FRONTIERS IN
CONTEMPORARY PHYSICS - III
QCD Working Group
Multiple Parton Interactions
Outgoing Parton
PT(hard)
Proton
AntiProton
Underlying Event
Underlying Event
in memory of Bob Panvini
Outgoing Parton
Rick Field
University of Florida
(for the CDF Collaboration)
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
May 23-28, 2005
Page 1
Studying the “Underlying Event”
at CDF
Outline of Talk
Scattering
Multiple“Hard”
Parton Interactions
 Discuss briefly the components of the
“underlying event” of a hard scattering
as described by the QCD parton-shower
Monte-Carlo Models.
OutgoingParton
Parton
Outgoing
PT(hard)
PT(hard)
Proton
Proton
AntiProton
AntiProton
Underlying Event
Underlying
Event
Underlying Event
Underlying
Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
Outgoing Parton
 Review the CDF Run 1 analysis which was used to
Charged Particle Jet
tune the multiple parton interaction parameters
in PYTHIA (i.e. Tune A).
Calorimeter Jet
 Review the study the “underlying event” in CDF
Run 2 and compare with PYTHIA Tune A (with
MPI) and HERWIG (without MPI).
HERWIG + JIMMY
PYTHIA 6.3
SHERPA
 Look at “what’s next”: CDF Run 2 publication,
more realistic Monte-Carlo models.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
JetClu R = 0.7
Page 2
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
parton-parton collision resulting in large
Final-State
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.
FCPIII - Vanderbilt
May 24, 2005
“Underlying Event”
Proton
AntiProton
Beam-Beam Remnants
Rick Field - Florida/CDF
Beam-Beam Remnants
“underlying event” has
initial-state radiation!
Initial-State
Radiation
Page 3
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.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 4
CDF Run 1 analysis!
“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”!
“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 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” and look at the density of charged particles and the charged PTsum density.
o
All three regions have the same size in h- space, hx = 2x120 = 4p/3.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 5
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.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 6
Run 1 “Transverse”
Charged Particle Density
"Transverse" Charged Particle Density: dN/dhd
Charged Jet #1
Direction
“Toward”
“Transverse”
“Transverse”
“Away”
CDF “Min-Bias” data
(|h|<1, PT>0.5 GeV)
<dNchg/dhd> = 0.25
"Transverse" Charged Density

1.25
CDF Data
CDF Min-Bias
Run 1 Analysis
CDF JET20
data uncorrected
1.00
0.75
0.50
Factor of 2!
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)
 Data on the average charge particle density (pT > 0.5 GeV, |h| < 1) in the “transverse”
(60<||<120o) region as a function of the transverse momentum of the leading charged
particle jet. Each point corresponds to the <dNchg/dhd> in a 1 GeV bin. The solid (open)
points are the Min-Bias (JET20) data. The errors on the (uncorrected) data include both
statistical and correlated systematic uncertainties.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 7
Run 1 “Transverse”
Charged PTsum Density
"Transverse" Charged PTsum Density: dPTsum/dhd
Charged Jet #1
Direction
“Toward”
“Transverse”
“Transverse”
“Away”
"Transverse" PTsum Density (GeV)

1.25
CDF Data
Run 1 Analysis
data uncorrected
1.00
CDF JET20
CDF Min-Bias
0.75
0.50
Increases with
PT(jet1)!
> factor of 2!
0.25
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
CDF “Min-Bias” data
(|h|<1, PT>0.5 GeV)
<dPTsum/dhd> = 0.23 GeV/c
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV/c)
 Data on the average charge scalar PTsum density (pT > 0.5 GeV, |h| < 1) in the “transverse”
(60<||<120o) region as a function of the transverse momentum of the leading charged
particle jet. Each point corresponds to the <dPTsum/dhd> in a 1 GeV bin. The solid (open)
points are the Min-Bias (JET20) data. The errors on the (uncorrected) data include both
statistical and correlated systematic uncertainties.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 8
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 1Data
"Transverse" Charged Density
“Toward”
ISAJET
"Transverse" Charged Particle Density: dN/dhd
Run 1 Analysis
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).
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 9
HERWIG 6.4
“Transverse” Density

