“Min-Bias” and the
“Underlying Event” at CDF
Outline of Talk
“Hard” Scattering
 Review what we learned at CDF in Run 1
Outgoing Parton
PT(hard)
about “min-bias”, the “underlying event”,
and “initial-state radiation”.
Proton
AntiProton
Underlying Event
 Compare the CDF Run 1 analysis which used
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
the leading “charged particle jet” to define the
“underlying event” with CDF Run 2 data.
Charged Particle Jet
Tuned to fit the charged particle component
of the “underlying event” in Run 1
 Study the “underlying event” in CDF Run 2 as
Calorimeter Jet
defined by the leading “calorimeter jet” and
compare with the “charged particle jet” analysis.
 Discuss PYTHIA Tune A and extrapolations
to the LHC.
JetClu R = 0.7
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Rick Field - Florida/CDF
Page 1
The “Underlying Event”
in Hard Scattering Processes
 What happens when a high energy
proton and an antiproton collide?
“Min-Bias”
“Soft” Collision (no hard scattering)
ProtonProton
AntiProton
AntiProton
2 TeV
 Most of the time the proton and
antiproton ooze through each other
and fall apart (i.e. no hard scattering).
“Hard” Scattering Outgoing Parton
The outgoing particles continue in
PT(hard)
roughly the same direction as initial
Are
proton and antiproton. A “Min-Bias” Proton
these
AntiProton
collision.
the
Underlying Event
Underlying Event
Initial-State
 Occasionally there will be a “hard”
same?
Radiation
Final-State
parton-parton collision resulting in large
Radiation
No!
transverse momentum outgoing partons.
Outgoing Parton
Also a “Min-Bias” collision.
 The “underlying event” is everything
except the two outgoing hard scattered
“jets”. It is an unavoidable background
to many collider observables.
MC Tools for the LHC
CERN July 31, 2003
“Underlying Event”
Proton
AntiProton
Beam-Beam Remnants
Rick Field - Florida/CDF
Beam-Beam Remnants
“underlying event” has
initial-state radiation!
Initial-State
Radiation
Page 2
Beam-Beam Remnants
“Hard” Collision
outgoing parton
“Hard” Component
Maybe not all “soft”!
“Soft?” Component
AntiProton
Proton
initial-state radiation
initial-state radiation
+
Beam-Beam Remnants
outgoing parton
outgoing jet
final-state radiation
final-state radiation
 The underlying event in a hardIfscattering
process
we are going
to lookhas
at a “hard” component (particles that
arise from initial & final-state “Min-Bias”
radiation and
fromasthe
collisions
a outgoing hard scattered partons)
guide to understanding
the
and a “soft?” component (“beam-beam
remnants”).
“beam-beam remnants”,
 Clearly? the “underlying event” then
in a hard
scattering
we better
study process should not look like a “MinBias” event because of the “hard” component
(i.e. initial & final-state radiation).
carefully the
“Min-Bias”
 However, perhaps “Min-Bias” collisions
are adata!
good model for the “beam-beam remnant”
component of the “underlying event”.
“Min-Bias” Collision
“Soft?” Component
color string
Are these the same?
Hadron
Hadron
color string
Beam-Beam Remnants
 The “beam-beam remnant” component is, however, color connected to the “hard”
component so this comparison is (at best) an approximation.
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Page 3
CDF Run 1 “Min-Bias” Data
Charged Particle Density
Charged Particle Density: dN/dhd
Charged Particle Pseudo-Rapidity Distribution: dN/dh
1.0
7
CDF Published
CDF Published
6
0.8
dN/dhd
dN/dh
5
4
3
0.6
0.4
2
0.2
CDF Min-Bias 630 GeV
CDF Min-Bias 1.8 TeV
1
CDF Min-Bias 1.8 TeV
all PT
CDF Min-Bias 630 GeV
-4
-3
-2
-1
0
1
2
3
4
-4
-3
-2
-1
0
1
2
3
<dNchg
/dh> = 4.2
Shows
CDF “Min-Bias”


4
Pseudo-Rapidity h
Pseudo-Rapidity h

all PT
0.0
0
<dNchg/dhd>
= 0.67 particles per unit pseudo-rapidity
data on the number
of charged
at 630 and 1,800 GeV. There are about 4.2 charged particles per unit h in “Min-Bias”
collisions at 1.8 TeV (|h| < 1, all PT).
Convert to charged particle density, dNchg/dhd, by dividing by 2p.
hx = 1
There are about 0.67 charged particles per unit h- in “Min-Bias”
 = 1
collisions at 1.8 TeV (|h| < 1, all PT).
0.67
0.25
There are about 0.25 charged particles per unit h- in “Min-Bias”
h = 1
collisions at 1.8 TeV (|h| < 1, PT > 0.5 GeV/c).
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Page 4
CDF Run 1 “Min-Bias” Data
PT Dependence
Lots of “hard” scattering
in “Min-Bias”!
Charged Particle Density
Charged Particle Density: dN/dhd
1.4
1.0E+01
14 TeV
Herwig "Soft" Min-Bias
1.2
CDF Preliminary
0.6
1.8 TeV
0.2
630 GeV
all PT
0.0
-6
-4
-2
0
2
4
6
Pseudo-Rapidity h
 Shows the energy dependence of the

