Search for Neutral Supersymmetric Higgs Bosons with the D

1
Search for Neutral Supersymmetric Higgs Bosons
with the DØ Detector at the Tevatron in Run II

• Andy HaasUniversity of Washingtonon behalf of
  the DØ Collaboration
• APS MeetingSession P14 Higgs
  PhysicsPhiladelphia, PAApril 7, 2003

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Supersymmetry and Higgs
Q
Bosons
Fermions

• A highly motivated new symmetry of nature
• Stabilizes the mass of a scalar particle, such as
  the Higgs
• Allows for the unification of gauge couplings at
  a high energy
• Provides a Cold Dark Matter candidate
• Demands pairs of Higgs doublet fields (to cancel
  anomalies)
• Hu couples to up-type quarks and leptons and Hd
  to down-type
• The ratio of their VEVs is defined as
• tan ? ltHugt/ltHdgt
• 5 Higgs particles after EWSB h0, H0, A0, H, H-
• h0 is guaranteed to be light
• mh0 lt 130 GeV (MSSM) lt 210 GeV (General
  SUSY)
• Other two-doublet models are possible as well

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Higgs Production and Large tan ?

• Low tan ?, ? Standard Model Higgs
• High tan ?, ? enhanced bbH
• Cross section rises like tan2?
• Recent work indicates that the LO cross-sections
  are an underestimate by a factor 3
• Some theoretical bias towards expecting tan ? gt
  30
• b-t-t Yukawa unification at the GUT scale ? mt/mb
  tan ? ?

CP-odd HiggsProduction
CP-even HiggsProduction
tan ?
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The Tevatron

• Worlds largest, highest-energy, running
  accelerator!
• Started Run II about 2 years ago
• Luminosity performance is still improving
• Producing about 1 pb-1 /day (10 h0bb events
  /day at high tan ? )
• Hope for 300 pb-1 this year

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The DØ Detector

• Same fine-grained, high-resolution compensating
  Calorimeter as Run I
• 3-level high-bandwidth trigger system with full
  event reconstruction at 1 kHz
• Forward muon system, with greatly improved halo
  shielding
• New inner tracking, with 2T solenoid and silicon
  vertex strip detector
• b-tagging possible at high pseudorapidity (lt 2.5)

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Signal

• Higgs decays 90 to a b-quark pair at high tan ?
• 4 b-jet final state

• Two hard, central b-jets
• roughly mh/2
• Another hard b-jet balancing the pT of the Higgs
• One softer, forward b-jet

CompHEPPythia MC
QCD
Signal
Mh120 GeV
pT gt 20 GeV
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Triggering

• Make full use of the 3-level trigger system
• Use the primary vertex to
• correct jet ET
• veto interactions beyond the fiducial silicon
  volume
• Demand 3 jets with ET gt (25,25,15) GeVorET gt
  (15,15,15) GeV and a muon
• Efficiency is gt70 (relative to loose offline
  cuts)
• Run I 8 efficient using
• 4 jets gt 15 GeV
• HT gt 125 GeV
• gt 50 pb-1 already on tape

Jet Trigger (2,25)(3,15)
Using L3 Vertex
RUN I
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b - Tagging

• Jets are tagged as coming from b-quarks
• High-resolution tracking-based tag
• Muon tag
• Soft-electron tag (being studied)
• In Monte Carlo 60 efficient and 1.5 fake
• Currently working on understanding and improving
  efficiency and rejection in data

b
b-tagging Efficiency (DØ Run II MC)
c
1.5 fake
Jet ?
Jet pT
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Di-b-jet Mass Resolution
Reconstructed Higgs mass in Monte CarloNo
backgrounds included!

• Need good b-jet ET resolution to see a Higgs peak
• Jet-energy corrections are used
• Various cone-sizes and jet algorithms were
  studied
• Jet reconstruction and energy-scale corrections
  do well in MC
• 12 mass resolution
• Need to study and improve resolution in data

CompHEP Pythia MCNO JES Corr.mh 120 GeV
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The bbH Analysis

• Backgrounds
• QCD heavy flavor bbjj, ccjj, cccc, bbcc, bbbb
• QCD fakes jjjj
• Top-quark production tt
• Electroweak Z(bb,cc), W(bb,cc)
• Kinematic cuts
• Optimize for each Higgs mass individually
• Demand no more than 4 jets?
• May be necessary to reduce the top quark
  background
• btagging
• Tag 3 or more jets in the event
• Use a combination of tracking-based, muon, and
  soft-electron tags
• Look at di-jet invariant masses of the leading
  b-jet combinations
• Search for an excess of events inside a
  mass-window optimized for each Higgs mass

CompHEP Pythia MCmh 120 GeV
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Summary / Outlook

• Lots of progress in the last year
• Theoretical signal cross-sections are now on
  firmer ground
• The Tevatron is producing decent, stable
  luminosity
• DØ recording data with gt 85 efficiency
• All pieces of DØ needed for this analysis are
  functional
• A specialized trigger for this signal has been
  commissioned and measured
• Basic analysis methods have been established and
  applied to the data

• Now need to understand the data in detail
• Measure b-tag efficiencies and fake rates in
  complicated multi-jet events
• Understand the di-b-jet mass resolution and
  optimize the Higgs mass peak reconstruction
• Hope for 100 pb-1 of luminosity, and the first
  results of this analysis by summer 2003!

4 b-tag event with mh113 GeV