Predicting “Min-Bias” and the
“Underlying Event” at the LHC
Extrapolations from the
Tevatron to RHIC and the LHC
Rick Field
University of Florida
Outline of Talk
 Studying the formation of the
“underlying event”.
CERN August 13, 2009
 The PYTHIA MPI energy scaling
Outgoing Parton
parameter PARP(90).
PT(hard)
 The “underlying event” at STAR.
Initial-State Radiation
CDF Run 2
Extrapolations to RHIC.
 LHC predictions for the “underlying event”
Proton
Proton
Underlying Event
Outgoing Parton
Underlying Event
Final-State
Radiation
(hard scattering QCD & Drell-Yan).
 LHC predictions for “Min-bias”.
 Summary & Conclusions.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
CMS at the LHC
Rick Field – Florida/CDF/CMS
UE&MB@CMS
Page 1
QCD Monte-Carlo Models:
High Transverse Momentum Jets
Hard Scattering
Initial-State Radiation
Hard Scattering “Jet”
Initial-State Radiation
“Jet”
Outgoing Parton
PT(hard)
Outgoing Parton
PT(hard)
Proton
“Hard Scattering” Component
AntiProton
Final-State Radiation
Outgoing Parton
Underlying Event
Underlying Event
Proton
“Jet”
Final-State Radiation
AntiProton
Underlying Event
Outgoing Parton
Underlying Event
“Underlying Event”
 Start with the perturbative 2-to-2 (or sometimes 2-to-3) parton-parton scattering and add initial and finalstate gluon radiation (in the leading log approximation or modified leading log approximation).
 The “underlying event” consists of the “beam-beam remnants” and from particles arising from soft or
semi-soft multiple parton interactions (MPI).
The “underlying
event” is“jet”
an unavoidable
 Of course the outgoing colored partons fragment
into hadron
and inevitably “underlying event”
background to most collider observables
observables receive contributions from initial
and final-state radiation.
and having good understand of it leads to
more precise collider measurements!
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 2
QCD Monte-Carlo Models:
Lepton-Pair Production
Lepton-Pair
Production
High
PT Z-Boson
Production
Anti-Lepton
Outgoing Parton
Initial-State
Initial-State Radiation
Radiation
High P
T Z-Boson Production
Lepton-Pair
Production
Initial-State
Initial-StateRadiation
Radiation
“Jet”
Proton
Proton
Final-State Radiation
Outgoing
Parton
Anti-Lepton
Final-State Radiation
“Hard Scattering” Component
AntiProton
AntiProton
Underlying Event
Lepton
Z-boson
Underlying Event
Proton
Lepton
Z-boson
AntiProton
Underlying Event
Underlying Event
“Underlying Event”
 Start with the perturbative Drell-Yan muon pair production and add initial-state gluon radiation (in the
leading log approximation or modified leading log approximation).
 The “underlying event” consists of the “beam-beam remnants” and from particles arising from soft or
semi-soft multiple parton interactions (MPI).
 Of course the outgoing colored partons fragment into hadron “jet” and inevitably “underlying event”
observables receive contributions from initial-state radiation.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 3
Proton-AntiProton Collisions
at the Tevatron
Elastic Scattering
The CDF “Min-Bias” trigger
picks up most of the “hard
core” cross-section plus a
Double
Diffraction
small
amount of single &
double diffraction.
M2
M1
Single Diffraction
M
stot = sEL + sIN
SD +sDD +sHC
1.8 TeV: 78mb
= 18mb
The “hard core” component
contains both “hard” and
“soft” collisions.
+ 9mb
+ (4-7)mb + (47-44)mb
CDF “Min-Bias” trigger
1 charged particle in forward BBC
AND
1 charged particle in backward BBC
Hard Core
“Inelastic Non-Diffractive Component”
“Hard” Hard Core (hard scattering)
Outgoing Parton
“Soft” Hard Core (no hard scattering)
Proton
AntiProton
PT(hard)
Beam-Beam Counters
3.2 < |h| < 5.9
Proton
AntiProton
Underlying Event
Underlying Event
Initial-State
Radiation
Final-State
Radiation
Outgoing Parton
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 4
Particle Densities
DhD = 4 = 12.6
2

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-
dNchg
chg/dhd = 1/4
3/4 = 0.08
0.24
13 GeV/c PTsum
0
-1
h
+1
Divide by 4
dPTsum/dhd = 1/4
3/4 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.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 5
CDF Run 1 “Min-Bias” Data
Charged Particle Density
Charged Particle Density: dN/dhd
Charged Particle Pseudo-Rapidity Distribution: dN/dh
1.0
7
CDF Published
CDF Published
6
0.8
dN/dhd
dN/dh
5
4
3
0.6
0.4
2
0.2
CDF Min-Bias 630 GeV
CDF Min-Bias 1.8 TeV
1
CDF Min-Bias 1.8 TeV
all PT
CDF Min-Bias 630 GeV
all PT
0.0
0
-4
-3
-2
-1
0
1
2
3
4
-4
-3
-1
0
1
2
3
4
Pseudo-Rapidity h
Pseudo-Rapidity h
<dNchg/dh> = 4.2
-2
<dNchg/dhd> = 0.67
 Shows CDF “Min-Bias” data on the number of charged particles per unit pseudo-rapidity
at 630 and 1,800 GeV. There are about 4.2 charged particles per unit h in “Min-Bias”
collisions at 1.8 TeV (|h| < 1, all pT).
DhxD = 1
 Convert to charged particle density, dNchg/dhd, by dividing by 2.
