“Min-Bias” and the “Underlying Event”
in Run 2 at CDF and the LHC
“Hard”
Scattering
Direct
Photon
Production
Z-boson
Production
Outline of Talk
 Discuss briefly the components of the “underlying
event” of a hard scattering as described by the
QCD parton-shower Monte-Carlo Models.
Photon
Z-boson
Outgoing
Parton
PT(hard)
PT()
PT(Z)
Proton
Proton
Proton
AntiProton
AntiProton
AntiProton
UnderlyingEvent
Event
Underlying
Event
Underlying
UnderlyingEvent
Event
Underlying
Underlying
Event
Initial-State
Initial-State
Initial-State
Radiation
Radiation
Radiation
 Review the CDF Run 1 analysis which was used to tune
OutgoingParton
Parton
Outgoing
Outgoing
Parton
the multiple parton interaction parameters in PYTHIA
(i.e. Tune A and Tune B).
Final-State
Final-State
Final-State
Radiation
Radiation
Radiation
Charged Particle Jet
 Study the “underlying event” in CDF Run 2 as defined
by the leading calorimeter jet and compare with
PYTHIA Tune A (with MPI) and HERWIG (without
MPI).
Calorimeter Jet
 Discuss the universality of PYTHIA Tune A.
Direct Photon Production – Z-boson Production – etc.
 Discuss extrapolations of HERWIG and PYTHIA Tune A
JetClu R = 0.7
to the LHC.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 1
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 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”).
 Clearly? the “underlying event” in a hard scattering process should not look like a “MinBias” event because of the “hard” component (i.e. initial & final-state radiation).
 However, perhaps “Min-Bias” collisions are a 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.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 2
MPI: Multiple Parton
Interactions
“Hard”
Collision
Multiple
Parton
Interaction
outgoing parton
“Hard” Component
“Semi-Hard” MPI
“Soft” Component
AntiProton
Proton
initial-state radiation
outgoing parton
final-state radiation
or
+
initial-state radiation
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).
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 3
The “Transverse” Regions
as defined by the Leading Jet
Jet #1 Direction
“Transverse” region is
very sensitive to the
“underlying event”!
Charged Particle  Correlations
2p
pT > 0.5 GeV/c |h| < 1
Away Region
“Toward-Side” Jet

Look at the charged
particle density in the
“transverse” region!
Jet #1 Direction
Transverse
Region 1

“Toward”
“Toward”
“Transverse”
“Transverse”
“Away”
“Trans 1”

Leading
Jet
“Trans 2”
Toward Region
Transverse
Region 2
“Away”
“Away-Side” Jet
Away Region
0
-1
h
+1
 Look at charged particle correlations in the azimuthal angle relative to the leading

calorimeter jet (JetClu R = 0.7, |h| < 2).
o
o
o
o
o
Define || < 60 as “Toward”, 60 < - < 120 and 60 <  < 120 as “Transverse 1” and
o
“Transverse 2”, and || > 120 as “Away”. Each of the two “transverse” regions have
o
area h = 2x60 = 4p/6. The overall “transverse” region is the sum of the two
o
transverse regions (h = 2x120 = 4p/3).
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 4
Particle Densities
h = 4p = 12.6
2p

