The “Underlying Event”
CDF-LHC Comparisons
High PT Jet Production
Outgoing Parton
Outline of Talk
PT(hard)
Initial-State
Radiation
Proton
AntiProton
Underlying Event
Underlying Event
 Jet Production: The “underlying event” in high
pT jet production in Run 2 at CDF.
Outgoing Parton
Final-State
Radiation
Drell-Yan Production
 PT(Z-boson): Tuning to fit the PT(Z)
distribution in Run 2 at CDF.
Lepton
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Anti-Lepton
Great process to study the
“underlying event”!
 Drell-Yan: The “underlying event” in
Drell-Yan production in Run 2 at CDF.
 Extrapolations to the LHC: The “underlying
event” in high pT jet production and DrellYan at CMS.
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 1
The “Transverse” Region
“Transverse” region is
very sensitive to the
“underlying event”!
as defined by the Leading Jet
Jet #1 Direction
Charged Particles (pT > 0.5 GeV/c, |h| < 1)
Calorimeter Towers (ET > 0.1 GeV, |h| < 1)
“Toward-Side” Jet

Look at the charged
particle density and the
ETsum density in the
“transverse” region!
2p
Away Region
Calorimeter Jet #1
Direction

Transverse
Region
“Toward”
“Toward”
“Transverse”

Leading
Jet
“Transverse”
“Transverse”
“Transverse”
Toward Region
Transverse
Region
“Away”
“Away”
Away Region
“Away-Side” Jet
0
-1
h
+1
 Look at the “transverse” region as defined by the leading calorimeter jet (MidPoint, R = 0.7, fmerge = 0.75,
|h| < 2).
 Define || < 60o as “Toward”, 60o < - < 120o and 60o <  < 120o as “Transverse 1” and “Transverse 2”,
and || > 120o as “Away”. Each of the two “transverse” regions have area h = 2x60o = 4p/6. The
overall “transverse” region is the sum of the two transverse regions (h = 2x120o = 4p/3).
 Study the charged particles (pT > 0.5 GeV/c, |h| < 1) and form the charged particle density, dNchg/dhdf,
and the charged scalar pT sum density, dPTsum/dhd, by dividing by the area in h- space.
 Study the calorimeter towers (ET > 0.1 GeV, |h| < 1) and form the scalar ET sum density, dETsum/dhd.
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 2
The “Transverse” Region
“Transverse” region
recieves contributions
from initial & finalstate radiation!
as defined by the Leading Jet
Jet #1 Direction
Charged Particles (pT > 0.5 GeV/c, |h| < 1)
Calorimeter Towers (ET > 0.1 GeV, |h| < 1)
“Toward-Side” Jet

Look at the charged
particle density and the
ETsum density in the
“transverse” region!
2p
Away Region
Calorimeter Jet #1
Direction

Transverse
Region
“Toward”
“Toward”
“Transverse”
“Transverse”
“Transverse”

Leading
Jet
“Transverse”
Toward Region
Jet #3
Transverse
Region
“Away”
“Away”
Away Region
“Away-Side” Jet
0
-1
h
+1
 Look at the “transverse” region as defined by the leading calorimeter jet (MidPoint, R = 0.7, fmerge = 0.75,
|h| < 2).
 Define || < 60o as “Toward”, 60o < - < 120o and 60o <  < 120o as “Transverse 1” and “Transverse 2”,
and || > 120o as “Away”. Each of the two “transverse” regions have area h = 2x60o = 4p/6. The
overall “transverse” region is the sum of the two transverse regions (h = 2x120o = 4p/3).
 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, by dividing by the area in h- space.
 Study the calorimeter towers (ET > 0.1 GeV, |h| < 1) and form the scalar ET sum density, dETsum/dhd.
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 3
The “Underlying Event” in
High PT Jet Production (CDF)
Jet #1 Direction

“Toward”
“Transverse”
HERWIG (without MPI)
lies below the data for
PT(jet#1) < 200 GeV/c!