D = 1
There are about 0.67 charged particles per unit h- in “Min-Bias”
0.25
0.67
collisions at 1.8 TeV (|h| < 1, all pT).
 There are about 0.25 charged particles per unit h- in “Min-Bias”
Dh = 1
collisions at 1.96 TeV (|h| < 1, pT > 0.5 GeV/c). <dNchg/dh> = 1.6!
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 6
CDF Run 1 Min-Bias “Associated”
Charged Particle Density
“Associated” densities do
not include PTmax!
Highest pT
charged particle!
Charged Particle Density: dN/dhd
PTmax Direction
PTmax Direction
0.5
D
Correlations in 
Charged Particle Density
CDF Preliminary
Associated Density
PTmax not included
data uncorrected
0.4
D
Charge Density
0.3
0.2
0.1
Min-Bias
Correlations
in 
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
PTmax
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
D (degrees)
 Use the maximum pT charged particle in the event, PTmax, to define a direction and look
It is more probable
to find
a particle
at the the “associated”
density, dN
chg/dhd,
in “min-bias” collisions (pT > 0.5 GeV/c, |h| <
accompanying
PTmax
than
it
is
to
1).
find a particle in the central region!
 Shows the data
on the D 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.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 7
CDF Run 1 Min-Bias “Associated”
Charged Particle Density Rapid rise in the particle
density in the “transverse”
region as PTmax increases!
Associated Particle Density: dN/dhd
PTmaxDirection
Direction
PTmax
D
“Toward”
“Transverse”
“Transverse”
Correlations in 
“Away”
Associated Particle Density
Jet #1
D
PTmax > 2.0 GeV/c
1.0
PTmax > 2.0 GeV/c
PTmax > 1.0 GeV/c
0.8
Charged Particles
(|h|<1.0, PT>0.5 GeV/c)
CDF Preliminary
data uncorrected
PTmax > 0.5 GeV/c
Transverse
Region
0.6
Transverse
Region
0.4
0.2
Jet #2
PTmax
PTmax not included
Min-Bias
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
D (degrees)
Ave Min-Bias
0.25 per unit h-
PTmax > 0.5 GeV/c
 Shows the data on the D 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!).
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 8
Min-Bias “Associated”
Charged Particle Density
PTmax Direction
Associated Charged
Charged
Particle
Density:
dN/dhd
Associated
"Transverse"
ChargedParticle
ParticleDensity:
Density:dN/dhd
dN/dhd
D
Associated Charged Particle Density: dN/dhd
10.0
Charged Particle Density
py Tune A generator level
“Toward” Region
PTmax > 2.0 GeV/c
PTmax > 5.0 GeV/c
1.0
PTmax > 10.0 GeV/c
“Transverse”
“Transverse”
0.1
Min-Bias
1.96 TeV
PTmax > 0.5 GeV/c
PTmax > 1.0 GeV/c
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
Density
"Transverse"
Charged
Density
Charged Particle
1.6
2.5
1.2
RDF Preliminary
RDF Preliminary
RDF Preliminary
py Tune A generator level
py Tune A generator level
1.0
2.0
1.2
0.8
1.5
Min-Bias
Min-Bias
Min-Bias
14 TeV
1.96 TeV
“Toward”
14 TeV
"Toward"
"Away"
"Toward"
“Transverse”
~ factor of "Away"
2!
“Transverse”
0.8
0.6
1.0
0.4
0.4
0.5
0.2
1.96 TeV
"Transverse"
"Transverse"
“Away”
Charged
ChargedParticles
Particles(|h|<1.0,
(|h|<1.0,PT>0.5
PT>0.5 GeV/c)
GeV/c)
Charged
Particles
(|h|<1.0,
PT>0.5
GeV/c)
0.0
0.0
0
30
60
90
120
150
180
210
240
270
300
330
360
00
2
D (degrees)
54
6
8
10
10
12
15
14
16
20
18
PTmax (GeV/c)
(GeV/c)
PTmax
 Shows the D 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 at 1.96 TeV with PTmax > 0.5, 1.0, 2.0, 5.0, and 10.0 GeV/c from PYTHIA
Tune A (generator level).
PTmax Direction
D
“Toward”
“Transverse”
“Transverse”
“Away”
 Shows the “associated” charged particle density in the “toward”, “away” and
“transverse” regions as a function of PTmax for charged particles (pT > 0.5
GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 1.96 TeV from
PYTHIA Tune A (generator level).
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 9
25
20
25
“Transverse” Charged Density
PTmax Direction
D
"Transverse" Charged Particle Density: dN/dhd
0.8
“Transverse”
“Transverse”
“Away”
ChgJet#1 Direction
D
“Toward”
“Transverse”
“Transverse”
“Away”
"Transverse" Charged Density
“Toward”
RDF Preliminary
1.96 TeV
py Tune A generator level
0.6
0.6
0.4
Jet#1
ChgJet#1
0.2
PTmax
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
Jet#1 Direction
D
0
5
10
15
20
25
30
PT(jet#1) or PT(chgjet#1) or PTmax (GeV/c)
“Toward”
“Transverse”
“Transverse”
“Away”
 Shows the charged particle density in the “transverse” region for charged particles (pT > 0.5
GeV/c, |h| < 1) at 1.96 TeV as defined by PTmax, PT(chgjet#1), and PT(jet#1) from PYTHIA
Tune A at the particle level (i.e. generator level).
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 10
Tuning PYTHIA:
Multiple Parton Interaction Parameters
Parameter
Default
PARP(83)
0.5
Double-Gaussian: Fraction of total hadronic
matter within PARP(84)
PARP(84)
0.2
Double-Gaussian: Fraction of the overall hadron
radius containing the fraction PARP(83) of the
total hadronic matter.
