Recent QCD Results from CDF
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Recent QCD Results Recent QCD Results from CDF from CDF Stefano Lami The Rockefeller University Inclusive Jet Cross Section Inclusive Jet Cross Section W + n Jets W + n Jets Diffractive Diffractive Dijet Production Dijet Production
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Recent QCD Results from CDF. Stefano Lami The Rockefeller University Inclusive Jet Cross Section W + n Jets Diffractive Dijet Production Underlying Event Studies. From high to lower Q2. Run 2 High E T Jets. - PowerPoint PPT Presentation
Transcript of Recent QCD Results from CDF
Recent QCD Results from CDFRecent QCD Results from CDF
Stefano LamiThe Rockefeller University
Inclusive Jet Cross SectionInclusive Jet Cross Section
W + n JetsW + n Jets
Diffractive Dijet Production Diffractive Dijet Production
Underlying Event StudiesUnderlying Event Studies
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Run 2 High ERun 2 High ETT Jets Jets
ET = 666 GeV
= 0.43
Highest mass di-jet event so far(corrected mass = 1364 GeV):
Entering an era of precision QCD measurements at Tevatron/LHCStudying `QCD backgrounds’ for more speculative phenomena
Probing ~10-19 m scale, best place to look for new physicsHigh statistics at TeV; x5 higher cross section ET
J>600 GeV
ET = 633 GeV
= -0.19 Calorimeter LEGO Plot
r-view
1.96s
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Inclusive Jet Cross SectionInclusive Jet Cross Section
177 pb-1 collected Feb 2002 - Summer 2003
Extending Run 1 reach by ~150 GeV
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Inclusive Jet Cross Section (2)Inclusive Jet Cross Section (2) Excitement about Run 1 high ET excess
SM explanation: gluon PDF not well constrained at high x
Data currently agree with NLO (EKS) prediction within errors
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Inclusive Jet Cross Section (3)Inclusive Jet Cross Section (3) Theoretical error dominated by PDFs Experimental systematic error dominated by energy scale
Working on:Reducing systematic errorMid-point, KT algorithmsForward jets
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W eW e + >= n jet cross section + >= n jet cross sectionTest QCD predictions at large Q2 for fundamental channel for Top/Higgs
Compared to LO ALPGEN + Herwig
Systematic uncertainty (10% in 1 to 40% in 4) limits the
measurement sensitivity
Backgrounds: Top dominates for 4jets, QCD important in all bins
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W eW e + >= n jet cross section (2) + >= n jet cross section (2)
From top: highest ET jet in W+>=1 jet, second highest ET jet
in W+>=2 jet, etcThe ratio Rn/(n-1) measures
the decrease in the cross section with the addition of
1 jet. It depends on s
Differential cross section as a function of jet ET , compared to theory:
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Run 2 Forward DetectorsRun 2 Forward Detectors
MiniPlug Calorimeters (3.5<<5.5) Beam Shower Counters (5.5<<7.5) Antiproton Roman Pot Spectrometer
MiniPlug
Hard diffraction process, signature in CDF: leading antiproton + rapidity gap + 2 high ET jets
Diffractive Dijet ProductionDiffractive Dijet Production
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Measure p momentum loss fraction) from calorimeter info
Compare diffractive events to ND
Measure diffractive structure function from RSD/ND vs x Bj
overlap events
Diffractive Dijet Production (2)Diffractive Dijet Production (2)
RP+J5 trigger
iiT
Xp eE
s
towerscal
1
flatlog
1
d
d
d
d
parton xBj
x
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Diffractive Dijet Structure FunctionDiffractive Dijet Structure Function
No dependence observed within 0.03< <0.1CONFIRMS RUN I RESULT
Ratio of SD to ND dijet event ratesas a function of xBj
for different values of Q2=ET2
No significant Q2 dependence observed within 100 < Q2 < 1600 GeV
NEW RESULT
seExjet
T
jetBj /
Ratio of SD to ND dijet event ratesas a function of xBj
compared with Run I data
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“Transverse” region is very sensitive to the “underlying event”!
