XXXIV International Meeting on
Fundamental Physics
From HERA and the TEVATRON
to the LHC
Physics at the Tevatron
Rick Field
University of Florida
(for the CDF & D0 Collaborations)
Real Colegio Maria Cristina, El Escorial, Spain
3nd Lecture
CDF Run 2
IMFP2006 - Day 3
April 5, 2006
Photons, Bosons, and Jets at the Tevatron
Rick Field – Florida/CDF/CMS
Page 1
Photons, Bosons, and Jets
at the Tevatron
Some Cross Sections Measured at the Tevatron
 The Direct Photon Cross-Section.
 The g + Heavy Quark Cross-Section.
 The g + g Cross-Section.
jet
photon
jet
jet
Z-boson
photon
jetW-boson
 The Z-Boson Cross-Section.
 The W-Boson Cross-Section.
 The W+Jets, Z+Jets, and Z+b-Jet
Cross-Sections.
and comparisons
with theory!
proton
Antiproton
W+jets
W
W
+++TeV
W
gg
W
ggJets
bZ
W-boson
Z-boson
1.96
Beam-Beam Remnants
uud
Beam-Beam Remnants
 The W+g and Z+g Cross-Sections.
 The W+W Cross-Section.
 H
The
→Higgs
W+W→
with
W+W
100Cross-Section.
times more data!
W-boson
W-boson
W-boson
jet
photon
b-quark
 The W+Z and Z+Z Cross-Sections.
 The Inclusive Jet and DiJet Cross-Sections.
IMFP2006 - Day 3
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Rick Field – Florida/CDF/CMS
Page 2
The 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 p0’s!
q
g
g
q
Note rise at low pT!
Highest pT(g) is 442 GeV/c
(3 events above 300 GeV/c
not displayed)!
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Rick Field – Florida/CDF/CMS
Page 3
g + b/c Cross Sections (CDF)
 b/c-quark tag based on displaced vertices. Secondary vertex mass
discriminates flavor.
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Rick Field – Florida/CDF/CMS
Page 4
g + b/c Cross Sections (CDF)
PYTHIA Tune A!
g+b
g+c
 PYTHIA Tune A correctly
CDF (pb)
predicts the relative amount
of u, d, s, c, b quarks within
the photon events.
s(b+g)
40.619.5(stat)+7.4(sys)-7.8(sys)
s(c+g)
486.2152.9(stat)+86.5(sys)-90.9(sys)
ET(g) > 25 GeV
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Rick Field – Florida/CDF/CMS
Page 5
g + g Cross Section (CDF)
QCD g + g
g + g Df
g + g mass
 Di-Photon cross section with 207 pb-1 of Run 2 data compared with next-toleading order QCD predictions from DIPHOX and ResBos.
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Rick Field – Florida/CDF/CMS
Page 6
Z-boson Cross Section (CDF)
QCD
Drell-Yan
 Impressive agreement between experiment
and NNLO theory (Stirling, van Neerven)!
s(Z→e+e-)
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CDF (pb)
NNLO (pb)
254.93.3(stat)4.6(sys)15.2(lum)
252.35.0
Rick Field – Florida/CDF/CMS
Page 7
Z-boson Cross Section (CDF)
 Impressive agreement between experiment and NNLO theory
(Stirling, van Neerven)!
s(Z→m+m-)
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CDF (pb)
NNLO (pb)
261.22.7(stat)6.9(sys)15.1(lum)
252.35.0
Rick Field – Florida/CDF/CMS
Page 8
The Z→tt Cross Section (CDF)
 Taus are difficult to reconstruct at hadron colliders
• Exploit event topology to suppress backgrounds (QCD & W+jet).
• Measurement of cross section important for Higgs and SUSY analyses.
Signal
cone
 CDF strategy of hadronic τ reconstruction:
• Study charged tracks define signal and isolation cone (isolation = require no
tracks in isolation cone).
• Use hadronic calorimeter clusters (to suppress electron background).
• π0 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.
Isolation
cone
 Channel for Z→ττ: electron + isolated track
• One t decays to an electron: τ→e+X (ET(e) > 10 GeV) .
• One t decays to hadrons: τ → h+X (pT > 15GeV/c).
 Remove Drell-Yan e+e- and apply event topology cuts for non-Z
background.
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Rick Field – Florida/CDF/CMS
Page 9
The Z→tt Cross Section (CDF)
 CDF Z→ττ (350 pb-1): 316 Z→ττ candidates.
 Novel method for background estimation: main contribution QCD.
 τ identification efficiency ~60% with uncertainty about 3%!