Determines the energy
Probability
that of
thethe
MPI
produces two gluons
dependence
MPI!
with color connections to the “nearest neighbors.
0.33
PARP(86)
0.66
PARP(89)
PARP(82)
PARP(90)
PARP(67)
1 TeV
1.9
GeV/c
0.16
1.0
Multiple Parton Interaction
Color String
Color String
Multiple PartonDetermine
Interactionby comparing
Probability thatAffects
the MPI
theproduces
amount two
of gluons
either as described
by PARP(85)
or as a closed
initial-state
radiation!
gluon loop. The remaining fraction consists of
quark-antiquark pairs.
with 630 GeV data!
Color String
Hard-Scattering Cut-Off PT0
Determines the reference energy E0.
The cut-off PT0 that regulates the 2-to-2
scattering divergence 1/PT4→1/(PT2+PT02)2
Determines the energy dependence of the cut-off
PT0 as follows PT0(Ecm) = PT0(Ecm/E0)e with
e = PARP(90)
A scale factor that determines the maximum
parton virtuality for space-like showers. The
larger the value of PARP(67) the more initialstate radiation.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
5
PYTHIA 6.206
e = 0.25 (Set A))
4
PT0 (GeV/c)
PARP(85)
Description
Take E0 = 1.8 TeV
3
2
e = 0.16 (default)
1
100
1,000
10,000
100,000
CM Energy W (GeV)
Reference point
at 1.8 TeV
Page 11
“Transverse” Cones
vs “Transverse” Regions
“Cone Analysis”
2
2
Transverse
Cone:
(0.7)2=0.49
Away Region
Transverse
Region

(Tano, Kovacs, Huston, Bhatti)
Cone 1

Leading
Jet
Leading
Jet
Toward Region
Transverse
Region:
2/3=0.67
Transverse
Region
Cone 2
Away Region
0
0
-1
h
+1
-1
h
+1
 Sum the PT of charged particles in two cones of radius
0.7 at the same h as the leading jet but with |DF| = 90o.
 Plot the cone with the maximum and minimum PTsum
versus the ET of the leading (calorimeter) jet.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 12
Energy Dependence
of the “Underlying Event”
“Cone Analysis”
(Tano, Kovacs, Huston, Bhatti)
630 GeV
1,800 GeV
PYTHIA 6.115
PT0 = 1.4 GeV
PYTHIA 6.115
PT0 = 2.0 GeV
 Sum the PT of charged particles (pT > 0.4 GeV/c) in two cones of radius 0.7 at the same h as the leading
jet but with |DF| = 90o. Plot the cone with the maximum and minimum PTsum versus the ET of the
leading (calorimeter) jet.
 Note that PYTHIA 6.115 is tuned at 630 GeV with PT0 = 1.4 GeV and at 1,800 GeV with PT0 = 2.0 GeV.
This implies that e = PARP(90) should be around 0.30 instead of the 0.16 (default).
 For the MIN cone 0.25 GeV/c in radius R = 0.7 implies a PTsum density of dPTsum/dhd = 0.16 GeV/c
and 1.4 GeV/c in the MAX cone implies dPTsum/dhd = 0.91 GeV/c (average PTsum density of 0.54
GeV/c per unit h-).
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 13
“Transverse” Charged Densities
Energy Dependence
"Transverse" Charged PTsum Density: dPTsum/dhd
"Min Transverse" PTsum Density: dPTsum/dhd
0.60
0.3
Charged PTsum Density (GeV)
Charged PTsum Density (GeV)
e = 0.25
HERWIG 6.4
0.40
e = 0.16
e=0
0.20
HERWIG 6.4
e = 0.25
0.2
Increasing e produces less energy
dependence for the
UE resulting
in
e = 0.16
e=0
less UE activity at the LHC!
CTEQ5L
Pythia 6.206 (Set A)
Pythia 6.206 (Set A)
630 GeV |h|<1.0 PT>0.4 GeV
0.1
CTEQ5L
630 GeV |h|<1.0 PT>0.4 GeV
0.0
0.00
0
5
10
15
20
25
30
35
40
45
50
0
5
10
20
25
30
Lowering PT0 at 630 GeV (i.e.
increasing e) increases UE activity
charged
PTsum density
resulting in
less energy dependence.
40
45
50
Hard-Scattering Cut-Off PT0
5
PYTHIA 6.206
e = 0.25 (Set A))
4
PT0 (GeV/c)
(|h|<1, PT>0.4 GeV) versus PT(charged jet#1) at 630
GeV predicted by HERWIG 6.4 (PT(hard) > 3
GeV/c, CTEQ5L) and a tuned version of PYTHIA
6.206 (PT(hard) > 0, CTEQ5L, Set A, e = 0, e = 0.16
(default) and e = 0.25 (preferred)).
 Also shown are the PTsum densities (0.16 GeV/c and
0.54 GeV/c) determined from the Tano, Kovacs,
Huston, and Bhatti “transverse” cone analysis at
630 GeV.
3
2
e = 0.16 (default)
1
100
1,000
Rick Field Fermilab MC Workshop
Reference point
E = 1.8 TeV
October 4, 2002!
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
35
PT(charged jet#1) (GeV/c)
PT(charged jet#1) (GeV/c)
 Shows the “transverse”
15
Rick Field – Florida/CDF/CMS
10,000
100,000
CM Energy W (GeV)
0
Page 14
All use LO as
with L = 192 MeV!
