Z and W Cross Sections at DZero

1
Z and W Cross Sections at DZero

• Sean Mattingly
• Brown University

Pheno 04 University of Wisconsin 26 April 2004
2
W/Z Production at the Tevatron
p
p
e,m
e, m
q
q
Z0/g
W
BR 10
BR 3
n
e-, m-

• Sensitive to
• QCD and PDFs
• Description of Electroweak, W/Z cross sections
  ratio ? indirect W width
• Well understood event signatures
• Increase understanding of detector by studying
  W/Z production
• Cross sections are relatively well known and high
• Eventually W production can be used to measure
  Tevatron luminosity

3
W/Z Event Signatures
W/Z0
Detector not in center of mass
/
q
e, m
Hadronic Recoil
Z Production
q
(LEP/PDG)
Hadronic Recoil
e-, m-
n
? Cant measure pZ of n
W Production
q
(LEP/TeV/PDG)
Hadronic Recoil
e,m
4
Event Selection Electron Channels

• Single EM triggers
• Electron ID
• High ET electrons from W/Zs ET gt 25
• hdet lt 1.1 (central cryostat) and not near
  module boundary
• Calorimeter shower consistent with EM shower
• Z candidates
• 2 Electrons w/ invariant mass 70-110 GeV
• W candidates
• 1 Electron missing ET gt 25 GeV

5
Backgrounds Electron Channels

• Z?ee
• QCD dijets where jets fake electrons (10)
• Reverse EM shower requirements ? pure background
• Fit background signal MC to invariant mass
  distribution and statistically subtract
  background
• Z?tt Drell-Yan (g) contributions from MC
  (2 total)
• W?en
• QCD events where jet fakes electron a poorly
  measured jets yields missing ET
• Statistically subtract background using data with
  signal and background track matching efficiencies
• Large but well understood background
• W?tn and Z?ee from MC (few total)

HM8 gt 35 Background
DZero Run II Preliminary
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Determining Efficiencies

• Geometric/kinematic acceptances from MC (CTEQ6)
• Object ID efficiencies from data
• tag-and-probe in Z events
• Subtract Z?ll backgrounds
• Efficiency of test criterion determined by
  fraction of leptons from Zs that satisfy the test
  criterion
• Used to determine trigger, tracking, and object
  ID efficiencies

Tag Lepton Satisfies all ID criteria
Fired trigger
Probe Lepton Allowed to fail the test
criterion (e.g. Track Match)
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Previous Run II Results Electron
Channels

• Using the first 50pb-1 of Run II luminosity
  (Preliminary)
• Dominant systematics
• Luminosity (cross sections only), trigger e,
  tracking e
• Ratio of Cross Sections Combined w/ CDF

Tree level NNLO QCD calc (Van Neerven)
SM EWK Calculation
PDG(LEP)
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Current Work Electron Channels

• More Luminosity (160 pb-1)
• Lower statistical errors improved efficiency
  measurements
• New luminosity constants 6.5 error (was 10
  before)
• Adding Calorimeter End Caps
• Adds acceptance out to hdet lt 2.3
• Further improves statistics
• Cross sections/R less PDF dependent (R
  uncertainty 1.2 ? 0.6), W/Z h distributions
  more PDF sensitive
• Improved systematic understanding
• Parameterize detector response vs. h, pT, f,
  time, etc.
• Goal is 1 understanding of systematics

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New Data Electron Channels
W?en Electron ET (GeV)
Z?ee Invariant Mass
DZero Run II Preliminary
DZero Run II Preliminary
Points Data Histo MC
W?en Transverse Mass (GeV)
DZero Run II Preliminary

• 14077 Z candidates
• 226089 W candidates
• 5x previous statistics

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Event Selection Muon Channels

• Muon ID
• hdet lt 1.8 (Z analysis), 1.6 (W analysis)
• Track matched to muon found in muon system
• Isolation in tracking and calorimeter
• Z candidates
• Dimuon Triggers
• 2 muons
• Track pT gt 15 GeV, Mmm gt 30 GeV, oppositely
  charged tracks, one muon must satisfy both cal
  and track isolation
• W candidates
• Single Muon Triggers
• 1 Track and Cal isolated muon gt 20 GeV, missing
  ET gt 20 GeV
• No other muons

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Backgrounds Muon Channels

• Z?mm
• Small backgrounds (1 total)
• bb and cosmics
• Estimated by looking at like-sign events and by
  looking at the events cut
• Z?tt Drell-Yan (g) contributions from MC
• W?mn
• Z?mm where one m is missed (4), W?tn (2) and
  Z?tt (0.1)
• Estimated from MC
• QCD semileptonic decays (2)
• Statistically subtract background using data with
  signal and background isolation efficiencies

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Previous Run II Results Muon
Channels

• Z?mm using 117 pb-1 of Run II data (preliminary)
• W?mn using 17.3 pb-1 of early Run II data
  (preliminary)

13
Current Work Muon Channels

• Increased Luminosity
• 148 pb-1 for Z, 104 pb-1 for W
• Lower statistical errors improves efficiency
  measurements
• Use full muon detector h lt 2.0
• Z?mm
• Increased efficiency by only requiring a total of
  2 out of possible 4 isolations satisfied
• Improved anti-cosmics cuts (DCA and acolinear)
• Adding triggers (further statistics increase)
• W?mn
• Cutting against background from In Flight Decays
• IFD ? events with high pT central
  
  tracks and low pT muon tracks
• Cuts on track c2 and track DCA
• Goal is 1 understanding of systematics

cosmics ? ? signal
c30cm/ns
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New Data Muon Channels
W?mn Muon ET (GeV)
Z?mm Invariant Mass
Points Data Histo MC
DZero Run II Preliminary
W?mn Transverse Mass (GeV)

• 14765 Z candidates
• 2x previous statistics
• 74886 W candidates
• 10x previous statistics

DZero Run II Preliminary
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Summary and Outlook

• Improved analyses approaching completion
• Larger datasets yield improved systematic
  understanding as well as smaller statistical
  errors
• Improved understanding of lumi errors 10? 6.5
• Understanding of detector response becoming more
  detailed
• Improvement of non-lumi parts of error 5?1
• Stepping stone toward W mass measurements
• Look for new DZero results at summer conferences