Charged Jet Evolution and the Underlying Event
in Proton-AntiProton Collisions at 1.8 TeV
Proton
AntiProton
“Min-Bias”
Rick Field
University of Florida
The CDF Collaboration
! Use the CDF “min-bias” data in conjunction with the CDF JET20
data to study the growth and development of “charged particle jets”.
! Study a variety of “local” leading charged jet observables and
compare with the QCD “hard” scattering Monte-Carlo models of
Herwig, Isajet, and Pythia.
! Study a number of “global” observables, where to fit the observable
the QCD Monte-Carlo models have to describe correctly the entire
event structure. In particular, examine carefully the “underlying
Min-Bias + JET20 data
event” in hard-scattering processes.
! Compare the “underlying event” in dijet versus Z-boson production.
DPF2000
Rick Field - Florida/CDF
Page 1
“Hard” Proton-Antiproton
Collisions
“Hard” Scattering
Outgoing Parton
PT(hard)
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
The “underlying event”
consists of the
beam-beam remnants
and
initial-state radiation
Final-State
Radiation
Outgoing Parton
! Illustration of a proton-antiproton collision in
which a “hard” 2-to-2 parton scattering with
transverse momentum, PT(hard), has
occurred (take PT(hard) > 3 GeV).
! Isajet, Herwig, and Pythia are QCD “hard”
scattering Monte-Carlo models.
DPF2000
Rick Field - Florida/CDF
Isajet 7.32
Herwig 5.9
Pythia 6.115
Pythia 6.125
Pythia No MS
Page 2
Multiple Parton
Interactions
Multiple Parton Interactions
Outgoing Parton
PT(hard)
Proton
AntiProton
Underlying Event
Pythia uses multiple parton
interactions to enhace
the underlying event.
Underlying Event
Pythia 6.115 and 6.125
differ in the amount
of multiple parton
interactions.
Outgoing Parton
! Pythia uses multiple parton scattering
to enhance the underlying event; Isajet
and Herwig do not.
! Isajet uses independent fragmentation;
Herwig and Pythia do not.
! Herwig and Pythia modify the leadinglog picture to include “color coherence
effects” which leads to “angle
ordering” within the parton shower;
Isajet does not.
DPF2000
Isajet 7.32
Herwig 5.9
Pythia 6.115
Pythia 6.125
Pythia No MS
Rick Field - Florida/CDF
No multiple parton
interactions.
Page 3
Comparing Data with
QCD Monte-Carlo Models
Charged Particle
Data
Select
“clean”
region
!
!
!
!
WYSIWYG
What you see is
what you get.
Almost!
Look only at the charged
particles measured by
the CTC.
Zero or one vertex
|zc-zv| < 2 cm, |CTC d0| < 1 cm
Require PT > 0.5 GeV, |η
η| < 1
Assume a uniform track finding
efficiency of 92%
! Errors include both statistical
and correlated systematic
uncertainties
Make
efficiency
corrections
! Require PT > 0.5 GeV, |η
η| < 1
! Make an 8% correction for the
compare
Uncorrected data
DPF2000
QCD
Monte-Carlo
track finding efficiency
! Errors (statistical plus
systematic) of around 5%
Corrected theory
Rick Field - Florida/CDF
Small
Corrections!
Page 4
Define “Charged Jets” as
Circular Regions in η-φ Space
η| < 1 PT >
! Order Charged Particles in PT (|η
“Charged Jets” contain particles
from the underlying event in
addition to particles from the
outgoing partons.
0.5 GeV).
! Start with highest PT particle and include in
η| < 1 PT > 0.5 GeV)
the “jet” all particles (|η
within radius R = 0.7.
! Go to next highest PT particle (not already
included in a previous jet) and include in the
η| < 1 PT > 0.5 GeV)
“jet” all particles (|η
within radius R = 0.7 (not already included in a
previous jet).
! Continue until all particles are in a “jet”.
! Maximum number of “jet” is about
6 particles
2
π)/(π(
π(0.7)
2(2)(2π
) or 16.