“Away”
High PT Jet Production
Proton
Outgoing Parton
PY Tune A
HW
0.4
MidPoint R = 0.7 |h(jet#1) < 2
0.2
1.96 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
50
100
150
200
250
300
350
400
450
PT(jet#1) (GeV/c)
2.0
Underlying Event
Final-State
Radiation
“Transverse” <Densities> vs PT(jet#1)
LPC Physics Group
December 15, 2005
0.6
"Transverse" Charged PTsum Density: dPT/dhd
AntiProton
Underlying Event
"Leading Jet"
data corrected to particle level
Outgoing Parton
PT(hard)
Initial-State
Radiation
CDF Run 2 Preliminary
0.8
"Transverse" PTsum Density (GeV/c)
“Transverse”
"Transverse" Charged Particle Density: dN/dhd
1.0
"Transverse" Charged Density
The “Underlying Event” in High
PT Jet Production
CDF Run 2 Preliminary
data corrected to particle level
"Leading Jet"
1.6
1.96 TeV
1.2
PY Tune A
0.8
MidPoint R = 0.7 |h(jet#1) < 2
HW
0.4
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
50
100
Rick Field - Florida/CMS/CDF
150
200
250
300
350
400
450
PT(jet#1) (GeV/c)
Page 4
The “Central” Region
in Drell-Yan Production
Drell-Yan Production
Lepton
Look at the charged
particle density and the
ETsum density in the
“central” region!
Charged Particles (pT > 0.5 GeV/c, |h| < 1)
Calorimeter Towers (ET > 0.1 GeV, |h| < 1)
2p
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation

Central Region
Anti-Lepton
Multiple Parton Interactions
Proton
Lepton
AntiProton
Underlying Event
0
-1
Underlying Event
Anti-Lepton
h
+1
After removing the leptonpair everything else is the
“underlying event”!
 Look at the “central” region after removing the lepton-pair.
 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, by dividing by the area in h-
space.
 Study the calorimeter towers (ET > 0.1 GeV, |h| < 1) and form the scalar ET sum density,
dETsum/dhd.
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 5
CDF Run 1 PT(Z)
PYTHIA 6.2 CTEQ5L
Parameter
Tune A
Tune
A25
Tune
A50
MSTP(81)
1
1
1
MSTP(82)
4
4
4
PARP(82)
2.0 GeV
2.0 GeV
2.0 GeV
PARP(83)
0.5
0.5
0.5
PARP(84)
0.4
0.4
0.4
PARP(85)
0.9
0.9
0.9
PARP(86)
0.95
0.95
0.95
s = 1.0
Z-Boson Transverse Momentum
0.12
PT Distribution 1/N dN/dPT
UE Parameters
CDF Run 1 Data
PYTHIA Tune A
PYTHIA Tune A25
PYTHIA Tune A50
s = 2.5
0.08
CDF Run 1
published
1.8 TeV
s = 5.0
Normalized to 1
0.04
0.00
0
2
4
6
8
10
12
14
16
18
20
Z-Boson PT (GeV/c)
ISR Parameter
PARP(89)
1.8 TeV
1.8 TeV
1.8 TeV
PARP(90)
0.25
0.25
0.25
PARP(67)
4.0
4.0
4.0
MSTP(91)
1
1
1
PARP(91)
1.0
2.5
5.0
PARP(93)
5.0
15.0
25.0
 Shows the Run 1 Z-boson pT distribution
(<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA
Tune A (<pT(Z)> = 9.7 GeV/c), Tune A25
(<pT(Z)> = 10.1 GeV/c), and
Tune A50
(<pT(Z)> = 11.2 GeV/c).
