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Soft QCD Phenomena in High-E T Jet Events at CDF. Andrey Korytov. (for the CDF Collaboration). Abstracts covered in this talk A356 Fragmentation Differences of Quark and Gluon Jets at CDF A362 Measurement of Jet Shapes and Energy Flows in Dijet Production at the Tevatron - PowerPoint PPT Presentation
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Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Soft QCD Phenomena in High-ET Jet Events at CDF
Abstracts covered in this talk• A356 Fragmentation Differences of Quark and Gluon Jets at CDF• A362 Measurement of Jet Shapes and Energy Flows in Dijet Production at the Tevatron• A353 Jet Evolution and the Underlying Event in Run 2 at CDF
Official Title Studies of Jet Shapes and Fragmentation Differences of Quark and Gluon Jets with the CDF Detector(note: Underlying Event fell out from the title)
Better TitleStudies of Soft QCD Phenomena in High-ET Jet Events with the CDF Detector
Andrey Korytov
(for the CDF Collaboration)
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Soft QCD Phenomena in High-ET Jet Events
Anatomy of events with high ET jets: hard scattered partons final state radiation initial state radiation multi-parton interactions proton/antiproton remnants Note: separation between sub-processes is not cleandue to entangled color connections…
Soft QCD Phenomena: Jet fragmentation is largely driven by soft QCD So is the UE physics
Tools available: re-summed pQCD approximations
(analytic, but only for limited number of observables) Monte Carlo generators (generic, but have many tunable ad-hoc
knobs)
JETS
UNDERLYINGEVENT
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Why bother?
Jet Fragmentation: Jet development physics:
• Parton shower stage—challenge for pQCD calculations at the very soft limit (kT~QCD)
• Hadronization stage—still remains a mystery
Many high-ET physics analyses depend on good understanding of jet properties
Underlying Event: UE physics is poorly understood:
• MC Generators implement UE differently and often with many (too many?) parameters
• Even when tuned to match the accessible data, MC predictions for LHC vary wildly
UE pollutes many analyses source of systematic errors
LHC MinBias
kT=1 GeV/c
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Results presented in this talk
Jets: Momentum distribution of charged particles in jets vs.
NLLA Multiplicities of charged particles in g- and q-jets vs.
NLLA Energy flow in jets (jet shapes) vs. MC
Underlying Event: Energy flow away from jets vs. MC Charged particle multiplicity flow away from jets vs. MC Momentum distribution of away-from-jet charged particles
vs. MC
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Jets: doing fragmentation analytically
Jet fragmentation: parton shower development:
MLLA’ Modified Leading Log Approximation
with one kT-cutoff parameter Qeff=Qcutoff=QCD
hadronization: LPHDHypothesis of Local Parton Hadron Duality with one parameter KLPHD=Nhadrons/Npartons
MLLA+LPHD:cannot describe all details…but all analytical…and works surprisingly well…
Momenta of charged particles in jets: Qeff = 230 40 MeV
KLPHD() = 0.56 0.10
CDFCharged particle momentum spectra (cone=0.47) and MLLA+LPHD fit
particle
jet
px
E
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Jets: gluon vs quark jet differences
Ratio r = Nhadrons(gluon jet) / Nhadrons(quark jet) recent calculations (for partons): extensions of NLLA, r=1.4-1.7
(Q=10-100 GeV) lots of results from LEP, not all self-consistent: r = 1 to 1.5
jet-ID biased, model-dependent, few “unbiased/model-independent”
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Jets: gluon vs quark jets at CDF
di-jet events (~60% gluon jets) and -jet events (~80% quark jets) di-jet or -jet center of mass frame: Ejet = ½Mjj or ½Mj
Nch multiplicity in cones with opening angle from ~0.3 to ~0.5 rad Energy scale Q=Ejet Results
• Ratio: r=1.60.2, almost energy scale independent• multiplicities in quark and gluon jets: see plot
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Jets: Energy flow inside jets (vs MC)
Run IICDF preliminary
Jet shape: fractional energy flow (r) = ET(0:r) / ET(0:R), where R=1
In central region, do it with• Calorimeter towers (●)
• Charged tracks (○)
Either way—shapes are nearly identical
Herwig and Pythia practically coincide and agree with data
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Run II CDF preliminary
Jets: Energy flow inside jets (vs MC)
In forward region, do it with• Calorimeter towers only
Data vs MC discrepancy:
the higher jet and
the smaller jet’s ET,
the larger the disagreement
Is it real or do we have simulation problems with the new plug calorimeter?• expand tracker analysis
to higher region…• any D0 data?
?
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
UE studies with charged tracks
Event sample: min-bias, jet events (central jets) Measure:
• Average Number of particles in direction transverse to leading jet: n=d2N / dd• PT spectrum of particles in direction transverse to leading jet: dn/dPT
• Average Energy summed over charged particles in transverse direction: d2ET/dd
Confront data and MC:• Identify importance of various MC knobs/parameters
Leading Jet
“Transverse” “Transverse”
“transverse” particlesas a probe of the underlying event
ET(jet)
Charged tracks:
• d2N/dd• d3N/dddPT
• d2ET/dd
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
UE: data vs. default Pythia and Herwig
Default Pythia and Herwig fail to reproduce data one way or another, e.g.:
Pythia 6.206 underestimates number of tracks in transverse direction…
Herwig 6.4 gives too soft spectrum for particles in transverse direction, especially in events with small ET jets (missing MPI now have been added)
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 5 10 15 20 25 30 35 40 45 50
PT(charged jet#1) (GeV/c)
"Tra
ns
ve
rse
" C
ha
rge
d D
en
sit
y
CTEQ3L CTEQ4L CTEQ5L CDF Min-Bias CDF JET20
1.8 TeV ||<1.0 PT>0.5 GeV
Pythia 6.206 (default)MSTP(82)=1
PARP(81) = 1.9 GeV/c
CDF Datadata uncorrectedtheory corrected
Charged Particle Density
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
0 2 4 6 8 10 12 14
PT (GeV/c)
Ch
arg
ed D
ensi
ty d
N/d
d d
PT
(1/
GeV
/c)
||<1CDF Preliminary
Min-Bias Data, 1.8 TeV
HW "Soft" Min-Biasat 0.63, 1.8, and 14 TeV
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
UE: tune Pythia to match CDF data
PYTHIA 6.206 and CDF Tune A (CTEQ5L)Parameter Default Tune Description
PARP(67) 1.0 4.0 Scale factor that governs the amount of initial-state radiation.