π(
5 “jets”
DPF2000
Rick Field - Florida/CDF
2π
φ
0
-1
η
+1
Page 5
The Evolution of “Charged Jets”
from 0.5 to 50 GeV
QCD “hard” scattering
predictions of
Herwig 5.9, Isajet 7.32,
and Pythia 6.115
Nchg (jet#1) versus PT(charged jet#1)
<Nchg> (Jet#1, R=0.7)
12
1.8 TeV |eta|<1.0 PT>0.5 GeV
10
8
6
4
CDF Preliminary
2
data uncorrected
theory corrected
JET20 data connects
on smoothly to the
Min-Bias data
0
0
5
10
15
20
25
30
35
40
45
Local “Jet” Observable
PT(charged jet#1) (GeV)
Herwig
Isajet
Pythia 6.115
CDF Min-Bias
50
CDF JET20
! Compares data on the average number of charged particles within Jet#1 (leading
jet, R = 0.7) with the QCD “hard” scattering predictions of Herwig 5.9, Isajet 7.32,
and Pythia 6.115.
! Use the JET20 data to extend the range to 0.5 < PT(chgjet#1) < 50 GeV. Plot shows
<Nchg(jet#1)> versus PT(chgjet#1).
! Only charged particles with |η
η| < 1 and PT > 0.5 GeV are included and the QCD
Monte-Carlo predictions have been corrected for efficiency.
DPF2000
Rick Field - Florida/CDF
Page 6
Jet#1 “Size” vs PT(chgjet#1)
Isajet 7.32
Jet #1 "Size" versus PT(charged jet#1)
<Jet#1 Radius>
0.5
Pythia
Isajet
R Containing 80% of Jet Particles
JET20 data connects
on smoothly to the
Min-Bias data
0.4
0.3
R Containing 80% of Jet PT
Herwig
Pythia 6.115
0.2
CDF Preliminary
0.1
data uncorrected
theory corrected
Herwig 5.9
1.8 TeV |eta|<1.0 PT>0.5 GeV
0.0
0
5
10
15
20
25
30
35
40
45
PT(charged jet#1) (GeV)
50
Local “Jet” Observable
! Compares data on the average radius containing 80% of the charged particles and
80% of the charged PTsum of jet#1 (leading charged jet) with the QCD “hard”
scattering predictions of Herwig 5.9, Isajet 7.32, and Pythia 6.115.
! Only charged particles with |η
η| < 1 and PT > 0.5 GeV are included and the QCD
Monte-Carlo predictions have been corrected for efficiency.
DPF2000
Rick Field - Florida/CDF
Page 7
Charged Particle ∆φ
Correlations
Charged Jet #1
Direction
“Toward-Side” Jet
∆φ
Charged Jet #1
Direction
∆φ
“Toward”
“Transverse”
“Toward”
“Transverse”
“Transverse”
“Transverse”
“Away”
“Away”
“Away-Side” Jet
! Look at charged particle correlations in the azimuthal angle ∆φ relative to the leading charged
!
!
particle jet.
o
o
o
o
Define |∆φ
∆φ|
∆φ|
∆φ|
∆φ < 60 as “Toward”, 60 < |∆φ
∆φ < 120 as “Transverse”, and |∆φ
∆φ > 120 as “Away”.
o
All three regions have the same size in η-φ
φ space, ∆ηx∆φ
∆η ∆φ = 2x120 .
DPF2000
Rick Field - Florida/CDF
Page 8
DiJet: Charged Multiplicity
versus PT(chgjet#1)
Charged Jet #1
Direction
∆φ
Nchg versus PT(charged jet#1)
<Nchg>
12
CDF Preliminary
“Toward”
"Toward"
data uncorrected
10
8
"Away"
6
“Transverse”
“Transverse”
4
"Transverse"
“Away”
2
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
Underlying event
“plateau”
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV)
Refer to the Min-Bias + JET20 data
as the “dijet” data.
o), “transverse” (60<|∆φ
o), and “away”
∆φ|<60
∆φ|<120
! Dijet data on the average number of “toward” (|∆φ
∆φ
∆φ
o) charged particles (P > 0.5 GeV, |η
(|∆φ
η| < 1, including jet#1) as a function of the transverse
∆φ|>120
∆φ
T
momentum of the leading charged particle jet. Each point corresponds to the <Nchg> 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.
DPF2000
Rick Field - Florida/CDF
Page 9
DiJet: Charged PTsum
versus PT(chgjet#1)
Charged Jet #1
Direction
∆φ
PTsum versus PT(charged jet#1)
<PTsum> (GeV)
50
CDF Preliminary
data unc o rre c te d
40
"Toward"
1.8 TeV |eta|<1.0 PT>0.5 GeV
“Toward”
“Transverse”
“Transverse”
30
20
"Away"
10
"Transverse"
“Away”
0
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV)
o), “transverse” (60<|∆φ
o), and
∆φ|<60
∆φ|<120
! Dijet data on the average scalar PT sum of “toward” (|∆φ
∆φ
∆φ
o) charged particles (P > 0.5 GeV, |η
“away” (|∆φ
∆φ|>120
η| < 1, including jet#1) as a function of the
∆φ
T
transverse momentum of the leading charged particle jet. Each point corresponds to the <PTsum>
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.
