Transcript Document

International Symposium
on Multiparticle Dynamics
22 Years!
Many of you were
at Volendam!
Rick Field (experimenter?)
“Min Bias and the Underlying
Events in Run 2 at CDF”
Rick Field (theorist?)
“Jet Formation in QCD”
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 1
“Min-Bias” and the “Underlying Event”
in Run 2 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 and Tune B).
Calorimeter 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).
JetClu R = 0.7
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
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
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.
ISMD2004
July 27, 2004
“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.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 4
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).
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 5
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”
“Trans 1”

Leading
Jet
“Trans 2”
Toward Region
Transverse
Region 2
“Away”
“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).
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 6
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.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 7
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
Run 1 Analysis
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)
ISMD2004
July 27, 2004
Default parameters give
very poor description of
the “underlying event”!
Rick Field - Florida/CDF
Page 10
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)
ISMD2004
July 27, 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 11
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
0.00
0
5
10
15
20
25
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
Hear more about PARP(67)
in Lee Sawyer’s talk
on Wednesday!
1.8 TeV |h|<1.0 PT>0.5 GeV
30
35
40
45
PT(charged jet#1) (GeV/c)
PT(charged jet#1) > 30 GeV/c
50
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)).
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 12
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”!
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 13
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.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 14
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.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 15
“Transverse” PTsum Density
versus ET(jet#1) Run 2
Jet #1 Direction

“Toward”
“Transverse”
“Transverse”
“Away”
“Back-to-Back”
Jet #1 Direction

“Toward”
“Transverse”
"AVE Transverse" PTsum Density: dPT/dhd
1.4
“Transverse”
"Transverse" PTsum Density (GeV/c)
“Leading Jet”
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.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 16
“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
Back-to-Back
Back-to-Back
HW
“Away”
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.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 17
“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.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 18
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
HERWIG
10.0
"Transverse"
Region
1.0
Hear more about the
CDF Preliminary
distribution of charged particles
within jets in Sasha Pronko’s talk
on Thursday! Data - Theory: Charged PTsum Density dPT/dhd
Data - Theory: Charged PTsum Density dPT/dhd
CDF Preliminary
Jet#1
"Transverse"
Region
data uncorrected
theory + CDFSIM
0.1
Charged Particles
30 < ET(jet#1) < 70 GeV
(|h|<1.0, PT>0.5 GeV/c)
Back-to-Back
Jet#1
data uncorrected
theory + CDFSIM
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
 (degrees)
180
210
240
270
300
330
360
300
330
360
 (degrees)
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)
150
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
 (degrees)
 (degrees)
ISMD2004
July 27, 2004
60
Rick Field - Florida/CDF
Page 19
“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).
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 21
Min-Bias “Associated”
Highest pT
charged particle!
Charged Particle Density
“Associated” densities do
not include PTmax!
Charged Particle Density: dN/dhd
PTmax Direction
0.5

Correlations in 
Charged Particle Density
CDF Preliminary
Associated Density
PTmax not included
data uncorrected
0.4
Charge Density
0.3
0.2
0.1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmax
Min-Bias
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

look at the the “associated” density, dNchg/dhd.
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.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 22
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
1.0


“Toward”
“Transverse”
“Transverse”
Correlations in 
“Away”
Associated Particle Density
Jet #1
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-
 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!).
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 23
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).
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 24
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
PTmaxT > 0.5 GeV/c
Jet #4??
"Jet#1"
Region
PTmaxT
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).
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 25
“Back-to-Back”
“Associated” Density
“Back-to-Back” vs “MinBias”
“Birth” ofCharge
jet#3 in the
“Associated”
Density
“transverse” region!
PTmaxT
Direction
Associated Particle Density: dN/dhd

“Min-Bias”
“Associated” Density
Associated Particle Density
Jet#2
Region
10.0
Jet#1
Region
PTmax Direction