31 charged
charged particles
particle
Charged Particles
pT > 0.5 GeV/c |h| < 1
CDF Run 2 “Min-Bias”
CDF Run 2 “Min-Bias”
Observable
Average
Nchg
Number of Charged Particles
(pT > 0.5 GeV/c, |h| < 1)
3.17 +/- 0.31
0.252 +/- 0.025
PTsum
(GeV/c)
Scalar pT sum of Charged Particles
(pT > 0.5 GeV/c, |h| < 1)
2.97 +/- 0.23
0.236 +/- 0.018
Average Density
per unit h-
chg/dhd = 1/4p
3/4p = 0.08
0.24
dNchg
13 GeV/c PTsum
0
-1
h
+1
Divide by 4p
dPTsum/dhd = 1/4p
3/4p GeV/c = 0.08
0.24 GeV/c
 Study the charged particles (pT > 0.5 GeV/c, |h| < 1) and form the charged
particle density, dNchg/dhd, and the charged scalar pT sum density,
dPTsum/dhd.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 5
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
TeV4LHC Fermilab
September 16, 2004
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 7
Tuned PYTHIA 6.206
Double Gaussian
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)
TeV4LHC Fermilab
September 16, 2004
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
Run 1 Analysis
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 9
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
PYTHIA 6.206 (Set B)
PARP(67)=1
CTEQ5L
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)).
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 10
PYTHIA 6.206
Tune A (CDF Default)
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”!
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 11
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)!
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 12
Charged Particle Density
 Dependence Run 2
Charged Particle Density: dN/dhd
Log Scale!
Jet #1 Direction
10.0
30 < ET(jet#1) < 70 GeV

“Toward”
“Transverse”
“Transverse”
Jet #3
“Away”
Charged Particle Density
CDF Preliminary
“Toward-Side” Jet
data uncorrected
"Transverse"
Region
1.0
Jet#1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
“Away-Side”
“Away-Side”
Jet Jet
0.1
0
30
60
90
Min-Bias
0.25 per unit h-
120
150
180
210
 (degrees)
240
270
300
Leading Jet
330
360
 Shows the  dependence of the charged particle density, dNchg/dhd, for charged
particles in the range pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for
“leading jet” events 30 < ET(jet#1) < 70 GeV.
 Also shows charged particle density, dNchg/dhd, for charged particles in the range pT >
0.5 GeV/c and |h| < 1 for “min-bias” collisions.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 13
Refer to this as a
“Leading Jet” event
Charged Particle Density
 Dependence Run 2
Jet #1 Direction

Particle Density:
Density: dN/dhd
dN/dhd
Charged Particle
“Toward”
“Transverse”
CDF Preliminary
“Transverse”
“Away”
Refer to this as a
“Back-to-Back” event
Jet #1 Direction

“Toward”
“Transverse”
Density
Charged Particle Density
Subset
10.0
10.0
data uncorrected
30 << ET(jet#1)
ET(jet#1)<<70
70GeV
GeV
30
Back-to-Back
Leading Jet
Min-Bias
"Transverse"
"Transverse"
Region
Region
1.0
1.0
Jet#1
Jet#1
Charged Particles
Charged
(|h|<1.0, PT>0.5 GeV/c)
(|h|<1.0,
“Transverse”
0.1
0.1
“Away”
00
30
60
90
120
150
180
180
210
210
240
240
270
270
300
300
330
330 360
360
 (degrees)
(degrees)
Jet #2 Direction
 Look at the “transverse” region as defined by the leading jet (JetClu R = 0.7, |h| < 2) or

by the leading two jets (JetClu R = 0.7, |h| < 2). “Back-to-Back” events are selected to
have at least two jets with Jet#1 and Jet#2 nearly “back-to-back” (12 > 150o) with
almost equal transverse energies (ET(jet#2)/ET(jet#1) > 0.8).
Shows the  dependence of the charged particle density, dNchg/dhd, for charged
particles in the range pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for 30
< ET(jet#1) < 70 GeV for “Leading Jet” and “Back-to-Back” events.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 14
“Transverse” PTsum Density
versus ET(jet#1) Run 2
“Leading Jet”
Jet #1 Direction