DPF2000
Rick Field - Florida/CDF
Page 10
DiJet: “Toward” Nchg
versus PT(chgjet#1)
Charged Jet #1
Direction
∆φ
12
Isajet Total
CDF Preliminary
10
data uncorrected
theory corrected
“Toward”
8
“Transverse”
ISAJET
"Toward" Nchg versus PT(charged jet#1)
<Nchg>
Outgoing Jets +
Final-State Radiation
“Transverse”
Outgoing Jets
6
1.8 TeV |eta|<1.0 PT>0.5 GeV
“Away”
4
Beam-Beam Remnants
Beam-Beam
Remnants
Initial-State Radiation
2
Initial-State
Radiation
0
0
5
10
15
20
25
30
35
40
45
50
PT (charged jet#1) (GeV)
! Plot shows the dijet “toward” <Nchg> vs PT(chgjet#1) compared to the QCD “hard”
scattering predictions of ISAJET 7.32.
! The predictions of ISAJET are divided into three categories: charged particles that
arise from the break-up of the beam and target (beam-beam remnants), charged
particles that arise from initial-state radiation, and charged particles that result from
the outgoing jets plus final-state radiation.
DPF2000
Rick Field - Florida/CDF
Page 11
DiJet: “Away” Nchg
versus PT(chgjet#1)
Charged Jet #1
Direction
∆φ
“Toward”
10
Outgoing Jets +
Final-State Radiation
CDF Preliminary
data uncorrected
theory corrected
8
Outgoing Jets
Isajet Total
1.8 TeV |eta|<1.0 PT>0.5 GeV
6
“Transverse”
ISAJET
"Away" Nchg versus PT(charged jet#1)
<Nchg>
“Transverse”
4
“Away”
Initial-State
Radiation
Initial-State Radiation
2
Beam-Beam Remnants
0
Beam-Beam
Remnants
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV)
! Plot shows the dijet “away” <Nchg> vs PT(chgjet#1) compared to the QCD “hard”
scattering predictions of ISAJET 7.32.
! The predictions of ISAJET are divided into three categories: charged particles that
arise from the break-up of the beam and target (beam-beam remnants), charged
particles that arise from initial-state radiation, and charged particles that result from
the outgoing jets plus final-state radiation .
DPF2000
Rick Field - Florida/CDF
Page 12
DiJet: “Transverse” Nchg
versus PT(chgjet#1)
Charged Jet #1
Direction
∆φ
“Toward”
Isajet 7.32
"Transverse" Nchg versus PT(charged jet#1)
<Nchg>
5
CDF Preliminary
data uncorrected
theory corrected
4
3
“Transverse”
“Transverse”
2
“Away”
Pythia 6.115
1
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
5
10
15
20
Herwig 5.9
25
30
35
40
45
50
PT(charged jet#1) (GeV)
Herwig
Isajet
Pythia 6.115
CDF Min-Bias
CDF JET20
! Plot shows “Transverse” <Nchg> in the vs PT(chgjet#1) compared to the QCD “hard”
scattering predictions of Herwig 5.9, Isajet 7.32, and Pythia 6.115.
! Only charged particles with |η
η| < 1 and PT > 0.5 GeV are included and the QCD MonteCarlo predictions have been corrected for efficiency.
DPF2000
Rick Field - Florida/CDF
Page 13
DiJet: “Transverse” Nchg
versus PT(chgjet#1)
Charged Jet #1
Direction
∆φ
“Toward”
“Transverse”
ISAJET
"Transverse" Nchg versus PT(charged jet#1)
<Nchg>
4
Isajet Total
CDF Pre liminary
data uncorrected
theory corrected
3
Initial-State
Radiation
“Transverse”
2
Initial-State Radiation
“Away”
1
Beam-Beam Remnants
1.8 TeV |eta|<1.0 PT>0.5 GeV
Beam-Beam
Remnants
Outgoing Jets +
Final-State Radiation
0
0
5
10
15
20
25
30
35
40
45
50
Outgoing Jets
PT(charged jet#1) (GeV)
! Plot shows the dijet “transverse” <Nchg> vs PT(chgjet#1) compared to the QCD “hard”
scattering predictions of ISAJET 7.32.