Intrensic KT
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 6
CDF Run 1 PT(Z)
PYTHIA 6.2 CTEQ5L
Parameter
Tune A
Tune AW
Z-Boson Transverse Momentum
UE Parameters
1
1
MSTP(82)
4
4
PARP(82)
2.0 GeV
2.0 GeV
PARP(83)
0.5
0.5
PARP(84)
0.4
0.4
PARP(85)
0.9
0.9
PARP(86)
0.95
0.95
PARP(89)
1.8 TeV
1.8 TeV
PARP(90)
0.25
0.25
PARP(62)
1.0
1.25
PARP(64)
1.0
0.2
PARP(67)
4.0
4.0
MSTP(91)
1
1
PARP(91)
1.0
2.1
PARP(93)
5.0
15.0
PT Distribution 1/N dN/dPT
MSTP(81)
0.12
CDF Run 1 Data
PYTHIA Tune AW
0.08
CDF Run 1
published
s = 2.1
1.8 TeV
Normalized to 1
0.04
0.00
ISR Parameters
Intrensic KT
LPC Physics Group
December 15, 2005
0
2
4
6
8
10
12
14
16
18
20
Z-Boson PT (GeV/c)
 Shows the Run 1 Z-boson pT distribution
(<pT(Z)> ≈ 11.5 GeV/c) compared with PYTHIA
Tune AW (<pT(Z)> = 11.7 GeV/c).
Effective Q cut-off, below which space-like showers are not evolved.
The Q2 = kT2 in as for space-like showers is scaled by PARP(64)!
Rick Field - Florida/CMS/CDF
Page 7
Drell-Yan Production
at CDF
Lepton-Pair
Drell-Yan Production
Lepton-Pair Transverse
Momentum
Proton
<PT(pair)> versus M(pair)
PT(pair)
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
Lepton-Pair Transverse Momentum
Lepton-Pair Transverse Momentum
20
20
RDF Preliminary
RDF Preliminary
PY Tune AW
15
Average Pair PT
Average Pair PT
HERWIG
generator level
generator level
10
PY Tune A
5
15
10
PY Tune AW
5
Drell-Yan
1.96 TeV
Z
Drell-Yan
1.96 TeV
Z
0
0
0
50
100
150
200
250
0
50
Lepton-Pair Invariant Mass (GeV)
100
150
200
250
Lepton-Pair Invariant Mass (GeV)
 Shows the lepton-pair average PT versus the  Shows the lepton-pair average PT versus the
lepton-pair invariant mass at 1.96 TeV for
lepton-pair invariant mass at 1.96 TeV for
PYTHIA Tune AW and HERWIG.
PYTHIA Tune AW and PYTHIA Tune A.
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 8
Drell-Yan Production
at CMS
Lepton-Pair
Drell-Yan Production
Lepton-Pair Transverse
Momentum
Proton
<PT(pair)> versus M(pair)
PT(pair)
AntiProton
Underlying Event
The lepton-pair <PT>
much larger at the LHC!
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
Lepton-Pair Transverse Momentum
Lepton-Pair Transverse Momentum
40
20
RDF Preliminary
HERWIG
RDF Preliminary
15
10
Average Pair PT
Average Pair PT
LHC
generator level
generator level
PY Tune AW
30
HERWIG
CDF
20
10
5
Drell-Yan
1.96 TeV
Z
Z
PY Tune AW
Drell-Yan
0
0
0
50
100
150
200
250
0
50
100
150
200
250
Lepton-Pair Invariant Mass (GeV)
Lepton-Pair Invariant Mass (GeV)
 Shows the lepton-pair average PT versus the  Shows the lepton-pair average PT versus the
lepton-pair invariant mass at 14 TeV for
lepton-pair invariant mass at 1.96 TeV for
PYTHIA Tune AW and HERWIG.
PYTHIA Tune AW and HERWIG.
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 9
Drell-Yan Production
at CMS
Lepton-Pair
Drell-Yan Production
Lepton-Pair Transverse
Momentum Squared Proton
PT(pair)
<(PT)2(pair)> versus M(pair)
AntiProton
Underlying Event
The lepton-pair <(PT)2>
much larger at the LHC!
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
Lepton-Pair PT2
Lepton-Pair PT2
3000
1000
RDF Preliminary
generator level
Average Pair PT-Squared
Average Pair PT-Squared
RDF Preliminary
800
HERWIG
600
400
PY Tune AW
200
Drell-Yan
1.96 TeV
Z
2500
generator level
LHC
2000
1500
HERWIG
1000
Z
500
Drell-Yan
PY Tune AW
0
0
0
50
100
150
200
250
0
50
100
150
200
250
Lepton-Pair Invariant Mass (GeV)
Lepton-Pair Invariant Mass (GeV)
 Shows the lepton-pair average (PT)2 versus
the lepton-pair invariant mass at 1.96 TeV
for PYTHIA Tune AW and HERWIG.
