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QCD Monte-Carlo Generators in Run 2 at CDF. Also I have included some thoughts from Michelangelo at the end of my talk. Outline of Talk. Review what we learned in Run 1 about “min-bias” , the “underlying event” , and “initial-state radiation”. - PowerPoint PPT Presentation
Citation preview
CDF Top Mass Workshop June 25, 2003
Rick Field Page 1
QCD Monte-Carlo GeneratorsQCD Monte-Carlo Generators
in Run 2 at CDFin Run 2 at CDF
Review what we learned in Run 1 about “min-bias”, the “underlying event”, and “initial-state radiation”.
Outline of Talk
Compare the Run 1 analysis which used the leading “charged particle jet” to define the “underlying event” with Run 2 data.
Study the properties of “charged particle jets” and “calorimeter jets” in Run 2.
Proton AntiProton
“Hard” Scattering
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
Study the “underlying event” in Run 2 as defined by the leading “calorimeter jet” and compare with the “charged particle jet” analysis.
Charged Particle Jet
Calorimeter Jet Compare with PYTHIA
Tune A
JetClu R = 0.7
AlsoI have included some
thoughts from Michelangeloat the end of my talk.
CDF Top Mass Workshop June 25, 2003
Rick Field Page 2
The “Underlying Event”The “Underlying Event”in Hard Scattering Processesin Hard Scattering Processes
What happens when a high energy proton and an antiproton collide? Proton AntiProton
“Soft” Collision (no hard scattering)
Proton AntiProton
“Hard” Scattering
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
Proton AntiProton 2 TeV Most of the time the proton and
antiproton ooze through each other and fall apart (i.e. no hard scattering). The outgoing particles continue in roughly the same direction as initial proton and antiproton. A “Min-Bias” collision.
Occasionally there will be a “hard” parton-parton collision resulting in large transverse momentum outgoing partons. Also a “Min-Bias” collision.
Proton AntiProton
“Underlying Event”
Beam-Beam Remnants Beam-Beam Remnants
Initial-State Radiation
The “underlying event” is everything except the two outgoing hard scattered “jets”. It is an unavoidable background to many collider observables.
Arethesethe
same?
“Min-Bias”
No!
“underlying event” has initial-state radiation!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 3
Beam-Beam RemnantsBeam-Beam Remnants
The underlying event in a hard scattering process has a “hard” component (particles that arise from initial & final-state radiation and from the outgoing hard scattered partons) and a “soft?” component (“beam-beam remnants”).
Proton AntiProton
“Hard” Collision
initial-state radiation
final-state radiation outgoing parton
outgoing parton
Clearly? the “underlying event” in a hard scattering process should not look like a “Min-Bias” event because of the “hard” component (i.e. initial & final-state radiation).
+
“Soft?” Component “Hard” Component
initial-state radiation
final-state radiation outgoing jet
Beam-Beam Remnants
“Soft?” Component
Beam-Beam Remnants
Hadron Hadron
“Min-Bias” Collision
However, perhaps “Min-Bias” collisions are a good model for the “beam-beam remnant” component of the “underlying event”.
Are these the same?
The “beam-beam remnant” component is, however, color connected to the “hard” component so this comparison is (at best) an approximation.
color string
color string
Maybe not all “soft”!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 4
MPI: Multiple PartonMPI: Multiple PartonInteractionsInteractions
PYTHIA models the “soft” component of the underlying event with color string fragmentation, but in addition includes a contribution arising from multiple parton interactions (MPI) in which one interaction is hard and the other is “semi-hard”.
Proton AntiProton
Multiple Parton Interaction
initial-state radiation
final-state radiation outgoing parton
outgoing parton
color string
color string
The probability that a hard scattering events also contains a semi-hard multiple parton interaction can be varied but adjusting the cut-off for the MPI.
One can also adjust whether the probability of a MPI depends on the PT of the hard scattering, PT(hard) (constant cross section or varying with impact parameter).
One can adjust the color connections and flavor of the MPI (singlet or nearest neighbor, q-qbar or glue-glue).
Also, one can adjust how the probability of a MPI depends on PT(hard) (single or double Gaussian matter distribution).
+
“Semi-Hard” MPI “Hard” Component
initial-state radiation
final-state radiation outgoing jet Beam-Beam Remnants
or
“Soft” Component
Proton AntiProton
“Hard” Collision
initial-state radiation
final-state radiation outgoing parton
outgoing parton
CDF Top Mass Workshop June 25, 2003
Rick Field Page 5
CDF Run 1 “Min-Bias” DataCDF Run 1 “Min-Bias” DataCharged Particle DensityCharged Particle Density
Shows CDF “Min-Bias” data on the number of charged particles per unit pseudo-rapidity at 630 and 1,800 GeV. There are about 4.2 charged particles per unit in “Min-Bias” collisions at 1.8 TeV (|| < 1, all PT).
Charged Particle Pseudo-Rapidity Distribution: dN/d
0
1
2
3
4
5
6
7
-4 -3 -2 -1 0 1 2 3 4
Pseudo-Rapidity
dN
/d
CDF Min-Bias 1.8 TeV
CDF Min-Bias 630 GeV all PT
CDF Published
<dNchg/d> = 4.2
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
-4 -3 -2 -1 0 1 2 3 4
Pseudo-Rapidity
dN
/d d
CDF Min-Bias 630 GeV
CDF Min-Bias 1.8 TeV all PT
CDF Published
<dNchg/dd> = 0.67
Convert to charged particle density, dNchg/dd by dividing by 2. There are about 0.67 charged particles per unit - in “Min-Bias” collisions at 1.8 TeV (|| < 1, all PT).
= 1
= 1
x = 1
0.67 There are about 0.25 charged particles per unit - in “Min-Bias” collisions at 1.8 TeV (|| < 1, PT > 0.5 GeV/c).
0.25
CDF Top Mass Workshop June 25, 2003
Rick Field Page 6
CDF Run 1 “Min-Bias” DataCDF Run 1 “Min-Bias” DataPPTT Dependence Dependence
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)C
har
ged
Den
sity
dN
/d d
dP
T (
1/G
eV/c
)
||<1CDF Preliminary
CDF Min-Bias Data at 1.8 TeV
HW "Soft" Min-Biasat 630 GeV, 1.8 TeV, and 14 TeV
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
-6 -4 -2 0 2 4 6
Pseudo-Rapidity
dN
/d d
630 GeV1.8 TeV
Herwig "Soft" Min-Bias 14 TeV
all PT
Shows the PT dependence of the charged particle density, dNchg/dddPT, for “Min-Bias” collisions at 1.8 TeV collisions compared with HERWIG “Soft” Min-Bias.
HERWIG “Soft” Min-Bias does not describe the “Min-Bias” data! The “Min-Bias” data contains a lot of “hard” parton-parton collisions which results in many more particles at large PT than are produces by any “soft” model.
Shows the energy dependence of the charged particle density, dNchg/dd for “Min-Bias” collisions compared with HERWIG “Soft” Min-Bias.
Lots of “hard” scattering in “Min-Bias”!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 7
Min-Bias: CombiningMin-Bias: Combining“Hard” and “Soft” Collisions“Hard” and “Soft” Collisions
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
-4 -3 -2 -1 0 1 2 3 4
Pseudo-Rapidity
dN
/d d
CDF Min-Bias Data Herwig Jet3 Herwig Min-Bias
1.8 TeV all PTHW "Soft" Min-Bias
HW PT(hard) > 3 GeV/c
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)C
har
ged
Den
sity
dN
/d
d d
PT
(1/
GeV
/c)
Herwig Jet3Herwig Min-BiasCDF Min-Bias Data
1.8 TeV ||<1
CDF Preliminary
HW PT(hard) > 3 GeV/c
HW "Soft" Min-Bias
HERWIG “hard” QCD with PT(hard) > 3 GeV/c describes well the high PT tail but produces too many charged particles overall. Not all of the “Min-Bias” collisions have a hard scattering with PT(hard) > 3 GeV/c!