1 and 3 tracks,
opposite sign
same sign,
opposite sign
s(Z→t+t-)
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CDF (pb)
NNLO (pb)
26520(stat)21(sys)15(lum)
252.35.0
Rick Field – Florida/CDF/CMS
Page 10
Higgs → tt Search (CDF)
140 GeV
Higgs Signal!
 Data mass distribution agrees with SM expectation:
• MH > 120 GeV: 8.4±0.9 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.
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W-boson Cross Section (CDF)
 Extend electron coverage to the forward
region (1.2 < |h| < 2.8)!
48,144 W candidates ~4.5% background
overall efficiency of signal ~7%
s(W)/s(Z)
s(W)
CDF
NNLO
10.920.15(stat)0.14(sys)
10.690.08
L
CDF (pb)
NNLO(pb)
Central
electrons
72 pb-1
277510(stat)53(sys)167(lum)
268754
Forward
electrons
223 pb-1
281513(stat)94(sys)169(lum)
268754
IMFP2006 - Day 3
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Rick Field – Florida/CDF/CMS
Page 12
20 Years of Measuring W & Z
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Rick Field – Florida/CDF/CMS
Page 13
W+Jets Production (CDF)
 Background to Top and Higgs Physics.
 Testing ground for pQCD in multi-jet environment.
L = 320 pb-1
 Restrict sW :
• W → e n, |he|< 1.1.
 JETCLU jets (R=0.4):
• ETjets>15 GeV, |hjet| < 2.
 Uncertainties dominated by
background subtraction and
Jet Energy Scale.
LO predictions normalized to data
integrated cross sections:
 Shape comparison only!
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Rick Field – Florida/CDF/CMS
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W+Jets Production (CDF)
di-jet DR distribution in the W+ ≥2 jet
 Important to study distributions and
topological structure of W + Jets!
di-jet invariant mass distribution in the W+ ≥2 jet
LO predictions normalized to data
integrated cross sections:
 Shape comparison only!
More exhaustive comparisons expected soon!!!
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Rick Field – Florida/CDF/CMS
Page 15
Z+Jets Production (DØ)
 Same physics as W + jets s(Z) ~ s(W)/10, but
Z→e+e- cleaner.
 Central electrons (|h|<1.1).
 MidPoint jets: (R = 0.5, pT > 20 GeV/c, |yjet|<2.5).
s n s [ Z / g * ( e  e  )  njets]
Rn 

s0
s [ Z / g * ( e  e  )]
L = 343 pb-1
PT distribution of the nth jet
Z+j
Z+2j
Z+3j
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MCFM: NLO for Z+1p or Z+2p  good description
of the measured cross sections.
ME + PS: with MADGRAPH tree level process up
to 3 partons  reproduce shape of Njet distributions
(Pythia used for PS).
Rick Field – Florida/CDF/CMS
Page 16
Z + b-Jet Production (CDF & DØ)
 Important background for new physics!





Leptonic decays for the Z.
Z associated with jets.
CDF: JETCLU, D0: MidPoint:
R = 0.7, |hjet| < 1.5, ET >20 GeV
Look for tagged jets in Z events.
CDF
Extract fraction of b-tagged jets from
secondary vertex mass distribution: NO
assumption on the charm content.
DØ
Assumption on the charm content
from theoretical prediction:
Nc=1.69Nb.
s ( Z  bjet)  0.96  0.32  0.14 pb
s [ Z  bjet ]
002
R
 0.021  0.004( stat ) 00..003
( syst )
s [ Z  bjet]
s [ Z  jet]
R
 0.0237  0.0078( stat )  0.0033( syst )
s [ Z  jet]
Agreement with NLO prediction:
IMFP2006 - Day 3
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s ( Z  bjet )  0.52 pb
Rick Field – Florida/CDF/CMS
R  0.018  0.004
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W + g Cross Sections (CDF)
ET(g) > 7 GeV
R(lg) > 0.7
s(W+g)*BR(W->ln)
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CDF (pb)
NLO (pb)
19.71.7(stat)2.0(sys)1.1(lum)
19.31.4
Rick Field – Florida/CDF/CMS
Page 18
Z + g Cross Sections (CDF)
Note: s(Wg)/s(Zg) ≈ 4
while s(W)/s(Z) ≈ 11
ET(g) > 7 GeV
R(lg) > 0.7
s(Z+g)*BR(Z->ll)
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CDF (pb)
NLO (pb)
5.30.6(stat)0.3(sys)0.3(lum)
5.40.3
Rick Field – Florida/CDF/CMS
Page 19
The W+W Cross-Section
Campbell & Ellis 1999
pb-1
CDF (pb)
NLO (pb)
s(WW) CDF
184
14.6+5.8(stat)-5.1(stat)1.8(sys)0.9(lum)
12.40.8
s(WW) DØ
240
13.8+4.3(stat)-3.8(stat)1.2(sys)0.9(lum)
12.40.8
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Page 20
The W+W Cross-Section (CDF)





WW→dileptons + MET
Two leptons pT > 20 GeV/c.