LPC Physics Group
December 15, 2005
CDF
 Shows the lepton-pair average (PT)2 versus
the lepton-pair invariant mass at 14 TeV for
PYTHIA Tune AW and HERWIG.
Rick Field - Florida/CMS/CDF
Page 10
The “Underlying Event” in
Drell-Yan Production (CDF)
Drell-Yan Production
Lepton
The “Underlying Event”
Proton
Underlying Event
Charged particle density
versus M(pair)
AntiProton
Underlying Event
HERWIG (without MPI)
is much less active than
PY Tune AW (with MPI)!
Initial-State
Radiation
Anti-Lepton
Charged Particle Density: dN/dhd
Charged Particle Density: dN/dhd
1.0
1.0
RDF Preliminary
generator level
Charged Particle Density
Charged Particle Density
RDF Preliminary
PY Tune AW
0.8
0.6
0.4
PY Tune A
Drell-Yan
1.96 TeV
0.2
Z
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
generator level
PY Tune AW
0.8
0.6
0.4
HERWIG
0.2
Drell-Yan
1.96 TeV
Z
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
0.0
0
50
100
150
200
250
0
50
Lepton-Pair Invariant Mass (GeV)
100
150
200
250
Lepton-Pair Invariant Mass (GeV)
 Shows the charged particle density versus the  Shows the charged particle density versus the
lepton-pair invariant mass at 1.96 TeV for
lepton-pair invariant mass at 1.96 TeV for
PYTHIA Tune AW and PYTHIA Tune A.
PYTHIA Tune AW and HERWIG (with no MPI).
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 11
The “Underlying Event” in
Drell-Yan Production (CMS)
Drell-Yan Production
Lepton
The “Underlying Event”
Proton
HERWIG (without MPI)
is much less active than
PY Tune AW (with MPI)!
Underlying Event
Charged particle density
versus M(pair)
AntiProton
“Underlying event” much
more active at the LHC!
Underlying Event
Initial-State
Radiation
Anti-Lepton
Charged Particle Density: dN/dhd
Charged Particle Density: dN/dhd
1.5
1.0
RDF Preliminary
generator level
PY Tune AW
0.8
0.6
0.4
HERWIG
0.2
Drell-Yan
1.96 TeV
Z
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
Charged Particle Density
Charged Particle Density
RDF Preliminary
LHC
generator level
1.0
PY Tune AW
CDF
0.5
Drell-Yan
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
HERWIG
0.0
0.0
0
50
100
150
200
250
0
50
100
150
200
250
Lepton-Pair Invariant Mass (GeV)
Lepton-Pair Invariant Mass (GeV)
 Charged particle density versus the lepton-  Charged particle density versus the lepton-pair
invariant mass at 14 TeV for PYTHIA Tune AW
pair invariant mass at 1.96 TeV for PYTHIA
and HERWIG (without MPI).
Tune AW and HERWIG (without MPI).
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 12
The “Underlying Event” in
Drell-Yan Production (CDF)
Drell-Yan Production
Lepton
The “Underlying Event”
Proton
AntiProton
Underlying Event
Charged PTsum density
versus M(pair)
Underlying Event
HERWIG (without MPI)
is much less active than
PY Tune AW (with MPI)!
Initial-State
Radiation
Anti-Lepton
Charged PTsum Density: dPT/dhd
Charged PTsum Density: dPT/dhd
1.6
RDF Preliminary
Charged PTsum Density (GeV/c)
Charged PTsum Density (GeV/c)
1.6
generator level
1.2
PY Tune AW
0.8
PY Tune A
0.4
Drell-Yan
1.96 TeV
Z
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
RDF Preliminary
generator level
1.2
PY Tune AW
Drell-Yan
1.96 TeV
0.8
0.4
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
HERWIG
0.0
0
50
100
150
200
250
0
Lepton-Pair Invariant Mass (GeV)
50
100
150
200
250
Lepton-Pair Invariant Mass (GeV)
 Shows the charged PTsum density versus the  Shows the charged PTsum density versus the
lepton-pair invariant mass at 1.96 TeV for
lepton-pair invariant mass at 1.96 TeV for
PYTHIA Tune AW and PYTHIA Tune A.