One cannot run the HERWIG “hard” QCD Monte-Carlo with PT(hard) < 3 GeV/c because the perturbative 2-to-2 cross-sections diverge like 1/PT(hard)4?
HERWIG “soft” Min-Bias does not fit the “Min-Bias” data!
No easy way to“mix” HERWIG “hard” with HERWIG “soft”.
Hard-Scattering Cross-Section
0.01
0.10
1.00
10.00
100.00
0 2 4 6 8 10 12 14 16 18 20
Hard-Scattering Cut-Off PTmin
Cro
ss
-Se
cti
on
(m
illi
ba
rns
)
PYTHIA
HERWIG
CTEQ5L1.8 TeV
HC
HERWIG diverges!
PYTHIA cuts off the divergence.
Can run PT(hard)>0!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 8
PYTHIA Min-BiasPYTHIA Min-Bias“Soft” + ”Hard”“Soft” + ”Hard”
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
-4 -3 -2 -1 0 1 2 3 4
Pseudo-Rapidity
dN
/d d
Pythia 6.206 Set A
CDF Min-Bias 1.8 TeV 1.8 TeV all PT
CDF Published
PYTHIA regulates the perturbative 2-to-2 parton-parton cross sections with cut-off parameters which allows one to run with PT(hard) > 0. One can simulate both “hard” and “soft” collisions in one program.
The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.
Charged Particle Density
1.0E-06
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
PT(charged) (GeV/c)C
har
ged
Den
sity
dN
/d d
dP
T (
1/G
eV/c
)
Pythia 6.206 Set A
CDF Min-Bias Data
CDF Preliminary
1.8 TeV ||<1
PT(hard) > 0 GeV/c
Tuned to fit the “underlying event”!
12% of “Min-Bias” events have PT(hard) > 5 GeV/c!
1% of “Min-Bias” events have PT(hard) > 10 GeV/c!
This PYTHIA fit predicts that 12% of all “Min-Bias” events are a result of a hard 2-to-2 parton-parton scattering with PT(hard) > 5 GeV/c (1% with PT(hard) > 10 GeV/c)!
Lots of “hard” scattering in “Min-Bias”!
PYTHIA Tune ACDF Run 2 Default
CDF Top Mass Workshop June 25, 2003
Rick Field Page 9
““Underlying Event”Underlying Event”as defined by “Charged particle Jets”as defined by “Charged particle Jets”
Charged Jet #1Direction
“Transverse” “Transverse”
“Toward”
“Away”
“Toward-Side” Jet
“Away-Side” Jet
Look at charged particle correlations in the azimuthal angle relative to the leading charged particle jet.
Define || < 60o as “Toward”, 60o < || < 120o as “Transverse”, and || > 120o as “Away”. All three regions have the same size in - space, x = 2x120o = 4/3.
Charged Jet #1Direction
“Toward”
“Transverse” “Transverse”
“Away”
Charged Particle Correlations PT > 0.5 GeV/c || < 1
Toward-side “jet”(always)
Away-side “jet”(sometimes)
Perpendicular to the plane of the 2-to-2 hard scattering
“Transverse” region is very sensitive to the “underlying event”!
-1 +1
2
0
Leading ChgJet
Toward Region
Transverse Region
Transverse Region
Away Region
Away Region
Look at the charged particle density in the “transverse” region!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 10
Run 1 Charged Particle DensityRun 1 Charged Particle Density
“Transverse” P“Transverse” PTT Distribution Distribution
Compares the average “transverse” charge particle density with the average “Min-Bias” charge particle density (||<1, PT>0.5 GeV). Shows how the “transverse” charge particle density and the Min-Bias charge particle density is distributed in PT.
CDF Run 1 Min-Bias data<dNchg/dd> = 0.25
PT(charged jet#1) > 30 GeV/c“Transverse” <dNchg/dd> = 0.56
Factor of 2!
“Min-Bias”
"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
nsv
erse
" C
har
ged
Den
sity
CDF Min-Bias
CDF JET20CDF Run 1data uncorrected
1.8 TeV ||<1.0 PT>0.5 GeV/c
Charged Particle Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
Charged Particle Density
1.0E-06
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
PT(charged) (GeV/c)C
har
ged
Den
sity
dN
/d
d d
PT
(1/
GeV
/c)
CDF Run 1data uncorrected
1.8 TeV ||<1 PT>0.5 GeV/c
Min-Bias
"Transverse"PT(chgjet#1) > 5 GeV/c
"Transverse"PT(chgjet#1) > 30 GeV/c
CDF Top Mass Workshop June 25, 2003
Rick Field Page 11
ISAJET 7.32ISAJET 7.32“Transverse” Density“Transverse” Density
Compares the average “transverse” charge particle density (||<1, PT>0.5 GeV) versus PT(charged jet#1) and the PT distribution of the “transverse” density, dNchg/dddPT with the QCD hard scattering predictions of ISAJET 7.32 (default parameters with PT(hard)>3 GeV/c) .
The predictions of ISAJET are divided into three categories: charged particles that arise from the break-up of the beam and target (beam-beam remnants), charged particles that arise initial-state radiation, and charged particles that arise from the outgoing jets plus final-state radiation..
Beam-BeamRemnants
ISAJETCharged Jet #1Direction
“Toward”
“Transverse” “Transverse”
“Away”
Initial-StateRadiation
"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
CDF Run 1 Datadata uncorrectedtheory corrected
1.8 TeV ||<1.0 PT>0.5 GeV
Isajet
IS Radiation
"Remnants"
Jets + FS
ISAJET uses a naïve leading-log parton shower-model which does
not agree with the data!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 12
ISAJET 7.32ISAJET 7.32“Transverse” Density“Transverse” Density
Plot shows average “transverse” charge particle density (||<1, PT>0.5 GeV) versus PT(charged jet#1) compared to the QCD hard scattering predictions of ISAJET 7.32 (default parameters with PT(hard)>3 GeV/c) .
The predictions of ISAJET are divided into two categories: charged particles that arise from the break-up of the beam and target (beam-beam remnants); and charged particles that arise from the outgoing jet plus initial and final-state radiation (hard scattering component).
Beam-BeamRemnants
ISAJETCharged Jet #1Direction
“Toward”
“Transverse” “Transverse”
“Away”
“Hard”Component
"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
CDF Run 1Datadata uncorrectedtheory corrected
1.8 TeV ||<1.0 PT>0.5 GeV
Isajet
"Remnants"
"Hard"
ISAJET uses a naïve leading-log parton shower-model which does
not agree with the data!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 13
HERWIG 6.4HERWIG 6.4“Transverse” Density“Transverse” Density
Plot shows average “transverse” charge particle density (||<1, PT>0.5 GeV) versus PT(charged jet#1) compared to the QCD hard scattering predictions of HERWIG 5.9 (default parameters with PT(hard)>3 GeV/c).
The predictions of HERWIG are divided into two categories: charged particles that arise from the break-up of the beam and target (beam-beam remnants); and charged particles that arise from the outgoing jet plus initial and final-state radiation (hard scattering component).
