Transcript 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.

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
Heavy Quarks, Bosons, & Photons
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 1
Heavy Quark & Boson
Production at the Tevatron
with 1 fb-1  Total inelastic s ~ 100 mb which is
tot
~1.4 x 1014
3
4
~1 x 1011
~6 x 106
~6 x 105
~14,000
~5,000
10 -10 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
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 2
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).
CDF
The CDF Secondary Vertex Trigger (SVT)
•Online (L2) selection of displaced tracks based on Silicon detector hits.
Lxy ~ 1 mm
B/D decay
Primary Vertex
Collision Point
Secondary Vertex
D0 K
Impact Parameter ( ~100mm)
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 3
Selecting Prompt Charm Production
Collision Point
Prompt D
Secondary D from B
Prompt
peak
Direct Charm Meson Fractions:
BD tail
D impact parameter
 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.
D0: fD=86.4±0.4±3.5%
D*+: fD=88.1±1.1±3.9%
D+: fD=89.1±0.4±2.8%
D+s: fD=77.3±3.8±2.1%
Most of reconstructed D
mesons are prompt!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 4
Prompt Charm Meson Production
Charm Meson PT Distributions
CDF prompt charm cross section result published in PRL (hep-ex/0307080)
s ( D 0 , pT  5.5GeV, | Y | 1)  13.3  0.2  1.5mb  Theory calculation from M. Cacciari and P.
Nason: Resummed perturbative QCD
s ( D * , pT  6GeV, | Y | 1)  5.2  0.1  0.8mb
(FONLL), JHEP 0309,006 (2003).

s ( D , pT  6GeV, | Y | 1)  4.3  0.1  0.7 mb
Fragmentation: ALEPH measurement,

CTEQ6M PDF.
s ( Ds , pT  8GeV, | Y | 1)  0.75  0.05  0.22mb
Data collected by SVT trigger from 2/2002-3/2002
L = 5.8±0.3 pb-1.
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 5
Comparisons with Theory
Ratio of Data to Theory
Next step is to study charm-anticharm correlations
to learn about the contributions from different
production mechanisms:
“flavor creation”
“flavor Excitation”
“gluon splitting”
 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!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 6
Bottom Quark Production
at the Tevatron
Tevatron Run 1 b-Quark Cross Section
 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).
 “Something is goofy” (Rick Field, CDF B
Group Talk, December 3, 1999).
Lecture 2: University of Chicago
July 10, 2006
Integrated b-quark Cross Section for PT > PTmin
1.0E+01
1.8 TeV
|y| < 1
1.0E+00
Cross Section (mb)
CDF Run 1 1999
CTEQ3L
1.0E-01
Pythia Creation
Isajet Creation
1.0E-02
Herwig Creation
D0 Data
CDF Data
1.0E-03
5
10
15
20
25
30
35
40
PTmin (GeV/c)
QCD Monte-Carlo
leading order “Flavor
Creation” is a factor of
four below the data!
Rick Field – Florida/CDF
Extrapolation of what
is measured (i.e. Bmesons) to the parton
level (i.e. b-quark)!
Page 7
Sources of Heavy Quarks
Leading-Log Order
QCD Monte-Carlo Model (LLMC)
“Flavor Creation”
Proton
Leading Order Matrix Elements
Q-quark
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Q-quark
 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).
ds (B)  Gpi  Gp j  ds (ij  bk)  FbD
(structure functions) × (matrix elements) × (Fragmentation)
+ (initial and final-state radiation: LLA)
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 8
Other Sources of Heavy Quarks
“Flavor Excitation”
“Gluon Splitting”
Q-quark
Proton
Proton
AntiProton
Underlying Event
AntiProton
Underlying Event
Underlying Event
Q-quark
Underlying Event
Initial-State
Radiation
Initial-State
Radiation
gluon, quark,
or antiquark
Q-quark
Q-quark
“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 2to-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
Q
g
Amp(gg→QQg)
s(gg→QQg)
= =
g
+
Amp (FC)
Q
g
Lecture 2: University of Chicago
July 10, 2006
Q
g
g
Q
g
Q
+
g
Q
Amp (FE)
Rick Field – Florida/CDF
g
Amp (GS)
g
Page 9
2
Inclusive b-quark Cross Section
Tevatron Run 1 b-Quark Cross Section
Integrated b-quark Cross Section for PT > PTmin
Total
1.0E+02
“Flavor Excitation”
PYTHIA 6.158
CTEQ3L PARP(67)=4
PY 6.158 (67=4) Total
Flavor Creation
Flavor Excitation
1.0E+01
“Flavor Creation”
Cross Section (mb)
Shower/Fragmentation
D0 Data
CDF Data
1.0E+00
1.0E-01
1.8 TeV
|y| < 1
1.0E-02
“Gluon Splitting”
1.0E-03
0
5
10
15
20
25
30
35
40
PTmin (GeV/c)