“Transverse”
“Away”
“Back-to-Back”
Jet #1 Direction

“Toward”
“Transverse”
“Transverse”
"Transverse" PTsum Density (GeV/c)
“Toward”
“Transverse”
"AVE Transverse" PTsum Density: dPT/dhd
1.4
uncorrected
datadata
uncorrected
theory + CDFSIM
PY Tune A
1.0
0.8
0.6
0.4
Back-to-Back
HW
0.2
1.96 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
50
“Away”
Jet #2 Direction
Leading Jet
2 Preliminary
CDF Run
Preliminary
1.2
100
150
200
250
ET(jet#1) (GeV)
Min-Bias
0.24 GeV/c per unit h-
 Shows the average charged PTsum density, dPTsum/dhd, in the “transverse” region (pT
> 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events.
 Compares the (uncorrected) data with PYTHIA Tune A and HERWIG after CDFSIM.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 15
“TransMIN” PTsum Density
versus ET(jet#1)
“Leading Jet”
Jet #1 Direction

"MIN Transverse" PTsum Density: dPT/dhd
“Toward”
“TransMAX”
"Transverse" PTsum Density (GeV/c)
0.6
CDF Run 2 Preliminary
Jet #1 Direction
“TransMIN”
“Away”
1.96 TeV
data uncorrected
theory + CDFSIM

Leading Jet
Jet
Leading
PY Tune A
0.4
“Toward”
“Back-to-Back”
Jet #1 Direction

“Toward”
“TransMAX”
“TransMIN”
“Away”
Jet #2 Direction
“TransMAX”
0.2
“TransMIN”
Min-Bias
“Away”
Back-to-Back
Back-to-Back
HW
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
50
“transMIN” is very sensitive to the
“beam-beam remnant” component
of the “underlying event”!
100
150
200
250
ET(jet#1) (GeV)
 Use the leading jet to define the MAX and MIN “transverse” regions on an event-byevent basis with MAX (MIN) having the largest (smallest) charged particle density.
 Shows the “transMIN” charge particle density, dNchg/dhd, for pT > 0.5 GeV/c, |h| < 1
versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 16
“Transverse” PTsum Density
PYTHIA Tune A vs HERWIG
“Leading Jet”
Jet #1 Direction

"AVE Transverse" PTsum Density: dPT/dhd
“Toward”
“Transverse”
“Transverse”
“Away”
“Back-to-Back”
Jet #1 Direction

“Toward”
“Transverse”
“Transverse”
"Transverse" PTsum Density (GeV/c)
1.4
Leading Jet
CDF Preliminary
1.2
data uncorrected
theory + CDFSIM
PY Tune A
1.0
0.8
0.6
0.4
Back-to-Back
HW
0.2
1.96 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
50
100
150
200
250
ET(jet#1) (GeV)
“Away”
Jet #2 Direction
Now look in detail at “back-to-back” events in
the region 30 < ET(jet#1) < 70 GeV!
 Shows the average charged PTsum density, dPTsum/dhd, in the “transverse” region (pT

> 0.5 GeV/c, |h| < 1) versus ET(jet#1) for “Leading Jet” and “Back-to-Back” events.
Compares the (uncorrected) data with PYTHIA Tune A and HERWIG after CDFSIM.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 17
Charged PTsum Density
PYTHIA Tune A vs HERWIG
HERWIG (without multiple parton
interactions) does not produces
enough PTsum in the “transverse”
region for 30 < ET(jet#1) < 70 GeV!
Charged PTsum Density: dPT/dhd
Charged PTsum Density: dPT/dhd
100.0
Charged Particles
30 < ET(jet#1) < 70 GeV
(|h|<1.0, PT>0.5 GeV/c)
Back-to-Back
PY Tune A
Charged PTsum Density (GeV/c)
Charged PTsum Density (GeV/c)
100.0
10.0
1.0
CDF Preliminary
Jet#1
"Transverse"
Region
data uncorrected
theory + CDFSIM
Charged Particles
30 < ET(jet#1) < 70 GeV
(|h|<1.0, PT>0.5 GeV/c)
Back-to-Back
HERWIG
10.0
"Transverse"
Region
1.0
CDF Preliminary
0.1
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
 (degrees)
150
180
210
240
270
300
330
360
330
360
 (degrees)
Data - Theory: Charged PTsum Density dPT/dhd
Data - Theory: Charged PTsum Density dPT/dhd
2
2
data uncorrected
theory + CDFSIM
1
Back-to-Back
30 < ET(jet#1) < 70 GeV
PYTHIA Tune A
CDF Preliminary
Data - Theory (GeV/c)
CDF Preliminary
Data - Theory (GeV/c)
Jet#1
data uncorrected
theory + CDFSIM
0
-1
"Transverse"
Region
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
data uncorrected
theory + CDFSIM
1
30 < ET(jet#1) < 70 GeV
Back-to-Back
HERWIG
0
-1
"Transverse"
Region
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
Jet#1
Jet#1
-2
-2
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
90
120
150
180
210
240
270
300
 (degrees)
 (degrees)
TeV4LHC Fermilab
September 16, 2004
60
Rick Field - Florida/CDF
Page 18
“Transverse” PTmax
versus ET(jet#1)
Jet #1 Direction
“Leading Jet”