Beam-BeamRemnants
HERWIG
Charged Jet #1Direction
“Toward”
“Transverse” “Transverse”
“Away”
"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 CDF Run 1Datadata uncorrectedtheory corrected
1.8 TeV ||<1.0 PT>0.5 GeV
Herwig 6.4 CTEQ5LPT(hard) > 3 GeV/c
Total "Hard"
"Remnants"
“Hard”Component
"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
CDF Run 1Datadata uncorrectedtheory corrected
1.8 TeV ||<1.0 PT>0.5 GeV
Isajet
"Remnants"
"Hard"
HERWIG uses a modified leading-log parton shower-model which
does agrees better with the data!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 14
HERWIG 6.4HERWIG 6.4“Transverse” P“Transverse” PTT Distribution Distribution
"Transverse" Charged Particle Density
1.0E-06
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
PT(charged) (GeV/c)C
har
ged
Den
sity
dN
/d
d d
PT
(1/
GeV
/c)
CDF Datadata uncorrectedtheory corrected
1.8 TeV ||<1 PT>0.5 GeV/c
PT(chgjet#1) > 5 GeV/c
PT(chgjet#1) > 30 GeV/c
Herwig 6.4 CTEQ5L
Herwig PT(chgjet#1) > 5 GeV/c<dNchg/dd> = 0.40
Herwig PT(chgjet#1) > 30 GeV/c“Transverse” <dNchg/dd> = 0.51
"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
nsv
erse
" C
har
ged
Den
sity
CDF Datadata uncorrectedtheory corrected
1.8 TeV ||<1.0 PT>0.5 GeV
Herwig 6.4 CTEQ5LPT(hard) > 3 GeV/c
Total "Hard"
"Remnants"
Compares the average “transverse” charge particle density (||<1, PT>0.5 GeV) versus PT(charged jet#1) and the PT distribution of the “transverse” density, dNchg/dddPT with the QCD hard scattering predictions of HERWIG 6.4 (default parameters with PT(hard)>3 GeV/c. Shows how the “transverse” charge particle density is distributed in PT.
HERWIG has the too steep of a PT dependence of the “beam-beam remnant”
component of the “underlying event”! Charged Jet #1Direction
“Toward”
“Transverse” “Transverse”
“Away”
CDF Top Mass Workshop June 25, 2003
Rick Field Page 15
PYTHIA: Multiple PartonPYTHIA: Multiple PartonInteraction ParametersInteraction Parameters
Pythia uses multiple partoninteractions to enhancethe underlying event.
Parameter Value
Description
MSTP(81) 0 Multiple-Parton Scattering off
1 Multiple-Parton Scattering on
MSTP(82) 1 Multiple interactions assuming the same probability, with an abrupt cut-off PTmin=PARP(81)
3 Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a single Gaussian matter distribution, with a smooth turn-off PT0=PARP(82)
4 Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a double Gaussian matter distribution (governed by PARP(83) and PARP(84)), with a smooth turn-off PT0=PARP(82)
Hard Core
Multiple parton interaction more likely in a hard
(central) collision!
and now HERWIG
!
Jimmy: MPIJ. M. Butterworth
J. R. ForshawM. H. Seymour
Proton AntiProton
Multiple Parton Interactions
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying EventUnderlying Event
Same parameter that cuts-off the hard 2-to-2 parton cross sections!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 16
Tuning PYTHIA:Tuning PYTHIA:Multiple Parton Interaction ParametersMultiple Parton Interaction Parameters
Parameter Default
Description
PARP(83) 0.5 Double-Gaussian: Fraction of total hadronic matter within PARP(84)
PARP(84) 0.2 Double-Gaussian: Fraction of the overall hadron radius containing the fraction PARP(83) of the total hadronic matter.
PARP(85) 0.33 Probability that the MPI produces two gluons with color connections to the “nearest neighbors.
PARP(86) 0.66 Probability 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 TeV Determines the reference energy E0.
PARP(90) 0.16 Determines the energy dependence of the cut-off
PT0 as follows PT0(Ecm) = PT0(Ecm/E0) with = PARP(90)
PARP(67) 1.0 A scale factor that determines the maximum parton virtuality for space-like showers. The larger the value of PARP(67) the more initial-state radiation.
Hard Core
Multiple Parton Interaction
Color String
Color String
Multiple Parton Interaction
Color String
Hard-Scattering Cut-Off PT0
1
2
3
4
5
100 1,000 10,000 100,000
CM Energy W (GeV)
PT
0
(Ge
V/c
)
PYTHIA 6.206
= 0.16 (default)
= 0.25 (Set A))
Take E0 = 1.8 TeV
Reference pointat 1.8 TeV
Determine by comparingwith 630 GeV data!
Affects the amount ofinitial-state radiation!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 17
"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)"T
ran
sver
se"
Ch
arg
ed D
ensi
ty
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
Default parameters give very poor description of the “underlying event”!
Note ChangePARP(67) = 4.0 (< 6.138)PARP(67) = 1.0 (> 6.138)
Parameter 6.115 6.125 6.158 6.206
MSTP(81) 1 1 1 1
MSTP(82) 1 1 1 1
PARP(81) 1.4 1.9 1.9 1.9
PARP(82) 1.55 2.1 2.1 1.9
PARP(89) 1,000 1,000 1,000
PARP(90) 0.16 0.16 0.16
PARP(67) 4.0 4.0 1.0 1.0
PYTHIA 6.206 DefaultsPYTHIA 6.206 Defaults
Plot shows the “Transverse” charged particle density versus PT(chgjet#1) compared to the QCD hard scattering predictions of PYTHIA 6.206 (PT(hard) > 0) using the default parameters for multiple parton interactions and CTEQ3L, CTEQ4L, and CTEQ5L.
PYTHIA default parameters
MPI constantprobabilityscattering
CDF Top Mass Workshop June 25, 2003
Rick Field Page 18
Old PYTHIA default(more initial-state radiation)
Parameter Tune B Tune A
MSTP(81) 1 1
MSTP(82) 4 4
PARP(82) 1.9 GeV 2.0 GeV
PARP(83) 0.5 0.5
PARP(84) 0.4 0.4
PARP(85) 1.0 0.9
PARP(86) 1.0 0.95
PARP(89) 1.8 TeV 1.8 TeV
PARP(90) 0.25 0.25
PARP(67) 1.0 4.0
Tuned PYTHIA 6.206Tuned PYTHIA 6.206
Plot shows the “Transverse” charged particle density versus PT(chgjet#1) compared to the QCD hard scattering predictions of two tuned versions of PYTHIA 6.206 (CTEQ5L, Set B (PARP(67)=1) and Set A (PARP(67)=4)).
"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
nsv
erse
" C
har
ged
Den
sity
1.8 TeV ||<1.0 PT>0.5 GeV
CDF Preliminarydata uncorrectedtheory corrected
CTEQ5L
PYTHIA 6.206 (Set A)PARP(67)=4
PYTHIA 6.206 (Set B)PARP(67)=1
Parameter Tune B Tune A
MSTP(81) 1 1
MSTP(82) 4 4
PARP(82) 1.9 GeV 2.0 GeV
PARP(83) 0.5 0.5
PARP(84) 0.4 0.4
PARP(85) 1.0 0.9
PARP(86) 1.0 0.95
PARP(89) 1.8 TeV 1.8 TeV
PARP(90) 0.25 0.25
PARP(67) 1.0 4.0
PYTHIA 6.206 CTEQ5L
New PYTHIA default(less initial-state radiation)
New PYTHIA default(less initial-state radiation)
Double Gaussian
Old PYTHIA default(more initial-state radiation)
Tune A CDFRun 2 Default!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 19
Azimuthal CorrelationsAzimuthal Correlations
Predictions of PYTHIA 6.206 (CTEQ5L) with PARP(67)=1 (new default) and PARP(67)=4 (old default) for the azimuthal angle, , between a b-quark with PT1 > 15 GeV/c, |y1| < 1 and bbar-quark with PT2 > 10 GeV/c, |y2|<1 in proton-antiproton collisions at 1.8 TeV. The curves correspond to d/d (b/o) for flavor creation, flavor excitation, shower/fragmentation, and the resulting total.