! The predictions of ISAJET are divided into three categories: charged particles that
arise from the break-up of the beam and target (beam-beam remnants), charged
particles that arise from initial-state radiation, and charged particles that result from
the outgoing jets plus final-state radiation.
DPF2000
Rick Field - Florida/CDF
Page 14
DiJet: “Transverse” Nchg
versus PT(chgjet#1)
Charged Jet #1
Direction
∆φ
4
CDF Preliminary
Pythia 6.115 Total
data uncorrected
theory corrected
“Toward”
3
“Transverse”
PYTHIA
"Transverse" Nchg versus PT(charged jet#1)
<Nchg>
“Transverse”
2
“Away”
Beam-Beam Remnants
1
Outgoing Jets +
Initial & Final-State Radiation
Beam-Beam
Remnants
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
5
10
15
20
25
30
PT(charged jet#1) (GeV)
35
40
45
50
Outgoing Jets
plus
Initial &
Final-State
Radiation
! Plot shows the dijet “transverse” <Nchg> vs PT(chgjet#1) compared to the QCD “hard”
scattering predictions of PYTHIA 6.115.
! The predictions of PYTHIA 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).
DPF2000
Rick Field - Florida/CDF
Page 15
DiJet: “Transverse” Nchg
versus PT(chgjet#1)
Charged Jet #1
Direction
∆φ
<Nchg>
3
Outgoing Jets +
Initial & Final-State Radiation
Isajet
PYTHIA
theory corrected
“Toward”
2
“Transverse”
ISAJET
"Transverse" Nchg versus PT(charged jet#1)
Pythia 6.115
“Transverse”
1
“Away”
HERWIG
Herwig
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV)
! QCD “hard” scattering predictions of HERWIG 5.9, ISAJET 7.32, and PYTHIA 6.115.
! Plot shows the dijet “transverse” <Nchg> vs PT(chgjet#1) arising from the outgoing jets
plus initial and finial-state radiation (hard scattering component).
! HERWIG and PYTHIA modify the leading-log picture to include “color coherence
effects” which leads to “angle ordering” within the parton shower. Angle ordering
produces less high PT radiation within a parton shower.
DPF2000
Rick Field - Florida/CDF
Page 16
DiJet: “Transverse” Nchg
versus PT(chgjet#1)
Charged Jet #1
Direction
∆φ
"Transverse" Nchg versus PT(charged jet#1)
<Nchg>
3
Beam-Beam Remnants
theory corrected
PYTHIA
1.8 TeV |eta|<1.0 PT>0.5 GeV
Pythia 6.115
Isajet
“Toward”
2
“Transverse”
ISAJET
“Transverse”
“Away”
1
Pythia 6.115 No MS
Herwig
HERWIG
0
0
5
10
15
20
25
30
PT(charged jet#1) (GeV)
35
40
45
50
PYTHIA with
No Multiple
Parton Scattering
! QCD “hard” scattering predictions of HERWIG 5.9, ISAJET 7.32, and PYTHIA 6.115.
! Plot shows the dijet “transverse” <Nchg> vs PT(chgjet#1) arising from the beam-beam
remnants. For Pythia the beam-beam remnants include contributions from multiple
parton scattering.
! Since we only include charged particles with PT > 0.5 GeV, the <Nchg> seen above is
related to the PT distribution of the beam-beam remnants compoment.
DPF2000
Rick Field - Florida/CDF
Page 17
The Underlying Event:
DiJet vs Z-Jet
“Hard” Scattering
Outgoing Parton
PT(hard)
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Refer to
Min-Bias +JET20
as
DiJet Data
Final-State
Radiation
Outgoing Parton
Z-boson Production
The “underlying event”
consists of the
beam-beam remnants
and
initial-state radiation
Z-boson
PT(Z)
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
DPF2000
Rick Field - Florida/CDF
Page 18
Charged Particle ∆φ
Correlations
Charged Jet #1
Direction
“Toward-Side” Jet
Charged Jet #1
or
Z-Boson
Direction
∆φ
Z-Boson
Direction
∆φ
“Toward”
∆φ
“Toward”
“Transverse”
“Transverse”
“Toward”
“Transverse”
“Transverse”
“Transverse”
“Transverse”
“Away”
“Away”
“Away-Side” Jet
“Away”
PT > 0.5 GeV |η| < 1
“Away-Side” Jet
! Look at charged particle correlations in the azimuthal angle ∆φ relative to the leading charged
!