“TransMIN”
Highest“TransMAX”
pT particle
in the
“transverse” region!
“Back-to-Back”
“Away”
Jet #1 Direction

“Toward”
“TransMAX”
PTmaxT
PTmaxT
“TransMIN”
“Away”
"Transverse" PTmax (GeV/c)
Jet #1 Direction
“Toward”
PTmaxT
"Transverse" Charged PTmax
3.0
CDF Run 2 Preliminary
1.96 TeV

2.5
data uncorrected
Leading Jet
2.0
“Toward”
1.5
“TransMAX”
1.0
“TransMIN”
0.5“Away”
Min-Bias
Back-to-Back
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
50
100
150
200
250
ET(jet#1) (GeV)
Jet #2 Direction
Min-Bias
 Use the leading jet to define the “transverse” region and look at the maximum pT
charged particle in the “transverse” region, PTmaxT.
 Shows the average PTmaxT, in the “transverse” region (pT > 0.5 GeV/c, |h| < 1) versus
ET(jet#1) for “Leading Jet” and “Back-to-Back” events compared with the average
maximum pT particle, PTmax, in “min-bias” collisions (pT > 0.5 GeV/c, |h| < 1).
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 20
Min-Bias “Associated”
Charged Particle Density
Highest pT
charged particle!
“Associated” densities do
not include PTmax!
Charged Particle Density: dN/dhd
PTmax Direction
0.5
PTmax
Direction

Correlations in 
Charged Particle Density
CDF Preliminary
Associated Density
PTmax not included
data uncorrected
0.4

Charge Density
0.3
0.2
0.1
Min-Bias
Correlations
in 
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmax
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
 Use the maximum pT charged particle in the event, PTmax, to define a direction and

is “associated”
more probable
to finddN
a chg
particle
look at the It
the
density,
/dhd, in “min-bias” collisions (pT > 0.5
PTmax than it is to
GeV/c, |h| <accompanying
1).
find a particle in the central region!
Shows the data on the  dependence of the “associated” charged particle density,
dNchg/dhd, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged
particle density, dNchg/dhd, for “min-bias” events.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 21
Min-Bias “Associated”
Rapid rise in the particle
density in the “transverse”
region as PTmax increases!
Charged Particle Density
Associated Particle Density: dN/dhd
PTmaxDirection
Direction
PTmax

“Toward”
“Transverse”
“Transverse”
Correlations in 
“Away”
Associated Particle Density
Jet #1