“Toward”
“Transverse”
“Transverse”
“Away”
1.00
CDF Run 1Data
"Transverse" Charged Density
Charged Jet #1
Direction
HERWIG uses a modified leadinglog parton shower-model which
does agrees better with the data!
"Transverse" Charged Particle Density: dN/dhd
Total
"Hard"
data uncorrected
theory corrected
0.75
Run 1 Analysis
0.50
0.25
"Remnants"
Beam-Beam
Remnants
HERWIG
Herwig 6.4 CTEQ5L
PT(hard) > 3 GeV/c
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
5
10
15
20
25
30
PT(charged jet#1) (GeV/c)
35
40
45
50
“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).
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 10
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”
Run 1 Analysis
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.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 11
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).
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 12
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)
FCPIII - Vanderbilt
May 24, 2005
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 13
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”!
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 14
Tuned PYTHIA (Tune A)
LHC Predictions
"Transverse" Charged Particle Density: dN/dhd
"Transverse" Charged PTsum Density: dPTsum/dhd
3.0
PYTHIA 6.206 (default)
"Transverse" PTsum Density (GeV)
"Transverse" Charged Density
3.5
HERWIG 6.4
3.0
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
0.0
PYTHIA 6.206 Set A
2.5
PYTHIA 6.206 (default)
14 TeV
2.0
HERWIG 6.4
Big difference!
1.5
1.0
1.8 TeV
0.5
|h|<1.0 PT>0 GeV
CTEQ5L
0.0
0
5
10
15
20
25
30
35
40
45
50
0
5
PT(charged jet#1) (GeV/c)
10
15
20
25
30
35
40
45
50
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
version of PYTHIA 6.206 (PT(hard) > 0, CTEQ5L, Tune 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 (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 and less than the PYTHIA default prediction.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 15
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).
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 16
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.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 17
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) and ET(jet#3) < 15 GeV.
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.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 18
“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.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 19
“TransMIN” PTsum Density
versus ET(jet#1)
Jet #1 Direction
“Leading Jet”

"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.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 20
“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.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 21
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)
FCPIII - Vanderbilt
May 24, 2005
60
Rick Field - Florida/CDF
Page 22
Tuned JIMMY versus
PYTHIA Tune A
JIMMY: MPI
J. M. Butterworth
J. R. Forshaw
M. H. Seymour
JIMMY
Runs with HERWIG and adds
multiple parton interactions!
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)
Leading Jet
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
0.1
RDF Preliminary
generator level
PYA TOT
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
JIMMY tuned to agree
with PYTHIA Tune A!
PT(jet#1) > 30 GeV/c
JM TOT
JM 2-to-2
10.0
"Transverse"
Region
JM ISR
JM MPI
1.0
Jet#1
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
 (degrees)
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
 (left) Shows the Run 2 data on the  dependence of the charged scalar PTsum density (|h|<1, pT>0.5
GeV/c) relative to the leading jet for 30 < ET(jet#1) < 70 GeV/c compared with PYTHIA Tune A
(after CDFSIM).
 (right) Shows the generator level predictions of PYTHIA Tune A and a tuned version of JIMMY
(PTmin=1.8 GeV/c) for the  dependence of the charged scalar PTsum density (|h|<1, pT>0.5 GeV/c)
relative to the leading jet for PT(jet#1) > 30 GeV/c. The tuned JIMMY and PYTHIA Tune A agree
in the “transverse” region.
 (right) For JIMMY the contributions from the multiple parton interactions (MPI), initial-state
radiation (ISR), and the 2-to-2 hard scattering plus finial-state radiation (2-to-2+FSR) are shown.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 23
JIMMY (MPI) versus
HERWIG (BBR)
Charged PTsum Density: dPT/dhd
ETsum Density: dET/dhd
2.5
0.8
generator level
0.6
JM MPI
HW BBR
RDF Preliminary
PT(jet#1) > 30 GeV/c
RDF Preliminary
generator level
ETsum Density (GeV)
Charged PTsum Density (GeV/c)
1.0
"Transverse"
Region
0.4
0.2
0.0
0
30
60
90
PT(jet#1) > 30 GeV
HW BBR
2.0
1.5
1.0
0.5
Jet#1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
JM MPI
Jet#1
"Transverse"
Region
All Particles
(|h|<1.0, PT>0 GeV/c)
0.0
120
150
180
210
240
270
300
330
360
0
30
 (degrees)
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
 (left) Shows the generator level predictions of JIMMY (MPI, PTmin=1.8 GeV/c) and HERWIG (BBR)
for the  dependence of the charged scalar PTsum density (|h|<1, pT>0.5 GeV/c) relative to the
leading jet for PT(jet#1) > 30 GeV/c.
 (right) Shows the generator level predictions of JIMMY (MPI, PTmin=1.8 GeV/c) and HERWIG
(BBR) for the  dependence of the scalar ETsum density (|h|<1, pT>0 GeV/c) relative to the leading
jet for PT(jet#1) > 30 GeV/c.
 The “multiple-parton interaction” (MPI) contribution from JIMMY is about a factor of two larger
than the “beam-beam remnant” (BBR) contribution from HERWIG. The JIMMY program replaces
the HERWIG BBR with its MPI.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 24
New Models: SHERPA
SHERPA
Taken from Stefan Höche’s
talk at HERA-LHC Workshop,
DESY, March 21, 2005.
 Uses the CKKW approach for combining matrix
elements and parton showers.
 Uses T. Sjöstand’s multiple parton interaction
formalism with parton showers for the multiple
interactions.
 Combines multiple parton interactions with
the CKKW merging procedure.
The SHERPA Group
Tanju Gleisberg
Stefan Höche
Frank Krauss
Caroline Semmling
Thomas Laubrich
Andreas Schälicke
Steffen Schumann
Jan Winter
Charged Particle Jet #1
Direction