!
particle jet or the Z-boson.
o
o
o
o
Define |∆φ
∆φ|
∆φ|
∆φ|
∆φ < 60 as “Toward”, 60 < |∆φ
∆φ < 120 as “Transverse”, and |∆φ
∆φ > 120 as “Away”.
o
All three regions have the same size in η-φ
φ space, ∆ηx∆φ
∆η ∆φ = 2x120 .
DPF2000
Rick Field - Florida/CDF
Page 19
Z-boson: Charged Multiplicity
versus PT(Z)
Z-boson
Direction
10
"Away"
∆φ
CDF Preliminary
data uncorrected
8
“Toward”
“Transverse”
Nchg versus PT(Z-boson)
<Nchg>
“Transverse”
6
4
2
"Toward"
“Away”
"Transverse"
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
10
20
30
40
50
60
70
80
90
100
PT(Z-boson) (GeV)
o), “transverse” (60<|∆φ
o), and
∆φ|<60
∆φ|<120
! Z-boson data on the average number of “toward” (|∆φ
∆φ
∆φ
o) charged particles (P > 0.5 GeV, |η
“away” (|∆φ
∆φ|>120
η| < 1, excluding decay products of the Z∆φ
T
boson) as a function of the transverse momentum of the Z-boson. The errors on the (uncorrected)
data include both statistical and correlated systematic uncertainties.
DPF2000
Rick Field - Florida/CDF
Page 20
Z-boson: Charged PTsum
versus PT(Z)
PTsum versus PT(Z-boson)
Z-boson
Direction
<PTsum> GeV
50
∆φ
CDF Preliminary
data uncorrected
40
“Toward”
“Transverse”
“Transverse”
30
"Away"
1.8 TeV |eta|<1.0 PT>0.5 GeV
20
"Transverse"
"Toward"
10
“Away”
0
0
10
20
30
40
50
60
70
80
90
100
PT(Z-boson) (GeV)
o), “transverse” (60<|∆φ
o), and
∆φ|<60
∆φ|<120
! Z-boson data on the average scalar PT sum of “toward” (|∆φ
∆φ
∆φ
o) charged particles (P > 0.5 GeV, |η
“away” (|∆φ
∆φ|>120
η| < 1, excluding decay products of the Z∆φ
T
boson) as a function of the transverse momentum of the Z-boson. The errors on the (uncorrected)
data include both statistical and correlated systematic uncertainties.
DPF2000
Rick Field - Florida/CDF
Page 21
DiJet vs Z-Jet
“Toward” Nchg
Charged Jet #1
or
Z-boson
Direction
∆φ
“Toward”
ISAJET
"Toward" Nchg vs PT(charged jet#1 or Z-boson)
<Nchg>
12
CDF Preliminary
10
data uncorrected
theory corrected
8
1.8 TeV |eta|<1.0 PT>0.5 GeV
6
“Transverse”
DiJet
“Transverse”
4
“Away”
2
0
0
5
10
Z-boson
15
20
25
30
35
40
45
50
PT (charged jet#1 or Z-boson) (GeV)
Isajet Z-jet
Isajet DiJet
CDF Z-boson
CDF Min-Bias
ISAJET
CDF JET20
! Comparison of the dijet and the Z-boson data on the average number of charged
particles (PT > 0.5 GeV, |η
η| <1) for the “toward” region.
! The plot shows the QCD Monte-Carlo predictions of ISAJET 7.32 for dijet (dashed)
and “Z-jet” (solid) production.
DPF2000
Rick Field - Florida/CDF
Page 22
Z-boson: “Toward” Nchg
versus PT(Z)
Z-boson
Direction
∆φ
“Toward”
ISAJET
"Toward" Nchg vs PT(Z-boson)
<Nchg>
5
CDF Preliminary
Isajet Z-jet
data uncorrected
theory corrected
4
1.8 TeV |eta|<1.0 PT>0.5 GeV
Beam-Beam
Remnants
3
“Transverse”
“Transverse”
Initial-State Radiation
2
Beam-Beam Remnants
“Away”
1
Initial-State
Radiation
Outgoing Jet + final-state Radiation
0
0
10
20
30
40
50
60
PT (Z-boson) (GeV)
70
80
90
100
Outgoing Jet
! Plot shows the Z-boson “toward” <Nchg> vs PT(Z) compared to the “Z+jet” QCD
Monte-Carlo predictions of ISAJET 7.32.
! The predictions of ISAJET are divided into three categories: charged particles that
arise from the break-up of the beam and target (beam-beam remnants), charged
particles that arise from initial-state radiation, and charged particles that result from
the outgoing jet plus final-state radiation .