MSTP(81) 1 1 Turns on multiple parton interactions (MPI).
MSTP(82) 1 4 Double Gaussian matter distribution.
PARP(82) 1.9 2.0 Cut-off for multiple parton interactions, PT0.
PARP(83) 0.5 0.5 Warm Core: 50% of matter in radius 0.4.
PARP(84) 0.2 0.4 Warm Core: 50% of matter in radius 0.4.
PARP(85) 0.33 0.9 Probability that the MPI produces two gluons with color connections to the "nearest neighbors".
PARP(86) 0.66 0.95Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop. The remaining fraction consists of quark-antiquark pairs.
PARP(89) 1,000.0 1,800.0 Determines the reference energy E0.
PARP(90) 0.16 0.25Determines the energy dependence of the cut-off PT0 as follows
PT0(Ecm) = PT0(Ecm/E0)PARP(90).
Pythia: CDF Tune A vs. Default 6.206• Enhanced initial state radiation• Smoothed out probability of Multi-Parton Interactions (vs. impact)• MPIs are more likely to produce gluons than quark-antiquark pairs
and MPI gluons are more likely to have color connection to p-pbar remnants
• …
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
UE: Pythia Tune A describes Data
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
1.25
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
"Tra
nsvers
e"
Ch
arg
ed
Den
sit
y CDF Run 1 Min-Bias
CDF Run 1 JET20
CDF Run 2
PY Tune A
||<1.0 PT>0.5 GeV/c
CDF Preliminarydata uncorrectedtheory corrected
"Transverse" Charged PTsum Density: dPTsum/dd
0.00
0.25
0.50
0.75
1.00
1.25
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
"Tra
nsv
erse
" P
Tsu
m D
ensi
ty (
GeV
)
CDF Run 1 Min-Bias
CDF Run 1 JET20
CDF Run 2
PY Tune A
CDF Preliminarydata uncorrectedtheory corrected
||<1.0 PT>0.5 GeV/c
"Transverse" Charged Particle Density
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
0 2 4 6 8 10 12 14 16 18 20
PT(charged) (GeV/c)
Ch
arg
ed D
ens
ity
d3 N
/d d
d
PT (
1/G
eV
/c)
CDF Preliminarydata uncorrected
theory corrected
PYTHIA Tune A 1.96 TeV
30 < PT(chgjet#1) < 70 GeV/c
70 < PT(chgjet#1) < 95 GeV/c
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Summary
Jet fragmentation
Momenta of charged particles in jets are well described by NLLA pQCD:• MLLA kT-cutoff Qeff=230 40 MeV• LPHD Nhadrons/Npartons = KKLPHD() = 0.56 0.10
Multiplicities in gluon and quark jets and their ratio r = 1.6 02 agree with extended NLLA pQCD and recent LEP data
Jet shapes mostly agree with PYTHIA and HERWIG, but more studies/tuning are needed for high- jets
Underlying event
Run II and Run I data agree, Run II analysis is being expanded
MC generators with default parameters do not quite work, but can be tuned to match data… insights into UE physics?
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
A few backup slides follow this page…
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Tevatron upgrade: Run II vs. Run I
Original Plan: Run I Run II
CM energy: 1.8 1.96 TeVBx spacing: 3.5 0.4 s Max luminosity: 2x1031 50x1031 cm-2 s-1
Integrated luminosity: 0.1 15 fb-1 (before LHC turn-on)
As of May 2003:
Peak luminosity so far: 4.5x1031 cm-2 s-1
Total delivered (incl. commissioning): 0.24 fb-1
On tape (CDF, incl. commissioning): 0.18 fb-1 Good for physics (CDF) >0.13 fb-1
CDF current data taking efficiency ~90%
Long-term plan (by end of 2008):
Base goal: 6 fb-1
Stretch goal: 11 fb-1
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
CDF upgrade: what is new
Retained from CDF I: Solenoid Central Calorimeters Central Muon System
Brand new in CDF II: 5-layer 3D vertex Si
detector Intermediate Si layers Central Drift Tracker Plug Calorimeter Mini-plug calorimeter Time of Flight System Expanded Muon Coverage TRIGGER, now includes:
• displaced vertex
• track pT>1.5 GeV/c
Faster Front End Electronics
• 3d vertex coverage: <2• Tracking coverage: <2• Calorimeter coverage: <3.6• Mini-plug calorimeter: 3.6<<5.1• Muon coverage: <1.5
Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen
Jets: Gluon vs Quark jets at CDF
Momentum distributions of charged particles in gluon and quark jets Ratio reaches max and flattens for soft part of spectrum at ~1.80.2 Same pattern was observed at LEP