Recent Results from D

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Recent Results from DØ

• Andy HaasUniversity of Washington
• ...for the DØ Collaboration
• UW-EPE Colloquium
• June 5, 2003

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Fermilab Tevatron

• Highest energy particle collider in the world
• 1.96 TeV center of mass energy
• Typical luminosity is 4e31 cm-2s-1
• DØ is centered at one of two interaction regions

DØ
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Luminosity So Far

• Run II began 2 years ago
• Luminosity has steadily increased
• 200 pb-1 delivered so far

Peak Luminosity
Integrated Luminosity
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Current Data / Efficiency
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DØ Detector
Retained from Run I LrAr calorimeter Central muon
detector Muon toroid

• New for Run II
• Magnetic tracker
• 2 Tesla solenoid
• Silicon microvertex tracker
• Scintillating fiber tracker
• Preshower detectors
• Forward muon detector
• Forward proton detector
• Front-end electronics
• Trigger and DAQ

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Trigger / Data Acquisition
L1Calorimeter EnergyMuon StubsCentral High-pT
Axial Tracks L2Clustered Calorimeter
EnergyMissing Transverse Cal. EnergyMatched
Muon StubsDisplaced High-pT Axial
Tracks L3JetsCentral Stereo TracksMuons
Matched to TracksPrimary VertexJet Lifetime
b-Tags
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Tracking / Vertexing
Silicon Microstrip Tracker
Central Fiber Tracker
IP resolution
?-gtee-
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Overview of Preliminary Physics Results

• The foundations of a long and exciting physics
  program for Run II
• Preliminary Results
• QCD Jet Physics
• b Physics
• W and Z Measurements
• Top Quark Production
• Searches for New Phenomena
• Higgs-search-related Physics
• Winter Conference Data
• Older Reconstruction Software and Geometry
• 60 pb-1

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QCD Jet Cross-Sections

• Central region
• Large energy-scale errors
• Agreement with theory

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QCD Di-jet Mass
pT 432 GeV/c
pT 394 GeV/c
Dijet Mass Spectrum
?
?
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B Cross-section / Lifetime

• Cross-section
• Important for tuning theoretical parameters
• Higher than theory by x2, consistent with Run I
• Main uncertainty is Jet Energy Scale
• Lifetime
• Errors still large, but measurement agrees with
  theory

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B Decays

• 110,000 J/?-gtµµ decays
• Good reconstruction efficiency
• Use to study b lifetime and Bd oscillation

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CP-violation

• Golden decay modes
• Bs available only at the Tevatron
• Both jet-charge and opposite-muon methods of
  flavor tagging have eD2 3

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Electro-Weak

• Ws and Zs are great calibration sources
• Well understood processes
• Test understanding of the detector
• Efficiencies / Backgrounds
• Triggers
• Resolutions
• Luminosity
• Simulation
• Use signals to tune reconstruction algorithms
• Preliminary to important RunII goals
• W mass
• Precision EW measurements
• Top and Higgs physics

e?ID 911
(scaled)
etrk 821
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Z
D0 RunII Preliminary
Z-gt??
Z-gtee
1139 Candidates
1585 Candidates
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W
W-gte?
W-gt??
27370 Candidates
7352 Candidates
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Top
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Top Channels
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Top Combined

• Evidence has been seen for the top quark at DØ in
  RunII

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Top with b-tags

• Jets in Wjet events are tagged using tracks
• Compare Wbjet events to Standard Model without
  the top-quark
• Excess is observed in the 3 and 4 jet final
  states, indicating a top-quark

D0 preliminary
Counting Signed Impact Parameter Tagger
jet multiplicity
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New Phenomena

• Variety of searches underway
• Results will soon surpass Run I limits

• Model Independent
• e? X
• Supersymmetry
• SUGRA-inspired
• Jets Missing ET (Squarks)
• Trileptons (Gauginos)
• GMSB
• Diphotons Missing ET

• Leptoquarks
• 1st and 2nd generations
• New Gauge Bosons
• Dielectrons
• Large Extra Dimensions
• Dielectrons Diphotons
• Dimuons

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Z

• Assume Z couples like Z
• Look for bump in ee- spectrum...

