University of Chicago

1
University of Chicago
Lecture 2 Things I would Like to See Measured at
the Tevatron
Rick Field University of Florida
Enrico Fermi Institute, University of Chicago
CDF Run 2
2
Heavy Quark Boson Production at the Tevatron
with 1 fb-1 1.4 x 1014 1 x 1011 6 x
106 6 x 105 14,000 5,000

• Total inelastic stot 100 mb which is 103-104
  larger than the cross section for D-meson or a
  B-meson.
• However there are lots of heavy quark events in 1
  fb-1!
• Want to study the production of charmed mesons
  and baryons D, D0, Ds , lc , cc , Xc, etc.
• Want to studey the production of B-mesons
  and baryons Bu , Bd , Bs , Bc , lb , Xb, etc.

• Two Heavy Quark Triggers at CDF
• For semileptonic decays we trigger on m and e.
• For hadronic decays we trigger on one or more
  displaced tracks (i.e. large impact parameter).

CDF-SVT
3
Selecting Heavy Flavor Decays

• To select charm and beauty in an hadronic
  environment requires
• High resolution tracking
• A way to trigger on the hadronic decays (i.e. a
  way to trigger on tracks)

• At CDF we have a Secondary Vertex Trigger (the
  SVT).

The CDF Secondary Vertex Trigger (SVT)

• Online (L2) selection of displaced tracks based
  on Silicon detector hits.

Collision Point
4
Selecting Prompt Charm Production
Collision Point
Prompt D
Secondary D from B

• Separate prompt (i.e. direct) and secondary charm
  based on their transverse impact parameter
  distribution.

• Prompt D-meson decays point back to primary
  vertex (i.e. the collision point).
• Secondary D-meson decays do not point back to the
  primary vertex.

Prompt peak
Direct Charm Meson Fractions D0
fD86.40.43.5 D fD88.11.13.9 D
fD89.10.42.8 Ds fD77.33.82.1
B?D tail
D impact parameter
Most of reconstructed D mesons are prompt!
5
Prompt Charm Meson Production
Charm Meson PT Distributions
CDF prompt charm cross section result published
in PRL (hep-ex/0307080)

• Theory calculation from M. Cacciari and P. Nason
  Resummed perturbative QCD (FONLL), JHEP 0309,006
  (2003). Fragmentation ALEPH measurement, CTEQ6M
  PDF.

Data collected by SVT trigger from 2/2002-3/2002
L 5.80.3 pb-1.
6
Comparisons with Theory
Next step is to study charm-anticharm
correlations to learn about the contributions
from different production mechanisms flavor
creation flavor Excitation gluon splitting
Ratio of Data to Theory

• NLO calculations compatible within errors?
• The pT shapes are consistent with the theory for
  the D mesons, but the measured cross section are
  a factor of about 1.5 higher!

7
Bottom Quark Production at the Tevatron
Tevatron Run 1 b-Quark Cross Section
CDF Run 1 1999

• Important to have good leading (or leading-log)
  order QCD Monte-Carlo model predictions of
  collider observables.
• The leading-log QCD Monte-Carlo model estimates
  are the base line from which all other
  calculations can be compared.
• If the leading-log order estimates are within a
  factor of two of the data, higher order
  calculations might be expected to improve the
  agreement.
• If a leading-log order estimate is off by more
  than a factor of two, it usually means that one
  has overlooked something.
• I see no reason why the QCD Monte-Carlo models
  should not qualitatively describe heavy quark
  production (in the same way they qualitatively
  describe light quark and gluon production).

QCD Monte-Carlo leading order Flavor Creation
is a factor of four below the data!
Extrapolation of what is measured (i.e. B-mesons)
to the parton level (i.e. b-quark)!

• Something is goofy (Rick Field, CDF B Group
  Talk, December 3, 1999).

8
Sources of Heavy Quarks
Leading-Log Order QCD Monte-Carlo Model (LLMC)
Leading Order Matrix Elements

• We do not observe c or b quarks directly. We
  measure D-mesons (which contain a c-quark) or we
  measure B-mesons (which contain a b-quark) or we
  measure c-jets (jets containing a D-meson) or we
  measure b-jets (jets containing a B-meson).