PYTHIA 6.2 Tunes
UE Parameters
ISR Parameter
Parameter
Tune AW
Tune DW
Tune D6
PDF
CTEQ5L
CTEQ5L
CTEQ6L
MSTP(81)
1
1
1
MSTP(82)
4
4
4
PARP(82)
2.0 GeV
1.9 GeV
1.8 GeV
PARP(83)
0.5
0.5
0.5
PARP(84)
0.4
0.4
0.4
PARP(85)
0.9
1.0
1.0
PARP(86)
0.95
1.0
1.0
PARP(89)
1.8 TeV
1.8 TeV
1.8 TeV
PARP(90)
0.25
0.25
0.25
PARP(62)
1.25
1.25
1.25
PARP(64)
0.2
0.2
0.2
PARP(67)
4.0
2.5
2.5
MSTP(91)
1
1
1
PARP(91)
2.1
2.1
2.1
PARP(93)
15.0
15.0
15.0
Uses CTEQ6L
Tune A energy dependence!
(not the default)
Intrinsic KT
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 15
All use LO as
with L = 192 MeV!
PYTHIA 6.2 Tunes
UE Parameters
Tune A
ISR Parameter
Parameter
Tune DWT
Tune D6T
ATLAS
PDF
CTEQ5L
CTEQ6L
CTEQ5L
MSTP(81)
1
1
1
MSTP(82)
4
4
4
PARP(82)
1.9409 GeV
1.8387 GeV
1.8 GeV
PARP(83)
0.5
0.5
0.5
ATLAS energy dependence!
(PYTHIA default)
Tune B
Tune AW
PARP(85)
1.0
0.33 tunes!
These are 1.0
“old” PYTHIA
6.2
PARP(86)
1.0
0.66
There 1.0
are new 6.420
tunes
by
Tune BW
PARP(89)
1.96 TeV
1.96 TeV
1.0 TeV
Peter Skands (Tune S320, update of S0)
PARP(90)
0.16
0.16
0.16
Peter
Skands
(Tune
N324,
N0CR)
PARP(62)
1.25
1.25
1.0
Hendrik
Hoeth
(Tune0.2P329, “Professor”)
PARP(64)
0.2
1.0
PARP(84)
0.4
0.4
0.5
PARP(67)
2.5
2.5
1.0
MSTP(91)
1
1
1
PARP(91)
Tune D
PARP(93)
Tune 2.1
DW
15.0
2.1
15.0
5.0
Tune D6T
Intrinsic KT
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
1.0
Tune D6
Rick Field – Florida/CDF/CMS
Page 16
Peter’s Pythia Tunes WEBsite
 http://home.fnal.gov/~skands/leshouches-plots/
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 17
Min-Bias “Associated”
Charged Particle Density
35% more at RHIC means
"Transverse" Charged Particle Density: dN/dhd
26% less at the LHC!
1.6
RDF Preliminary
"Transverse" Charged Density
0.3
"Transverse" Charged Density
"Transverse" Charged Particle Density: dN/dhd
PY Tune DW
generator level
0.2
~1.35
PY Tune DWT
0.1
Min-Bias
0.2 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
RDF Preliminary
PY Tune DWT
generator level
1.2
~1.35
0.8
PY Tune DW
0.4
Min-Bias
14 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
14
16
18
20
0
2
4
6
8
PTmax Direction
D
“Toward”
“Transverse”
12
14
16
18
20
PTmax (GeV/c)
PTmax (GeV/c)
RHIC
10
PTmax Direction
0.2 TeV → 14 TeV
(~factor of 70 increase)
“Transverse”
“Away”
D
“Toward”
LHC
“Transverse”
“Transverse”
“Away”
 Shows the “associated” charged particle density in the “transverse” regions as a function of
PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events
at 0.2 TeV and 14 TeV from PYTHIA Tune DW and Tune DWT at the particle level (i.e. generator
level). The STAR data from RHIC favors Tune DW!
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 18
Min-Bias “Associated”
Charged Particle Density
About a factor of 2.7 increase in
Associated Charged Particle Density: dN/dhd
the “transverse” region!
1.2
1.6
py Tune DW generator level
RDF Preliminary
Min-Bias
1.96 TeV
Charged Particle Density
RDF Preliminary
Charged Particle Density
Associated Charged Particle Density: dN/dhd
1.2
"Toward"
"Away"
0.8
"Transverse"
0.4
py Tune DW generator level
Min-Bias
0.2 TeV
"Away"
0.8
"Toward"
0.4
"Transverse"
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
16
18
20
0
2
4
6
8
10
PTmax (GeV/c)
PTmax (GeV/c)
PTmax Direction
PTmax Direction
D
“Toward”
Tevatron
14
“Transverse”
1.96 TeV ← 0.2 TeV
(~factor of 10 increase)
“Transverse”
12
14
D
“Toward”
RHIC
“Transverse”
“Transverse”
“Away”
“Away”
 Shows the “associated” charged particle density in the “toward”, “away” and “transverse” regions
as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for
“min-bias” events at 1.96 TeV and at 0.2 TeV from PYTHIA Tune DW at the particle level (i.e.
generator level).
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 19
Min-Bias “Associated”
Charged Particle Density
About a factor of 2 increase in the
Associated Charged Particle Density: dN/dhd
“transverse” region!