PTmax > 2.0 GeV/c
1.0
PTmax > 2.0 GeV/c
PTmax > 1.0 GeV/c
0.8
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
CDF Preliminary
data uncorrected
PTmax > 0.5 GeV/c
Transverse
Region
0.6
Transverse
Region
0.4
0.2
Jet #2
PTmax
PTmax not included
Min-Bias
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
Ave Min-Bias
0.25 per unit h-
PTmax > 0.5 GeV/c
 Shows the data on the  dependence of the “associated” charged particle density,
dNchg/dhd, for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) relative
to PTmax (rotated to 180o) for “min-bias” events with PTmax > 0.5, 1.0, and 2.0 GeV/c.
 Shows “jet structure” in “min-bias” collisions (i.e. the “birth” of the leading two jets!).
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 22
Back-to-Back “Associated”
Charged Particle Densities
Maximum pT particle in
the “transverse” region!
Jet #1 Direction
PTmaxT
Direction
“Associated” densities do
not include PTmaxT!


“Toward”
“TransMAX”
PTmaxT
“TransMIN”

PTmaxT
Direction
Jet#1
Region
Jet#2
Region
Jet#1
Region
Jet#2
Region
“Away”
Jet #2 Direction
 Use the leading jet in “back-to-back” events to define the “transverse” region and look
at the maximum pT charged particle in the “transverse” region, PTmaxT.
 Look at the  dependence of the “associated” charged particle and PTsum densities,
dNchg/dhd and dPTsum/dhd for charged particles (pT > 0.5 GeV/c, |h| < 1, not including
PTmaxT) relative to PTmaxT.
 Rotate so that PTmaxT is at the center of the plot (i.e. 180o).
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 25
Back-to-Back “Associated”
Charged Particle Density
“Associated” densities do
not include PTmaxT!
PTmaxT
Direction
Jet #1
Jet#1
Region
Associated Particle Density

Jet #2
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
CDF Preliminary
Jet #3
Jet#2
Region
Associated Particle Density: dN/dhd
10.0
data uncorrected
Back-to-Back
30 < ET(jet#1) < 70 GeV
PTmaxT not included
1.0
Jet#2
Region
PTmaxT > 2.0 GeV/c
PTmaxT > 1.0 GeV/c
Jet #4??
"Jet#1"
Region
PTmaxT
PTmaxT > 0.5 GeV/c
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
Log Scale!
 Look at the  dependence of the “associated” charged particle density, dNchg/dhd for
charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmaxT) relative to PTmaxT
(rotated to 180o) for PTmaxT > 0.5 GeV/c, PTmaxT > 1.0 GeV/c and PTmaxT > 2.0
GeV/c, for “back-to-back” events with 30 < ET(jet#1) < 70 GeV .
 Shows “jet structure” in the “transverse” region (i.e. the “birth” of the 3rd & 4th jet).
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 26
Jet Topologies
QCDThree
Four
Jet
QCD
Jet Topology
Topology Charged Particle Density: dN/dhd
QCD
2-to-4
Scattering
Multiple Parton Interactions
2
Preliminary
CDF
Final-State
Jet #1
data uncorrected
Radiation
Outgoing Parton
346
10
14
30 < ET(jet#1) < 70 GeV
Outgoing Parton
Outgoing PartonBack-to-Back
18
30
34
38
326
42
322
46
318
Jet #1
PT(hard)
50
54
Jet#1
306
58
PT(hard)
302
298
PTmaxT
Proton
Direction
Proton
6
358
26
330
310
Jet #3
354
22
334
314
Jet#1
Region
350
342
338
62
66
70
294
Jet #4
74
290
78
286
Jet #4
AntiProton
AntiProton
"Transverse"
Jet #3
Region
282
278
274
Jet#2
Region
Underlying Event
Underlying Event
PTmaxT
270
86
90
94
98
266
Underlying Event
102
262
Jet #2
0.5
258
Underlying Event
106
254
110
Jet #2
250
114
1.0
246
118
126
238
1.5
234
230
130
134
138
226
Particles
ChargedFinal-State
GeV/c)
(|h|<1.0, PT>0.5
Radiation
Associated Density
PTmaxT > 2 GeV/c
(not included)
142
222
2.0
218
214
146
150
154
210
Polar Plot
Initial-State
Radiation
122
242