PTmaxT > 2.0 GeV/c
PTmax > 2.0 GeV/c
Charged Particles
Particles
Charged
(|h|<1.0, PT>0.5
PT>0.5 GeV/c)
GeV/c)
(|h|<1.0,
3030< <ET(jet#1)
ET(jet#1)< <7070GeV
GeV
1.0
Min-Bias x 1.65
PTmaxT
PTmaxT
PTmax
PTmax
Min-Bias
PTmaxT,
PTmaxT,PTmax
PTmaxnot
notincluded
included
CDFPreliminary
Preliminary
CDF
data
uncorrected
data
uncorrected
0.1
Correlations in 
0
30
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
Log Scale!
“Birth” of jet#1 in
 Shows the  dependence of the “associated” charged particle density,“min-bias”
dNchg/dhd
for
collisions!
pT > 0.5 GeV/c, |h| < 1 (not including PTmaxT) relative to PTmaxT (rotated to 180o) for
PTmaxT > 2.0 GeV/c, for “back-to-back” events with 30 < ET(jet#1) < 70 GeV.
 Shows the data on the  dependence of the “associated” charged particle density,
dNchg/dhd, pT > 0.5 GeV/c, |h| < 1 (not including PTmax) relative to PTmax (rotated to
180o) for “min-bias” events with PTmax > 2.0 GeV/c.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 27
Jet Topologies
QCDThree
Four
Jet
QCD
JetTopology
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
6
358
10
14
30 < ET(jet#1) < 70 GeV
Outgoing Parton
Outgoing PartonBack-to-Back
18
26
30
34
330
38
326
42
322
46
318
Jet #1
PT(hard)
310
50
54
Jet#1
306
58
PT(hard)
302
298
Jet #3
354
22
334
314
Jet#1
Region
350
342
338
62
66
70
294
Jet #4
PTmaxT
Proton
Direction
Proton
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.
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 29
“Associated” PTsum Density
PYTHIA Tune A vs HERWIG
HERWIG (without multiple parton
interactions) does not produce
enough “associated” PTsum in the
direction of PTmaxT!
Associated PTsum Density: dPT/dhd
PTmaxT > 0.5 GeV/cAssociated PTsum Density: dPT/dhd
10.0
Associated PTsum Density (GeV/c)
Associated PTsum Density (GeV/c)
10.0
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT > 0.5 GeV/c
Back-to-Back
30 < ET(jet#1) < 70 GeV
PY Tune A
CDF Preliminary
PTmaxT
data uncorrected
theory + CDFSIM
"Jet#1"
Region
0.1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT > 0.5 GeV/c
HERWIG
CDF Preliminary
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
 (degrees)
"Jet#1"
Region
2
CDF Preliminary
And HERWIG (without multiple
parton interactions) does not 2
Charged Particles
produceBack-to-Back
enough PTsum in the
(|h|<1.0, PT>0.5 GeV/c) 30 < ET(jet#1) < 70 GeV
direction
opposite of PTmaxT!1
PTmaxT not included
PYTHIA Tune A
Data - Theory (GeV/c)
data uncorrected
theory + CDFSIM
150
180
210
240
270
300
330
360
 (degrees)
Data - Theory: Associated PTsum Density dPT/dhd
Data - Theory: Associated PTsum Density dPT/dhd
Data - Theory (GeV/c)
PTmaxT
data uncorrected
theory + CDFSIM
0.1
0
1
Back-to-Back
30 < ET(jet#1) < 70 GeV
0
-1
PTmaxT
CDF Preliminary
data uncorrected
theory + CDFSIM
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
Back-to-Back
30 < ET(jet#1) < 70 GeV
PTmaxT not included
0
-1
PTmaxT
HERWIG
"Jet#1"
Region
"Jet#1"
Region
-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
330
360
 (degrees)
 (degrees)
ISMD2004
July 27, 2004
60
Rick Field - Florida/CDF
Page 31
“Associated” PTsum Density
PYTHIA Tune A vs HERWIG
For PTmaxT > 2.0 GeV both
PYTHIA and HERWIG produce
slightly too much “associated” PTsum
in the direction of PTmaxT!
PTmaxT > 2 GeV/c Associated PTsum Density: dPT/dhd
Associated PTsum Density: dPT/dhd
10.0
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
Associated PTsum Density (GeV/c)
Associated PTsum Density (GeV/c)
10.0
1.0
PTmaxT > 2.0 GeV/c
Back-to-Back
30 < ET(jet#1) < 70 GeV
PY Tune A
CDF Preliminary
PTmaxT
data uncorrected
theory + CDFSIM
"Jet#1"
Region
0.1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmaxT not included
1.0
PTmaxT > 2.0 GeV/c
CDF Preliminary
PTmaxT
data uncorrected
theory + CDFSIM
"Jet#1"
Region
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
60
90
120
 (degrees)
CDF Preliminary
240
270
300
330
360
Data - Theory
PTmaxT
0
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
"Jet#1"
Region
PTmaxT > 2.0 GeV/c (not included)
Back-to-Back
30 < ET(jet#1) < 70 GeV
HERWIG
data uncorrected
theory + CDFSIM
-1
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
210
Data - Theory: Associated Particle Density dN/dhd
1
0.0
-1.0
180
2
PYTHIA Tune A
theory + CDFSIM
1.0
150
 (degrees)
But HERWIG (without multiple
Data - Theory: Associated
Particleinteractions)
Density dN/dhd
parton
produces
too few particles
in the
Back-to-Back
CDF Preliminary
direction
opposite
of
PTmaxT!
30
<
ET(jet#1)
<
70 GeV
data uncorrected
2.0
Data - Theory
Back-to-Back
30 < ET(jet#1) < 70 GeV
HERWIG
PTmaxT
"Jet#1"
Region
PTmaxT > 2.0 GeV/c (not included)
-2.0
-2
0
30
60
90
120
150
180
210
240
270
300
330
360
0
30
 (degrees)
ISMD2004
July 27, 2004
60
90
120
150
180
210
240
270
300
330
360
 (degrees)
Rick Field - Florida/CDF
Page 33
Summary
“Leading Jet”
Jet #1 Direction