(structure functions)
(matrix elements)
(Fragmentation)
(initial and final-state radiation LLA)
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Other Sources of Heavy Quarks
Flavor Excitation (LLMC) corresponds to the
scattering of a b-quark (or bbar-quark) out of
the initial-state into the final-state by a gluon
or by a light quark or antiquark.
Gluon-Splitting (LLMC) is where a b-bbar pair
is created within a parton shower or during the
the fragmentation process of a gluon or a light
quark or antiquark. Here the QCD hard 2-to-2
subprocess involves only gluons and light quarks
and antiquarks.

• In the leading-log order Monte-Carlo models
  (LLMC) the separation into flavor creation,
  flavor excitation, and gluon splitting is
  unambiguous, however at next to leading order the
  same amplitudes contribute to all three processes!

and there are interference terms!
Next to Leading Order Matrix Elements
2


10
Inclusive b-quark Cross Section
Tevatron Run 1 b-Quark Cross Section
Total
Flavor Excitation
Flavor Creation
Gluon Splitting

• Data on the integrated b-quark total cross
  section (PT gt PTmin, y lt 1) for
  proton-antiproton collisions at 1.8 TeV compared
  with the QCD Monte-Carlo model predictions of
  PYTHIA 6.158 (CTEQ3L, PARP(67)4). The four
  curves correspond to the contribution from
  flavor creation, flavor excitation, gluon
  splitting, and the resulting total.

11
Conclusions from Run 1
Nothing is goofy Rick Field, Cambridge
Workshop, July 18, 2002
All three sources are important at the Tevatron!

• All three sources are important at the Tevatron
  and the QCD leading-log Monte-Carlo models do a
  fairly good job in describing the majority of the
  b-quark data at the Tevatron.
• We should be able experimentally to isolate the
  individual contributions to b-quark production by
  studying b-bbar correlations find out in much
  greater detail how well the QCD Monte-Carlo
  models actually describe the data.
• One has to be very careful when the experimenters
  extrapolate to the parton level and publish
  parton level results. The parton level is not an
  observable! Experiments measure hadrons! To
  extrapolate to the parton level requires making
  additional assumptions that may or may not be
  correct (and often the assumptions are not
  clearly stated or are very complicated). It is
  important that the experimenters always publish
  the corresponding hadron level result along with
  their parton level extrapolation.
• One also has to be very careful when theorists
  attempt to compare parton level calculations with
  experimental data. Hadronization and
  initial/final-state radiation effects are almost
  always important and theorists should embed their
  parton level results within a parton-shower/hadron
  ization framework (e.g. HERWIG or PYTHIA).

MC_at_NLO!
12
The Run 2 J/Y Cross Section

• The J/y inclusive cross-section includes
  contribution from the direct production of J/y
  and from decays from excited charmonium, Y(2S)?,
  and from the decays of b-hadrons, B? J/y X.

J/y coming from b-hadrons will be displaced from
primary vertex!
Down to PT 0!
39.7 pb-1
Primary vertex (i.e. interaction point)
13
CDF Run 2 B-hadron Cross Section
PRD 71, 032001 (2005)

• Run 2 B-hadron PT distribution compared with
  FONLL (CTEQ6M).

Cacciari, Frixone, Mangano, Nason, Ridolfi

• Good agreement between theory and experiment!

39.7 pb-1
Y lt 1.0
B-hadron pT
14
CDF Run 2 b-Jet Cross Section
Collision point

• b-quark tag based on displaced vertices.
  Secondary vertex mass discriminates flavor.

• Require one secondary vertex tagged b-jet within
  0.1 lt ylt 0.7 and plot the inclusive jet PT
  distribution (MidPoint, R 0.7).

15
CDF Run 2 b-Jet Cross Section

• Shows the CDF inclusive b-jet cross section
  (MidPoint, R 0.7, fmerge 0.75) at 1.96 TeV
  with L 300 pb-1.

• Shows data/theory for NLO (with large scale
  uncertainties).

• Shows data/theory for PYTHIA Tune A.

16
The b-bbar DiJet Cross-Section

• ET(b-jet1) gt 30 GeV, ET(b-jet2) gt 20 GeV,
  h(b-jets) lt 1.2.