1.6
py Tune DW generator level
Min-Bias
14 TeV
RDF Preliminary
Min-Bias
1.96 TeV
Charged Particle Density
RDF Preliminary
Charged Particle Density
Charged Particle Density: dN/dhd
2.5
1.2
"Toward"
"Away"
0.8
"Transverse"
0.4
py Tune DW generator level
2.0
"Toward"
"Away"
1.5
"Transverse"
1.0
0.5
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0.0
0
2
4
6
8
10
12
14
16
18
20
0
5
10
Tevatron
“Transverse”
25
PTmax Direction
PTmax Direction
“Toward”
20
PTmax (GeV/c)
PTmax (GeV/c)
D
15
1.96 TeV → 14 TeV
(~factor of 7 increase)
“Transverse”
D
“Toward”
LHC
“Transverse”
“Transverse”
“Away”
“Away”
 Shows the “associated” charged particle density in the “toward”, “away” and “transverse” regions
as a function of PTmax for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for
“min-bias” events at 1.96 TeV and at 14 TeV from PYTHIA Tune DW at the particle level (i.e.
generator level).
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 20
Min-Bias “Associated”
Charged Particle Density
"Transverse" Charged Particle Density: dN/dhd
"Transverse" Charged Density
1.2
RDF Preliminary
14 TeV
Min-Bias
py Tune DW generator level
0.8
~1.9
0.4
1.96 TeV
~2.7
0.2 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
5
10
15
20
25
PTmax (GeV/c)
PTmax Direction
D
“Toward”
RHIC
“Transverse”
“Transverse”
0.2 TeV → 1.96 TeV
(UE increase ~2.7 times)
Tevatron
“Away”
PTmax Direction
D
“Toward”
“Transverse”
PTmax Direction
1.96 TeV → 14 TeV
(UE increase ~1.9 times)
LHC
“Transverse”
“Away”
D
“Toward”
“Transverse”
“Transverse”
“Away”
 Shows the “associated” charged particle density in the “transverse” region as a function of PTmax
for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 0.2
TeV, 1.96 TeV and 14 TeV predicted by PYTHIA Tune DW at the particle level (i.e. generator
level).
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 21
The “Underlying Event” at STAR
 At STAR they have measured the “underlying event at W = 200 GeV (|h| < 1, pT > 0.2 GeV)
and compared their uncorrected data with PYTHIA Tune A + STAR-SIM.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 22
The “Underlying Event” at STAR
Charged PTsum Density
Charged PTsum
"Transverse"
PTsumDensity
Density (GeV/c)
(GeV/c)
"Transverse"
PTsum Density:
dPT/dhd
ChargedCharged
PTsum Density:
dPT/dhd
2.0
100.0
1.6
“Back-to-Back”
Charged Particles (|h|<1.0, PT>0.2 GeV/c)
Data uncorrected
PYTHIA Tune A + STAR-SIM
CDF
Run
2 Preliminary
CDF
Run
2 Preliminary
data corrected
particle level
datatocorrected
10.0
1.2
pyA
generator level
1.96
TeV
"Leading Jet"
"Toward"
PY Tune A
"Away"
“Toward”
"Transverse"
0.8
1.0
"Back-to-Back"
"Leading Jet"
MidPoint R=0.7 |h(jet#1)|<2
0.4
0.1
0.0
0
0
50
“Away”
MidPoint
R = Particles
0.7 |h(jet#1)
< 2 PT>0.5 GeV/c)
Charged
(|h|<1.0,
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
HW
50
0.55
100
150
200
250
100
150
200
250
300
300
350
350
400
400
450
Preliminary
~1.5
PT(jet#1) (GeV/c)
PT(jet#1) (GeV/c)
Jet #1 Direction
D
D
“Leading Jet”
“Toward”
“Transverse”
“Transverse”
“Away”
“Transverse”
Jet #1 Direction
0.37
“Toward”
“Transverse”
PT(jet#1) (GeV/c)
“Transverse”
“Away”
“Back-to-Back”
Jet #2 Direction
 Data on the charged particle scalar pT sum density, dPT/dhd, as a function of the leading jet pT for the
“toward”, “away”, and “transverse” regions compared with PYTHIA Tune A.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 23
Min-Bias “Associated”
Charged Particle Density
RDF LHC Prediction!
"Transverse" Charged Particle Density: dN/dhd
"Transverse" Charged Particle Density: dN/dhd
1.6
RDF Preliminary
PY64 Tune P329
"Transverse" Charged Density
"Transverse" Charged Density
0.8
generator level
0.6
0.4
PY Tune A
PY64 Tune N324
0.2
PY64 Tune S320
Min-Bias
1.96 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
PY ATLAS
RDF Preliminary
PY Tune DWT
generator level
1.2
0.8
PY64 Tune P329
PY Tune A
0.4
PY Tune DW
PY64 Tune S320
Min-Bias
14 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
If the LHC data are not in
the range shown here then
we learn new (QCD) physics!
0.0
0
2
4
6
8
10
12
14
16
18
20
0
5
10
PTmax (GeV/c)
PTmax Direction
D
“Transverse”
20
25
PTmax Direction
D
“Toward”
“Toward”
“Transverse”
15
PTmax (GeV/c)
Tevatron
LHC
“Transverse”
“Transverse”
“Away”
“Away”
 Shows the “associated” charged particle density in the “transverse” region as a function of PTmax
for charged particles (pT > 0.5 GeV/c, |h| < 1, not including PTmax) for “min-bias” events at 1.96
TeV from PYTHIA Tune A, Tune S320, Tune N324, and Tune P329 at the particle level (i.e.
generator level).
 Extrapolations of PYTHIA Tune A, Tune DW, Tune DWT, Tune S320, Tune P329, and pyATLAS to the
LHC.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 24
The Drell-Yan Cross Section
Drell-Yan
Cross Section
Z-Bosonm+mProduction
at theRatio
LHC
Z-Boson
Production
at the
Tevatron
Drell-Yan
m+m- Cross
Section
1000.0
60%
RDF
RDFPreliminary
Preliminary
1.0E+02
Tune DW
generator
generator
levellevel
Drell-Yan 1.96 TeV proton-antiproton
1.0E+01
Percent of Events
ds/dMPercent
(pb/GeV)
of Events
50%
Pythia Tune AW
40%
1.0E+00
70 < M(m+m-) < 110 GeV
|h(m-pair)| < 6
30%
1.0E-01
5.8% heavy flavor at the
Tevatron!