“Toward”
“Transverse”
“Transverse”
“Away”
 Shows the published CDF (Run 1) data on the average “transverse” charged PTsum (|h|<1, pT>0.5
GeV) as a function of the transverse momentum of the leading charged particle jet compared with
SHERPA.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 25
New Models: PYTHIA 6.3
New parton shower model
with “interleaved” multiple
parton interactions!
Taken from Peter Skand’s
TeV4LHC talk, December, 2004.
 T. Sjöstand and P. Skands, “Transverse-Momentum Ordered Showers and Interleaved Multiple
Interactions”, hep-ph/0408302. T. Sjostand and P. Skands, “Multiple Interactions and the Structure
of Beam Remnants”, JHEP 0403 (2004) 053.
 Compares PYTHIA 6.3 with PYTHIA 6.2 Tune A for the average PT of charged particles versus the
number of charged particles.
FCPIII - Vanderbilt
May 24, 2005
Rick Field - Florida/CDF
Page 26
Outlook
 We have made a lot of progress
in understanding the “underlying
event” at CDF!
Outgoing Parton
PT(hard)
Initial-State Radiation
Proton
AntiProton
Underlying Event
Underlying Event
 More to come from CDF!
Final-State
Radiation
Outgoing Parton
We are
learning
more about
nature works!
 Run 2 “underlying
event”
publication
(thishow
summer!):
Although we cannot yet predict what the
• MidPoint algorithm.
Jet #1 Direction
“underlying
event” will
look like at the LHC,
• “Leading Jet”
and “Back-to-Back”
events.

we
are
improving
the
analysis
“tools”
that
• Data corrected to the particle level.
willasbe
used at
the next generation collider.
• Energy as well
charged
particles.
Calorimeter Jet
“Toward”
“Trans 1”
 HERWIG + JIMMY running within CDF framework.
 PYTHIA 6.3 running within CDF framework.
 SHERPA running within CDF framework.
“Trans 2”
“Away”
MidPoint Algorithm
 The theorists are making good progress in constructing more realistic
models of multiple parton interactions and the “underlying event”!
HERWIG + JIMMY
FCPIII - Vanderbilt
May 24, 2005
PYTHIA 6.3
Rick Field - Florida/CDF
SHERPA
Page 27