Data on the integrated b-quark total cross section (PT > PTmin, |y| < 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.
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 10
Conclusions from Run 1
“Flavor Creation”
“Flavor Excitation”
b-quark
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
b-quark
“Gluon Splitting”
b-quark
Proton
AntiProton
Underlying Event
Underlying Event
b-quark
Initial-State
Radiation
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
gluon, quark,
or antiquark
Q-quark
Q-quark
All three sources are important at the Tevatron!




“Nothing is goofy”
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.
Rick Field, Cambridge Workshop,
We should be able experimentally to isolate the individual contributions to b-quark production by
July 18, 2002
studying b-bbar correlations find out in much greater detail how well the QCD Monte-Carlo models
actually describe the data.
MC@NLO!
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/hadronization framework
(e.g. HERWIG or PYTHIA).
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 11
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!
m
J/y
m
Down to
PT = 0!
39.7 pb-1
B
K
CDF (mb)
s(J/Y, |Y(J/Y)| < 0.6)
Lecture 2: University of Chicago
July 10, 2006
4.080.02(stat)+0.36(sys)-0.48(sys)
Rick Field – Florida/CDF
Primary vertex
(i.e. interaction point)
Page 12
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| < 1.0
B-hadron pT
s(B-hadron)
CDF (mb)
FONLL (mb)
29.40.6(stat)6.2(sys)
27.5+11-8.2
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 13
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 < |y|< 0.7 and
plot the inclusive jet PT distribution (MidPoint, R = 0.7).
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 14
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.
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 15
The b-bbar DiJet Cross-Section
 ET(b-jet#1) > 30 GeV, ET(b-jet#2) > 20
GeV, |h(b-jets)| < 1.2.
Preliminary CDF Results:
Systematic
Uncertainty
sbb = 34.5  1.8  10.5 nb
QCD Monte-Carlo Predictions:
PYTHIA Tune A
CTEQ5L
38.71 ± 0.62 nb
HERWIG CTEQ5L
21.53 ± 0.66 nb
MC@NLO
28.49 ± 0.58 nb
“Flavor Creation”
Proton
b-quark
AntiProton
Underlying Event
Differential Cross Section as a function of
the b-bbar DiJet invariant mass!
Underlying Event
Predominately
Flavor creation!
Initial-State
Radiation
 Large Systematic Uncertainty:
 Jet Energy Scale (~20%).
 b-tagging Efficiency (~8%)
b-quark
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 16
The b-bbar DiJet Cross-Section
 ET(b-jet#1) > 30 GeV, ET(b-jet#2) > 20
GeV, |h(b-jets)| < 1.2.
Preliminary CDF Results:
sbb = 34.5  1.8  10.5 nb
QCD Monte-Carlo Predictions:
PYTHIA Tune A
CTEQ5L
38.7 ± 0.6 nb
HERWIG CTEQ5L
21.5 ± 0.7 nb
MC@NLO
28.5 ± 0.6 nb
MC@NLO + Jimmy
35.7 ± 2.0 nb
Differential Cross Section as a function of
the b-bbar DiJet invariant mass!
JIMMY
Runs with HERWIG and adds
multiple parton interactions!
“Flavor Creation”
b-quark
Initial-State Radiation
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!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Proton
AntiProton
Underlying Event
Underlying Event
b-quark
Final-State
Radiation
Page 17
Top Decay Channels