82
"Transverse"
Region
158
206
162
202
198
194
190
178
186
174
170
166
182
Parton
Outgoing
Outgoing
Shows the  dependence
ofParton
the “associated” charged particleOutgoing
density,Parton
dNchg/dhd, pT > 0.5
GeV/c, |h| < 1, PTmaxT > 2.0 GeV/c (not including PTmaxT) relative to PTmaxT (rotated to
180o) and the charged particle density, dNchg/dhd, pT > 0.5 GeV/c, |h| < 1, relative to jet#1
(rotated to 270o) for “back-to-back events” with 30 < ET(jet#1) < 70 GeV.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 30
“Associated” Charge Density
PYTHIA Tune A vs HERWIG
HERWIG (without multiple parton
interactions) too few “associated”
particles in the direction of PTmaxT!
Associated Particle Density: dN/dhd
Associated Particle Density: dN/dhd
10.0
10.0
data uncorrected
theory + CDFSIM
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
CDF Preliminary
Back-to-Back
30 < ET(jet#1) < 70 GeV
Associated Particle Density
Associated Particle Density
CDF Preliminary
1.0
PTmaxT > 0.5 GeV/c
PY Tune A
PTmaxT
"Jet#1"
Region
0.1
data uncorrected
theory + CDFSIM
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT
PTmaxT > 0.5 GeV/c
HERWIG
"Jet#1"
Region
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
 (degrees)
And HERWIG (without multiple
parton interactions) too few particles
1.0
Back-to-Back
in Tune
the direction
opposite of PTmaxT!
PYTHIA
A
1.0
CDF Preliminary
0.0
-0.5
CDF Preliminary
240
270
300
330
360
PTmaxT
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
"Jet#1"
Region
-1.0
Back-to-Back
30 < ET(jet#1) < 70 GeV
0.0
-0.5
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
210
HERWIG
data uncorrected
theory + CDFSIM
0.5
Data - Theory
0.5
180
Data - Theory: Associated Particle Density dN/dhd
30 < ET(jet#1) < 70 GeV
data uncorrected
theory + CDFSIM
150
 (degrees)
Data - Theory: Associated Particle Density dN/dhd
Data - Theory
Back-to-Back
30 < ET(jet#1) < 70 GeV
PTmaxT
"Jet#1"
Region
-1.0
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
 (degrees)
TeV4LHC Fermilab
September 16, 2004
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
Rick Field - Florida/CDF
Page 31
“Associated” Charge Density
PYTHIA Tune A vs HERWIG
For PTmaxT > 2.0 GeV both
PYTHIA and HERWIG produce
slightly too many “associated”
particles in the direction of PTmaxT!
Associated Particle Density: dN/dhd
Associated Particle Density: dN/dhd
10.0
10.0
data uncorrected
theory + CDFSIM
1.0
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
data uncorrected
theory + CDFSIM
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT
"Jet#1"
Region
PTmaxT
PTmaxT > 2.0 GeV/c
HERWIG
"Jet#1"
Region
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
 (degrees)
1.6
150
180
210
240
270
300
330
360
 (degrees)
1.0
PYTHIA Tune A
direction
data uncorrected
theory + CDFSIM
Back-to-Back
opposite
of PTmaxT!
30 < ET(jet#1)
< 70 GeV
0.0
-0.8
data uncorrected
theory + CDFSIM
0.5
Data - Theory
0.8
Data - Theory
Back-to-Back
30 < ET(jet#1) < 70 GeV
Next Step
Look at the jet topologies
(2 jet vs 3 jet vs 4 jet etc).
See if there is an excess of
But HERWIG
(without
multipledue to multiple
4
jet
events
parton
interactions)
produces
Data - Theory: Associated Particle Density dN/dhd
Data - Theory: Associated
Particle
Density dN/dhd
too few particles
in the interactions!
parton
CDF Preliminary
CDF Preliminary
PTmaxT > 2.0 GeV/c
PY Tune A
0.1
CDF Preliminary
Back-to-Back
30 < ET(jet#1) < 70 GeV
Associated Particle Density
Associated Particle Density
CDF Preliminary
HERWIG
0.0
-0.5
Charged Particles
PTmaxT
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT > 2.0 GeV/c (not included)
Back-to-Back
30 < ET(jet#1) < 70 GeV
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
"Jet#1"
Region
PTmaxT
"Jet#1"
Region
PTmaxT > 2.0 GeV/c (not included)
-1.6
-1.0
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
 (degrees)
TeV4LHC Fermilab
September 16, 2004
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
Rick Field - Florida/CDF
Page 33
The Universality of
PYTHIA Tune A
DirectZ-boson
Photon
Production
“Hard”
Scattering
Production
Multiple
Parton
Interactions
“Flavor
Creation”
Photon
Z-boson
Outgoing
Parton
Outgoing
Parton
b-quark
 We would like to have a
PT()
PT(hard)
PT(hard)
PT(Z)
“universal” tune of PYTHIA!
 QCD Hard Scattering
 Direct Photon Production
 Z-Boson Production
 Heavy Flavor Production
Proton
Proton
Proton
Proton
AntiProton
AntiProton
AntiProton
AntiProton
Underlying
UnderlyingEvent
Event
Underlying
Event
Underlying Event
Underlying
Event
Underlying
Event
Underlying
Event
Underlying Event
Initial-State
Initial-State
Initial-State
Radiation
Radiation
Radiation
b-quark
Outgoing
Parton
Final-State
Radiation
Radiation
Outgoing Parton
 I working on a “universal” PYTHIA Run 2 tune!