Charged Density dN/dhddPT (1/GeV/c)
dN/dhd
0.8
0.4

|h|<1
1.0E+00
1.0
1.0E-01
CDF Min-Bias Data at 1.8 TeV
1.0E-02
1.0E-03
HW "Soft" Min-Bias
at 630 GeV, 1.8 TeV, and 14 TeV
1.0E-04
1.0E-05
charged particle density, dNchg/dhd, for
1.0E-06
“Min-Bias” collisions compared with
0
2
4
6
8
10
12
14
PT (GeV/c)
HERWIG “Soft” Min-Bias.
Shows the PT dependence of the charged particle density, dNchg/dhddPT, 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.
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Page 5
Min-Bias: Combining
“Hard” and “Soft” Collisions
No easy way to
“mix” HERWIG “hard”
with HERWIG “soft”.
sHC
Hard-Scattering Cross-Section
Charged
Particle Density
100.00
Charged Particle Density: dN/dhd
1.6
CTEQ5L
1.8 TeV
Cross-Section (millibarns)
1.0E+01
1.4
Herwig Jet3
Herwig Min-Bias
CDF Min-Bias Data
10.00
CDF Preliminary
1.2
1.0E+00
1.0
HW PT(hard) > 3 GeV/c
0.8
0.6
0.4
0.2
HW "Soft" Min-Bias
1.8 TeV all PT
0.0
-4
-3
-2
-1
0
1
2
3
4
Pseudo-Rapidity h
CDF Min-Bias Data
Herwig Jet3
Herwig 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!
Charged Density dN/dhddPT (1/GeV/c)
dN/dhd
HERWIG diverges!
1.0E-01
1.0E-02
1.00
1.8 TeV |h|<1
0.10
PYTHIA
HERWIG
HW PT(hard) > 3 GeV/c
0.01
0
2
4
6
8
10
12
14
16
18
PYTHIA cuts off
the divergence.
HW "Soft" Min-Bias
Can run
PT(hard)>0!
1.0E-03
1.0E-04
1.0E-05
1.0E-06
0
2
4
6
8
10
12
14
PT (GeV/c)
HERWIG “soft”
Min-Bias does not fit
the “Min-Bias” data!
 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?
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20
Hard-Scattering Cut-Off PTmin
Rick Field - Florida/CDF
Page 6
PYTHIA Min-Bias
PYTHIA Tune A
“Soft” + ”Hard”
CDF Run 2 Default
Tuned to fit the
“underlying event”!
Charged Particle Density
Charged Particle Density: dN/dhd
1.0
1.0E+00
CDF Published
Pythia 6.206 Set A
0.8
CDF Min-Bias Data
0.6
0.4
0.2
Pythia 6.206 Set A
1.8 TeV all PT
CDF Min-Bias 1.8 TeV
0.0
-4
-3
-2
-1
0
1
2
3
4
Pseudo-Rapidity h
 PYTHIA regulates the perturbative 2-to-2
parton-parton cross sections with cut-off
parameters
which allows one to run with
Lots of “hard” scattering
PT(hard)in>“Min-Bias”!
0. One can simulate both “hard”
and “soft” collisions in one program.
Charged Density dN/dhddPT (1/GeV/c)
dN/dhd
1.0E-01
1.8 TeV |h|<1
1.0E-02
12% of “Min-Bias” events
have PT(hard) > 5 GeV/c!
PT(hard) > 0 GeV/c
1.0E-03
1% of “Min-Bias” events
have PT(hard) > 10 GeV/c!
1.0E-04
1.0E-05
CDF Preliminary
1.0E-06
0
2
4
6
8
10
12
14
PT(charged) (GeV/c)
 The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.
 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)!
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Page 7
Studying the “Underlying Event”
at CDF
Outgoing Parton
The Underlying Event:
beam-beam remnants
initial-state radiation
multiple-parton interactions
PT(hard)
Initial-State Radiation
Proton
Underlying Event
AntiProton
Underlying Event
 The underlying event in a hard scattering
Final-State
process is a complicated and not very well
Radiation
Outgoing Parton
understood object. It is an interesting
RunII
I CDF
Run
CDF
region since it probes the interface
Compares 630 GeV
“Evolution
of
Charged
“Evolution of Jets”
between perturbative and nonwith 1.8 TeV!
RickParticle
Field Jets
Charged
perturbative physics.
Stuart
andDavid
Calorimeter
Jets”
 There are now four CDF analyses which
Rich Field
Haas
Rick
quantitatively study the underlying event Run I CDF
and compare with the QCD Monte-Carlo “Cone Analysis”
models (2 Run I and 2 Run II).
Valeria Tano
Run II CDF
Eve Kovacs
 It is important to model this region well
“Jet Shapes & Energy Flow”
since it is an unavoidable background to
Joey Huston
all collider observables. Also, we need a
Mario Martinez
Anwar Bhatti
good model of “min-bias” collisions.
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Page 8
“Underlying Event”
as defined by “Charged particle Jets”
Look at the charged
particle density in the
“transverse” region!
Charged Particle  Correlations
PT > 0.5 GeV/c |h| < 1
Charged Jet #1
“Transverse” regionDirection
is
very sensitive to the
“underlying event”!
“jet”
(always)
Toward-side
“Toward-Side”
Jet

2p
Charged Jet #1
Direction

Away Region
Transverse
Region
“Toward”
“Toward”

“Transverse”
“Transverse”
“Transverse”
Leading
ChgJet
“Transverse”
Toward Region
“Away”
Transverse
Region
“Away”
“Away-Side” Jet
Away-side “jet”
(sometimes)
Away Region
Perpendicular to the plane of the
2-to-2 hard scattering
0
-1
h
+1
 Look at charged particle correlations in the azimuthal angle  relative to the leading


charged particle jet.
o
o
o
o
Define || < 60 as “Toward”, 60 < || < 120 as “Transverse”, and || > 120 as
“Away”.
o
All three regions have the same size in h- space, hx = 2x120 = 4p/3.
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Page 9
Run 1 Charged Particle Density
“Transverse” PT Distribution
"Transverse" Charged Particle Density: dN/dhd
Charged Particle Density
Charged Particle Jet #1
Direction
"Transverse"
PT(chgjet#1) > 5 GeV/c
1.0E+00
CDF Min-Bias
CDF Run 1
CDF JET20
data uncorrected
0.75
0.50
Factor of 2!
0.25
1.8 TeV |h|<1.0 PT>0.5 GeV/c
0.00
0
5
10
15
20
25
30
35
40
45
PT(charged jet#1) (GeV/c)
PT(charged jet#1) > 30 GeV/c
“Transverse” <dNchg/dhd> = 0.56
“Min-Bias”
50
Charged Density dN/dhddPT (1/GeV/c)
"Transverse" Charged Density
1.00
CDF Run 1
data uncorrected
1.0E-01
“Toward”
"Transverse"
PT(chgjet#1) > 30 GeV/c
1.0E-02
“Transverse”
“Transverse”
1.0E-03
“Away”
1.0E-04
Min-Bias
1.0E-05
1.8 TeV |h|<1 PT>0.5 GeV/c
1.0E-06
CDF Run 1 Min-Bias data
<dNchg/dhd> = 0.25
0
2
4
6
8
10
12
14
PT(charged) (GeV/c)
 Compares the average “transverse” charge particle density with the average “Min-Bias”
charge particle density (|h|<1, PT>0.5 GeV). Shows how the “transverse” charge particle
density and the Min-Bias charge particle density is distributed in PT.
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Page 10
ISAJET 7.32
“Transverse” Density
ISAJET uses a naïve leading-log
parton shower-model which does
not agree with the data!
Charged Jet #1
Direction
1.00

“Transverse”
“Transverse”
“Away”
CDF Run 1 Data
"Transverse" Charged Density
“Toward”
Isajet
data uncorrected
theory corrected
0.75
IS Radiation
0.50
0.25
"Remnants"
Jets + FS
Beam-Beam
Remnants
ISAJET
"Transverse" Charged Particle Density: dN/dhd
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
5
10
15
20
25
30
35
40
45
50
Initial-State
Radiation
PT(charged jet#1) (GeV/c)
 Compares the average “transverse” charge particle density (|h|<1, PT>0.5 GeV) versus PT(charged
jet#1) and the PT distribution of the “transverse” density, dNchg/dhddPT 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.
MC Tools for the LHC
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Rick Field - Florida/CDF
Page 11
ISAJET 7.32
“Transverse” Density
ISAJET uses a naïve leading-log
parton shower-model which does
not agree with the data!
1.00