mt>mW+mb so dominant decay tWb.
The top decays before it hadronizes.
B(W  qq) ~ 67%.
B(W  ln) ~ 11% l = e, m, t.
dilepton
lepton + jets
all hadronic
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
BR
~5%
~30%
~65%
background
low
moderate
high
Page 19
Dilepton Channel
Selection:
•
•
•
•
•
Backgrounds:
2 leptons ET > 20 GeV with opposite sign.
• Physics: Drell-Yan, WW/WZ/ZZ, Z
 tt
>=2 jets ET > 15 GeV.
Missing ET > 25 GeV (and away from any jet). • Instrumental: fake lepton
HT=pTlep+ETjet+MET > 200 GeV.
Z rejection.
65 events
20 events
background
s(tt) = 8.3 ± 1.5 (stat) ± 1.0 (syst) + 0.5 (lumi) pb
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 20
Lepton+Jets Channel
Kinematics
 Selection:
• 1 lepton with pT > 20 GeV/c.
• >= 3 jets with pT > 15GeV/c.
• Missing ET > 20 GeV.
 Backgrounds:
• W+jets
• QCD
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!
s(tt) = 6.0 ± 0.6 (stat) ± 0.9 (syst) pb
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 21
Lepton+Jets Channel
 Require b-jet to be tagged for
discrimination.
b-Tagging
1 b tag
Tagging efficiency for b jets~50%
for c jets~10%
for light q jets < 0.1%
2 b tags
HT>200GeV
~150 events ~45 events
Small
background!
s(tt) = 8.2 ± 0.6 (stat) ± 1.1 (syst) pb
Lecture 2: University of Chicago
July 10, 2006
2.0
s (tt )  8.81.2
(stat)
1.1
1.3 (syst)pb
Rick Field – Florida/CDF
Page 22
Tevatron Top-Pair
Cross-Section
CDF Run 2 Preliminary
Theory
0.7
s (tt )  6.70.9
pb
Bonciani et al., Nucl. Phys. B529, 424 (1998)
Kidonakis and Vogt, Phys. Rev. D68, 114014 (2003)
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 23
CDF Mtop Results
Transverse
decay length!
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
CDF Lepton+jets:
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 24
Top Quark Mass
Summer 2005
New since Summer 2005
Dilepton:
CDF-II MtopME = 164.5 ± 5.5 GeV
Lepton+Jets:
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
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 25
Top Cross-Section vs Mass
Tevatron Summer 2005
CDF Winter 2006
CDF combined
Updated CDF+DØ combined result is coming soon!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 26
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!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 27
Future Top Mass Measurements
Systematic
Source
Uncertainty
(GeV/c2)
ISR/FSR
0.7
Model
0.7
b-jet
0.6
Method
0.6
PDF
0.3
Total
1.3
Jet Energy
2.5
CDF
 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!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 28
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!
Tevatron Run I + LEP2
Summer 05
Spring 2006
Light Higgs very interesting for the
Tevatron!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 29
Top: Charge, Branching,
Lifetime, W Helicity
Top Charge
DØ Prelim.
365 pb-1
Top Lifetime
CDF Prelim.
318 pb-1
Exclude |Q| = 4/3 at 94% CL
ttop< 1.75x10-13s
cttop< 52.5mm
at 95%CL
Everything consistent with the
Standard Model (so far)!
Reconstructed Top Charge (e)
Impact Parameter (mm)
370 pb-1
f+ (DØ combined) = 0.04
± 0.11(stat) ± 0.06(syst)
f+ (SM pred.) = 0
SM
signal
hep-ex/0603002
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
signal+bgrnd
bgrnd
Page 30
Other Sources of Top Quarks
Strongly Produced tt Pairs
 Dominant production mode
sNLO+NLL = 6.7  1.2 pb
 Relatively clean signature
 Discovery in 1995
g
~15%
Lecture 2: University of Chicago
July 10, 2006
~85%
t
t
q
g

ElectroWeak Production: Single Top
 Larger background
 Smaller cross section s ≈ 2 pb
 Not yet observed!
q

Rick Field – Florida/CDF


Page 31
Single Top Production
s-channel
qq  W  t b
*
tW associated production
t-channel
bg  tW
qb  q t
'
(mtop=175 GeV/c2)
s-channel
t-channel
Associated tW
Tevatron sNLO
0.88  0.11 pb
1.98  0.25 pb
~ 0.1 pb
LHC sNLO
10.6  1.1 pb
247  25 pb
62+17 -4 pb
Run I
CDF
< 18 pb
< 13 pb
95% C.L.
D0
< 17 pb
< 22 pb
< 14 pb
B.W. Harris et al.:Phys.Rev.D66,054024
Z.Sullivan Phys.Rev.D70:114012
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Combine
(s+t)
T.Tait: hep-ph/9909352
Belyaev,Boos: hep-ph/0003260
Page 32
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:
1.9
0.1
σt ch  0.60.6
(stat)0.1
(syst)pb
2.2
0.5
σ sch  0.30.3
(stat)-0.3
(syst) pb
The CDF limits!
t-channel:
s < 3.1 pb @ 95% C.L.
s-channel:
s < 3.2 pb @ 95% C.L.
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 33
Single Top at the Tevatron
95% C.L. limits on single top cross-section
Channel
CDF (696 pb-1)
DØ (370 pb-1)
Combined
3.4 pb (2.9 pb)
s-channel
3.2 pb (0.9 pb)
5.0 pb
t-channel
3.1 pb (2 pb)
4.4 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 !!!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 34
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!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 35
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 0’s!
q

