Electroweak Measurements at the Tevatron

1
Electroweak Measurements at the Tevatron

• Cairo International Conference on HEP
• January 9, 2001
• Results from D0 and CDFs Run I
• Prospects for the 1st 2 fb-1 of Run II

Tom Diehl Fermi National Accelerator
Laboratory Batavia, Illinois
2
Acknowledgements

• Thanks as always to D0 and CDF collaborations.
• Some material in this talk comes from previous
  presentations by
• Uli Heintz, Meena Narain, Georg Steinbruck, John
  Butler, Natalia Sotnikova, and Darien Wood.

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Electroweak Measurements at the Tevatron

• Introduction
• W and Z Boson Properties
• General Features of Production
• Inclusive Cross Section
• W Boson Width Mass
• Trilinear Gauge Boson Couplings
• Top Quark Properties
• General Features
• Top Pair Production Cross Section Production
  Dynamics
• Top Quark Mass
• Branching Ratios Rare Decays
• Electroweak Top Quark Production
• Standard Model Higgs Boson
• M(top), M(W), and M(Higgs)
• Standard Model Higgs Boson Search

Run 1 Results and Prospects for Run II
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The Run 1 D0 Detector
Non-magnetic central tracking and no silicon
detector
Large muon toroids s(1/p)0.18(1/p)0.003
(p in GeV/c)

• Calorimeter Hermetic ?lt4
• D ? x D f0.1 x 0.1
• s(EM)15/E1/2
• s(had)50/E1/2

Electroweak analyses use all of the detector
capability
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Run 1 CDF Detector
Magnetic central tracking w/ large radius a
silicon detector for vertices

• Calorimeter
• s(EM)15/E1/2
• s(had)50/E1/2

Muon detector provides ID. Momentum measurement
from central tracker
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D0 Upgrade
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CDF Upgrade
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W/Z Physics
W Bosons Detected

• Topics
• General Features of Production
• Inclusive Cross Section
• W Boson Width
• W Boson Mass Preliminaries
• W Boson Mass
• Trilinear Gauge Boson Couplings

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General Features of W and Z Production
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Inclusive Cross Section

• sB(W-gt l n) 2.2 nb
• sB(Z-gt l l-) 0.22 nb
• Cross section measurement uncertainty
• Stat Å Sys 2,
• Luminosity error 4
• Theory prediction uncertainty
• 3, NNLO, O(as2)
• Dominated by PDFs at NLO
• (need NNLO)

Luminosity L(D0) 1.062 x L(CDF) D0 uses world
avg. s(pp)inel, CDF uses CDF measurement
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W Boson Width

• Indirect Method

• Direct Method (CDF)
• Model independent
• Study high-end tail of MT(ln).

(SM2.093 0.002)
Form ratio
SM EW
Perturbative QCD
LEP
CDFD0 combined
(LEP combined2.12 0.11)
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W Boson Mass Preliminaries

• Input from theorists calculations tuned by our
  measurements.

PT(W) Ladinsky-Yuan
A sample of our published results
W Boson Production Decay Model
PDFs
D0 very recent
W Spin Orientation E. Mirkes. (1992)
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W Boson Mass

• Uncertainty example (CDF electrons)
• Statistical 65 MeV/c2
• Systematic 92 MeV/c2
• ET Scale 75 MeV/c2
• Detector resolution 25 MeV/c2
• PDFs 15 MeV/c2
• PT(W) 15 MeV/c2
• Recoil Model 37 MeV/c2
• Backgrounds 5 MeV/c2

• W Mass measurements from
• MT(W) _at_ CDFD0
• PT(lepton) _at_ D0
• ET(n) _at_ D0
• Using
• electron channels _at_ CDFD0
• muon channels _at_ CDF

D0 CC electron channel

• CDF (em) combined (2000)
• D0 Run 1 (e) Result (2000)

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Gauge Boson Self-Interactions

• Self-interactions are a direct consequence of the
  non-Abelian SU(2)L x U(1)Y gauge symmetry.
• Trilinear Coupling Diagrams are involved in
  Vector Boson Pair Production.
• SM makes specific predictions for the strength of
  the couplings.
• WWg and WWZ Couplings related to the static W
  properties