“Transverse”
“Transverse”
“Away”
CDF Run 1Data
"Transverse" Charged Density
“Toward”
ISAJET
"Transverse" Charged Particle Density: dN/dhd
Charged Jet #1
Direction
Isajet
data uncorrected
theory corrected
0.75
"Hard"
0.50
0.25
“Hard”
Component
"Remnants"
1.8 TeV |h|<1.0 PT>0.5 GeV
Beam-Beam
Remnants
0.00
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV/c)
 Plot shows average “transverse” charge particle density (|h|<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).
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Rick Field - Florida/CDF
Page 12
HERWIG 6.4
“Transverse” Density

“Toward”
“Transverse”
“Transverse”
“Away”
1.00
1.00
CDF Run 1Data
CDF
"Transverse" Charged Density
Charged Jet #1
Direction
HERWIG uses a modified leadinglog parton shower-model which
does agrees better with the data!
"Transverse"
"Transverse"Charged
ChargedParticle
ParticleDensity:
Density:dN/dhd
dN/dhd
Isajet
Total
"Hard"
data uncorrected
theory corrected
0.75
0.75
"Hard"
0.50
0.50
0.25
0.25
"Remnants"
"Remnants"
Beam-Beam
Remnants
HERWIG
Herwig 6.4 CTEQ5L
PT(hard) > 3 GeV/c
1.8TeV
TeV|h|<1.0
|h|<1.0PT>0.5
PT>0.5GeV
GeV
1.8
0.00
0.00
0
5
10
10
15
15
20
20
25
25
30
30
3535
PT(chargedjet#1)
jet#1) (GeV/c)
(GeV/c)
PT(charged
4040
4545
5050
“Hard”
Component
 Plot shows average “transverse” charge particle density (|h|<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).
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Page 13
HERWIG 6.4
“Transverse” PT Distribution
HERWIG has the too steep of a PT
dependence of the “beam-beam remnant”
"Transverse" Chargedcomponent
Particle Density:
dN/dhd
of the
“underlying event”!
"Transverse" Charged Particle Density
Charged Jet #1
Direction
CDF Data
"Hard"
Total
data uncorrected
theory corrected
0.75
1.0E+00
Herwig 6.4 CTEQ5L
PT(hard) > 3 GeV/c

0.50
0.25
"Remnants"
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
5
10
CDF Data
PT(chgjet#1) > 5 GeV/c
15
20
25
30
35
40
45
PT(charged jet#1) (GeV/c)
Herwig PT(chgjet#1) > 30 GeV/c
“Transverse” <dNchg/dhd> = 0.51
50
Charged Density dN/dhddPT (1/GeV/c)
"Transverse" Charged Density
1.00
data uncorrected
theory corrected
1.0E-01
“Toward”
1.8 TeV |h|<1 PT>0.5 GeV/c
1.0E-02
“Transverse”
1.0E-03
“Transverse”
“Away”
1.0E-04
1.0E-05
PT(chgjet#1) > 30 GeV/c
Herwig 6.4 CTEQ5L
1.0E-06
Herwig PT(chgjet#1) > 5 GeV/c
<dNchg/dhd> = 0.40
0
2
4
6
8
10
12
14
PT(charged) (GeV/c)
 Compares the average “transverse” charge particle density (|h|<1, PT>0.5 GeV) versus
PT(charged jet#1) and the PT distribution of the “transverse” density, dNchg/dhddPT 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.
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Page 14
MPI: Multiple Parton
Interactions
“Hard”
Collision
Multiple
Parton
Interaction
outgoing parton
“Hard” Component
“Semi-Hard” MPI
“Soft” Component
AntiProton
Proton
initial-state radiation
initial-state radiation
outgoing parton
final-state radiation
or
+
outgoing jet
final-state radiation
 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”.
Beam-Beam Remnants
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).
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Page 15
PYTHIA: Multiple Parton
Interaction Parameters
Multiple Parton Interactions
Outgoing Parton
PT(hard)
Proton
AntiProton
Underlying Event
Underlying Event
ParameterOutgoingValue
Parton
MSTP(81)
MSTP(82)
Same parameter that
cuts-off the hard 2-to-2
parton cross sections!
Pythia uses multiple parton
interactions to enhance
the underlying event.
Description
0
Multiple-Parton Scattering off
1
Multiple-Parton Scattering on
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 turnoff 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)
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and now
HERWIG
!
Jimmy: MPI
J. M. Butterworth
J. R. Forshaw
M. H. Seymour
Multiple parton
interaction more
likely in a hard
(central) collision!
Hard Core
Page 16
Tuning PYTHIA:
Multiple 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.
Multiple Parton Interaction
Color String
Color String
PARP(86)
0.33
0.66
PARP(89)
1 TeV
PARP(90)
0.16
PARP(67)
1.0
MC Tools for the LHC
CERN July 31, 2003
Probability that the MPI produces two gluons
with color connections to the “nearest neighbors.
Multiple PartonDetermine
Interactionby comparing
with 630 GeV data!
Probability that the MPI produces two gluons
either as described by PARP(85) or as a closed
gluon
loop.
remaining
fraction consists of
Affects
the The
amount
of
quark-antiquark
pairs.
initial-state radiation!
Color String
Hard-Scattering Cut-Off PT0
5
Determines the reference energy E0.
Determines the energy dependence of the cut-off
PT0 as follows PT0(Ecm) = PT0(Ecm/E0)e with
e = PARP(90)
A scale factor that determines the maximum
parton virtuality for space-like showers. The
larger the value of PARP(67) the more initialstate radiation.
Rick Field - Florida/CDF
PYTHIA 6.206
e = 0.25 (Set A))
4
PT0 (GeV/c)
PARP(85)
Take E0 = 1.8 TeV
3
2
e = 0.16 (default)
1
100
1,000
10,000
100,000
CM Energy W (GeV)
Reference point
at 1.8 TeV
Page 17
PYTHIA 6.206 Defaults
MPI constant
probability
scattering
PYTHIA default parameters
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
4.0
1.0
1.0
PARP(67)
4.0
1.00
"Transverse" Charged Density
Parameter
"Transverse" Charged Particle Density: dN/dhd
CDF Data
Pythia 6.206 (default)
MSTP(82)=1
PARP(81) = 1.9 GeV/c
data uncorrected
theory corrected
0.75
0.50
0.25
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV/c)
CTEQ3L
CTEQ4L
CTEQ5L
CDF Min-Bias
CDF JET20
 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.
Note Change
PARP(67) = 4.0 (< 6.138)
PARP(67) = 1.0 (> 6.138)
MC Tools for the LHC
CERN July 31, 2003
Default parameters give
very poor description of
the “underlying event”!
Rick Field - Florida/CDF
Page 20
Tuned PYTHIA 6.206
Tune A CDF
Double
Gaussian
Run 2 Default!
PYTHIA 6.206 CTEQ5L
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
New PYTHIA default
(less initial-state radiation)
MC Tools for the LHC
CERN July 31, 2003
1.00
"Transverse" Charged Density
Parameter
"Transverse" Charged Particle Density: dN/dhd
CDF Preliminary
PYTHIA 6.206 (Set A)
PARP(67)=4
data uncorrected
theory corrected
0.75
0.50
0.25
CTEQ5L
PYTHIA 6.206 (Set B)
PARP(67)=1
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV/c)
 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)).
Old PYTHIA default
(more initial-state radiation)
Rick Field - Florida/CDF
Page 21
Azimuthal Correlations
PYTHIA Tune A
(more initial-state radiation)
PYTHIA Tune B
(less initial-state radiation)
b-quark Correlations: Azimuthal  Distribution
b-quark Correlations: Azimuthal  Distribution
0.01000
0.01000
1.8 TeV
PT1 > 15 GeV/c
PT2 > 10 GeV/c
|y1| < 1 |y2| < 1
PYTHIA 6.206
CTEQ5L PARP(67)=1
ds/d (mb/deg)
ds/d (mb/deg)
1.8 TeV
PT1 > 15 GeV/c
PT2 > 10 GeV/c
|y1| < 1 |y2| < 1
0.00100
0.00010
0.00100
0.00010
"Away"
"Toward"
"Away"
"Toward"
PYTHIA 6.206
CTEQ5L PARP(67)=4
0.00001
0.00001
0
30
60
90
120
150
180
0
30
60
 (degrees)
PY62 (67=1) Total
Flavor Creation
Flavor Excitation
90
120
150
180
 (degrees)
Shower/Fragmentation
PY62 (67=4) Total
Flavor Creation
Flavor Excitation
Shower/Fragmentation
b-quark
direction