Systematic Uncertainty
Preliminary CDF Results
sbb 34.5 ? 1.8 ? 10.5 nb
QCD Monte-Carlo Predictions
Differential Cross Section as a function of the
b-bbar DiJet invariant mass!
Predominately Flavor creation!

• Large Systematic Uncertainty
• Jet Energy Scale (20).
• b-tagging Efficiency (8)

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The b-bbar DiJet Cross-Section

• ET(b-jet1) gt 30 GeV, ET(b-jet2) gt 20 GeV,
  h(b-jets) lt 1.2.

Preliminary CDF Results
sbb 34.5 ? 1.8 ? 10.5 nb
QCD Monte-Carlo Predictions
Differential Cross Section as a function of the
b-bbar DiJet invariant mass!
JIMMY Runs with HERWIG and adds multiple parton
interactions!
JIMMY MPI J. M. Butterworth J. R. Forshaw M. H.
Seymour
Adding multiple parton interactions (i.e. JIMMY)
to enhance the underlying event increases the
b-bbar jet cross section!
18
b-bbar DiJet Correlations
Tune A!
Differential Cross Section as a function of Df of
the two b-jets!

• The two b-jets are predominately back-to-back
  (i.e. flavor creation)!

• Pythia Tune A agrees fairly well with the Df
  correlation!

Not an accident!
19
Top Decay Channels

• mtgtmWmb so dominant decay t?Wb.
• The top decays before it hadronizes.
• B(W ? qq) 67.
• B(W ? ln) 11 l e, m, t.

20
Dilepton Channel

• Backgrounds
• Physics Drell-Yan, WW/WZ/ZZ, Z ? tt
• Instrumental fake lepton

• Selection
• 2 leptons ET gt 20 GeV with opposite sign.
• gt2 jets ET gt 15 GeV.
• Missing ET gt 25 GeV (and away from any jet).
• HTpTlepETjetMET gt 200 GeV.
• Z rejection.

65 events
20 events background
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LeptonJets Channel
Kinematics

• Backgrounds
• Wjets
• QCD

• Selection
• 1 lepton with pT gt 20 GeV/c.
• gt 3 jets with pT gt 15GeV/c.
• Missing ET gt 20 GeV.

central

• Use 7 kinematic variables in neural net to
  discriminate signal from background!

One of the 7 variables!
spherical
binned likelihood fit
Neural net output!
22
LeptonJets Channel
b-Tagging

• Require b-jet to be tagged for discrimination.

1 b tag
Tagging efficiency for b jets50
for c jets10 for light q jets lt
0.1
2 b tags
HTgt200GeV
150 events
45 events
Small background!
23
Tevatron Top-Pair Cross-Section
CDF Run 2 Preliminary
Theory
Bonciani et al., Nucl. Phys. B529, 424
(1998) Kidonakis and Vogt, Phys. Rev. D68, 114014
(2003)
24
CDF Mtop Results
Transverse decay length!
CDF Leptonjets Mtop (template)
173.4 2.5 (stat. jet E) 1.3 (syst.)
GeV Mtop (matrix element) 174.1 2.5 (stat.
jet E) 1.4 (syst.) GeV Mtop (Lxy) 183.9
15.7-13.9 (stat.) 5.6 (syst.) GeV CDF
Dilepton Mtop (matrix element) 164.5 4.5
(stat.) 3.1 (jet E. syst.) GeV
25
Top Quark Mass
Summer 2005
New since Summer 2005
Dilepton
CDF-II MtopME 164.5 5.5
GeV LeptonJets
CDF-II MtopTemp 174.1 2.8 GeV
CDF-II MtopME 173.4 2.9 GeV CDF Combined
MtopCDF 172.0
1.6 2.2 GeV 172.0 2.7 GeV
26
Top Cross-Section vs Mass
Tevatron Summer 2005
CDF Winter 2006
CDF combined
Updated CDFDØ combined result is coming soon!
27
Is Anything Goofy?

• Possible discrepancy between l jets and the
  dilepton channel measurements of the top mass??
• Is it statistical?
• Unlikely!
• Is there a missing systematic?
• This is probably nothing, but we should keep an
  eye on it!