b-quark Correlations: Azimuthal Distribution
0.00001
0.00010
0.00100
0.01000
0 30 60 90 120 150 180
(degrees)
d /
d
(b
/deg
)
PY62 (67=1) Total Flavor Creation Flavor Excitation Shower/Fragmentation
1.8 TeVPT1 > 15 GeV/cPT2 > 10 GeV/c|y1| < 1 |y2| < 1
PYTHIA 6.206 CTEQ5L PARP(67)=1
"Away""Toward"
b-quark direction
“Toward”
“Away”
bbar-quark
b-quark Correlations: Azimuthal Distribution
0.00001
0.00010
0.00100
0.01000
0 30 60 90 120 150 180
(degrees)
d /
d
(b
/de
g)
PY62 (67=4) Total Flavor Creation Flavor Excitation Shower/Fragmentation
1.8 TeVPT1 > 15 GeV/cPT2 > 10 GeV/c|y1| < 1 |y2| < 1
PYTHIA 6.206 CTEQ5L PARP(67)=4
"Away""Toward"
PYTHIA Tune B(less initial-state radiation)
PYTHIA Tune A(more initial-state radiation)
CDF Top Mass Workshop June 25, 2003
Rick Field Page 20
Azimuthal CorrelationsAzimuthal Correlations
Predictions of HERWIG 6.4 (CTEQ5L) for the azimuthal angle, , between a b-quark with PT1 > 15 GeV/c, |y1| < 1 and bbar-quark with PT2 > 10 GeV/c, |y2|<1 in proton-antiproton collisions at 1.8 TeV. The curves correspond to d/d (b/o) for flavor creation, flavor excitation, shower/fragmentation, and the resulting total.
b-quark Correlations: Azimuthal Distribution
0.00001
0.00010
0.00100
0.01000
0 30 60 90 120 150 180
(degrees)
d /
d
(b
/de
g)
HW64 Total Flavor Creation Flavor Excitation Shower/Fragmentation
1.8 TeVPT1 > 15 GeV/cPT2 > 10 GeV/c|y1| < 1 |y2| < 1
HERWIG 6.4 CTEQ5L
"Away""Toward"
b-quark direction
“Toward”
“Away”
bbar-quark
b-quark Correlations: Azimuthal Distribution
0.000001
0.000010
0.000100
0.001000
0.010000
0 30 60 90 120 150 180
(degrees)
d /
d
(b
/deg
)
1.8 TeVPT1 > 15 GeV/cPT2 > 10 GeV/c|y1| < 1 |y2| < 1
"Flavor Creation" CTEQ5L
"Away""Toward"
HERWIG 6.4
PYTHIA 6.206PARP(67)=1
PYTHIA 6.206PARP(67)=4
“Flavor Creation”
PYTHIA Tune B(less initial-state radiation)
PYTHIA Tune A(more initial-state radiation)
CDF Top Mass Workshop June 25, 2003
Rick Field Page 22
Tuned PYTHIA 6.206Tuned PYTHIA 6.206“Transverse” P“Transverse” PTT Distribution Distribution
"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
nsv
erse
" C
har
ged
Den
sity
1.8 TeV ||<1.0 PT>0.5 GeV
CDF Preliminarydata uncorrectedtheory corrected
CTEQ5L
PYTHIA 6.206 (Set A)PARP(67)=4
PYTHIA 6.206 (Set B)PARP(67)=1
PARP(67)=4.0 (old default) is favored over PARP(67)=1.0 (new default)!
PT(charged jet#1) > 30 GeV/c
Can we distinguish between PARP(67)=1 and PARP(67)=4?
No way! Right!
"Transverse" Charged Particle Density
1.0E-06
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
PT(charged) (GeV/c)C
har
ged
Den
sity
dN
/d d
dP
T (
1/G
eV/c
)
CDF Datadata uncorrectedtheory corrected
1.8 TeV ||<1 PT>0.5 GeV/c
PT(chgjet#1) > 5 GeV/c
PT(chgjet#1) > 30 GeV/c
PYTHIA 6.206 Set APARP(67)=4
PYTHIA 6.206 Set BPARP(67)=1
Compares the average “transverse” charge particle density (||<1, PT>0.5 GeV) versus PT(charged jet#1) and the PT distribution of the “transverse” density, dNchg/dddPT with the QCD Monte-Carlo predictions of two tuned versions of PYTHIA 6.206 (PT(hard) > 0, CTEQ5L, Set B (PARP(67)=1) and Set A (PARP(67)=4)).
CDF Top Mass Workshop June 25, 2003
Rick Field Page 24
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
PT(charged) (GeV/c)C
har
ged
Den
sity
dN
/d d
dP
T (
1/G
eV/c
)
CDF Run 1data uncorrectedtheory corrected
1.8 TeV ||<1 PT>0.5 GeV/c
CDF Min-Bias
"Transverse"PT(chgjet#1) > 5 GeV/c
"Transverse"PT(chgjet#1) > 30 GeV/c
PYTHIA 6.206 Set A
CTEQ5L
"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
nsv
erse
" C
har
ged
Den
sity
1.8 TeV ||<1.0 PT>0.5 GeV/c
CDF Run 1data uncorrectedtheory corrected
PYTHIA 6.206 Set A
Tuned PYTHIA 6.206Tuned PYTHIA 6.206Run 1 Tune ARun 1 Tune A
Compares the average “transverse” charge particle density (||<1, PT>0.5 GeV) versus PT(charged jet#1) and the PT distribution of the “transverse” and “Min-Bias” densities with the QCD Monte-Carlo predictions of a tuned version of PYTHIA 6.206 (PT(hard) > 0, CTEQ5L, Set A).
Set A Min-Bias<dNchg/dd> = 0.24
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
-4 -3 -2 -1 0 1 2 3 4
Pseudo-Rapidity
dN
/d d
Pythia 6.206 Set A
CDF Min-Bias 1.8 TeV 1.8 TeV all PT
CDF Published
Describes “Min-Bias” collisions! Describes the “underlying event”!
“Min-Bias”
Set A PT(charged jet#1) > 30 GeV/c“Transverse” <dNchg/dd> = 0.60
Describes the rise from “Min-Bias” to “underlying event”!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 27
Charged Particle Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
1.25
0 5 10 15 20 25 30 35 40 45 50
PT(charged jet#1) (GeV/c)"T
ran
sver
se"
Ch
arg
ed D
ensi
ty
CDF Run 1 Min-Bias
CDF Run 1 JET20CDF Run 1 Data
data uncorrected
1.8 TeV ||<1.0 PT>0.5 GeV
"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)"T
ran
sver
se"
Ch
arg
ed D
ensi
ty
CDF Run 1 Min-Bias
CDF Run 1 JET20
||<1.0 PT>0.5 GeV
CDF Preliminarydata uncorrected
“ “Transverse” Transverse” Charged Particle DensityCharged Particle Density
Shows the data on the average “transverse” charge particle density (||<1, PT>0.5 GeV) as a function of the transverse momentum of the leading charged particle jet from Run 1.
Compares the Run 2 data (Min-Bias, JET20, JET50, JET70, JET100) with Run 1. The errors on the (uncorrected) Run 2 data include both statistical and correlated systematic uncertainties.
"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)"T
ran
sver
se"
Ch
arg
ed D
ensi
ty
CDF Run 2
“Transverse” region as defined by the leading “charged particle jet”
"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)"T
ran
sver
se"
Ch
arg
ed D
ensi
ty CDF Run 1 Published
CDF Run 2 Preliminary
||<1.0 PT>0.5 GeV/c
CDF Preliminarydata uncorrected
Excellent agreement between Run 1 and 2!
"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)"T
ran
sver
se"
Ch
arg
ed D
ensi
ty
CDF Run 1 Published
CDF Run 2 Preliminary
PYTHIA Tune A
||<1.0 PT>0.5 GeV/c
CDF Preliminarydata uncorrectedtheory corrected
PYTHIA Tune A was tuned to fit the “underlying event” in Run I!
Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after CDFSIM).
CDF Top Mass Workshop June 25, 2003
Rick Field Page 28
“ “Transverse” Transverse” Charged PTsum DensityCharged PTsum Density
Shows the data on the average “transverse” charged PTsum density (||<1, PT>0.5 GeV) as a function of the transverse momentum of the leading charged particle jet from Run 1.