We study gauge boson couplings by investigating
properties of vector boson pair production Wg,
WW, WZ, Zg, ZZ in various final states
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WWg and WWZ Couplings

• In Run 1
• Established the EW coupling of W to g and W to
  Z.
• The Wg and WW processes were observed. Candidate
  WZ events observed.
• Anomalous Coupling Limits Wg, WW, and
  combined WZ results from D0 (equal gZ
  couplings)
• Another set of relations among couplings

eng mng

• In 2 fb-1
• 2000 engmng events per exp.
• Observe radiation zero
• Sensitivity to anomalous couplings 2-3X better.

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ZZg, Zgg, and ZZZ Couplings

• Zphoton final state
• Tests ZZg and Zgg couplings
• ZZg and Zgg 0 in SM (no s-channel diagrams)

• Run 1 Limits on coupling parameters

At 95 CL
(Zgg coupling limits similar)

• In 2 fb-1 we expect
• 600 Zg events per experiment
• sensitivity to limits about 5X smaller
• Our first ZZZ limits (CDF observed ZZ candidate
  with 4 muons in 1995)

PRD 4/1/98
nng 14 pb-1 eeg mmg 110 pb-1
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Top Physics

• Topics
• General Features
• Top Pair Production Cross Section Production
  Dynamics
• Top Quark Mass
• Branching Ratios Rare Decays
• Electroweak Top Quark Production

• Pair production mechanisms provide cross section
  which depends on top mass.
• Top heavier than m(b)m(W) decays primarily to Wb.

The Tevatron is the only place where we can
produce top.
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Top Physics General Features

• All hadronic and tauX have big
  backgrounds
• Lepton jets, Dilepton are our best measured
  channels

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Top-AntiTop Production
Run 1 Results
Run II Prospects

• Run 1 result at 1.8 TeV
• Run 2
• Tevatron beam energy is increased from 1.8 TeV to
  2.0 TeV gt increase in s(ttbar) of 40.
• Uncertainties on signal and backgrounds scale by
  N-1/2 . Uncertainty on luminosity doesnt (5
  in Run 1).

• Event Yields In Run 2a (per experiment)
• Expect ds/s8 _at_D0 (similar _at_ CDF).

unpublished update of 1998 CDF Pub.
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Top Quark Production Dynamics

• Properties of the top events (D0CDF)

Distributions as expected from SM ttbar
production
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Top Quark Mass in Run I
D0 Lepton Jets
CDF Lepton Jets
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Top Quark Mass Uncertainties

• How thats improved in Run II (2fb-1)
• Conservative Estimates
• Systematic 2.5 GeV/c2
• Jet Energy Scale 2.2 GeV/c2
• Recalibrate jet energy scale with gjet, Zjet,
  Z-gtb-bbar, W-gtjj in top events. There is room for
  improvement here.
• M. C. Signal Model 1.0 GeV/c2
• Constrain top production w/ data
• Background Model 0.5 GeV/c2
• Statistical 1.0-1.3 GeV/c2
• Reduce combinatorics because of double tags
• Total 2.8 GeV/c2

• Uncertainties in Run I Leptonjets mass
  measurement _at_ D0 (CDF)
• Total Systematic 5.5 (4.9) GeV/c2
• Jet energy scale 4.0 (4.4) GeV/c2
• Monte Carlo Top Modeling 3.5 (2.3) GeV/c2
• Principally from uncertainty in Initial and final
  state radiation
• Background model (Vecbos flavors) 2.0 (1.3)
  GeV/c2
• Methods 1.2 (0) GeV/c2
• Statistical 13 GeV/c2 per event 5.6 (4.8)
  GeV/c2

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Top Branching Ratios and Rare Decays

• Within the Standard Model
• Using indirect estimates of Vtd and Vts,
  unitarity, assuming 3 gens 0.99989 lt
  Vtblt0.9993 _at_ 90 CL

• CDF Result (new)
• uses ratios of tags in leptonjets and
  dilepton events. 01double2 tags and assuming 3
  gens.