PYTHIA Tune AW and HERWIG (without MPI).
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 13
The “Underlying Event” in
Drell-Yan Production (CMS)
Drell-Yan Production
Lepton
The “Underlying Event”
Proton
HERWIG (without MPI)
is much less active than
PY Tune AW (with MPI)!
AntiProton
Underlying Event
Charged PTsum density
versus M(pair)
“Underlying event” much
more active at the LHC!
Underlying Event
Initial-State
Radiation
Anti-Lepton
Charged PTsum Density: dPT/dhd
Charged PTsum Density: dPT/dhd
2.5
RDF Preliminary
generator level
1.2
PY Tune AW
Drell-Yan
1.96 TeV
0.8
0.4
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
HERWIG
0.0
Charged PTsum Density (GeV/c)
Charged PTsum Density (GeV/c)
1.6
RDF Preliminary
LHC
PY Tune AW
generator level
2.0
Drell-Yan
1.5
HERWIG
1.0
CDF
0.5
Z
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
0.0
0
50
100
150
200
250
0
Lepton-Pair Invariant Mass (GeV)
50
100
150
200
250
Lepton-Pair Invariant Mass (GeV)
 Charged PTsum density versus the lepton-pair  Charged PTsum density versus the leptonpair invariant mass at 14 TeV for PYTHIA
invariant mass at 1.96 TeV for PYTHIA Tune
Tune AW and HERWIG (without MPI).
AW and HERWIG (without MPI).
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 14
The “Underlying Event” in
Drell-Yan Production (CMS)
Drell-Yan Production
Lepton
The “Underlying Event”
Proton
ETsum density versus M(pair)
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Anti-Lepton
Transverse Energy Density: dET/dhd
Transverse Energy Density: dET/dhd
5.0
2.0
RDF Preliminary
RDF Preliminary
ETsum Density (GeV)
ETsum Density (GeV)
generator level
1.5
PY Tune AW
1.0
HERWIG
0.5
Drell-Yan
1.96 TeV
Z
3.0
HERWIG
2.0
CDF
1.0
All Particles (|h|<1.0, all PT)
(excluding lepton-pair )
Drell-Yan
0.0
0.0
0
50
100
150
200
250
LHC
PY Tune AW
generator level
4.0
0
50
All Particles (|h|<1.0, all PT)
(excluding lepton-pair )
Z
100
150
200
250
Lepton-Pair Invariant Mass (GeV)
Lepton-Pair Invariant Mass (GeV)
 ETsum density versus the lepton-pair
 ETsum density versus the lepton-pair invariant
invariant mass at 1.96 TeV for PYTHIA Tune
mass at 14 TeV for PYTHIA Tune AW and
AW and HERWIG (without MPI).
HERWIG (without MPI).
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 15
The “Underlying Event”
Drell-Yan vs Jets at CDF
The “Underlying Event” in High PT Lepton-Pair and Jet Production
Charged Particle Density: dN/dhd
Charged PTsum Density: dPT/dhd
1.0
1.6
Charged Particle Density
"Leading Jet"
generator level
0.8
Charged PTsum Density (GeV/c)
PY Tune AW
RDF Preliminary
0.6
Drell-Yan
0.4
HERWIG
0.2
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
1.96 TeV
0.0
RDF Preliminary
"Leading Jet"
generator level
1.2
1.96 TeV
PY Tune AW
0.8
Drell-Yan
0.4
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
HERWIG
0.0
0
50
100
150
200
250
300
350
400
450
500
0
50
100
PT(jet#1) or Lepton-Pair Mass
150
200
250
300
350
400
450
500
PT(jet#1) or Lepton-Pair Mass
2p
2p
Away Region
Lepton
Jet #1 Direction

Transverse
Region
“Toward”
“Central Region”


Central Region
“Transverse”
Leading
Jet
“Transverse”
Toward Region
Transverse
Region
“Away”
Anti-Lepton
Drell-Yan
LPC Physics Group
December 15, 2005
0
-1
h
+1
“Leading Jet”
Rick Field - Florida/CMS/CDF
Away Region
0
-1
h
+1
Page 16
The “Underlying Event” in
High PT Jet Production (CMS)
The “Underlying Event”
High PT Jet Production
Outgoing Parton
Charged particle density
versus PT(jet#1)
AntiProton
PT(hard)
Initial-State
Radiation
Proton
Underlying Event
Underlying Event
Final-State
Radiation
Outgoing Parton
"Transverse" Charged Particle Density: dN/dhd
"Transverse" Charged Particle Density: dN/dhd
1.0
2.0
RDF Preliminary
LHC
RDF Preliminary
generator level
0.8
0.6
PY Tune AW
HERWIG
0.4
1.96 TeV
0.2
"Leading Jet"
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
"Transverse" Charged Density
"Transverse" Charged Density
“Underlying event” much
more active at the LHC!