"Transverse" Charged PTsum Density: dPTsum/dd
0.00
0.25
0.50
0.75
1.00
1.25
0 5 10 15 20 25 30 35 40 45 50
PT(charged jet#1) (GeV/c)"T
ran
sver
se"
PT
sum
Den
sity
(G
eV) CDF JET20
CDF Min-BiasCDF Run 1 Data
data uncorrected
1.8 TeV ||<1.0 PT>0.5 GeV
Compares the Run 2 data (Min-Bias, JET20, JET50, JET70, JET100) with Run 1. The errors on the (uncorrected) Run 2 data include both statistical and correlated systematic uncertainties.
"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)"T
ran
sver
se"
PT
sum
Den
sity
(G
eV)
CDF JET20
CDF Min-Bias
CDF Preliminarydata uncorrected
||<1.0 PT>0.5 GeV
Charged Particle Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
"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)"T
ran
sver
se"
PT
sum
Den
sity
(G
eV)
CDF Run 2
“Transverse” region as defined by the leading “charged particle jet”
"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)"T
ran
sver
se"
PT
sum
Den
sity
(G
eV/c
)
CDF Run 1 Published
CDF Run 2 Preliminary
CDF Preliminarydata uncorrected
||<1.0 PT>0.5 GeV/c
Excellent agreement between Run 1 and 2!
"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)"T
ran
sver
se"
PT
sum
Den
sity
(G
eV/c
)
CDF Run 1 Published
CDF Run 2 Preliminary
PYTHIA Tune A
CDF Preliminarydata uncorrectedtheory corrected
||<1.0 PT>0.5 GeV/c
Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after CDFSIM).
PYTHIA Tune A was tuned to fit the “underlying event” in Run I!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 30
JetClu Jet #1 Direction
“Transverse” “Transverse”
“Toward”
“Away”
“Toward-Side” Jet
“Away-Side” Jet
““Underlying Event”Underlying Event”as defined by “Calorimeter Jets”as defined by “Calorimeter Jets”
Look at charged particle correlations in the azimuthal angle relative to the leading JetClu jet.
Define || < 60o as “Toward”, 60o < || < 120o as “Transverse”, and || > 120o as “Away”. All three regions have the same size in - space, x = 2x120o = 4/3.
Charged Particle Correlations PT > 0.5 GeV/c || < 1
Away-side “jet”(sometimes)
Perpendicular to the plane of the 2-to-2 hard scattering
“Transverse” region is very sensitive to the “underlying event”!
JetClu Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
-1 +1
2
0
Leading Jet
Toward Region
Transverse Region
Transverse Region
Away Region
Away Region
Look at the charged particle density in the “transverse” region!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 31
““Transverse” Transverse” Charged Particle DensityCharged Particle Density
Shows the data on the average “transverse” charge particle density (||<1, PT>0.5 GeV) as a function of the transverse energy of the leading JetClu jet (R = 0.7, |(jet)| < 2) from Run 2.
JetClu Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
Compares the “transverse” region of the leading “charged particle jet”, chgjet#1, with the “transverse” region of the leading “calorimeter jet” (JetClu R = 0.7), jet#1.
JetClu Jet #1 or ChgJet#1
Direction
“Toward”
“Transverse” “Transverse”
“Away”
, compared with PYTHIA Tune A after CDFSIM.
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
"Tra
nsv
erse
" C
har
ged
Den
sity
CDF Preliminarydata uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu (R = 0.7, |(jet#1)| < 2)
“Transverse” region as defined by the leading
“calorimeter jet” "Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
"Tra
nsv
erse
" C
har
ged
Den
sity
PYTHIA Tune A
CDF Run 2 PreliminaryCDF Preliminary
data uncorrectedtheory corrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu (R = 0.7, |(jet#1)| < 2)
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150 175 200 225 250
PT(chgjet#1) or ET(jet#1) (GeV)
"Tra
nsv
erse
" C
har
ged
Den
sity CDF Preliminary
data uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
ChgJet#1 R = 0.7
JetClu Jet#1 (R = 0.7,|(jet)|<2)
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150 175 200 225 250
PT(chgjet#1) or ET(jet#1) (GeV)
"Tra
nsv
erse
" C
har
ged
Den
sity
CDF Preliminarydata uncorrectedtheory corrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
ChgJet#1 R = 0.7
JetClu Jet#1 (R = 0.7, |(jet)|<2)
PYTHIA Tune A 1.96 TeV
CDF Top Mass Workshop June 25, 2003
Rick Field Page 32
““Transverse” Transverse” Charged PTsum DensityCharged PTsum Density
Shows the data on the average “transverse” charged PTsum density (||<1, PT>0.5 GeV) as a function of the transverse energy of the leading JetClu jet (R = 0.7, |(jet)| < 2) from Run 2.
JetClu Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
Compares the “transverse” region of the leading “charged particle jet”, chgjet#1, with the “transverse” region of the leading “calorimeter jet” (JetClu R = 0.7), jet#1.
JetClu Jet #1 or ChgJet#1
Direction
“Toward”
“Transverse” “Transverse”
“Away”
, compared with PYTHIA Tune A after CDFSIM.
"Transverse" Charged PTsum Density: dPTsum/dd
0.0
0.5
1.0
1.5
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
"Tra
nsv
erse
" P
Tsu
m D
ensi
ty (
GeV
/c)
CDF Preliminarydata uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu (R = 0.7, |(jet#1)| < 2)
“Transverse” region as defined by the leading
“calorimeter jet” "Transverse" Charged PTsum Density: dPTsum/dd
0.0
0.5
1.0
1.5
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
"Tra
nsv
erse
" P
Tsu
m D
ensi
ty (
GeV
/c)
PYTHIA Tune A
CDF Run 2 Preliminary
CDF Preliminarydata uncorrectedtheory corrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu (R = 0.7, |(jet#1)| < 2)
"Transverse" Charged PTsum Density: dPTsum/dd
0.0
0.5
1.0
1.5
0 25 50 75 100 125 150 175 200 225 250
PT(chgjet#1) or ET(jet#1) (GeV)
"Tra
nsv
erse
" P
Tsu
m D
ensi
ty (
GeV
/c)
CDF Preliminarydata uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c) ChgJet#1 R = 0.7
JetClu Jet#1 (R = 0.7,|(jet)|<2)
"Transverse" Charged PTsum Density: dPTsum/dd
0.0
0.5
1.0
1.5
0 25 50 75 100 125 150 175 200 225 250
PT(chgjet#1) or ET(jet#1) (GeV)
"Tra
nsv
erse
" P
Tsu
m D
ensi
ty (
GeV
/c)
CDF Preliminarydata uncorrectedtheory corrected
Charged Particles (||<1.0, PT>0.5 GeV/c) ChgJet#1 R = 0.7
JetClu Jet#1 (R = 0.7,|(jet)|<2)
PYTHIA Tune A 1.96 TeV
CDF Top Mass Workshop June 25, 2003
Rick Field Page 33
““Transverse” Transverse” Charged Particle DensityCharged Particle Density
Shows the data on the average “transverse” charge particle density (||<1, PT>0.5 GeV) as a function of the transverse energy of the leading JetClu jet (R = 0.7, |(jet)| < 2) from Run 2.
JetClu Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
Shows the generated prediction of PYTHIA Tune A before CDFSIM.
, compared with PYTHIA Tune A after CDFSIM.
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)"T
ran
sver
se"
Ch
arg
ed D
ensi
ty
CDF Preliminarydata uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu (R = 0.7, |(jet#1)| < 2)
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)"T
ran
sver
se"
Ch
arg
ed D
ensi
ty
PYTHIA Tune A
CDF Run 2 PreliminaryCDF Preliminary
data uncorrectedtheory corrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu (R = 0.7, |(jet#1)| < 2)
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)"T
ran
sver
se"
Ch
arg
ed D
ensi
ty
PY Tune A Generated
PY Tune A Corrected
CDF Run 2 Preliminary
CDF Preliminarydata uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu (R = 0.7, |(jet#1)| < 2)
“Transverse” region as defined by the leading
“calorimeter jet”
CDFSIM/Generated: "Transverse" dN/dd
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
CD
FS
IM/G
ener
ated
JetClu (R = 0.7, |(jet#1)| < 2)
Charged Particles (||<1.0, PT>0.5 GeV/c)
PYTHIA Tune A 1.96 TeV
Shows the ratio CDFSIM/Generated for PYTHIA Tune A.