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 ds/d (mb/o)
for flavor creation, flavor excitation, shower/fragmentation,
and the resulting total.
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF

“Toward”
“Away”
bbar-quark
Page 22
Azimuthal Correlations
PYTHIA Tune A
(more initial-state radiation)
b-quark Correlations: Azimuthal  Distribution
b-quark Correlations: Azimuthal  Distribution
0.01000
0.010000
1.8 TeV
PT1 > 15 GeV/c
PT2 > 10 GeV/c
|y1| < 1 |y2| < 1
HERWIG 6.4
CTEQ5L
0.001000
0.00100
ds/d (mb/deg)
ds/d (mb/deg)
1.8 TeV
PT1 > 15 GeV/c
PT2 > 10 GeV/c
|y1| < 1 |y2| < 1
0.00010
"Flavor Creation"
CTEQ5L
HERWIG 6.4
0.000100
PYTHIA 6.206
PARP(67)=4
PYTHIA 6.206
PARP(67)=1
0.000010
"Away"
"Toward"
0.00001
30
60
90
120
150
180
 (degrees)
HW64 Total

"Away"
"Toward"
0
Flavor Creation
Flavor Excitation
0.000001
0
30
60
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
ds/d (mb/o) for flavor creation, flavor
excitation, shower/fragmentation, and the
resulting total.
90
120
150
180
 (degrees)
Shower/Fragmentation
b-quark
direction
PYTHIA Tune B
(less initial-state radiation)

“Toward”
“Away”
“Flavor Creation”
bbar-quark
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 23
DiPhoton Correlations
DiPhoton Correlations: Azimuthal  Distribution
Diphoton System Transverse Momentum
0.25
0.14
PYC5 DiPhoton PARP(67)=1
PYC5 DiPhoton PARP(67)=4
PYC5 DiPhoton PARP(67)=4
0.20
PYC5 DiPhoton PARP(67)=1
CDF DiPhoton Data
New Pythia
1.8 TeV PT > 12 GeV |h| < 0.9
1/s ds/d (1/deg)
1/s ds/dPT (1/GeV/c)
0.12
CDF DiPhoton Data
Old Pythia
0.15
0.10
0.10
New Pythia
1.8 TeV PT > 12 GeV |h| < 0.9
Old Pythia
0.08
0.06
0.04
0.05
0.02
0.00
0.00
0
2
4
6
8
10
12
14
16
18
90

105
120
135
150
165
180
 (degrees)
Diphoton System PT (GeV/c)
Predictions of PYTHIA 6.158 (CTEQ5L) with
PARP(67)=1 (new default) and PARP(67)=4 (old default)
for diphoton system PT and the azimuthal angle, ,
between a photon with PT1 > 12 GeV/c, |y1| < 0.9 and
photon with PT2 > 12 GeV/c, |y2|< 0.9 in protonantiproton collisions at 1.8 TeV compared with CDF data.
Photon
direction