1.0E-02
20%
1.0E-03
1.0E-04
LHC
0%
1.0E-05
40%
30%
u ubar
d dbar
1.0E-06
s sbar
c cbar
Tevatron Run2
0
250
500
750
1000
1250
1500
m+m- Mass (GeV)
+ -
22.2% heavy flavor at
the LHC!
10.0
1.0
0
250
500
750
1000
m+m- Mass (GeV)
u ubar
1.0E-07
70 < M(m m ) < 110 GeV
|h(m-pair)| < 6
0%
b bbar
Drell-Yan 14 TeV proton-proton
20%
10%
10%
RDF
RDFPreliminary
Preliminary
generator
level level
Tune DW
generator
50%
Pythia Tune AW
100.0
LHC/Tevatron Run 2
1.0E+03
60%
d dbar
s sbar
c cbar
b bbar
 Shows the ratio (LHC/Tevatron) of the DrellYan Lepton-Pair (m+m-) cross section, ds/dM,
versus the lepton-pair invariant mass from
PYTHIA Tune AW.
 Shows the Drell-Yan Lepton-Pair (m+m-) cross
section, ds/dM, at the 1.96 TeV (Tevatron Run
2) and at 14 TeV (LHC) versus the lepton-pair
invariant mass from PYTHIA Tune AW.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 25
Drell-Yan Production
Tevatron vs LHC
Lepton-Pair
Drell-Yan Production
Lepton-Pair Transverse
Momentum
PT(pair)
Proton
AntiProton
Underlying Event
<pT(m+m-)> is much
larger at the LHC!
Underlying Event
Initial-State
Radiation
Shapes of the pT(m+m-)
distribution at the Z-boson mass.
Final-State
Radiation
Outgoing Parton
Drell-Yan PT(m+m-) Distribution
Lepton-Pair Transverse1.0E+02
Momentum
80
Drell-Yan
generator level
1.0E+01
LHC
40
20
Z
0
1/N dN/dPT (1/GeV)
60
ds/dPT (pb/GeV)
Average Pair PT
Drell-Yan PT(m+m-) Distribution
RDF Preliminary
generator level
Drell-Yan
0.10
1.0E+00
Tevatron Run 2
1.0E-01
generator level
Tevatron Run2
0.08
Pythia Tune AW (solid)
Herwig (dashed)
PY Tune DW (solid)
HERWIG (dashed)
0.06
70 < M(m-pair) < 110 GeV
|h(m-pair)| < 6
0.04
LHC
0.02
PY Tune DW (solid)
HERWIG
1.0E-02(dashed)
LHC
Normalized to 1
0.00
0
100
200
300
400
500
600
700
800
900
1000
1.0E-03
Lepton-Pair Invariant Mass (GeV)
70 < M(m-pair) < 110 GeV
|h(m-pair)| < 6
0
5
10
15
20
25
30
35
40
PT(m+m-) (GeV/c)
Tevatron Run2
1.0E-04
 Average Lepton-Pair transverse
momentum  Shape of the Lepton-Pair pT distribution at the
0
50
100
150
250
Z-boson
mass 200
at the Tevatron
and the LHC for
at the Tevatron and the LHC for PYTHIA
PT (m+m-) (GeV/c)
PYTHIA Tune DW and HERWIG (without MPI).
Tune DW and HERWIG (without MPI).
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 26
Z-Boson: “Towards” Region
RDF LHC
Prediction!
"Toward" Charged Particle Density:
dN/dhd
"Toward" Charged Particle Density: dN/dhd
RDF Preliminary
PY Tune AW
PY Tune DW
generator level
RDF Preliminary
Drell-Yan
1.96 TeV
"Toward" Charged Density
"Toward" Charged Density
PY ATLAS
1.6
0.8
0.6
0.4
PY64 Tune P329
PY64 Tune S320
0.2
70 < M(pair) < 110 GeV
PY Tune DWT
generator level
1.2
0.8
PY Tune DW
PY64 Tune P329
PY64 Tune S320
0.4
70 < M(pair) < 110 GeV
Drell-Yan
14 TeV
If the LHC data are not in
the range shown here then
we learn new (QCD) physics!
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0.0
0
25
50
75
100
125
150
0
25
D
“Transverse”
100
125
Z-BosonDirection
D
“Toward”
“Toward”
“Transverse”
75
Lepton-Pair PT (GeV/c)
Lepton-Pair PT (GeV/c)
Z-BosonDirection
50
Tevatron
LHC
“Transverse”
“Transverse”
“Away”
“Away”
 Data at 1.96 TeV on the density of charged particles, dN/dhd, with pT > 0.5 GeV/c and |h| < 1 for “Z-
Boson” events as a function of PT(Z) for the “toward” region from PYTHIA Tune AW, Tune DW, Tune
S320, and Tune P329 at the particle level (i.e. generator level).
 Extrapolations of PYTHIA Tune AW, Tune DW, Tune DWT, Tune S320, and Tune P329, and pyATLAS to
the LHC.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 27
150
PYTHIA Tune A Min-Bias
“Soft” + ”Hard”
Tuned to fit the CDF Run 1
“underlying event”!