generator level
1.5
PY Tune AW
HERWIG
1.0
CDF
0.5
"Leading Jet"
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
50
100
150
200
250
300
350
400
450
500
0
250
500
PT(particle jet#1) (GeV/c)
750
1000
1250
1500
1750
2000
2250
2500
PT(particle jet#1) (GeV/c)
 Charged particle density in the “Transverse”  Charged particle density in the “Transverse”
region versus PT(jet#1) at 1.96 TeV for PY
region versus PT(jet#1) at 14 TeV for PY Tune
Tune AW and HERWIG (without MPI).
AW and HERWIG (without MPI).
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 17
The “Underlying Event” in
High PT Jet Production (CMS)
The “Underlying Event”
High PT Jet Production
Outgoing Parton
PT(hard)
Initial-State
Radiation
Proton
Underlying Event
Underlying Event
“Underlying event” much
more active at the LHC!
Final-State
Radiation
Outgoing Parton
"Transverse" PTsum Density: dPT/dhd
"Transverse" PTsum Density: dPT/dhd
RDF Preliminary
PY Tune AW
generator level
1.5
"Leading Jet"
1.0
HERWIG
0.5
1.96 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
"Transverse" PTsum Density (GeV/c)
8.0
2.0
"Transverse" PTsum Density (GeV/c)
Charged PTsum density versus
PT(jet#1)
AntiProton
RDF Preliminary
LHC
PY Tune AW
generator level
6.0
"Leading Jet"
HERWIG
4.0
2.0
CDF
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0.0
0
50
100
150
200
250
300
350
400
450
500
0
250
 Charged PTsum density in the “Transverse”
region versus PT(jet#1) at 1.96 TeV for PY
Tune AW and HERWIG (without MPI).
LPC Physics Group
December 15, 2005
500
750
1000
1250
1500
1750
2000
2250
2500
PT(particle jet#1) (GeV/c)
PT(particle jet#1) (GeV/c)
 Charged PTsum density in the “Transverse”
region versus PT(jet#1) at 14 TeV for PY Tune
AW and HERWIG (without MPI)..
Rick Field - Florida/CMS/CDF
Page 18
The “Underlying Event” in
High PT Jet Production (CMS)
The “Underlying Event”
High PT Jet Production
Outgoing Parton
PT(hard)
Initial-State
Radiation
Proton
AntiProton
Underlying Event
Underlying Event
Outgoing Parton
“Underlying event” much
more active at the LHC!
Final-State
Radiation
"Transverse" ETsum Density: dET/dhd
"Transverse" ETsum Density: dET/dhd
4.0
14.0
"Transverse" ETsum Density (GeV)
"Transverse" ETsum Density (GeV)
ETsum density versus PT(jet#1)
RDF Preliminary
generator level
PY Tune AW
3.0
"Leading Jet"
2.0
HERWIG
1.0
1.96 TeV
All Particles (|h|<1.0, all PT)
0.0
RDF Preliminary
12.0
LHC
PY Tune AW
generator level
10.0
"Leading Jet"
8.0
HERWIG
6.0
4.0
2.0
CDF
All Particles (|h|<1.0, all PT)
0.0
0
50
100
150
200
250
300
350
400
450
500
0
250
PT(particle jet#1) (GeV/c)
500
750
1000
1250
1500
1750
2000
2250
2500
PT(particle jet#1) (GeV/c)
 ETsum density in the “Transverse” region
 ETsum density in the “Transverse” region
versus PT(jet#1) at 1.96 TeV for PY Tune AW
versus PT(jet#1) at 14 TeV for PY Tune AW and
and HERWIG (without MPI).