“Toward”
“Away”
Photon
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 24
Tuned PYTHIA 6.206
“Transverse” PT Distribution
"Transverse" Charged Particle Density
"Transverse" Charged Particle Density: dN/dhd
1.0E+00
CDF Preliminary
PYTHIA 6.206 (Set A)
PARP(67)=4
data uncorrected
theory corrected
0.75
CDF Data
0.50
0.25
CTEQ5L
PYTHIA 6.206 (Set B)
PARP(67)=1
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
5
10
15
20
25
30
35
40
45
PT(charged jet#1) (GeV/c)
PT(charged jet#1) > 30 GeV/c
50
Charged Density dN/dhddPT (1/GeV/c)
"Transverse" Charged Density
1.00
PT(chgjet#1) > 30 GeV/c
1.0E-01
data uncorrected
theory corrected
PYTHIA 6.206 Set A
PARP(67)=4
1.0E-02
1.0E-03
1.0E-04
PT(chgjet#1) > 5 GeV/c
1.0E-05
PYTHIA 6.206 Set B
PARP(67)=1
1.8 TeV |h|<1 PT>0.5 GeV/c
PARP(67)=4.0 (old default) is favored
over PARP(67)=1.0 (new default)!
1.0E-06
0
Can we distinguish between
2
4
6
8
10
12
PARP(67)=1
and
PARP(67)=4?
PT(charged)
(GeV/c)
No way! Right!
14
 Compares the average “transverse” charge particle density (|h|<1, PT>0.5 GeV) versus
PT(charged jet#1) and the PT distribution of the “transverse” density, dNchg/dhddPT 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)).
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 25
Tuned PYTHIA 6.206
Run 1 Tune A
Describes the rise
from “Min-Bias” to
1.0E+00
“underlying event”!
"Transverse" Charged Particle Density: dN/dhd
1.00
PYTHIA 6.206 Set A
data uncorrected
theory corrected
0.75
0.50
0.25
1.8 TeV |h|<1.0 PT>0.5 GeV/c
0.00
0
5
10
15
20
25
30
35
40
45
PT(charged jet#1) (GeV/c)
Charged Particle Density: dN/dhd
1.0
CDF Published
dN/dhd
“Min-Bias”
50
Set A PT(charged jet#1) > 30 GeV/c
“Transverse” <dNchg/dhd> = 0.60
0.8
0.6
PYTHIA 6.206 Set A
CDF Run 1
Charged Density dN/dhddPT (1/GeV/c)
"Transverse" Charged Density
CDF Run 1
Charged Particle Density
data uncorrected
theory corrected
"Transverse"
PT(chgjet#1) > 5 GeV/c
1.0E-01
"Transverse"
PT(chgjet#1) > 30 GeV/c
1.0E-02
1.0E-03
1.0E-04
CDF Min-Bias
CTEQ5L
1.8 TeV |h|<1 PT>0.5 GeV/c
0.4
1.0E-05
Set A Min-Bias
<dNchg/dhd> = 0.24
0
0.2
2
4
6
8
10
12
14
Pythia 6.206 Set A
1.8 TeV all PT
CDF Min-Bias 1.8 TeV
PT(charged) (GeV/c)
0.0
-4
-3
-2
-1
0
1
2
3
4
Pseudo-Rapidity h
 Compares the average “transverse” charge particle density (|h|<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). Describes “Min-Bias” collisions! Describes the “underlying event”!
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 27
“Transverse”
Charged Particle Density
“Transverse” region as
defined by the leading
“charged particle jet”
“Toward”
“Transverse”
“Transverse”
“Away”
1.25
1.25
1.25
"Transverse"Charged
ChargedDensity
Density
Charged
Density
"Transverse"
"Transverse"
Charged Particle Jet #1
Direction

"Transverse"
"Transverse" Charged
Charged Particle
Particle
Density:
dN/dhd
Particle Density:
Density: dN/dhd
dN/dhd
CDF Run 1 Min-Bias
CDFRun
Run11Published
Min-Bias
CDF
CDF
Run
1 JET20
CDF
Run
1 Published
CDFRun
Run21Preliminary
JET20
CDF
CDF Run 2 Preliminary
PYTHIA
Tune
CDF
RunA2
CDFPreliminary
Run 1 Data
CDF
CDF
Preliminary
CDFdata
Preliminary
uncorrected
1.00
1.00
1.00
data
uncorrected
data
uncorrected
data
uncorrected
theory corrected
0.75
0.75
0.75
0.50
0.50
0.25
0.25
1.8
TeV
|h|<1.0
PT>0.5
GeV
|h|<1.0
|h|<1.0
PT>0.5
PT>0.5
GeV/c
GeV/c
|h|<1.0
PT>0.5
GeV
0.00
0.00
00
10 5 20
10
30
30
40
4015 50
50
20
60
60
70
702580
80
30
40 130
50
90
90 100
10035110
110 120
120
13045140
140 150
150
PT(charged
PT(charged jet#1)
jet#1) (GeV/c)
(GeV/c)
(GeV/c)
Excellent agreement
between Run 1 and 2!
 Shows the data on the average “transverse” charge particle density (|h|<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 Tune
correlated
PYTHIA
A was tuned to fit
the “underlying event” in Run I!
systematic uncertainties.
Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after
CDFSIM).
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 30
“Transverse”
Charged PTsum Density
“Transverse” region as
defined by the leading
“charged particle jet”
“Toward”
“Transverse”
“Transverse”
“Away”
"Transverse"
PTsum
Density
(GeV)
"Transverse"
"Transverse"PTsum
PTsumDensity
Density(GeV/c)
(GeV)
Charged Particle Jet #1
Direction

"Transverse" Charged
Charged PTsum
PTsum Density: dPTsum
sum/dhd
"Transverse"
1.25
1.25
1.25
CDFPreliminary
Preliminary
CDF
CDF
Run
1 Data
CDF JET20
CDF Min-Bias
data
uncorrected
data
datauncorrected
uncorrected
1.00
1.00
1.00
theory corrected
0.75
0.75
0.75
CDF Run
1Run
Published
CDF
2
CDF Run
1 Published
CDF Run 2 Preliminary
CDF
CDF
RunJET20
2 Preliminary
PYTHIA Tune A
CDF Min-Bias
0.50
0.50
0.50
0.25
0.25
0.25
|h|<1.0
PT>0.5
|h|<1.0GeV
PT>0.5GeV
GeV/c
1.8 TeV |h|<1.0 PT>0.5
0.00
0.00
0.00
000
10 5 20
20
10
30
30
10
40
4015 50
50
60
60
20
70
70 2580
80
90
140
90
10035110
110 120
120
130 45
140 150
150
30 100
40 130
50
PT(charged
PT(charged jet#1)
jet#1) (GeV/c)
(GeV/c)
 Shows the
Excellent agreement
between
Run average
1 and 2!
data
on the
“transverse” charged PTsum density (|h|<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
PYTHIA
Tune A was
tuned to fit
the “underlying event” in Run I!
uncertainties.
 Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after
CDFSIM).
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 31
Charged Particle Density
“Transverse” PT Distribution
"Transverse" Charged Particle Density: dN/dhd
Charged Particle Density
CDF Run 1 Min-Bias
CDF
Run
11
Published
CDF
Run
JET20
CDF Run 2 Preliminary
CDF Run 2
CDF Preliminary
Preliminary
CDF
datauncorrected
uncorrected
data
1.00
0.75
0.50
0.25
|h|<1.0
PT>0.5
|h|<1.0
PT>0.5
GeV GeV/c
0.00
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
 Compares the average “transverse”
charge particle density (|h|<1, PT>0.5
GeV) versus PT(charged
jet#1)agreement
with the
Excellent
PT distribution of the between
“transverse”
Run 1 and 2!
density, dNchg/dhddPT. Shows how the
“transverse” charge particle density is
distributed in PT.
MC Tools for the LHC
CERN July 31, 2003
1.0E+00
1.0E+00
"Transverse"
PT(chgjet#1) > 30 GeV/c
1.0E-01
1.0E-01
Charged Density
(1/GeV/c)
Density dN/dhddPT
dN/dhddPT (1/GeV/c)
Charged
"Transverse"
"Transverse" Charged
Charged Density
Density
1.25
Run 1
Preliminary
CDF CDF
uncorrected
datadata
uncorrected
uncorrected
data
"Transverse"
Run 2 Min-Bias Preliminary
PT(chgjet#1) > 30 GeV/c
Run 1 Min-Bias Preliminary
1.0E-02
1.0E-02
Run 2 Preliminary
Run 1 Published
1.0E-03
1.0E-03
1.0E-04
1.0E-04
1.0E-05
1.0E-05
Min-Bias
1.0E-06
1.0E-06
Charged
Charged Particles
Particles |h|
|h| << 1.0
1.0
1.0E-07
1.0E-07
00
22
44
66
88
10
10
12
12
14
14
16
16
18
18
20
20
PT(charged) (GeV/c)
 Compares the Run 2 data (Min-Bias,
JET20, JET50, JET70, JET100) with
Run 1.
Rick Field - Florida/CDF
Page 32
Charged Particle Density
“Transverse” PT Distribution
"Transverse" Charged Particle Density: dN/dhd
"Transverse" Charged Particle Density
1.0E+00
CDF Preliminary
CDF
Run
Published
CDF
Run
11
Published
CDF
Run
Preliminary
CDF
Run
22
Preliminary
PYTHIA Tune A
data uncorrected
uncorrected
data
theory corrected
1.00
0.75
0.50
0.25
|h|<1.0
PT>0.5
GeV/c
|h|<1.0
PT>0.5
GeV/c
0.00
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
CDF Preliminary
Charged Density dN/dhddPT (1/GeV/c)
"Transverse" Charged
Charged Density
Density
"Transverse"
1.25
data uncorrected
theory corrected
1.96 TeV |h|<1.0
1.0E-01
PYTHIA Tune A 1.96 TeV
70 < PT(chgjet#1) < 95 GeV/c
1.0E-02
1.0E-03
1.0E-04
70 < PT(charged jet#1) > 95 GeV/c
“Transverse” <dNchg/dhd> = 0.62
30 < PT(chgjet#1) < 70 GeV/c
1.0E-05
30 < PT(charged jet#1) < 50 GeV/c
“Transverse” <dNchg/dhd> = 0.59
0
2
4
6
8
10
12
14
16
18
20
PT(charged) (GeV/c)
 Compares the average “transverse” charge particle density (|h|<1, PT>0.5 GeV) versus
PT(charged jet#1) with the PT distribution of the “transverse” density, dNchg/dhddPT.
 Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after
CDFSIM).
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 33
“Underlying Event”
as defined by “Calorimeter Jets”
JetClu Jet #1
Charged Particle  Correlations
Direction
PT > 0.5 GeV/c |h| < 1
“Transverse” region is
2p
very sensitive to the
JetClu Jet #1
“Toward-Side” Jet
“underlying event”!
Direction