PYTHIA Tune A
CDF Run 2 Charged
DefaultParticle Density
Charged Particle Density: dN/dhd
1.0
CDF Published
1.0E+00
0.8
CDF Min-Bias Data
1.0E-01
0.6
0.4
0.2
Pythia 6.206 Set A
1.8 TeV all PT
CDF Min-Bias 1.8 TeV
0.0
-4
-3
-2
-1
0
1
2
3
4
Pseudo-Rapidity h
 PYTHIA regulates the perturbative 2-to-2
parton-parton cross sections with cut-off
parameters
which allows one to run with
Lots of “hard” scattering in
PT“Min-Bias”
(hard) > 0.
One
can simulate both “hard”
at the
Tevatron!
and “soft” collisions in one program.
Charged Density dN/dhddPT (1/GeV/c)
dN/dhd
Pythia 6.206 Set A
1.8 TeV |h|<1
1.0E-02
12% of “Min-Bias” events
have PT(hard) > 5 GeV/c!
PT(hard) > 0 GeV/c
1.0E-03
1% of “Min-Bias” events
have PT(hard) > 10 GeV/c!
1.0E-04
1.0E-05
CDF Preliminary
1.0E-06
0
2
4
6
8
10
12
14
PT(charged) (GeV/c)
 The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.
 This PYTHIA fit predicts that 12% of all “Min-Bias” events are a result of a hard 2-to-2
parton-parton scattering with PT(hard) > 5 GeV/c (1% with PT(hard) > 10 GeV/c)!
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 28
PYTHIA Tune A
LHC Min-Bias Predictions
Hard-Scattering in Min-Bias Events
Charged Particle Density
50%
12% of “Min-Bias”
events
have|h|<1
PT(hard) > 10 GeV/c!
1.0E+00
Pythia 6.206 Set A
Pythia 6.206 Set A
40%
% of Events
Charged Density dN/dhddPT (1/GeV/c)
1.0E-01
1.0E-02
PT(hard) > 5 GeV/c
PT(hard) > 10 GeV/c
30%
20%
1.8 TeV
1.0E-03
10%
14 TeV
1.0E-04
0%
100
1,000
10,000
100,000
CM Energy W (GeV)
630 GeV
LHC?
1.0E-05
 Shows the center-of-mass energy dependence
CDF Data
1.0E-06
0
2
4
6
8
PT(charged) (GeV/c)
1% of “Min-Bias” events
have PT(hard) > 10 GeV/c!
10
12
14
of the charged particle density,
dNchg/dhddPT, for “Min-Bias” collisions
compared with PYTHIA Tune A with
PT(hard) > 0.
 PYTHIA Tune A predicts that 1% of all “Min-Bias” events at 1.8 TeV are a result of a hard
2-to-2 parton-parton scattering with PT(hard) > 10 GeV/c which increases to 12% at 14 TeV!
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 29
Charged Particle Density: dN/dh
Charged Particle Density: dN/dh
Charged Particle Density: dN/dh
5.0
2.0
Charged Particle Density
Charged Particle Density
generator level
4.0
3.0
PY Tune DW
2.0
PY64 Tune S320
PY64 Tune P329
1.0
PY64 Tune P329
PY Tune A
RDF Preliminary
Min-Bias
1.96 TeV
Charged Particles (all PT)
RDF Preliminary
generator level
1.5
PY Tune DW
PY Tune A
1.0
PY64 Tune S320
0.5
Min-Bias
1.96 TeV
Charged Particles (PT>0.5 GeV/c)
0.0
0.0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
PseudoRapidity h
-4
-2
0
2
4
6
8
PseudoRapidity h
Charged particle (all pT) pseudo-rapidity Charged particle (pT>0.5 GeV/c) pseudodistribution, dNchg/dhd, at 1.96 TeV for
inelastic non-diffractive collisions from
PYTHIA Tune A, Tune DW, Tune S320, and
Tune P324.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
rapidity distribution, dNchg/dhd, at 1.96
TeV for inelastic non-diffractive collisions
from PYTHIA Tune A, Tune DW, Tune
S320, and Tune P324.
Rick Field – Florida/CDF/CMS
Page 30
Charged Particle Density: dN/dh
RDF LHC Prediction!
Charged Particle Density: dN/dh
Charged Particle Density: dN/dh
5.0
8.0
Charged Particle Density
Charged Particle Density
PY Tune A
RDF Preliminary
generator level
4.0
PY ATLAS
3.0
PY Tune DW
2.0
PY64 Tune S320
PY64 Tune P329
1.0
Min-Bias
1.96 TeV
Charged Particles (all PT)
0.0
PY64 Tune P329
RDF Preliminary
generator level
PY Tune DWT
6.0
PY ATLAS
4.0
PY Tune DW
PY Tune A
PY64 Tune S320
2.0
If the LHC data are not in
the range shown here then
we learn new (QCD) physics!
0.0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
-4
-2
PseudoRapidity h
“Minumum Bias” Collisions
Proton
Min-Bias
14 TeV
Charged Particles (all PT)
2
4
6
PseudoRapidity h
AntiProton
Tevatron
0
Proton
“Minumum Bias” Collisions
Proton
LHC
Charged particle (all pT) pseudo-rapidity distribution, dNchg/dhd, at 1.96 TeV for
inelastic non-diffractive collisions from PYTHIA Tune A, Tune DW, Tune S320, and
Tune P324.
Extrapolations (all pT) of PYTHIA Tune A, Tune DW, Tune S320, Tune P324. and
ATLAS to the LHC.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 31
8
Charged Particle Density: dN/dh
RDF LHC Prediction!
