson flavor at production time (initial state) – Proper time reconstruction for each meson candidate Essential ingredients of a mixing analysis B s mixing studies at DØ: The Tevatron B-factory and the new DØ B s oscillates at least 30 times faster than B 0 !  a B s mixing measurement is extremely challenging. We think we understand the mixing of B’s… A deviation from this simple diagram is a deviation from the Standard Model (New Physics) Theoretical uncertainties reduced in ratio (10%  4%) SM or NP ? jet charge Decay mode tags b flavor at decay 2 nd B tags production flavor Dilution D = 1 – 2w w = mistag probability  = efficiency  D 2 = effective tagging power Proper decay time from displacement (L) and momentum (p) Average statistical significance # of reconstructed events Flavor tagging signal purity proper time resolution Measure asymmetry A as a function of proper decay time t “unmixed”: particle decays as particle For a fixed value of  m s, data should yield Amplitude “A” is true value of  m s Amplitude “A” is 0 otherwise “mixed”: particle decays as antiparticle Units: [  m] = h ps -1, h =1 then  m in ps -1. Multiply by x to convert to eV Amplitude method: H-G. Moser, A. Roussarie, NIM A384 p. 491 (1997)  m s < 21 ps 90% CL assuming Gaussian errors First direct two-sided bound on  m s PRL 97, (2006) Amplitude Scan Log-likelihood Scan New Result: Combination of additional D s decay modes Future Prospects: Add Same Side Tagging, hadronic modes Add more data (4-8 fb -1 in next 3 years) with improved detector – additional layer of silicon between beampipe and Silicon Tracker (Layer0) – better impact parameter resolution Future Prospects: Add Same Side Tagging, hadronic modes Add more data (4-8 fb -1 in next 3 years) with improved detector – additional layer of silicon between beampipe and Silicon Tracker (Layer0) – better impact parameter resolution µ, e