D0 Run II Preliminary
Z x 10
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Standard Model Higgs 101
MH lt 130 GeV H?bb gg ?H ?bb hopeless (H ???
maybe) H(W ? l?) and H(Z ? ll/??) best processes
MH gt150 GeV H ?WW gg ?H ?(W ? l?)(W ?l?)
best process Also (H ?WW)(W ?l? / Z ?ll)
...study backgrounds for now...
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HW Backgrounds
Major background source W dijets Compare data
with Monte Carlo No b-tagging applied yet...
Errors include statistical and systematic error
from Jet Energy Scale
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HZ Backgrounds
Major background source Z dijets Compare data
with Monte Carlo No b-tagging applied yet...
Errors include statistical and systematic error
from Jet Energy Scale
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H-gtWW
Use spin correlations between leptons from the
Ws to reject backgrounds Need factor of 400
more significance -gt about 20 times more data to
start to exclude SM Higgs
WW candidate
Signal (x 50)
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Z-gtbb

• Cross-sections
• QCD, pTgt20 GeV 35,000,000 nb
• bb, pTgt20 GeV 100,000 nb
• Z-gtbb (4.594 x Z-gtee) 1180 nb

b
b
CDF Run I3.23 sigma91-30 -19 events103-7
pb-1hep-ex/9806022
DØ Run IIZ-gtbb Candidate
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Why Z-gtbb ?

• Measure b-jet energy scale
• Reduce final Run II uncertainty on mt from 2.7 -gt
  1.6 GeV
• Measure b-jet energy resolution
• Crucial for placing limits on Higgs production
  (with H-gtbb)
• Measure b-jet tagging efficiency and fake rate
• And kinematic dependence vs. pT , vs. eta

The Z-gtbb peak is a standard candle for b-jets
Observing and measuring the Z-gtbb decay proves
that tools used to look for the Higgs really work!
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Double-tag Excess in mujet Data

• Selection
• pT gt 25 GeV, full JES corrections
• eta of jets lt 2.0 (fiducial tags)
• d-phi gt 2.5 (loose back-to-back)
• 2 loose secondary vertex b-tags
• Fit double-tagged sample to S B
• Subtract background and fit to Gaus.
• Compare to Z-gtbb Monte Carlo
• Use the CDF Run I method
• Get background from 1-tagged sample
• Also correct for ET turn-on of the second b-tag
  (using 0-1 tag method)
• Compare with bb Monte Carlo
• Pythia direct bb MC (26,000 evts)with pTgt20 GeV
  and eta lt 3
• Same trigger/skimming efficiency for bb as Z-gtbb,
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• Shape, position of peak agrees with MC
• Peak in data is wider by 50

2s excess
DØ Run II52pb-1
bb MC 8840 events-gt3763 events pred.
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Multi-jet Double-tags

• Fit the double-tagged invariant mass spectrum to
  a sum of backgrounds
• QCD Heavy Flavor
• Shape estimated from b-tagging kinematic
  corrections to the single-tagged sample
• Normalization left a free parameter (bbjj
  cross-section poorly known)
• Fake double-tag fraction estimated from fake-tag
  rates and kinematics
• Z-gtbb and tt backgrounds are included from Monte
  Carlo normalized to the relatively well-known
  cross-sections
• Know to expect Z-gtbb background from CDF Run I
  analysis
• We verify the qualitative observation of Z-gtbb
  background

CDF Run I - Preliminary
Z-gtbb tt
Fakes
QCD HF
D0 Run II - Preliminary Multi-jet Sample
53pb-12 Tight-3track-SV tags
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Luminosity Outlook
Short term
Long term
3 fb-1 by 2007 5 or 8 fb-1 by 2009?
Stretch
Integrated Luminosity (fb-1)
Base
gt200 pb-1 in 2003
10,000 pb-1 by 2009 ?
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Prospects / Conclusions

• Tevatron is off to a slow start delivering
  luminosity
• DØ has proven it can do the physics it was
  designed to
• Commissioning largely done... an incredible
  amount of hard work by hundreds of engineers,
  technicians and physicists
• Now entering a fine-tuning stage of operations
• Expect first RunII physics results within a year
  using 200 pb-1 of data
• Exciting analyses within the next few years using
  2-3 fb-1 of data