“Toward”
Look at the charged
particle density in the
“transverse” region!
Away Region

Transverse
Region
“Toward”

“Transverse”
“Transverse”
“Transverse”
Leading
Jet
“Transverse”
Toward Region
“Away”
Transverse
Region
“Away”
“Away-Side” Jet
Away-side “jet”
(sometimes)
Away Region
Perpendicular to the plane of the
2-to-2 hard scattering
0
-1
h
+1
 Look at charged particle correlations in the azimuthal angle  relative to the leading


JetClu jet.
o
o
o
o
Define || < 60 as “Toward”, 60 < || < 120 as “Transverse”, and || > 120 as
“Away”.
o
All three regions have the same size in h- space, hx = 2x120 = 4p/3.
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 34
“Transverse”
Charged Particle Density


“Toward”
“Toward”
“Transverse”
“Transverse”
“Transverse”
“Transverse”
“Away”
“Away”
"Transverse"
Charged Particle
Particle Density: dN/dhd
"Transverse" Charged
1.00
1.00
1.00
Density
"Transverse"
"Transverse" Charged
Charged Density
Density
JetClu Jet #1
JetClu
Jet #1
or
ChgJet#1
Direction
Direction
“Transverse” region as
defined by the leading
“calorimeter jet”
CDF
CDF
Preliminary
CDFPreliminary
CDF
data Preliminary
uncorrected
data
data uncorrected
uncorrected
data uncorrected
theory
theorycorrected
corrected
0.75
0.75
0.75
PYTHIA Tune A
JetCluJetClu
Jet#1 (R
= 0.7,
Jet#1
(R |h(jet)|<2)
= 0.7,|h(jet)|<2)
CDF Run 2 Preliminary
0.50
0.50
ChgJet#1 R = 0.7
PYTHIA
Tune A 1.96
JetClu (R
= 0.7, |h(jet#1)|
< 2)TeV
ChgJet#1 R = 0.7
0.25
0.25
Charged
Particles
(|h|<1.0,
PT>0.5
GeV/c)
Charged
Particles
(|h|<1.0,
PT>0.5
GeV/c)
Charged
Particles
(|h|<1.0,
PT>0.5
GeV/c)
0.00
0.00
00
25
25
50
50
75
75
100
100
125
125
150
150
175
175
200
225
250
ET(jet#1)
(GeV) (GeV)
PT(chgjet#1)
or ET(jet#1)
 Shows the data on the average “transverse” charge particle density (|h|<1, PT>0.5 GeV)
as a function of the transverse energy of the leading JetClu jet (R = 0.7, |h(jet)| < 2)
from Run 2., compared with PYTHIA Tune A after CDFSIM.
 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.
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 35
“Transverse”
Charged PTsum Density
“Transverse” region as
defined by the leading
“calorimeter jet”
"Transverse" Charged PTsum Density: dPTsum/dhd
JetClu Jet #1
JetClu
Jet #1
or ChgJet#1
Direction