DPF2000
Rick Field - Florida/CDF
Page 23
DiJet vs Z-Jet
“Toward” Nchg
Charged Jet #1
or
Z-boson
Direction
∆φ
“Toward”
PYTHIA
"Toward" Nchg vs PT(charged jet#1 or Z-boson)
<Nchg>
12
CDF Preliminary
10
data uncorrected
theory corrected
8
1.8 TeV |eta|<1.0 PT>0.5 GeV
6
“Transverse”
DiJet
“Transverse”
4
“Away”
2
0
Z-boson
0
5
10
15
20
25
30
35
40
45
50
PT (charged jet#1 or Z-boson) (GeV)
Pythia Z-jet
Pythia DiJet
CDF Z-boson
CDF Min-Bias
PYTHIA
CDF JET20
! Comparison of the dijet and the Z-boson data on the average number of charged
particles (PT > 0.5 GeV, |η
η| <1) for the “toward” region.
! The plot shows the QCD Monte-Carlo predictions of PYTHIA 6.115 for dijet (dashed)
and “Z-jet” (solid) production.
DPF2000
Rick Field - Florida/CDF
Page 24
Z-boson: “Toward” Nchg
versus PT(Z)
Z-boson
Direction
∆φ
“Toward”
“Transverse”
ISAJET Z+jet
"Toward" Nchg vs PT(Z-boson)
<Nchg>
“Transverse”
5
CDF Preliminary
Isajet Z-jet
data uncorrected
theory corrected
4
3
2
“Away”
Pythia Z-jet
Pythia Z
1
Herwig Z
HERWIG Z
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
10
20
30
40
50
60
70
80
90
100
PYTHIA Z+jet
PT (Z-boson) (GeV)
! Z-boson data on the average number of charged particles (PT > 0.5 GeV and |η
η| < 1) as
a function of PT(Z) for the “toward” region compared with the QCD Monte-Carlo
predictions of HERWIG 5.9 (“Z”), ISAJET 7.32 (“Z-jet”), and PYTHIA 6.115 (“Z”,
“Z-jet”).
DPF2000
Rick Field - Florida/CDF
Page 25
DiJet vs Z-Jet
“Away” Nchg
Charged Jet #1
or
Z-boson
Direction
∆φ
“Toward”
“Transverse”
“Transverse”
ISAJET
"Away" Nchg vs PT(charged jet#1 or Z-boson)
<Nchg>
10
CDF Preliminary
data uncorrected
theory corrected
8
6
4
DiJet
2
“Away”
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
Z-boson
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1 or Z-boson) (GeV)
Isajet Z-jet
Isajet DiJet
CDF Z-boson
CDF Min-Bias
CDF JET20
! Comparison of the dijet and the Z-boson data on the average number of charged
particles (PT > 0.5 GeV, |η
η| <1) for the “away” region.
! The plot shows the QCD Monte-Carlo predictions of ISAJET 7.32 for dijet (dashed)
and “Z-jet” (solid) production.
DPF2000
Rick Field - Florida/CDF
Page 26
DiJet vs Z-Jet
“Away” Nchg
Charged Jet #1
or
Z-boson
Direction
∆φ
<Nchg>
10
CDF Preliminary
data uncorrected
theory corrected
8
“Toward”
“Transverse”
“Transverse”
“Away”
PYTHIA
"Away" Nchg vs PT(charged jet#1 or Z-boson)
6
4
DiJet
2
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
5
10
Z-boson
15
20
25
30
35
40
45
50
PT(charged jet#1 or Z-boson) (GeV)
Pythia Z-jet
Pythia DiJet
CDF Z-boson
CDF Min-Bias
CDF JET20
! Comparison of the dijet and the Z-boson data on the average number of charged
particles (PT > 0.5 GeV, |η
η| <1) for the “away” region.
! The plot shows the QCD Monte-Carlo predictions of PYTHIA 6.115 for dijet (dashed)
and “Z-jet” (solid) production.
DPF2000
Rick Field - Florida/CDF
Page 27
DiJet vs Z-Jet
“Transverse” Nchg
Charged Jet #1
or
Z-boson
Direction
∆φ
“Toward”
“Transverse”
“Transverse”
ISAJET
"Transverse" Nchg vs PT(charged jet#1 or Z-boson)
<Nchg>
5
CDF Preliminary
data uncorrected
data corrected
4
3
2
1
“Away”
DiJet
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1 or Z-boson) (GeV)
Z-boson
Isajet Z-jet
Isajet DiJet
CDF Z-boson
CDF Min-Bias
CDF JET20
! Comparison of the dijet and the Z-boson data on the average number of charged
particles (PT > 0.5 GeV, |η
η| <1) for the “transverse” region.