Z veto.
MET > 20 GeV.
Zero jets with ET>15 GeV
and |h|<2.5.
We are beginning to study the details
of 95 events with
Observe
37.2 background!
Di-Boson production at the Tevatron!
s(WW)
L
CDF (pb)
NLO (pb)
825 pb-1
13.72.3(stat)1.6(sys)1.2(lum)
12.40.8
Missing ET!
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Lepton-Pair Mass!
Rick Field – Florida/CDF/CMS
ET Sum!
Page 21
The Z+W, Z+Z Cross Sections
W+Z → trileptons + MET
Observe 2 events with a
background of 0.9±0.2!
Upper Limits
W+Z, Z+Z
Limit (pb)
NLO (pb)
CDF (194 pb-1) sum
< 15.2 (95% CL)
5.00.4
DØ (300 pb-1) W+Z
< 13.3 (95% CL)
3.70.1
CDF (825 pb-1) W+Z
< 6.34 (95% CL)
3.70.1
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Rick Field – Florida/CDF/CMS
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Di-Bosons at the Tevatron
W
We are getting closer to
the Higgs!
Z
W+g
Z+g
W+W
W+Z
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Rick Field – Florida/CDF/CMS
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Generic Squark and Gluino Search
 Selection:
 3 jets with ET>125 GeV, 75 GeV and
25 GeV.
 Missing ET>165 GeV.
 HT=∑ jet ET > 350 GeV.
 Missing ET not along a jet direction:
• Avoid jet mismeasurements.
 Background:
 W/Z+jets with Wln or Znn.
 Top.
 QCD multijets:
• Mismeasured jet energies lead to
missing ET.
PYTHIA Tune A
Observe: 3, Expect: 4.1±1.5.
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Rick Field – Florida/CDF/CMS
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Future Higgs & SUSY Searches
 CDF and Tevatron running great!
 Often world’s best constraints.
 Many searches on SUSY, Higgs and other
new particles.
 Most currewnt 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.
 If Tevatron finds no new physics it will
provide further important constraints:
 And hopefully LHC will then do the job!
If we find something the
real fun starts: What Is It?
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Jets at Tevatron
“Theory Jets”
“Tevatron Jets”
Next-to-leading order
parton level calculation
0, 1, 2, or 3 partons!
 Experimental Jets: The study of “real” jets requires a “jet algorithm” and the different
algorithms correspond to different observables and give different results!
 Experimental Jets: The study of “real” jets requires a good understanding of the calorimeter
response!
 Experimental Jets: To compare with NLO parton level (and measure structure functions)
requires a good understanding of the “underlying event”!
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Jet Corrections
 Calorimeter Jets:
 We measure “jets” at the “hadron level” in the calorimeter.
 We certainly want to correct the “jets” for the detector resolution and
effieciency.
 Also, we must correct the “jets” for “pile-up”.
 Must correct what we measure back to the true “particle level” jets!
 Particle Level Jets:
 Do we want to make further model dependent corrections?
 Do we want to try and subtract the “underlying event” from the
“particle level” jets.
 This cannot really be done, but if you trust the Monte-Carlo
models modeling of the “underlying event” you can try and do it
by using the Monte-Carlo models (use PYTHIA Tune A).
 Parton Level Jets:
 Do we want to use our data to try and extrapolate back to the
parton level?
PT(hard)
 This also cannot really be done, but again if you trust the MonteInitial-State Radiation
AntiProton Carlo models you can try and do it by using the Monte-Carlo
models.
Underlying Event
Outgoing Parton
Proton
Underlying Event
Outgoing Parton
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Final-State
Radiation
The “underlying event” consists of
hard initial & final-state radiation
plus the “beam-beam remnants” and
possible multiple parton interactions.
Rick Field – Florida/CDF/CMS
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Inclusive Jet Cross Section (DØ )
 MidPoint Cone Algorithm
(R = 0.7, fmerge = 0.5)
 L = 378 pb-1
 Two rapidity bins
 Highest PT jet is 630 GeV/c
 Compared with NLO QCD
(JetRad, No Rsep)
Note that DØ does not make any
corrections for hadronization
and the “underlying event”!?
They compare the NLO parton level
directly to their hadron level data!
Log-Log Scale!
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Di-Jet Cross Section (DØ)
 MidPoint Cone Algorithm
= 0.7, fmerge = 0.5)
 L = 143 pb-1
 |yjet| < 0.5
 Compared with NLO QCD
(JetRad, Rsep = 1.3)
 Update expected soon!