Small correction (about 10%) independent of ET(jet#1)!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 34
The Leading The Leading “Charged Particle” Jet“Charged Particle” Jet
Shows the data on the average number of charged particles within the leading “charged particle jet” (||<1, PT>0.5 GeV, R = 0.7) as a function of the transverse momentum of the leading “charged particle jet” from Run 1.
Nchg(chgjet#1) versus PT(chgjet#1)
0
2
4
6
8
10
12
0 5 10 15 20 25 30 35 40 45 50
PT(charged jet#1) (GeV/c)
Ave
rave
Nch
g
CDF Run 1 Min-Bias
CDF Run 1 JET20
CDF Run 1 Datadata uncorrected
1.8 TeV ||<1.0 PT>0.5 GeV R = 0.7
Nchg(chgjet#1) versus PT(chgjet#1)
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
Ave
rave
Nch
g
CDF Run 1 Min-Bias
CDF Run 1 JET20
CDF Preliminarydata uncorrected
||<1.0 PT>0.5 GeV R = 0.7
Compares the Run 2 data (Min-Bias, JET20, JET50, JET70, JET100) with Run 1. The errors on the (uncorrected) Run 2 data include both statistical and correlated systematic uncertainties.
Nchg(chgjet#1) versus PT(chgjet#1)
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
Ave
rave
Nch
g
CDF Run 2
Nchg(chgjet#1) versus PT(chgjet#1)
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
Ave
rave
Nch
g
CDF Run 1 Min-Bias
CDF Run 1 JET20
CDF Run 2
CDF Preliminarydata uncorrected
||<1.0 PT>0.5 GeV/c R = 0.7
Nchg(chgjet#1) versus PT(chgjet#1)
0
2
4
6
8
10
12
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
Ave
rave
Nch
g
CDF Run 1 Min-Bias
CDF Run 1 JET20
CDF Run 2
PY Tune A
||<1.0 PT>0.5 GeV/c R = 0.7
CDF Preliminarydata uncorrectedtheory corrected
Excellent agreement between Run 1 and 2!
PYTHIA produces too many charged particles in the leading
“charged particle jet”!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 35
The Leading The Leading “Calorimeter” Jet“Calorimeter” Jet
Shows the Run 2 data on the average number of charged particles (||<1, PT>0.5 GeV, R = 0.7) within the leading “calorimeter jet” (JetClu R = 0.7, |(jet)|< 0.7) as a function of the transverse energy of the leading “calorimeter jet”.
Compares the number of charged particles within the leading “charged particle jet”, chgjet#1, with the number of charged particles within the leading “calorimeter jet” (JetClu R = 0.7), jet#1.
Nchg(jet#1) versus ET(jet#1)
0
2
4
6
8
10
12
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
Ave
rave
Nch
gCharged Particles (||<1.0, PT>0.5 GeV/c) JetClu R = 0.7 |(jet)| < 0.7
CDF Preliminarydata uncorrected
Nchg(jet#1) versus ET(jet#1)
0
2
4
6
8
10
12
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
Ave
rave
Nch
gCharged Particles (||<1.0, PT>0.5 GeV/c) JetClu R = 0.7 |(jet)| < 0.7
CDF Preliminarydata uncorrectedtheory corrected
PYTHIA Tune A 1.96 TeV
PYTHIA produces too many charged particles in the
leading “calorimeter jet”!
Nchg(jet#1) and Nchg(charged jet#1)
0
2
4
6
8
10
12
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) or PT(charged jet#1) (GeV)
Ave
rave
Nch
gCharged Particles (||<1.0, PT>0.5 GeV/c) JetClu R = 0.7 |(jet)| < 0.7
CDF Preliminarydata uncorrected
Nchg(jet#1)
Nchg(chgjet#1)
Nchg(jet#1) and Nchg(charged jet#1)
0
2
4
6
8
10
12
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) or PT(charged jet#1) (GeV)
Ave
rave
Nch
gCharged Particles (||<1.0, PT>0.5 GeV/c) JetClu R = 0.7 |(jet)| < 0.7
CDF Preliminarydata uncorrectedtheory corrected
PYTHIA Tune A 1.96 TeV
Nchg(jet#1)
Nchg(chgjet#1)
CDF Top Mass Workshop June 25, 2003
Rick Field Page 36
The Leading “Jet”The Leading “Jet”
Shows charged particle multiplicity distribution (||<1, PT>0.5 GeV/c) within the leading “charged particle jet” and in the “transverse” region as defined by the leading “charged particle jet” for the range 30 < PT(chgjet#1) < 70 GeV/c compared with PYTHIA Tune A.
Shows charged particle multiplicity distribution (||<1, PT>0.5 GeV/c) within the leading “calorimeter jet” (JetClu, R = 0.7, |(jet)| < 0.7) and in the “transverse” regions as defined by the leading “calorimeter jet” (JetClu, R = 0.7, |(jet)| < 2) for the range 30 < ET(jet#1) < 70 GeV compared with PYTHIA Tune A.
But PYTHIA produces too many charged particles within the leading “jet”!
Charged Particle Multiplicity
0%
5%
10%
15%
20%
25%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
N (charged)
% E
ven
ts
CDF Preliminarydata uncorrectedtheory corrected
||<1.0 PT>0.5 GeV/c
R = 0.7 30 < PT(chgjet#1) < 70 GeV
"Transverse"
ChgJet#1
PYTHIA Tune A 1.96 TeV
Charged Particle Multiplicity
0%
5%
10%
15%
20%
25%
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
N (charged)
% E
ven
ts
CDF Preliminarydata uncorrectedtheory corrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
PYTHIA Tune A 1.96 TeV
JetClu R = 0.7 30 < ET(jet#1) < 70 GeV
"Transverse"
Jet#1
PYTHIA Tune A describes the “underlying event”!
PYTHIA Tune A describes the “underlying event”!
But PYTHIA produces too many charged particles within the leading “jet”!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 37
The Leading “Calorimeter” JetThe Leading “Calorimeter” JetCharged Particle MultiplicityCharged Particle Multiplicity
Shows the Run 2 data on the average number of charged particles (||<1, PT>0.5 GeV, R = 0.7) within the leading “calorimeter jet” (JetClu R = 0.7, |(jet)|< 0.7) as a function of ET(jet#1) compared with PYTHIA Tune A after CDFSIM.
Shows the generated prediction of PYTHIA Tune A before CDFSIM.
Calorimeter Jet CDFSIM/Generated: Leading Jet Nchg
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
CD
FS
IM/G
ener
ated
PYTHIA Tune A 1.96 TeV JetClu R = 0.7 |(jet)| < 0.7
Charged Particles (||<1.0, PT>0.5 GeV/c)
Shows the ratio CDFSIM/Generated for PYTHIA Tune A.
Correction becomes large for ET(jet#1) > 100 GeV and
depends on ET(jet#1)!
Shows “corrected” Run 2 data compared with PYTHIA Tune A (uncorrected).