Run 2a (2fb-1) dVtb2

• CDF FCNC Search S.M. Pred. O(10-10)

(95 CL)
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Top Quark Decay Vertex

• Top Quark is unique in that it usually decays
  before it hadronizes, V-A implies
• W is l.h. (h-1) or long. (h0)
• i.e. charged lepton tends to be emitted in
  direction opposite to W line-of-flight.

• S.M. f long 0.7

Kane, Ladinsky, Yuan PRD 1992
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Top Quark Decay Correlation

• Measure angle between the off-diagonal basis and
  the lepton flight direction in rest frame of the
  top ?-, ?
• Spin correlation ? correlation in q vs q- space.
  (SM k ? 0.9)
• D0 Measured

• Spin Configurations
• Optimal spin quantization axis
• Determined once the velocity and scattering angle
  is known
• Only like-spin combinations are produced in this
  optimized basis
• G. Mahlon and S. Parke, PLB 411, 173 (1997)

n
k gt -0.25 _at_ 68 CL
Fermilab-Pub-00/046-E
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Single Top Production

• Direct access to W ? tb vertex
• Measure top quark width and Vtb
• Measure of CKM element without any assumptions on
  number of generations
• ?(qq ? tb) ? ? (t ? Wb) ? Vtb2

• Theoretical predictions SmithWillenbrock,
  Stelzer et al. For M(top) 175 GeV

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Single Top Results Run 1 vs. Run 2
Accepted for pub. in PRD

• D0 Run 1 result at 1.8 TeV
• Signature is e(m)njj events where one jet is
  b-tagged with a muon. 90 pb-1. Acceptances
• Bkgds (Wjets, QCD, top) is 15 events. Expected
  signal lt 1
• Observe 17 events.
• _at_95CL

• CDFs has better Run I b-tagging (SVX)

CDF Preliminary ? lt 13.5 pb at 95 CL

• Run 2a (2 fb-1) will provide a 20
  measurement of s(tb) giving dVtb of 14 at both
  D0 and CDF.

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Top Quark Mass and W Boson Mass
W boson mass top mass Constrains Higgs mass
Tevatron Averages M(top)174.3-5.1
GeV M(W)80.454-0.063
Run 1
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Search for SM Higgs in Run II
Branching Fractions vs. M(Higgs)
s(HX) at Tevatron (2 TeV)
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Search for SM Higgs in Run II
Best Options for finding Higgs depend on M(Higgs)

• For M(Higgs)gt135 GeV/c2
• Backgrounds are more prosaic forms of diboson
  production and t-tbar.
• longitudinally polarized W and Z provides some
  handles on angular distributions
• S/B depends on M(Higgs)
• Varies from 3/30 to 1/4

• For M(Higgs)lt135 GeV/c2
• depends most on b-tagging efficiency and
  background rejection
• a few signal events per fb-1.
• Background is Wjets
• S/B 1/10

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Search for SM Higgs in Run II
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Top Quark Mass and W Boson Mass
W boson mass top mass Constrains Higgs mass
dM(top)3.0 GeV dM(W)40 MeV
Run 2

• Uncertainties shown are slightly bigger than
  what we think we can do in 2 fb-1.
• At Run I central values of M(W) M(top)

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Conclusions

• The D0 and CDF p-pbar collider experiments have a
  rich set of preliminary and published results
  including
• Vector Boson Properties
• W mass, W width, Trilinear gauge boson couplings,
  and W and Z production properties.
• 3.2 million W to mn and en expected (per
  experiment) in 2 fb-1.
• dM(W) 30 MeV/c2 per experiment in first 2 fb-1.
  
• Top Quark Properties
• Top Pair Production Cross Section Production
  Dynamics, Top Quark Mass, Branching ratios and
  Rare Decays.
• dM(top) 2.8 GeV/c2 per experiment in first 2
  fb-1.
• SM Higgs Boson
• Measurements of M(W) and M(top) hint it is light.
• We restrict the allowed range and find it
  depending on its mass.