Must specify the PDF!
Must specify MPI parameters!
Must specify Q2 scale!
Must specify intrinsic kT!
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 35
New CDF Run 2 Analysis
Photon and Z-boson
Refer to this as a
“Leading Photon” event
Refer to this as a
“Leading Jet” event
Jet #1 Direction

“Toward”
“Transverse”
“Transverse”
“Away”
Z-boson
Direction
Photon #1
Direction


“Toward”
“Transverse”
“Transverse”
“Away”
Refer to this as a “Zboson” event
“Toward”
“Transverse”
“Transverse”
“Away”
 Study the  distribution of the charged particle density, dNchg/dhd, and the charged
scalar pT sum density, dPTsum/dhd, for charged particles in the region pT > 0.5 GeV/c,
|h| < 1) in “leading jet” events. and “leading photon” events! and “Z-boson” events!
 Study the average charged particle and PTsum density in the “toward”, “transverse”, and
“away” regions versus ET(jet#1) in “leading jet” events.and “leading photon” events!
and “Z-boson” events!
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 36
Charged Particle Density
 Dependence
rdfsoft!
PY Tune A
Jet #1 Direction

Charged Particle Density: dN/dhd
“Toward”
“Transverse”
10.0
RDF Preliminary
“Transverse”
Leading Jet
“Away”
Photon #1
Direction

“Toward”
“Transverse”
“Transverse”
Z-boson
Direction

“Away”
Charged Particle Density
PYTHIA Tune A
Z-boson
1.0
“Toward”
“Transverse”
Leading Photon
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
“Transverse”
Jet#1
Photon
Z-boson
"Transverse"
Region
0.1
“Away”
0
30
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
 Shows the  dependence of the density, dNchg/dhd, for charged particles in the range