Jet #1 Direction
“Back-to-Back”
“Toward”
“Toward”
“Trans 1”

“Trans 1”
“Trans 2”
“Trans 2”
“Away”
“Away”
Jet #2 Direction
 There are some interesting correlations between the “transverse 1” and
“transverse 2” regions both for “Leading-Jet” and “Back-to-Back” events!
 PYTHIA Tune A (with multiple parton scattering) does a much better job in
describing these correlations than does HERWIG (without multiple parton
scattering).
Question: Is this a probe of
multiple parton interactions?
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 34
Summary
“Leading Jet”
Jet #1 Direction
Jet #1 Direction

“Back-to-Back”

“Toward”
“Toward”
“Transverse”
“Transverse”
“Transverse”
“Transverse”
“Away”
“Away”
Jet #2 Direction
 “Back-to-Back” events have less “hard scattering” (initial and final state
radiation) component in the “transverse” region which allows for a closer look at
the “beam-beam remnant” and multiple parton scattering component of the
“underlying” event.
 PYTHIA Tune A (with multiple parton scattering) does a much better job in
describing the “back-to-back” events than does HERWIG (without multiple
parton scattering).
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 35
Summary
Max pT in the
“transverse” region!
“Associated” densities do
not include PTmaxT!
Jet #1 Direction

PTmaxT
Direction
PTmax Direction

“Toward”
“TransMAX”
“TransMIN”
Jet#2
Region

Jet#1
Region
Next Step
Correlations in 
Look at the jet topologies
Jet #2 Direction
(2 jet vs 3 jet vs 4 jet etc).
 The “associated” densities
strong
correlations
Seeshow
if there
is an
excess of(i.e. jet structure) in the
“transverse” region both for “Leading Jet” and “Back-to-Back” events.
4 jet events due to multiple
interactions!
 The “birth” of the 1st jet inparton
“min-bias”
collisions looks very similar to the
PTmaxT
“Away”
“birth” of the 3rd jet in the “transverse” region of hard scattering “Back-toBack” events.
Question: Is the topology
3 jet or 4 jet?
ISMD2004
July 27, 2004
Rick Field - Florida/CDF
Page 36