“Toward”
“Transverse”
“Transverse”
“Transverse”
“Away”
"Transverse"
"Transverse" PTsum
PTsum Density
Density (GeV/c)
(GeV/c)
1.5
CDF Preliminary
CDF
Preliminary
data uncorrected
data
uncorrected
theory
corrected
1.0
JetClu Jet#1 (R = 0.7,|h(jet)|<2)
JetClu Jet#1 (R = 0.7,|h(jet)|<2)
0.5
PYTHIA Tune A
ChgJet#1 RR= =0.7
0.7
CDF ChgJet#1
Run 2 Preliminary
PYTHIA Tune A 1.96 TeV
JetClu (R = 0.7, |h(jet#1)| < 2)
Charged Particles
Particles (|h|<1.0,
(|h|<1.0, PT>0.5
PT>0.5 GeV/c)
GeV/c)
Charged
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
25
50
75
100
125
150
175
200
225
250
PT(chgjet#1)
or ET(jet#1)
ET(jet#1)
(GeV) (GeV)
 Shows the data on the average “transverse” charged PTsum density (|h|<1, PT>0.5
GeV) as a function of the transverse energy of the leading JetClu jet (R = 0.7, |h(jet)| <
2) from Run 2., compared with PYTHIA Tune A after CDFSIM.
 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.
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 36
Charged Particle Density
“Transverse” PT Distribution
"Transverse" Charged Particle Density: dN/dhd
"Transverse" Charged Particle Density
CDF Preliminary
CDF Preliminary
CDF Run 2 Preliminary
data uncorrected
theory corrected
0.75
1.0E+00
PYTHIA Tune A
0.50
JetClu (R = 0.7, |h(jet#1)| < 2)
0.25
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.00
0
25
50
data uncorrected
theory corrected
JetClu R = 0.7 |h(jet)| < 2
75
100
125
150
175
200
225
250
ET(jet#1) (GeV)
Charged Density dN/dhddPT (1/GeV/c)
"Transverse" Charged Density
1.00
1.0E-01
PYTHIA Tune A 1.96 TeV
1.0E-02
95 < ET(jet#1) < 130 GeV
1.0E-03
1.0E-04
1.0E-05
30 < ET(jet#1) < 70 GeV
95 < ET(jet#1) > 130 GeV
“Transverse” <dNchg/dhd> = 0.65
Charged Particles |h| < 1.0
1.0E-06
0
30 < ET(jet#1) < 70 GeV/c
“Transverse” <dNchg/dhd> = 0.61
5
10
15
20
25
PT(charged) (GeV/c)
 Compares the average “transverse” charge particle density (|h|<1, PT>0.5 GeV) versus
ET(jet#1) with the PT distribution of the “transverse” density, dNchg/dhddPT.
 Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after
CDFSIM).
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 37
Charged Particle Density
“Transverse” PT Distribution
"Transverse" Charged Particle Density: dN/dhd
"Transverse" Charged Particle Density
CDF Preliminary
CDF
Preliminary
data uncorrected
1.0E+00
Jet#1
(R|h(jet)|<2)
= 0.7,|h(jet)|<2)
JetClu JetClu
Jet#1 (R
= 0.7,
CDF Preliminary
data uncorrected
theory
corrected
0.75
0.50
PYTHIA Tune A 1.96 TeV
ChgJet#1 R = 0.7
ChgJet#1 R = 0.7
0.25
Charged Particles
Particles (|h|<1.0,
(|h|<1.0, PT>0.5
PT>0.5 GeV/c)
GeV/c)
Charged
0.00
0
25
50
75
100
125
150
175
200
PT(chgjet#1) or ET(jet#1) (GeV)
30 < PT(charged jet#1) < 50 GeV/c
“Transverse” <dNchg/dhd> = 0.59
30 < ET(jet#1) < 70 GeV/c
“Transverse” <dNchg/dhd> = 0.61
225
250
"Transverse" Density dN/dhddPT (1/GeV/c)
"Transverse" Charged Density
1.00
data uncorrected
theory corrected
1.0E-01
1.96 TeV
PYTHIA Tune A 1.96 TeV
1.0E-02
30 < PT(chgjet#1) < 70 GeV/c
1.0E-03
1.0E-04
30 < ET(jet#1) < 70 GeV
1.0E-05
Charged Particles |h| < 1.0
1.0E-06
0
5
10
15
20
25
PT(charged) (GeV/c)
 Compares the average “transverse” as defined by “calorimeter jets” (JetClu R = 0.7) with the
“transverse” region defined by “charged particle jets”.
 Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after
CDFSIM).
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 38
Relationship Between
“Calorimeter” and “Charged Particle” Jets
PT(chgjet#1)/ET(matched jet) vs PT(chgjet#1)
ET(matched jet) vs PT(charged jet#1)
1.2
160
CDF Preliminary
140
data uncorrected
theory corrected
120
PYTHIA Tune A
100
CDF Run 2 Preliminary
80
60
JetClu (R = 0.7, |h(jet#1)| < 2)
40
PT(chgjet#1)/ET(matched jet)
Matched Jet ET (GeV)
180
1.0
0.8
PYTHIA Tune A
CDF Run 2 Preliminary
0.6
data uncorrected
theory corrected
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
20
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.2
0
0
10
20
30
40
50
60
70
80
90
0
100 110 120 130 140 150
10
20
30
40
60
70
80
90
100 110 120 130 140 150
versus the transverse momentum of the
leading “charged particle jet” (closest
jet within R = 0.7 of the leading chgjet).
The leading
chgjet
from a
Shows the EM
fraction
of comes
the “matched”
JetClu jet that is, on the average,
JetClu jet and the
EM
fraction
about
90%
charged!of a
"Calorimeter Jet" EM Fraction
 Shows the
ratio of PT(chgjet#1) to the
0.8
Electromagnetic Fraction
 Shows the “matched” JetClu jet ET
typical JetClu jet.
50
PT(charged jet#1) (GeV/c)
PT(charged jet#1) (GeV/c)

JetClu (R = 0.7, |h(jet#1)| < 2)
CDF Preliminary
0.4
0.7
0.6
PYTHIA Tune A 1.96 TeV
CDF Preliminary
“matched”
JetClu jet ET versus
PT(chgjet#1).
Leading Jet
|h(jet)| < 0.7
data uncorrected
theory corrected
0.5
0.4
Jet matching
ChgJet#1
0.3
JetClu R = 0.7
0.2
0
25
50
75
100
125
150
175
200
225
250
PT(chgjet#1) or ET(jet#1) (GeV)
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 39
Tuned PYTHIA (Set A)
LHC Predictions
"Transverse" Charged PTsum Density: dPTsum/dhd
"Transverse" Charged Particle Density: dN/dhd
2.5
3.0
"Transverse" PTsum Density (GeV)
"Transverse" Charged Density
HERWIG 6.4
14 TeV
2.5
2.0
1.5
1.8 TeV
1.0
PYTHIA 6.206 Set A
0.5
CTEQ5L
|h|<1.0 PT>0 GeV
PYTHIA 6.206 Set A
2.0
14 TeV
Factor of 2!
HERWIG 6.4
1.5
1.0
1.8 TeV
0.5
CTEQ5L
|h|<1.0 PT>0 GeV
0.0
0.0
0
5
10
15
20
25
30
35
40
45
50
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV/c)
PT(charged jet#1) (GeV/c)
 Shows the average “transverse” charge particle and PTsum density (|h|<1, PT>0) versus
PT(charged jet#1) predicted by HERWIG 6.4 (PT(hard) > 3 GeV/c, CTEQ5L). and a tuned
versions of PYTHIA 6.206 (PT(hard) > 0, CTEQ5L, Set A) at 1.8 TeV and 14 TeV.
 At 14 TeV tuned PYTHIA (Set A) predicts roughly 2.3 charged particles per unit h- (PT > 0)