28
Future Top Mass Measurements

• Expect significant reduction in jet energy scale
  uncertainty with more data.
• Today we have CDF-II Mtop(Temp) 174.1 2.8 GeV
  (0.7 fb-1).
• CDF should be able to achieve 1.5 GeV uncertainty
  on top mass!

29
Constraining the Higgs Mass

• Top quark mass is a fundamental parameter of SM.
• Radiative corrections to SM predictions dominated
  by top mass.
• Top mass together with W mass places a constraint
  on Higgs mass!

Summer 05
Light Higgs very interesting for the Tevatron!
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Top Charge, Branching, Lifetime, W Helicity
Top Charge
Top Lifetime
Everything consistent with the Standard Model
(so far)!
CDF Prelim. 318 pb-1
DØ Prelim. 365 pb-1
?toplt 1.75x10-13s c?toplt 52.5?m at 95CL
Exclude Q 4/3 at 94 CL
Reconstructed Top Charge (e)
Impact Parameter (?m)
370 pb-1
f (DØ combined) 0.04 0.11(stat)
0.06(syst) f (SM pred.) 0
SM
signal
signalbgrnd
bgrnd
hep-ex/0603002
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Other Sources of Top Quarks

• Dominant production mode ?NLONLL 6.7 ? 1.2 pb
• Relatively clean signature
• Discovery in 1995

85
15
ElectroWeak Production Single Top

• Larger background
• Smaller cross section s 2 pb
• Not yet observed!

32
Single Top Production
tW associated production
s-channel
t-channel
(mtop175 GeV/c2)
Run I 95 C.L.
B.W. Harris et al.Phys.Rev.D66,054024
T.Tait hep-ph/9909352 Z.Sullivan
Phys.Rev.D70114012 Belyaev,Boos
hep-ph/0003260
33
Single Top Results from CDF

• To the network 2D output, CDF applies a maximum
  likelihood fit and the best fits for t and
  s-channels are

The CDF limits!
t-channel ? lt 3.1 pb _at_ 95
C.L. s-channel ? lt 3.2 pb _at_ 95 C.L.
34
Single Top at the Tevatron
95 C.L. limits on single top cross-section
(2.9 pb)
(0.9 pb)
(2 pb)

• The current CDF and DØ analyses not only provide
  drastically improved limits on the single top
  cross-section, but set all necessary tools and
  methods toward a possible discovery with a larger
  data sample!
• Both collaborations are aggressively working on
  improving the results!

Theory!
We should see single top soon !!!
35
Top-AntiTop Resonances
CDF Run 1
Excess is reduced!
Phys.Rev.Lett. 85, 2062 (2000)

• CDF observed an intriguing excess of events with
  top-antitop invariant mass around 500 GeV!

36
Direct Photon Cross-Section

• DØ uses a neural network (NN) with track
  isolation and calorimeter shower shape variables
  to separate direct photons from background
  photons and p0s!

Note rise at low pT!
Highest pT(g) is 442 GeV/c (3 events above 300
GeV/c not displayed)!
37
g b/c Cross Sections
L 67 pb-1

• b/c-quark tag based on displaced vertices.
  Secondary vertex mass discriminates flavor.

38
g b/c Cross Sections
L 67 pb-1
PYTHIA Tune A!
g b
g c

• PYTHIA Tune A correctly predicts the relative
  amount of u, d, s, c, b quarks within the photon
  events.

ET(g) gt 25 GeV
39
g g Cross Section
L 207 pb-1
QCD g g
g g Df
g g mass

• Di-Photon cross section with 207 pb-1 of Run 2
  data compared with next-to-leading order QCD
  predictions from DIPHOX and ResBos.

40
Z-boson Cross Section
L 72 pb-1
QCD Drell-Yan

• Impressive agreement between experiment and NNLO
  theory (Stirling, van Neerven)!

41
Z-boson Cross Section
L 337 pb-1

• Impressive agreement between experiment and NNLO
  theory (Stirling, van Neerven)!