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(R
Rick Field – Florida/CDF/CMS
Page 29
Inclusive Jet Cross Section (CDF)
 Run 1 showed a possible excess at
large jet ET (see below).
 This resulted in new PDF’s with
more gluons at large x.
 The Run 2 data are consistent with
the new structure functions
(CTEQ6.1M).
CTEQ4M PDFs
CTEQ4HJ PDFs
CTEQ4HJ
CTEQ4M
Run I CDF Inclusive Jet Data
(Statistical Errors Only)
JetClu RCONE=0.7
0.1<|h|<0.7
mR=mF=ET /2 RSEP=1.3
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Inclusive Jet Cross Section (CDF)
 MidPoint Cone Algorithm
(R
= 0.7, fmerge = 0.75)
 Data corrected to the hadron level
 L = 1.04 fb-1
 0.1 < |yjet| < 0.7
 Compared with NLO QCD
(JetRad, Rsep = 1.3)
Sensitive to UE + hadronization
effects for PT < 200 GeV/c!
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KT Algorithm
Begin
 kT Algorithm:







For each precluster, calculate
di  pT2,i
For each pair of preculsters, calculate
( y  y j ) 2  (fi  f j ) 2
dij  min( pT2 ,i , pT2 , j ) i
D2
Find the minimum of all di and dij.
Merge
i and j
yes
Minumum
is dij?
Cluster together calorimeter towers by their kT proximity.
Infrared and collinear safe at all orders of pQCD.
No splitting and merging.
No ad hoc Rsep parameter necessary to compare with parton level.
Every parton, particle, or tower is assigned to a “jet”.
No biases from seed towers.
Favored algorithm in e+e- annihilations!
no
Move i to list of jets
yes
Will the KT algorithm be
effective in the collider
environment where there is
an “underlying event”?
Any
Preclusters
left?
Raw Jet ET = 533 GeV
KT Algorithm
Raw Jet ET = 618 GeV
no
End
Outgoing Parton
PT(hard)
Initial-State Radiation
Proton
AntiProton
Underlying Event
Underlying Event
CDF Run 2
Outgoing Parton
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Final-State
Radiation
Only towers with ET > 0.5 GeV are shown
Rick Field – Florida/CDF/CMS
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KT Inclusive Jet Cross Section (CDF)





KT Algorithm (D = 0.7)
Data corrected to the hadron level
L = 385 pb-1
0.1 < |yjet| < 0.7
Compared with NLO QCD (JetRad)
corrected to the hadron level.
Sensitive to UE + hadronization
effects for PT < 300 GeV/c!
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Hadronization and
“Underlying Event” Corrections
 Compare the hadronization and “underlying event” corrections for th KT algorithm (D = 0.7)
and the MidPoint algorithm (R = 0.7)!
 We see that the KT algorithm (D = 0.7) is slightly more sensitive to the underlying event than
the cone algorithm (R = 0.7), but with a good model of the “underlying event” both cross
sections can be measured at the Tevatrun!
Note that DØ does not make any
corrections for hadronization
and the “underlying event”!?
MidPoint Cone Algorithm (R = 0.7)
The KT algorithm is slightly more
sensitive to the “underlying event”!
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KT Inclusive
Jet Cross
Section (CDF)
D = 0.5
D = 1.0
NLO parton level theory
corrected to the “particle level”!
Data at the “particle level”!
7
Correction factors
applied to NLO theory!
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7
8
Corrections increase as
D increases!
Rick Field – Florida/CDF/CMS
Page 35
High x Gluon PDF
from Run I
 Forward jets measurements put
constraints on the high x gluon
distribution!
Uncertainty on gluon
PDF (from CTEQ6)
Big uncertainty for
high-x gluon PDF!
x
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KT Inclusive Jet Cross Section (CDF)
 KT Algorithm (D = 0.7).
 Data corrected to the hadron
level.
 L = 385 pb-1.
 Five rapidity regions:
 |yjet| < 0.1




0.1 < |yjet| < 0.7
0.7 < |yjet| < 1.1
1.1 < |yjet| < 1.6
1.6 < |yjet| < 2.1
 Compared with NLO QCD
(JetRad) with CTEQ6.1
Excellent agreement over
all rapidity ranges!
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Jet-Jet Correlations (DØ)
Jet#1-Jet#2 Df Distribution
Df Jet#1-Jet#2
 MidPoint Cone Algorithm (R = 0.7, fmerge = 0.5)
 L = 150 pb-1 (Phys. Rev. Lett. 94 221801 (2005))
 Data/NLO agreement good. Data/HERWIG
agreement good.
 Data/PYTHIA agreement good provided PARP(67)
= 1.0→4.0 (i.e. like Tune A, best fit 2.5).
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