Underlying Event StudiesUnderlying Event Studies
Proton AntiProton
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
The Underlying Event is everything but the two outgoing Jets, including: initial/final gluon radiation, beam-beam remnants and possible multiple parton interactions
Central Tracking to study low momenta
• Direction of leading jet to define 3 regions
Charged Particle Density: dN/dd
0.1
1.0
10.0
0 30 60 90 120 150 180 210 240 270 300 330 360
(degrees)
Ch
arg
ed
Pa
rtic
le D
en
sit
y
Back-to-Back
Leading Jet
Min-Bias
CDF Preliminarydata uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
30 < ET(jet#1) < 70 GeV
"Transverse" Region
Jet#1
Min-Bias0.25 per unit -
Charged Particle Correlations
pT > 0.5 GeV/c || < 1
Jet #1 Direction
“Transverse” “Transverse”
“Toward”
“Away”
“Toward-Side” Jet
“Away-Side” Jet
UE unavoidable backgroundUE unavoidable background to be removed from the jets before comparing to NLO QCD predictions
Run 2Run 2
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Underlying Event Studies (2)Underlying Event Studies (2)
Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
Jet #2 Direction
Shows the average charged particle density, dN/dd, in the “transverse” region (pT > 0.5 GeV/c, || < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events compared with PYTHIA Tune A and HERWIG after CDFSIM.
“Leading Jet”
“Back-to-Back”(12>150o,ET
j2/ETj1>0.8)
"AVE Transverse" Charge Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
0 50 100 150 200 250
ET(jet#1) (GeV)
"Tra
ns
ve
rse
" C
ha
rge
De
ns
ity
CDF Preliminarydata uncorrectedtheory + CDFSIM
1.96 TeV Charged Particles (||<1.0, PT>0.5 GeV/c)
Leading Jet
Back-to-Back
PY Tune A
HW
Min-Bias0.25 per unit -
Interplay between pQCD and non-pQCD physics.Current MC with default parameters fail to reproduce data.In Run 1 PYTHIA 6.206 tuned adding multi-parton interactions.
Run 2 data:Run 2 data:
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"AVE Transverse" PTsum Density: dPT/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 50 100 150 200 250
ET(jet#1) (GeV)
"Tra
nsv
erse
" P
Tsu
m D
ensi
ty (
GeV
/c)
CDF Preliminarydata uncorrectedtheory + CDFSIM
Charged Particles (||<1.0, PT>0.5 GeV/c)
Back-to-Back
Leading Jet
PY Tune A
HW
1.96 TeV
Underlying Event Studies (3)Underlying Event Studies (3)
Run 2 data:Run 2 data: Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
Jet #2 Direction
“Leading Jet”
“Back-to-Back”(12>150o,ET
j2/ETj1>0.8)
PYTHIA tuned (on Run 1 data) reproduces well Run 2 data.HERWIG (with no multi-parton interaction) works only at high ET
j1.
Min-Bias0.24 GeV/c per unit -
Average charged PTsum density, dPT/dd, in the “transverse” region
(pT > 0.5 GeV/c, || < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events compared with PYTHIA Tune A and HERWIG after CDFSIM.
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ConclusionsConclusionsCDF is now accumulating large samples of interesting eventsRun 2 data will enable the measurement of s and PDFs
•Measured inclusive jet cross section agrees with NLO QCD (CTEQ 6.1) Work on reducing systematic uncertainty (calorimeter jet energy scale 3%)
and include Forward Jets and Run 2 jet algorithms KT and Mid-Point
•Study of W+n jets is important to test QCD predictions at large Q2
It is a gold channel for Top/Higgs/SUSY physics
•Exciting Diffractive physics program with dedicated forward detector/triggers
Preliminary Dijet results show no Q2 dependence in SD/ND
•Modeling the Underlying Event is important for precise Jet measurements A tuned version of PYTHIA reproduces well CDF data
Very exciting and important QCD Physics program at CDFVery exciting and important QCD Physics program at CDF
