Tevatron Results on Top Quarks, Leptoquarks, and Higgs Bosons

1
Tevatron Results on Top Quarks, Leptoquarks, and
Higgs Bosons

• Richard Partridge
• Brown University
• For the DØ and CDF Collaborations
• Orbis Scientiae
• Physics of Mass
• December 12-15, 1997

2
Top Quarks

• What have we learned since 1995?
• The top quark has now been observed in all of its
  SM decay channels
• Top pair production cross section is in good
  agreement with SM predictions
• Top quark mass is known with superb precion
• mt 174.1 5.4 GeV/c2

3
Top Production Cross Section
4
Lepton Jets Mass Analysis

• 2C Fitting Hypothesis
• Select four highest ET jets
• Correct jets for out-of-cone energy
• Perform kinematic fits for the 12 possible jet
  permutations (6 for b-tagged events)
• Reject fits with bad ?2
• Calculate the Fitted mass for each event
• Fit distribution of Fitted Masses to obtain top
  mass

5
Some Complications

• Gluon Radiation from initial and final states
  broadens fitted mass distribution
• 50 probability of picking the b, b, q, q jets
• 20-30 probability of correct jet assignment
• Backgrounds reduce mass sensitivity
• CDF fits lifetime tags, double tags, lepton tags,
  and untagged samples separately to optimize mass
  resolution
• DØ forms multivariate discriminants to separate
  top from background based on 4 variables that are
  nearly uncorrelated with the fitted mass
• Warning CDF jet ET cuts are before corrections,
  DØ cuts are after corrections

6
Effects of Gluon Radiation
7
CDF Mass Fits
8
CDF Combined Mass Fit

• mt 175.9 4.8 (stat) 4.9 (syst) GeV/c2

9
DØ Event Selection Variables
10
DØ Mass Fit

• mt 173.3 5.6 (stat) 5.5 (syst) GeV/c2

11
Observation of tWb

• Double tagged events have only one jet
  combination
• mjj78.15.9, in good agreement with the measured
  W mass

12
Dilepton Mass Analysis

• 0C Kinematic fit if top mass is known
• Quartic equation gives 0-4 physical solutions
• Based on work of Kondo (J. Phys. Soc. Japan 57,
  4126 and 60, 836) and Dalitz and Goldstein (Phys.
  Rev. D45, 1531)
• D0 extensions to remove cross section bias and
  include detector resolution smearing
• Sensitivity to top mass through
• production kinematics (structure functions)
• decay kinematics (lepton energies)
• resolution smearing (tests if event lies in a
  probable region of phase space)

13
CDF Dilepton Mass Analysis
14
DØ Dilepton Weights
15
DØ Weight Distributions
16
DØ Dilepton Mass Results
17
Analysis of D0 e-? Events

• Event selection from cross section analysis
• Focus on low background e-? channel
• 3 events, expected background nb0.360.09
• Use peak of likelihood curve as mass estimator
• Two likelihoods for events with ???jets
• use only two highest ET jets
• use three highest ET jets with empirical
  weighting factor for each initial/final state
  radiation hypothesis
• Average 2-Jet and 3-Jet mass estimates
• MC studies demonstrate improved mass resolution
  when the 2-jet/3-jet mass difference is large

18
Dilepton Mass Fit

• Likelihood fit of e-? mass distribution
• Statistical error from ensemble analysis
• mt 158 24 (stat) GeV/c2
• Consistent results obtained for other fits
• 2-Jet likelihood mt14927-19 GeV/c2
• 3-Jet likelihood mt16519-31 GeV/c2
• All three dilepton channels mt151 21 GeV/c2

19
Neutrino Weighting Method

• Focus on phase space part of likelihood
• Perform limited phase space integral over
  neutrino pseudorapidities
• Gaussian approximation of prior probabilities for
  neutrino pseudorapidities with width taken from
  MC
• Solve for missing ET components and form Gaussian
  likelihood comparing missing ET solution with our
  measured missing ET
• Includes detector resolution smearing
• mt 157 23 9 GeV/c2

20
CDF Alljets Mass Analysis

• Event selection requires ³6 jets, lifetime b-tag,
  and kinematical cuts
• Choose jet combination with lowest 3C ?2

21
Top Mass Summary

• Unofficial CDF DØ combined top mass
• mt 174.1 5.4 GeV/c2

22
Top Mass in Run 2

• Statistics will increase by a factor of gt25
• 3.5 GeV/c2 0.7 GeV/c2 ??
• Reducing systematic errors will be more difficult
• Jet ener

23
Search for Leptoquarks
24
CDF Leptoquark Search
25
D0 eejj Leptoquark Mass Fits
26
DØ Optimized eejj Analysis
27
DØ eejj enjj Mass Limits
28
Higgs Search
29
Indirect Higgs Search
30
Higgs Mass Limits
31
DØ Charged Higgs Search
32
CDF Charged Higgs Search
33
Direct Higgs Search in Run 2
34
Tevatrons Higgs Reach
35
Summary