! The plot shows the QCD Monte-Carlo predictions of ISAJET 7.32 for dijet (dashed)
and “Z-jet” (solid) production.
DPF2000
Rick Field - Florida/CDF
Page 28
DiJet vs Z-Jet
“Transverse” Nchg
Charged Jet #1
or
Z-boson
Direction
∆φ
“Toward”
“Transverse”
“Transverse”
"Transverse" Nchg vs PT(charged jet#1 or Z-boson)
<Nchg>
PYTHIA
5
CDF Preliminary
data uncorrected
data corrected
4
3
2
1
“Away”
DiJet
1.8 TeV |eta|<1.0 PT>0.5 GeV
0
0
Z-boson
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1 or Z-boson) (GeV)
Pythia Z-jet
Pythia DiJet
CDF Z-boson
CDF Min-Bias
CDF JET20
! Comparison of the dijet and the Z-boson data on the average number of charged
particles (PT > 0.5 GeV, |η
η| <1) for the “transverse” region.
! The plot shows the QCD Monte-Carlo predictions of PYTHIA 6.115 for dijet (dashed)
and “Z-jet” (solid) production.
DPF2000
Rick Field - Florida/CDF
Page 29
Z-boson: “Transverse” Nchg
versus PT(Z)
Z-boson
Direction
∆φ
“Toward”
5
CDF Preliminary
Isajet Z-jet
data uncorrected
data corrected
4
ISAJET
"Transverse" Nchg vs PT(Z-boson)
<Nchg>
Initial-State
Radiation
1.8 TeV |eta|<1.0 PT>0.5 GeV
“Transverse”
“Transverse”
“Away”
3
Initial-State Radiation
Beam-Beam Remnants
2
1
Outgoing Jet + Final-State Radiation
0
Beam-Beam
Remnants
0
10
20
30
40
50
60
PT(Z-boson) (GeV)
70
80
90
100
Outgoing Jet
! Plot shows the Z-boson “transverse” <Nchg> vs PT(Z) compared to the “Z+jet” QCD
Monte-Carlo predictions of ISAJET 7.32.
! The predictions of ISAJET are divided into three categories: charged particles that
arise from the break-up of the beam and target (beam-beam remnants), charged
particles that arise from initial-state radiation, and charged particles that result from
the outgoing jets plus final-state radiation.
DPF2000
Rick Field - Florida/CDF
Page 30
Z-boson: “Transverse” Nchg
versus PT(Z)
Z-boson
Direction
∆φ
“Toward”
"Transverse" Nchg vs PT(charged jet#1 or Z-boson)
<Nc hg >
5
CDF Preliminary
Pythia Z-jet
data uncorrected
data corrected
4
PYTHIA
1.8 TeV |eta|<1.0 PT>0.5 GeV
“Transverse”
“Transverse”
“Away”
3
2
Beam-Beam Remnants
1
Outgoing Jet +
Initial & Final-State Radiation
Beam-Beam
Remnants
0
0
10
20
30
40
50
60
PT(Z-boson) (GeV)
70
80
90
100
Outgoing Jet
plus
Initial &
Final-State
Radiation
! Plot shows the Z-boson “transverse” <Nchg> vs PT(Z) compared to the “Z+jet” QCD
Monte-Carlo predictions of PYTHIA 6.115.
! The predictions of PYTHIA 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).
DPF2000
Rick Field - Florida/CDF
Page 31
Z-boson: “Transverse” Nchg
versus PT(Z)
Z-boson
Direction
∆φ
“Toward”
“Transverse”
“Transverse”
“Away”
ISAJET Z+jet
"Transverse" Nchg vs PT(charged jet#1 or Z-boson)
<Nchg>
5
CDF Preliminary
Isajet Z-jet
data uncorrected
data corrected
4
3
2
Pythia Z-jet
Pythia Z
1
Herwig Z
1.8 TeV |eta|<1.0 PT>0.5 GeV
HERWIG Z
PYTHIA Z+jet
0
0
10
20
30
40
50
60
70
80
90
100
PT(Z-boson) (GeV)
! Z-boson data on the average number of charged particles (PT > 0.5 GeV and |η
η| < 1) as
a function of PT(Z) for the “transverse” region compared with the QCD Monte-Carlo
predictions of HERWIG 5.9 (“Z”), ISAJET 7.32 (“Z-jet”), and PYTHIA 6.115 (“Z”,
“Z-jet”).