g
q
Note rise at low pT!
Highest pT() is 442 GeV/c
(3 events above 300 GeV/c
not displayed)!
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 36
 + b/c Cross Sections
 b/c-quark tag based on displaced vertices. Secondary vertex mass
discriminates flavor.
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 37
 + b/c Cross Sections
PYTHIA Tune A!
+b
+c
 PYTHIA Tune A correctly
predicts the relative amount
of u, d, s, c, b quarks within
the photon events.
CDF (pb)
s(b+)
40.619.5(stat)+7.4(sys)-7.8(sys)
s(c+)
486.2152.9(stat)+86.5(sys)-90.9(sys)
ET() > 25 GeV
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 38
 +  Cross Section
QCD  + 
 +  Df
 +  mass
 Di-Photon cross section with 207 pb-1 of Run 2 data compared with next-toleading order QCD predictions from DIPHOX and ResBos.
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 39
Z-boson Cross Section
QCD
Drell-Yan
 Impressive agreement between experiment
and NNLO theory (Stirling, van Neerven)!
s(Z→e+e-)
Lecture 2: University of Chicago
July 10, 2006
CDF (pb)
NNLO (pb)
254.93.3(stat)4.6(sys)15.2(lum)
252.35.0
Rick Field – Florida/CDF
Page 40
Z-boson Cross Section
 Impressive agreement between experiment and NNLO theory
(Stirling, van Neerven)!
s(Z→m+m-)
Lecture 2: University of Chicago
July 10, 2006
CDF (pb)
NNLO (pb)
261.22.7(stat)6.9(sys)15.1(lum)
252.35.0
Rick Field – Florida/CDF
Page 41
The Z→tt Cross Section
 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.
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 42
The Z→tt Cross Section
 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-)
Lecture 2: University of Chicago
July 10, 2006
CDF (pb)
NNLO (pb)
26520(stat)21(sys)15(lum)
252.35.0
Rick Field – Florida/CDF
Page 43
Higgs → tt Search
140 GeV
Higgs Signal!
Let’s find the Higgs!
 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.
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 44
W-boson Cross Section
 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
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 45
20 Years of Measuring W & Z
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 46
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| < 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:
Lecture 2: University of Chicago
July 10, 2006
s (Z  bjet)  0.52 pb
Rick Field – Florida/CDF
R  0.018  0.004
Page 47
W +  Cross Sections
ET() > 7 GeV
R(l) > 0.7
s(W+)*BR(W->ln)
Lecture 2: University of Chicago
July 10, 2006
CDF (pb)
NLO (pb)
19.71.7(stat)2.0(sys)1.1(lum)
19.31.4
Rick Field – Florida/CDF
Page 48
Z +  Cross Sections
Note: s(W)/s(Z) ≈ 4
while s(W)/s(Z) ≈ 11
ET() > 7 GeV
R(l) > 0.7
s(Z+)*BR(Z->ll)
Lecture 2: University of Chicago
July 10, 2006
CDF (pb)
NLO (pb)
5.30.6(stat)0.3(sys)0.3(lum)
5.40.3
Rick Field – Florida/CDF
Page 49
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
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 50
W+W Cross-Section





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!
Lecture 2: University of Chicago
July 10, 2006
Lepton-Pair Mass!
Rick Field – Florida/CDF
ET Sum!
Page 51
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
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 52
Di-Bosons at the Tevatron
W
We are getting closer to
the Higgs!
Z
W+
Z+
W+W
W+Z
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 53
Generic Squark & Gluino Search
 Selection:
It will be a long time before ATLAS
& CMS understand their missing
ET spectrum this well!
 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.
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 54
Future Higgs & SUSY Searches
 CDF and Tevatron running great!
 Often world’s 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!
Let’s find the Higgs!
 We may be able to tell the LHC where to
look!
If we find something the
real fun starts: What Is It?
Lecture 2: University of Chicago
July 10, 2006
Rick Field – Florida/CDF
Page 55