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B mixing and flavor oscillations at DØ
Cano Ay University Mainz for the DØ
Collaboration 23 may 2005 Frontiers in
Contemporary Physics III Vanderbilt University
Nashville, Tennesse
Cano Ay , Johannes Gutenberg Universität ,
ayc_at_uni-mainz.de
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Outline

• Motivation
• Mixing and Oscillation
• Tevatron and DØ Detector
• Flavor tagging
• Bd Mixing Limit
• Bs Mixing Limit
• Prospects and plans
• Summary

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Motivation

• The ratio Dms/Dmd constrains one side of the
  unitarity triangle
• also study CP violation in Bs system
• studied in Kaon and Bd system
• Belle and Babar not sensitiv
• LHCB not running
• Tevatron currently only place to study Bs Mixing

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Mixing
Particle ? Antiparticle
The transition of a neutral particle into its
antiparticle is called Mixing.
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Unitarity triangle
Standard Model expectation ?ms 14
....28ps-1 ?md 0.5ps-1 measurement of
?ms/?md ? Vts/Vtd constrain unitarity
triangle
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Mixing (2)
high uncertainties f(QCD)
reduce uncertainties by taking ratio
Measure Dm ? asymmetry
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Mixing (3)

• From the CKM fit Dms 18 ps-1
• Heavy Flavor Averaging group
• combined LEP, SLD, CDF1 results
• Dms gt 14.5 ps-1

flavor tagging performance resolution
selection
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Tevatron
Big advantage for B physics Bs meson production
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Luminosity
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D0 Detector

• Semileptonic decays
• trigger on muon
• good muon system
• reconstruct tracks and vertex
• good tracking system

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Silicon Microstrip Tracker (SMT)

• Silicon Microstrip Tracker
• 800.000 channels
• point resolution 10?m
• Secondary vertex resolution
• 40?m (r-?)
• 80?m (r-z)

• Trackers
• Silicon Tracker ?lt3
• Fiber Tracker ?lt2
• Magnetic field 2T

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Muon Sytem

• 2 Tesla toroid magnet between A und
• BC Layer ? Muon momentum
• propotional drift tubes
• pixel scintillators

• Muon system coverage ?lt2 and
• good shielding

A minidrift tube with cover partially removed
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B production and decay
B production Fermilab s O(100µb) L1 Trigger
acceptance (DØ Muon) s O(3-5µb)
Used Decays
B0s ? D-s µnµ D-s ? ?(KK-)?-
B0d ? D(2010)-µ nµ D(2010)-?D0(K?-)?
- B ? D0µ nµ D0? K-?

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Flavor tagging
Flavor tagging determine b-flavor at production
time!
reconstructed side
opposite side
oscillated not oscillated

• Soft Lepton Tag (SLT)
• Opposite Jet charge (Jetq)
• Same Side Tag
• (currently only used for Bd)

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Bd Sample

• angle and distance
• distance PV ? D Vertex (xy-plane)
• D Vertex not before B Vertex
• Angle between PV ? B Vertex
• and PV ? D Vertex

• Charged tracks
• pT gt 0.65 GeV/c
• impact parameter significance

Single µ data 200pb-1
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Bd Mixing Limit
SLT D0 (44.8?5.1) JetqSST D0
(14.9?1.5)
JetqSST D? 27.9
Asymmetry
Asymmetry
Dmd0.456?0.034ps-1(stat) ?0.025ps-1(syst)
consistent with Dmd0.502?0.007ps-1 (world
average)
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Bs Mixing analysis procedure

• Currently only using a single semileptonic
  decay of the Bs
• Bs ? Ds ? X (Ds ?? p) (? ? K K)
• Using ? SV vertex tag (Opposite side tag,
  independent of reconstructed side)
• The goal was to develop tools and to allow a
  baseline to build on for the future

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Bs Sample

• Charged tracks
• pT gt 0.7 GeV/c
• impact parameter significance
• Invariant KK mass
• 1.006 lt M(KK) lt 1.30

• angle and distance
• distance PV ? D Vertex (xy-plane)
• D Vertex not before B Vertex
• Angle between PV ? B Vertex and PV ? D Vertex
• Angle between PV ? D Vertex and D momentum

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Bs Mixing fitting procedure

• Inputs to the fitting procedure
• MC
• Sample composition
• K-factor to take non-reconstructed particles
  into account
• Efficiencies
• Visible Proper Decay Length (VPDL) resolution
• VPDL resolution has been tuned using data
• Dilution from B0d and Bu semileptonic samples

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Sample Composition and efficiency
Decay Sample composition
Bs?Dsµ? 20.6
Bs?Dsµ? 57.2
Bs?D0sµ? 1.4
Bs?D1sµ? 2.9
Bs?DsDsX 11.3
B0?DsDX 3.2
B-?DsDX 3.4
VPDL (cm)
Efficiency drop at low VPDL due to impact
parameter cuts on tracks from Ds decay
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K-factors
K
K x VPDL
Decay ltkgt
Bs?Dsµ? 0.878
Bs?Dsµ? 0.857
Bs?D0sµ? 0.829
Bs?D1sµ? 0.817
Bs?DsDsX 0.738
B0?DsDX 0.681
B-?DsDX 0.687
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VPDL Resolution MC tuned with data

• VPDL resolution parametrized with three Gaussians
• Track by track
• smearing dependant on track momentum and polar
  angle
• Tuning results with one scale factor 1.095

no smearing after smearing
VPDLrec VPDLgen cm
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Dilution

• SLT SV Jetq D0 (39.0?3.2) D?
  (47.6?2.0)
• use mean Davr(45.4?1.7) for Bs asymmetry

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Bs Mixing Limit
No obvious oscillations in the µDssample
Dms gt 5.0 ps-1 at 95 CL using Amplitude
method
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Sensitivity vs. Luminosity Semileptonic channels

• Scaling of the current sensitivity with
  luminosity
• if analysis remains
• unchanged
• with expected
• improvements

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Bs Mixing Projections

• Use both semileptonic and hadronic Bs samples
• More statistics in semileptonics
• Better proper decay time resolution in hadronics
  (no n)
• DZero has access to hadronic Bs sample triggering
  on opposite side muon
• Muon is used as high purity tag
• Detector addition in fall
• Layer 0 Silicon detector
• Proposal to increase rate to tape from 50 to 100
  Hz in fall
• sample limited by L3 trigger and offline CPU
  expect large gain in yield thanks
• to dedicated B-physics bandwidth

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Summary

• measured, which is in agreement with world
  average
• Dmd0.456?0.034ps-1(stat) ?0.025ps-1(syst)
• developed a procedure to measure Dms using
  semileptonic channel Bs?Ds(??)???
• Dms gt 5.0ps-1 at 95 CL
• will add more semileptonic channels and hadronic
  channels
• Layer 0 Silicon detector and increasing L3
  rate will improve resolution and increase
  statistics