DPF2000
Rick Field - Florida/CDF
Page 32
Z-boson: “Transverse” Nchg
versus PT(Z)
Z-boson
Direction
<Nchg>
3
∆φ
“Toward”
“Transverse”
ISAJET Z+jet
"Transverse" Nchg versus PT(Z-boson)
Outgoing Jet +
Initial & Final-State Radiation
2
PYTHIA Z+jet
Isajet Z-jet
1.8 TeV |eta|<1.0 PT>0.5 GeV
theory corrected
Pythia Z-jet
“Transverse”
Pythia Z
1
“Away”
Herwig Z
0
0
10
20
30
40
50
60
PT(Z-boson) (GeV)
70
80
90
100
HERWIG Z
! QCD Monte-Carlo predictions of HERWIG 5.9 (“Z”), ISAJET 7.32 (“Z-jet”), and
PYTHIA 6.115 (“Z”, “Z-jet”).
! Plot shows the Z-boson “transverse” <Nchg> vs PT(Z) arising from the outgoing jets
plus initial and finial-state radiation (hard scattering component).
! Same effect seen in dijet production.
DPF2000
Rick Field - Florida/CDF
Page 33
Z-boson: “Transverse” Nchg
versus PT(Z)
Z-boson
Direction
"Transverse" Nchg versus PT(Z-boson)
<Nchg>
3
∆φ
Beam-Beam Remnants
1.8 TeV |eta|<1.0 PT>0.5 GeV
theory corrected
“Toward”
PYTHIA
Pythia Z-jet
Pythia Z
2
ISAJET
“Transverse”
“Transverse”
1
“Away”
Isajet Z-jet
Herwig Z
0
0
10
20
30
40
50
60
70
80
90
100
HERWIG
PT(Z-boson) (GeV)
! QCD Monte-Carlo predictions of HERWIG 5.9 (“Z”), ISAJET 7.32 (“Z-jet”), and
PYTHIA 6.115 (“Z”, “Z-jet”).
! Plot shows the Z-boson “transverse” <Nchg> vs PT(Z) arising from the beam-beam
remnants. For PYTHIA the beam-beam remnants include contributions from multiple
parton scattering.
DPF2000
Rick Field - Florida/CDF
Page 34
Charged Particle Jets:
Summary & Conclusions
Proton
AntiProton
“Min-Bias”
The Evolution
of “Charged Jets”
! Charge particle jets (R = 0.7) are “born” somewhere around PT of about 1 GeV
!
!
with, on the average, about 2 charged particles, and grow to, on the average,
about 10 charged particles at 50 GeV.
The QCD hard-scattering Monte-Carlo models agree qualitatively well with the
multiplicity distribution of the charged particles within a jet, the distribution of
charged multiplicity and PTsum around the jet direction, the size of the jets, and
momentum distribution of charged particles within the jet. They agree as well
with 2 GeV jets as they do with 50 GeV jets!
The charged jets in the Min-Bias data are simply the extrapolation (down to
small PT) of the high transverse momentum jets observed in the JET20 data.
The Min-Bias data are a mixture of “hard” and “soft” and to completely
describe the data will require combining a model for the “soft” collisions with a
QCD perturbative Monte-Carlo model of the “hard” collisions.
DPF2000
Rick Field - Florida/CDF
Page 35
The Underlying Event:
Summary & Conclusions
“Hard” Scattering
Outgoing Parton
PT(hard)
Proton
AntiProton
Underlying Event
The “Underlying Event”
Underlying Event
Initial-State
Radiation
! The underlying event is very similar in dijet and the Z-boson production as
Final-State
Radiation
Outgoing Parton
!
!
predicted by the QCD Monte-Carlo models. The “toward” region in Z-boson
production is a direct measure of the underlying event.
The number of charged particles per unit rapidity (height of the “plateau”) is
at least twice that observed in “soft” collisions at the same corresponding
energy.
None of the QCD Monte-Carlo models correctly describe the underlying event.
Herwig and Pythia 6.125 do not have enough activity in the underlying event.
Pythia 6.115 has about the right amount of activity in the underlying event, but
as a result produces too much overall multiplicity. Isajet has a lot of activity in
the underlying event, but with the wrong dependence on PT(jet#1) or PT(Z).
None of the Monte-carlo models have the correct PT dependence of the beambeam remnant component of the underlying event.
DPF2000
Rick Field - Florida/CDF
Page 36