42
The Z?tt Cross Section

• Taus are difficult to reconstruct at hadron
  colliders
• Exploit event topology to suppress backgrounds
  (QCD Wjet).
• Measurement of cross section important for Higgs
  and SUSY analyses.
• CDF strategy of hadronic t reconstruction
• Study charged tracks define signal and isolation
  cone (isolation require no tracks in isolation
  cone).
• Use hadronic calorimeter clusters (to suppress
  electron background).
• p0 detected by the CES detector and required to
  be in the signal cone.
• CES resolution 2-3mm, proportional strip/wire
  drift chamber at 6X0 of EM calorimeter.

New

• Channel for Z?tt electron isolated track
• One t decays to an electron t?eX (ET(e) gt 10
  GeV) .
• One t decays to hadrons t ? hX (pT gt 15GeV/c).
• Remove Drell-Yan ee- and apply event topology
  cuts for non-Z background.

43
The Z?tt Cross Section

• CDF Z?tt (350 pb-1) 316 Z?tt candidates.
• Novel method for background estimation main
  contribution QCD.
• t identification efficiency 60 with
  uncertainty about 3!

44
Higgs ? tt Search
Lets find the Higgs!
events
140 GeV Higgs Signal!
1 event

• Data mass distribution agrees with SM
  expectation
• MH gt 120 GeV 8.40.9 expected, 11 observed.
• Fit mass distribution for Higgs Signal (MSSM
  scenario)
• Exclude 140 GeV Higgs at 95 C.L.
• Upper limit on cross section times branching
  ratio.

45
W-boson Cross Section

• Extend electron coverage to the forward region
  (1.2 lt h lt 2.8)!

W Acceptance
48,144 W candidates 4.5 background overall
efficiency of signal 7
46
20 Years of Measuring W Z
47
Z b-Jet Production

• Important background for new physics!

• Leptonic decays for the Z.
• Z associated with jets.
• CDF JETCLU, D0 MidPoint
• R 0.7, hjet lt 1.5, ET gt20 GeV
• Look for tagged jets in Z events.

L 335 pb-1
L 180 pb-1
Extract fraction of b-tagged jets from secondary
vertex mass distribution NO assumption on the
charm content.
CDF
Assumption on the charm content from theoretical
prediction Nc1.69Nb.
DØ
Agreement with NLO prediction
48
W g Cross Sections
ET(g) gt 7 GeV R(lg) gt 0.7
49
Z g Cross Sections
Note ?(W?)/?(Z?) 4 while ?(W)/?(Z) 11
ET(g) gt 7 GeV R(lg) gt 0.7
50
WW Cross-Section
Campbell Ellis 1999
51
WW Cross-Section
L 825 pb-1
We are beginning to study the details
of Di-Boson production at the Tevatron!

• WW?dileptons MET
• Two leptons pT gt 20 GeV/c.
• Z veto.
• MET gt 20 GeV.
• Zero jets with ETgt15 GeV and hlt2.5.

New
Observe 95 events with 37.2 background!
Missing ET!
Lepton-Pair Mass!
ET Sum!
52
ZW, ZZ Cross Sections
Observe 2 events with a background of 0.90.2!
Upper Limits
53
Di-Bosons at the Tevatron
W
We are getting closer to the Higgs!
Z
Wg
Zg
WW
WZ
54
Generic Squark Gluino Search
It will be a long time before ATLAS CMS
understand their missing ET spectrum this well!

• Selection
• 3 jets with ETgt125 GeV, 75 GeV and 25 GeV.
• Missing ETgt165 GeV.
• HT? jet ET gt 350 GeV.
• Missing ET not along a jet direction
• Avoid jet mismeasurements.
• Background
• W/Zjets with W?l? or Z???.
• Top.
• QCD multijets
• Mismeasured jet energies lead to missing ET.

PYTHIA Tune A

• Observe 3, Expect 4.11.5.

55
Future Higgs SUSY Searches

• CDF and Tevatron running great!
• Often worlds best constraints.
• Many searches on SUSY, Higgs and other new
  particles.
• Most current analyses based on up to 350 pb-1
• We will analyze 1 fb-1 by summer 2006.
• Anticipate 4.4 - 8.6 fb-1 by 2009.
• The Tevatron has a chance of finding new physics
  before the ATLAS and CMS understand their
  dectors!
• We may be able to tell the LHC where to look!

Lets find the Higgs!
If we find something the real fun starts What
Is It?