pT > 0.5 GeV/c and |h| < 1 relative to jet#1 (rotated to 270o) for ET(jet#1) > 30 GeV for
“Leading Jet” events from PYTHIA Tune A.
Shows the  dependence of the density, dNchg/dhd, for charged particles in the range
pT > 0.5 GeV/c and |h| < 1 relative to pho#1 (rotated to 270o) for PT(pho#1) > 30 GeV
for “Leading Photon” events from PYTHIA Tune A.
Shows the  dependence of the density, dNchg/dhd, for charged particles in the range
pT > 0.5 GeV/c and |h| < 1 relative to the Z (rotated to 270o) for PT(Z) > 30 GeV for “Zboson” events from PYTHIA Tune A.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 37
Not “Blessed”
Yet!
Preliminary
Results
Outgoing Parton
Direct Photon Production
PT(hard)
Z-boson Production
Photon
Z-boson
PT(Z)
PT()
Initial-State Radiation
Proton
AntiProton
Underlying Event
Underlying Event
Proton
AntiProton
Underlying Event
Underlying Event
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Initial-State
Radiation
Outgoing Parton
Final-State
Radiation
Final-State
Radiation
Final-State
Radiation
Outgoing Parton
Outgoing Parton
Charged
Particle Density:
dN/dhd
 PYTHIA Tune A agrees well with the density, dN
chg/dhd,
for charged
10.0

Charged Particle Density

RDF Preliminary
Leading
Jet region p
particles and the scalar PTsum density, dPT
sum/dhd, for
the
T > 0.5
PYTHIA Tune A
Leading Photon
Z-boson for both direct
GeV/c and |h| < 1 in the “toward” and “transverse” regions
photon and Z-boson events at 1.96 TeV.
1.0
However, I probably should increase the intrensic kT. PYTHIA Tune A uses the
default value.
Jet#1
Photon
Z-boson
Charged
Particles
"Transverse"
In addition to specifying the PDF and the(|h|<1.0,
MPI
parameters,
one must
specify
Region
PT>0.5 GeV/c)
0.1
2 = 4p 2 for QCD jets and direct
the Q2 scale for each process. For Tune
AQ
0
30
60
90T 120 150 180 210 240 270 300 330 360
2
2
photons and Q = Mz for Z-boson production.
 (degrees)
The data looks like
PYTHIA Tune A!
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 38
PYTHIA Tune 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 PYTHIA
Tune A (PT(hard) > 0, CTEQ5L) at 1.8 TeV and 14 TeV.
 At 14 TeV tuned PYTHIA Tune 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 Tune 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.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 39
PYTHIA Tune 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 PYTHIA Tune A with
PT(hard) > 0.
 PYTHIA Tune A 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!
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 43
LHC Predictions
Summary & Conclusions
Outgoing Parton
PT(hard)
Initial-State Radiation
Proton
AntiProton
Underlying Event
Tevatron
LHC
Underlying Event
Warning!
12 times more likely
These predictions cannot
to find be
a 10 GeV
 PYTHIA Tune A predicttrusted!
a 40-45% rise in dNchg/dhd
at
h
= 0 in going from the Tevatron
“jet” in “Min-Bias”
We
need
to
improve
the
the LHC!
(1.8 TeV) to the LHC (14 TeV). 4 charged particles peratunit
h at the Tevatron becomes 6
per unit h at the LHC. modeling of the “beam-beam”
“multiple-parton
 PYTHIA Tune A predictsremnants
that 1% ofand
all “Min-Bias”
events at the Tevatron Twice
(1.8 TeV)
are
as much
activity
in
the
the result of a hard 2-to-2 parton-parton
scattering with PT(hard) > 10 GeV/c which
interactions”.
“underlying event”
What we are learning at
the Tevatron will result
in improved models!
Outgoing Parton


Final-State
Radiation
increases to 12% at LHC (14 TeV)!
at the LHC!
For the “underlying event” in hard scattering processes the predictions of HERWIG and
PYTHIA Tune 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.
PYTHIA Tune A predicts about a factor of two increase in the charged PTsum density of
the “underlying event” in going from the Tevatron to the LHC.
TeV4LHC Fermilab
September 16, 2004
Rick Field - Florida/CDF
Page 44