in the “transverse” region (14 charged particles per unit h) which is larger than the HERWIG
prediction.
At 14 TeV tuned PYTHIA (Set A) predicts roughly 2 GeV/c charged PTsum per unit h- (PT
> 0) in the “transverse” region at PT(chgjet#1) = 40 GeV/c which is a factor of 2 larger than
at 1.8 TeV and much larger than the HERWIG prediction.
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 40
Tuned PYTHIA (Set A)
LHC Predictions
"Transverse" Charged Particle Density: dN/dhd
"Transverse" Charged PTsum Density: dPTsum/dhd
2.5
"Transverse" PTsum Density (GeV)
"Transverse" Charged Density
3.0
PYTHIA 6.206 Set A
2.5
2.0
1.5
HERWIG 6.4
1.0
0.5
CTEQ5L
14 TeV |h|<1.0 PT>0 GeV
0.0
PYTHIA 6.206 Set A
2.0
Big difference!
1.5
1.0
HERWIG 6.4
0.5
CTEQ5L
14 TeV |h|<1.0 PT>0 GeV
0.0
0
10
20
30
40
50
60
70
80
90
100
0
10
PT(charged jet#1) (GeV/c)
20
30
40
50
60
70
80
90
100
PT(charged jet#1) (GeV/c)
 Shows the average “transverse” charge particle and PTsum density (|h|<1, PT>0) versus

PT(charged jet#1) predicted by HERWIG 6.4 (PT(hard) > 3 GeV/c, CTEQ5L). and a tuned
versions of PYTHIA 6.206 (PT(hard) > 0, CTEQ5L, Set A) at 1.8 TeV and 14 TeV. Also
shown is the 14 TeV prediction of PYTHIA 6.206 with the default value e = 0.16.
Tuned PYTHIA (Set A) predicts roughly 2.5 GeV/c per unit h-
(PT > 0) from charged particles in the “transverse” region for
3.8 GeV/c (charged)
PT(chgjet#1) = 100 GeV/c. Note, however, that the “transverse”
in cone of
radius R=0.7
charged PTsum density increases rapidly as PT(chgjet#1)
at 14 TeV
increases.
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 42
Tuned PYTHIA (Set A)
LHC Predictions
Charged Particle Density: dN/dhd
Charged Particle Density: dN/dhd
1.4
1.4
Pythia 6.206 Set A
CDF Data
14 TeV
Charged density dN/dhd
1.0
dN/dhd
Pythia 6.206 Set A
CDF Data
UA5 Data
Fit 2
Fit 1
1.2
1.2
1.8 TeV
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
all PT
630 GeV
1.0
h=0
0.0
-6
-4
-2
0
Pseudo-Rapidity h
2
4
6
LHC?
0.0
10
100
1,000
10,000
100,000
CM Energy W (GeV)
 Shows the center-of-mass energy dependence of the charged particle density, dNchg/dhd,
for “Min-Bias” collisions compared with the a tuned version of PYTHIA 6.206 (Set A) with
PT(hard) > 0.
 PYTHIA was tuned to fit the “underlying event” in hard-scattering processes at 1.8 TeV
and 630 GeV.
 PYTHIA (Set A) predicts a 42% rise in dNchg/dhd at h = 0 in going from the Tevatron (1.8
TeV) to the LHC (14 TeV).
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 43
Tuned PYTHIA (Set A)
LHC Predictions
Charged Particle Density
12% of “Min-Bias” events
50%
have PT(hard) > 10 GeV/c!
1.0E+00
|h|<1
Pythia 6.206 Set A
Hard-Scattering in Min-Bias Events
Pythia 6.206 Set A
40%
% of Events
Charged Density dN/dhddPT (1/GeV/c)
1.0E-01
1.0E-02
PT(hard) > 5 GeV/c
PT(hard) > 10 GeV/c
30%
20%
1.8 TeV
1.0E-03
10%
14 TeV
1.0E-04
0%
100
630 GeV
100,000
LHC?
 Shows the center-of-mass energy
CDF Data
1.0E-06
2
10,000
CM Energy W (GeV)
1.0E-05
0
1,000
4
6
8
PT(charged) (GeV/c)
1% of “Min-Bias” events
have PT(hard) > 10 GeV/c!
10
12
14
dependence of the charged particle density,
dNchg/dhddPT, for “Min-Bias” collisions
compared with the a tuned version of
PYTHIA 6.206 (Set A) with PT(hard) > 0.
 This PYTHIA fit predicts that 1% of all “Min-Bias” events at 1.8 TeV are a result of a hard
2-to-2 parton-parton scattering with PT(hard) > 10 GeV/c which increases to 12% at 14
TeV!
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 44
Summary & Conclusions
Outgoing Parton
PT(hard)
Initial-State Radiation
Proton
AntiProton
Underlying Event
Outgoing Parton
Underlying Event
The “Underlying Event”
Final-State
Radiation
 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!
Also see Mario’s
Run
PYTHIA Tune A does a good job of describing the “underlying
event”
in2 the
flow”
Run 2 data as defined by “charged particle jets” and as“energy
defined
by analysis!
“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”. Also, more to come on the energy in the “underlying
event”!
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 46
LHC Predictions
Summary & Conclusions
Outgoing Parton
PT(hard)
Initial-State Radiation
Proton
AntiProton
Underlying Event


Tevatron
LHC
Underlying Event
12 times more likely
Final-State
Radiation
“Min-Bias” at the LHC contains
to find a 10 GeV
much PYTHIA
more hard (Set
collisions
than at athe
Both HERWIG and the tuned
A) predict
40-45% rise
inindN
“jet”
“Min-Bias”
chg/dhd at h
Tevatron!
At the
Tevatron
at theparticles
LHC!
= 0 in going from the Tevatron
(1.8 TeV)
to the
LHC the
(14 TeV). 4 charged
per
“underlying
event”
is athe
factor
of 2
unit h at the Tevatron becomes
6 per unit
h at
LHC.
more active than “Tevaron Min-Bias”.
Twice as much
The tuned PYTHIA (SetAt
A)the
predicts
that
1% of allevent”
“Min-Bias”
events at the Tevatron
LHC the
“underlying
will
activity in the
(1.8 TeV) are the result of a hard
> 10
be at2-to-2
least a parton-parton
factor of 2 more scattering with PT(hard)
“underlying event”
GeV/c which increases to 12%
at LHC
(14 TeV)!
active
than “LHC
Min-Bias”!
at the LHC!
Outgoing Parton
 For the “underlying event” in hard scattering processes the predictions of HERWIG and

the tuned PYTHIA (Set A) differ greatly (factor of 2!). HERWIG predicts a smaller
increase in the activity of the “underlying event” in going from the Tevatron to the LHC.
The tuned PYTHIA (Set A) predicts about a factor of two increase at the LHC in the
charged PTsum density of the “underlying event” at the same PT(jet#1) (the “transverse”
charged PTsum density increases rapidly as PT(jet#1) increases).
MC Tools for the LHC
CERN July 31, 2003
Rick Field - Florida/CDF
Page 47