Nchg(jet#1) versus ET(jet#1)
0
2
4
6
8
10
12
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)A
vera
ve N
chg
Charged Particles (||<1.0, PT>0.5 GeV/c) JetClu R = 0.7 |(jet)| < 0.7
CDF Preliminarydata uncorrectedtheory corrected
PYTHIA Tune A 1.96 TeV
Nchg(jet#1) versus ET(jet#1)
0
2
4
6
8
10
12
14
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)A
vera
ve N
chg
PY Tune A Generated
PY Tune A + CDFSIM
CDF Run 2 Uncorrected Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu R = 0.7 |(jet)| < 0.7
CDF Preliminarydata uncorrected
Nchg(jet#1) versus ET(jet#1)
0
2
4
6
8
10
12
14
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)A
vera
ve N
chg
Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu R = 0.7 |(jet)| < 0.7
CDF Preliminarydata corrected
theory uncorrected
PYTHIA Tune A 1.96 TeV
Multiply data by the “unfolding function” (i.e. Generated/CDFSIM) determined from PYTHIA Tune A to get “corrected” data.
CDF Top Mass Workshop June 25, 2003
Rick Field Page 39
The Leading “Jet”The Leading “Jet”
Shows the transverse momentum distribution of charged particles (||<1) within the leading “charged particle jet” compared with PYTHIA Tune A. The plot shows dNchg/dz with z = PT/PT(chgjet#1) for the range 30 < PT(chgjet#1) < 70 GeV/c.
Shows the transverse momentum distribution of charged particles (||<1) within the leading “calorimeter jet” (JetClu, R = 0.7, |(jet)| < 0.7) compared with PYTHIA Tune A. The plot shows dNchg/dz with z = PT/ET(jet#1) for the range 30 < ET(jet#1) < 70 GeV.
PYTHIA produces too many “soft” charged particles within
the leading “jet”!
The integral of F(z) is the average number of charged particles within the
leading “charged particle jet”.
Leading Charged Particle Jet
0.1
1.0
10.0
100.0
0.0 0.2 0.4 0.6 0.8 1.0
z = PT/PT(chgjet#1)
F(z
) =
dN
/dz
CDF Preliminarydata uncorrectedtheory corrected
R = 0.7 30 < PT(chgjet#1) < 70 GeV
||<1.0 PT>0.5 GeV/c
PYTHIA Tune A 1.96 TeV
Leading Calorimeter Jet
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
0.0 0.2 0.4 0.6 0.8 1.0 1.2
z = PT/ET(Jet#1)
F(z
) =
dN
/dz
CDF Preliminarydata uncorrectedtheory corrected
JetClu R = 0.7 30 < ET(jet#1) < 70 GeV
Charged Particles (||<1.0, PT>0.5 GeV/c)
PYTHIA Tune A 1.96 TeV
PYTHIA produces too many “soft” charged particles within
the leading “jet”!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 40
The Leading The Leading “Calorimeter Jet”“Calorimeter Jet”
Shows average charged PTsum fraction, PTsum/ET(jet#1), and the average charged PTmax fraction, PTmax/ET(jet#1), within the leading “calorimeter jet” (JetClu, R = 0.7, |(jet)| < 0.7) compared with PYTHIA Tune A.
Shows distribution of the charged PTsum fraction, z = PTsum/ET(jet#1), and the distribution of charged PTmax fraction, z = PTmax/ET(jet#1), within the leading “calorimeter jet” (JetClu, R = 0.7, |(jet)| < 0.7) for the range 95 < ET(jet#1) < 130 GeV compared with PYTHIA Tune A.
Charged Fraction within the Leading Jet
0
2
4
6
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
z = PTmax/ET(jet#1) or PTsum/ET(jet#1)
(1/N
) d
N/d
z
CDF Preliminarydata uncorrectedtheory corrected
JetClu R = 0.7 95 < ET(jet#1) < 130 GeV
Charged Particles (||<1.0, PT>0.5 GeV/c)
PYTHIA Tune A 1.96 TeV
PTmax/ET(jet#1)
PTsum/ET(jet#1)
PYTHIA does okay on the charged PTmax fraction!PYTHIA does okay on the charged PTmax fraction!
But PYTHIA does not do well on the charged PTsum fraction!
But PYTHIA does not do as well on the charged PTsum fraction!
PTsum/ET(Jet#1) and PTmax/ET(jet#1)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
Ave
rag
e F
ract
ion
JetClu R = 0.7 |(jet)| < 0.7
CDF Preliminarydata uncorrectedtheory corrected
PYTHIA Tune A 1.96 TeV
Charged Particles (||<1.0, PT>0.5 GeV/c)
PTsum(chg)/ET(jet#1)
PTmax(chg)/ET(jet#1)
CDF Top Mass Workshop June 25, 2003
Rick Field Page 41
The Leading “Calorimeter” JetThe Leading “Calorimeter” JetCharged PTCharged PTsumsum Fraction Fraction
Shows average charged PTsum fraction, PTsum/ET(jet#1), within the leading “calorimeter jet” (JetClu, R = 0.7, |(jet)| < 0.7) compared with PYTHIA Tune A after CDFSIM.
Calorimeter Jet
Shows the generated prediction of PYTHIA Tune A before CDFSIM.
CDFSIM/Generated: Leading Jet PTsum Fraction
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)
CD
FS
IM/G
ener
ated
PYTHIA Tune A 1.96 TeV
Charged Particles (||<1.0, PT>0.5 GeV/c)
JetClu R = 0.7 |(jet)| < 0.7
Shows the ratio CDFSIM/Generated for PYTHIA Tune A.
Very large correction that depends on ET(jet#1)!
Shows “corrected” Run 2 data compared with PYTHIA Tune A (uncorrected).
Leading Jet: Charged PTsum/ET(Jet#1)
0.2
0.3
0.4
0.5
0.6
0.7
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)C
har
ged
PT
sum
/ET
(jet
#1)
JetClu R = 0.7 |(jet)| < 0.7
CDF Preliminarydata uncorrectedtheory corrected
PYTHIA Tune A 1.96 TeV
Charged Particles (||<1.0, PT>0.5 GeV/c)
Leading Jet: Charged PTsum/ET(jet#1)
0.2
0.3
0.4
0.5
0.6
0.7
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)C
har
ged
PT
sum
/ET
(jet
#1)
PY Tune A Generated
PY Tune A + CDFSIM
CDF Run 2 Uncorrected
JetClu R = 0.7 |(jet)| < 0.7CDF Preliminarydata uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
Leading Jet: Charged PTsum/ET(jet#1)
0.2
0.3
0.4
0.5
0.6
0.7
0 25 50 75 100 125 150 175 200 225 250
ET(jet#1) (GeV)C
har
ged
PT
sum
/ET
(jet
#1)
JetClu R = 0.7 |(jet)| < 0.7CDF Preliminary
data correctedtheory uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
PYTHIA Tune A 1.96 TeV
Multiply data by the “unfolding function” (i.e. Generated/CDFSIM) determined from PYTHIA Tune A to get “corrected” data.
CDF Top Mass Workshop June 25, 2003
Rick Field Page 43
Inclusive Cross-SectionInclusive Cross-Section“Correction Factors”“Correction Factors”
Shows PYTHIA Tune A + CDFSIM inclusive cross-section for JetClu (R = 0.7) jets compared with the “true” cross-section where “true” is the PTsum of all hadrons (partons) with PT > 0 in R = 0.7 cone around JetClu.
Inclusive Cross-Section: d/dET
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
1.0E+03
0 25 50 75 100 125 150 175 200 225 250
ET (GeV)
d /
dE
T ( b
/Ge
V)
ET(particles in R)
ET(partons in R)
ET(jetclu)
PYTHIA Tune A 1.96 TeV
0.1<|DET|<0.7
R = 0.7
Inclusive X-Sec Ratio: (PTsum in R=0.7)/ET(jetclu)
0.5
1.0
1.5
2.0
2.5
3.0
0 25 50 75 100 125 150 175 200 225 250
ET(jetclu) (GeV)
Cro
ss
-Se
cti
on
Ra
tio
PYTHIA Tune A 1.96 teV
0.1<|DET|<0.7
Particles
Partons
Measured
“True”
Correction factors!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 44
Inclusive Cross-SectionInclusive Cross-Section“Jet Energy Scale”“Jet Energy Scale”
Shows PYTHIA Tune A + CDFSIM inclusive cross-section for JetClu (R = 0.7) jets compared with the “true” cross-section where “true” is the PTsum of all hadrons (partons) with PT > 0 in R = 0.7 cone around JetClu.