HERWIG (without MPI).
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 19
The “Underlying Event”
Drell-Yan vs Jets at CMS
The “Underlying Event” in High PT Lepton-Pair and Jet Production
Charged PTsum Density: dPT/dhd
Charged Particle Density: dN/dhd
8.0
"Leading Jet"
Charged Particle Density
RDF Preliminary
generator level
1.5
PY Tune AW
HERWIG
1.0
14 TeV
0.5
Drell-Yan
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
0.0
Charged PTsum Density (GeV/c)
2.0
RDF Preliminary
"Leading Jet"
PY Tune AW
generator level
6.0
HERWIG
4.0
14 TeV
2.0
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
(excluding lepton-pair )
Drell-Yan
0.0
0
250
500
750
1000
1250
1500
1750
2000
2250
2500
0
250
500
750
PT(jet#1) orLepton-Pair Mass
1000
1250
1500
1750
2000
2250
2500
PT(jet#1) or Lepton-Pair Mass
2p
2p
Away Region
Lepton
Jet #1 Direction

Transverse
Region
“Toward”
“Central Region”


Central Region
“Transverse”
Leading
Jet
“Transverse”
Toward Region
Transverse
Region
“Away”
Anti-Lepton
Drell-Yan
LPC Physics Group
December 15, 2005
0
-1
h
+1
“Leading Jet”
Rick Field - Florida/CMS/CDF
Away Region
0
-1
h
+1
Page 20
UE&MB@CMS
UE&MB@CMS
Rick Field (Florida)
Darin Acosta (Florida)
Albert De Roeck (CERN)
Paolo Bartalini (UF Postdoc at CERN)
Livio Fano' (INFN/Perugia at CERN)
Filippo Ambroglini (INFN/Perugia at CERN)
Khristian Kotov (UF Student, Acosta)
Me at CMS!
 Measure Min-Bias and the “Underlying Event” at CMS
 The plan involves two phases.
 Phase 1 would be to measure min-bias and the “underlying event”
as soon as possible (when the luminosity is low), perhaps during
commissioning. We would then tune the QCD Monte-Carlo models
for all the other CMS analyses. Phase 1 would be a service to the
rest of the collaboration. As the measurements become more
reliable we would re-tune the QCD Monte-Carlo models if
necessary and begin Phase 2.
 Phase 2 is “physics” and would include comparing the min-bias and
“underlying event” measurements at the LHC with the
measurements we have done (and am doing now) at CDF and then
writing a physics publication.
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Darin
Page 21
UE&MB@CMS
“Minimum-Bias” Collisions
Proton
Proton
High PT Jet Production
Outgoing Parton
PT(hard)
Initial-State
Radiation
Proton
 Min-Bias Studies: Charged particle distributions and
correlations. Construct “charged particle jets” and look
at “mini-jet” structure and the onset of the “underlying
event”. (requires only charged tracks)
Proton
Underlying Event
Outgoing Parton
Underlying Event
Final-State
Radiation
Drell-Yan Production
Lepton
Proton
 “Underlying Event” Studies: The “transverse region” in
“leading Jet” and “back-to-back” jet production. The
“central region” in Drell-Yan production. (requires charged
tracks and calorimeter and muons for Drell-Yan)
Proton
Underlying Event
Underlying Event
Initial-State
Radiation
Anti-Lepton
Drell-Yan Production
Lepton-Pair
PT(pair)
Proton
Proton
Underlying Event
 Drell-Yan Studies: Transverse momentum distribution of
the lepton-pair versus the mass of the lepton-pair,
<pT(pair)>, <pT2(pair)>, ds/dpT(pair) (only requires
muons). Event structure for large lepton-pair pT (i.e. mm
+jets, requires muons and calorimeter).
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
LPC Physics Group
December 15, 2005
Rick Field - Florida/CMS/CDF
Page 22