Charged Particle Density: dN/dh
Charged
ChargedParticle
Particle Density:
Density:dN/dh
dN/dh
4.0
generator
generatorlevel
level
1.5
1.5
PY
PYTune
TuneDW
DW
PY ATLAS
PY64
PY64Tune
TuneS320
S320
0.5
0.5
Min-Bias
Min-Bias
1.96
1.96TeV
TeV
Charged
ChargedParticles
Particles(PT>0.5
(PT>0.5GeV/c)
GeV/c)
0.0
0.0
PY64 Tune P329
generator level
3.0
PY64 Tune S320
2.0
PY Tune A
PY Tune DW
1.0
Min-Bias
14 TeV
Charged Particles (PT>0.5 GeV/c)
If the LHC data are not in
the range shown here then
we learn new (QCD) physics!
0.0
-8
-8
-6
-6
-4
-4
-2
-2
00
22
44
66
88
-8
-6
-4
-2
PseudoRapidity
PseudoRapidityhh
“Minumum Bias” Collisions
Proton
PY ATLAS
RDF Preliminary
PY
PYTune
TuneAA
1.0
1.0
PY Tune DWT
PY64
PY64Tune
TuneP329
P329
RDF
RDFPreliminary
Preliminary
Charged Particle Density
Charged Particle
Particle Density
Density
Charged
2.0
2.0
2
4
6
8
PseudoRapidity h
AntiProton
Tevatron
0
Proton
“Minumum Bias” Collisions
Proton
LHC
Charged particle (pT > 0.5 GeV/c) pseudo-rapidity distribution, dNchg/dhd, at 1.96 TeV
for inelastic non-diffractive collisions from PYTHIA Tune A, Tune DW, Tune S320, and
Tune P324.
Extrapolations (pT > 0.5 GeV/c) of PYTHIA Tune A, Tune DW, Tune S320, Tune P324.
and ATLAS to the LHC.
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 32
LHC Predictions
“Minumum Bias” Collisions
Proton
AntiProton
Charged Particle Density: dN/dh
8.0
Charged Particle Density
I believe because of the STAR analysis we are now
in a position to make some predictions at the LHC!
 The amount of activity in “min-bias” collisions.
Underlying Event
Final-State
Radiation
PY Tune DW
PY Tune A
PY64 Tune S320
2.0
-8
-6
-4
-2
“Away”
scattering events.
0
2
4
6
8
PseudoRapidity h
"Transverse" Charged Particle Density: dN/dhd
“Toward”
“Transverse”
Min-Bias
14 TeV
Charged Particles (all PT)
1.6
 The amount of activity in the “underlying event” in hard
Drell-Yan Production
4.0
If the LHC data are not in
the range shown here then
we learn new (QCD) physics!
“Transverse”
Outgoing Parton
PY ATLAS
0.0
"Transverse" Charged Density
AntiProton
PY Tune DWT
6.0
D
Initial-State Radiation
Underlying Event
generator level
PTmax Direction
Outgoing Parton
PT(hard)
Proton
PY64 Tune P329
RDF Preliminary
PY ATLAS
RDF Preliminary
PY Tune DWT
generator level
1.2
0.8
PY64 Tune P329
PY Tune A
0.4
PY Tune DW
PY64 Tune S320
Min-Bias
14 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
5
10
Z-BosonDirection
15
20
25
PTmax (GeV/c)
D
Lepton
"Toward" Charged Particle Density: dN/dhd
“Toward”
Underlying Event
Underlying Event
PY ATLAS
RDF Preliminary
AntiProton
“Transverse”
“Transverse”
“Away”
Anti-Lepton
 The amount of activity in the “underlying event” in DrellYan events.
"Toward" Charged Density
Proton
1.6
PY Tune DWT
generator level
1.2
0.8
PY Tune DW
PY64 Tune P329
PY64 Tune S320
0.4
70 < M(pair) < 110 GeV
Drell-Yan
14 TeV
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
25
50
75
100
125
150
Lepton-Pair PT (GeV/c)
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
Page 33
Summary & Conclusions
However, I believe that the
better fits to the LEP
fragmentation data at high z
will lead to small improvements
Outgoing Parton
of Tune A at the
Tevatron!
 We are making good progress in understanding and modeling the
“underlying event”. RHIC data at 200 GeV are very important!
PT(hard)
Initial-State Radiation
Proton
 The new Pythia pT ordered tunes (py64 S320 and py64 P329)
are very similar to Tune A, Tune AW, and Tune DW. At present
the new tunes do not fit the data better than Tune AW and Tune
DW. However, the new tune are theoretically preferred!
AntiProton
Underlying Event
Underlying Event
Outgoing Parton
Final-State
Radiation
Hard-Scattering Cut-Off PT0
PYTHIA 6.206
e = 0.25 (Set A))
4
PT0 (GeV/c)
 It is clear now that the default value PARP(90) = 0.16 is
not correct and the value should be closer to the Tune A
value of 0.25.
 The new and old PYTHIA tunes are beginning to
converge and I believe we are finally in a position to make
some legitimate predictions at the LHC!
5
3
2
e = 0.16 (default)
1
 All tunes with the default value PARP(90) = 0.16 are
wrong and are overestimating the activity of min-bias and
the underlying event at the LHC! This includes all my
“T” tunes and the ATLAS tunes!
 Need to measure “Min-Bias” and the “underlying
event” at the LHC as soon as possible to see if there is
new QCD physics to be learned!
Joint Meeting on Early LHC Physics
CERN - August 14, 2009
Rick Field – Florida/CDF/CMS
100
1,000
10,000
100,000
CM Energy W (GeV)
UE&MB@CMS
Page 34