Inclusive Cross-Section: d/dET
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
1.0E+03
0 25 50 75 100 125 150 175 200 225 250
ET (GeV)
d /
dE
T ( b
/Ge
V)
ET(particles in R)
ET(partons in R)
ET(jetclu)
PYTHIA Tune A 1.96 TeV
0.1<|DET|<0.7
R = 0.7
Inclusive Cross-Section: d/dET
1.0E-07
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
1.0E+02
1.0E+03
0 25 50 75 100 125 150 175 200 225 250
ET (GeV)
d /
dE
T ( b
/Ge
V)
ET(particles in R)
ET(partons in R)
ET(jetclu) x 1.12
PYTHIA Tune A 1.96 TeV
0.1<|DET|<0.7
R = 0.7
To approximately correct the observed inclusive cross-section back to the
particle level multiply ET(jetclu) by a “scale factor” of 1.12!
Warning!This is only approximate!
The scale shift dependson ET and is only for theinclusive cross-section!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 45
Summary & ConclusionsSummary & Conclusions
Initial-State Radiation
Systematic errors due to initial-state radiation can be estimated by comparing PYTHIA Tune A (more radiation) and PYTHIA Tune B (less radiation).
But it is also important it always compare PYTHIA and HERWIG!The best is to compare all three: PYTHIA (Tune A & B) and
HERWIG.
Proton AntiProton
“Hard” Scattering
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
CDF Top Mass Workshop June 25, 2003
Rick Field Page 46
Summary & ConclusionsSummary & Conclusions
The “Underlying Event”
There is excellent agreement between the Run 1 and the Run 2. The “underlying event” is the same in Run 2 as in Run 1 but now we can study the evolution out to much higher energies!
PYTHIA Tune A does a good job of describing the “underlying event” in the Run 2 data as defined by “charged particle jets” and as defined by “calorimeter jets”. HERWIG Run 2 comparisons will be coming soon!
Lots more CDF Run 2 data to come including MAX/MIN “transverse” and MAX/MIN “cones”.
Proton AntiProton
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
Also see Mario’s Run 2 “energy flow” analysis!
CDF Top Mass Workshop June 25, 2003
Rick Field Page 47
MichelangeloMichelangeloA Few Thoughts
The determination of the top mass will unfortunately have to rely on some MC input. This is true even in absence of backgrounds. It is therefore useful to start right away separating the background-related issues with the signal-related ones. Let us start from the signal.
Let us assume there is no background contamination and we isolated a pure sample of t-tbar events. The key experimental systematics will then be related to
• light jet energy scale
• b jet energy scale
• initial/final-state radiation effects
• acceptance/event selection biases Information on the corrections which have to be applied to the data is obtained through
control samples (e.g. gamma+jet or Z+jets for the e-scale of light jets). However more work is required to transport these energy corrections to the physically different environment of light jets in a t-tbar final state. The "porting" procedure, which is driven by MC modeling, needs to be validated, and its systematics established.
CDF Top Mass Workshop June 25, 2003
Rick Field Page 48
MichelangeloMichelangeloA Few Thoughts
Reasons why the porting of e-scale corrections is non-trivial (namely requires model-dependent corrections) include:• light jets in top events arise from W decays. Their properties (energy, multiplicity,
fragmentation function) are fixed in the W rest frame. When the W is boosted, the jets' ET will change, but properties like multiplicity and fragmentation function won't (up to detector effects). Therefore a 20 GeV or an 80 GeV light jet in top decays behave as a 40 GeV jet, boosted to 20 or 80 GeV, rather than as a 20 or 80 GeV jet produced as a recoil to a gamma or a Z.
• a similar comment applies to b jets, for the same reason.• light jets in top decays are dominated by quarks, while in any other control sample there
will typically be gluons as well; so the features of the jets are different. Studies which should be performed to validate the procedures should include:
• a study of the fragmentation function (or even more inlcusive observables, such as jet shapes, jet energy profiles) for light jets and b-tagged jets in top-rich samples.
• a study of frag-function (or more inclusive observables, as above) in the e-cale-fixing contorl samples (gamma+jet, Z+jet).
CDF Top Mass Workshop June 25, 2003
Rick Field Page 49
MichelangeloMichelangeloA Few Thoughts
The exercise can start even before the data have statistics large enough. For example, it would be good to compare the properties of the jets in the two MC samples (in other words, to compare the MC predictions for the structure of a 40 GeV jet recoiling against a gamma, and a 40 gev jet form top decay), as well as simulating how large the MC predicts the corrections will have to be. If the differences/corrections are small, we can gain confidence that this won't be a problem (the same exercise will have to be repeated using PYTHIA and HERWIG, at least). If the differences/corrections are large, we will need a careful planning of MC-validation measurements.
Information about the description of the ISR and FSR has to be brought into the game. All studies done on the structure of the UE in Z/W events (see work done by Rick) have to be brought into a t-mass measurement perspective. Assuming that most extra jet form ISR in top events will come at large rapidity, a possible first observable could be the rapidity distribution of soft jets in t-tbar events. In order to test the ISR performance of the MC’s on control samples which share some of the physics of t-tbar events, I would propose the following:
• large-mass DY events (take events with DY masses as close as possible to 2 mtop; the stastistics is lousy, if non 0. one should then go to masses as large as possible, and monitor the jet activity as a function of DY mass).
CDF Top Mass Workshop June 25, 2003
Rick Field Page 50
MichelangeloMichelangeloA Few Thoughts
• large mass dijets: take events with two high-pt, central jets (within eta<1), and study the extra-jet activity as a function of the dijet mass. Extra jets well separated from the leading 2 jets will most likely arise from ISR (the MC can help deciding how to define the extra jets to optimize this requirement; mayve a cut in deltaR is enough, maybe a request eta>2 is better). Tests done in the region of dijet mass close to 400 gev will provide strong constraints on the mc description of isr in t-tbar events.
Other issues:• Calibrating the light jets "on site" using the W mass constraint on an event-by-event basis is useful,
but is not an unambiguous procedure. Since we have two jets, there is an infinite number of ways in which the energy of the two jets can be independently rescaled, all leading to the W mass, but each leading to a different value fo the W momentum (which is the ingredient entering in the top mass fit). Whatever the recipe to calibrate light jets, the impact of this ambiguity should be established (the MC, however inaccurate, should be enough to assess this systematics).
• In W decays we'll typically have a 3rd jet. Whether or not this appears as an independent jet after the W boost requires some study. Any algorithm aimed at establishing rules for the acceptance or rejection of extra jets (or for the dynamical rescaling of the jet cones, to try absorb the extra jet) ultimately requires validation, and to first approximation requires an evaluation of the systematics based on the MC.
CDF Top Mass Workshop June 25, 2003
Rick Field Page 51
MichelangeloMichelangeloA Few Thoughts
In general, I would expect the MC to describe well these decays, since the physics was constrained by the 3 jet decays at LEP. It is important to verify whether the MC has matrix element corrections. PYTHIA, as well as the most recent versions of HERWIG, have them in,
Background issues: Here the problem is mostly to understand how the background affects the MC validation procedures which use the top-enhanced sample.
The issue can be tackled by ensuring that the MC's for the background correctly reproduce the jet properties in background-dominated samples. So the above analyses should be repeated using, for example, non-b tagged W+3/4 jets final states (or,even better, Z+3/4 jets). The statistics is larger, so I would look at fragmentation functions, jet shapes, inter-jet radiation patterns.
The whole process will take a long time, and will need coordination with the QCD group. The question "what do we do if the MC's don't describe the data or "ok, the MC seems fine, what's next" can only be addressed once we have made a first pass.