Constraining CKM Matrix with Bs Oscillations at D: Exploring Mixing in the B System

1. Search for Bs oscillations at D Constraining the CKM matrix What is mixing ? SM or NP ? • 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: mq= m(Boheavy) - m(Bolight)  mq |VtbVtq|2 Mixing parameters xq=  mq/q and yq= q/ q where q=d,s First oscillations observed at ARGUS (’87) in the Bd system  signaled a large top quark mass(later verified by CDF and DØ) We think we understand the mixing of B’s… A deviation from this simple diagram is a deviation from the Standard Model (New Physics) Large uncertainty • Precise measurement of Vtd • properly constrain the CKM matrix • yield info on strength of CP-violation but large QCD effects dominate the extraction of Vtd • Vtd can be measured via • rare kaon decay • mixing in the B system Theoretical uncertainties reduced in ratio (10%  4%) from Lattice QCD  consider ratio md has been precisely measured: the world average is • a direct measurement of ms + md(current value) + Vts(relatively well known)  Vtd Bs oscillates at least 30 times faster than B0 !  a Bs mixing measurement is extremely challenging. The Tevatron B-factory and the new DØ Essential ingredients of a mixing analysis • 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 Central Scintillator Forward Scint Forward Mini-drift chamb’s Central PDTs Large production cross-section All B species, including Bs, Bc, b Shielding Decay mode tags b flavor at decay Calorimeter Tracking: Solenoid,Silicon,Fiber Tracker,Preshowers µ, e New Electronics,Trigger,DAQ • Rich B Physics program at DØ benefits from : • Large muon acceptance: || < 2 • Forward tracking coverage: || < 1.7 (tracking), || < 3 (silicon) • Robust muon trigger jet charge Proper decay time from displacement (L) and momentum (p) 2nd B tags production flavor Average statistical significance proper time resolution Dilution D = 1 – 2w w = mistag probability  = efficiency D2 = effective tagging power Flavor tagging signal purity # of reconstructed events Bs mixing studies at DØ: Measure asymmetry A as a function of proper decay time t New Result: Combination of additional Ds decay modes Amplitude Scan “unmixed”:particle decays as particle “mixed”:particle decays as antiparticle For a fixed value of ms, data should yield Amplitude “A” is 1 @ true value of ms Amplitude “A” is 0 otherwise Amplitude method: H-G. Moser, A. Roussarie, NIM A384 p. 491 (1997) Log-likelihood Scan Units: [m] = h ps-1, h =1 then m in ps-1. Multiply by 6.582 x 10-4 to convert to eV 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 17<Dms<21 ps-1 @ 90% CL assuming Gaussian errors First direct two-sided bound on ms PRL 97, 021802 (2006)