Physics and Techniques
of Event Generators
IPPP Durham, April 18-20, 2007
Min-Bias and the Underlying Event
at the TEVATRON and the LHC
Rick Field
University of Florida
(for the CDF & CMS Collaborations)
1st Lecture
UE&MB@CMS
 The early days of event generators.
 “Min-Bias” at the Tevatron.
Outgoing Parton
and extrapolations to the LHC.
PT(hard)
Initial-State Radiation
 Studying the “underlying event” in
Run 1 at CDF.
Proton
Underlying Event
CMS at the LHC
CDF Run 2
MCnet07 - Durham - Part 1
April 18-20, 2007
AntiProton
Underlying Event
Rick Field – Florida/CDF/CMS
Outgoing Parton
Final-State
Radiation
Page 1
Toward and Understanding of
Hadron-Hadron Collisions
Feynman-Field Phenomenology1
Feynman
 From 7 GeV/c
and
hat!
Field
Outgoing Parton
p0’s
to 600 GeV/c
Jets. The early days of trying to
understand and simulate
hadron-hadron collisions.
PT(hard)
Initial-State Radiation
Proton
AntiProton
Underlying Event
Outgoing Parton
MCnet07 - Durham - Part 1
April 18-20, 2007
st
Rick Field – Florida/CDF/CMS
Underlying Event
Final-State
Radiation
Page 2
The Feynman-Field Days
1973-1983
“Feynman-Field
Jet Model”
 FF1: “Quark Elastic Scattering as a Source of High Transverse Momentum
Mesons”, R. D. Field and R. P. Feynman, Phys. Rev. D15, 2590-2616 (1977).
 FFF1: “Correlations Among Particles and Jets Produced with Large Transverse
Momenta”, R. P. Feynman, R. D. Field and G. C. Fox, Nucl. Phys. B128, 1-65
(1977).
 FF2: “A Parameterization of the properties of Quark Jets”, R. D. Field and R. P.
Feynman, Nucl. Phys. B136, 1-76 (1978).
 F1: “Can Existing High Transverse Momentum Hadron Experiments be
Interpreted by Contemporary Quantum Chromodynamics Ideas?”, R. D. Field,
Phys. Rev. Letters 40, 997-1000 (1978).
 FFF2: “A Quantum Chromodynamic Approach for the Large Transverse
Momentum Production of Particles and Jets”, R. P. Feynman, R. D. Field and G.
C. Fox, Phys. Rev. D18, 3320-3343 (1978).
 FW1: “A QCD Model for e+e- Annihilation”, R. D. Field and S. Wolfram, Nucl.
Phys. B213, 65-84 (1983).
My 1st graduate
student!
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 3
Hadron-Hadron Collisions
FF1 1977 (preQCD)
 What happens when two hadrons
collide at high energy?
Hadron
Hadron
Feynman quote from FF1
???
“The model we shall choose is not a popular one,
 Most of the time the hadrons
ooze
so that we will not duplicate too much of the
through each other andwork
fall apart
(i.e.who are similarly analyzing
of others
no hard scattering). The
outgoing
various
models (e.g. constituent interchange
particles continue in roughly
the same
model, multiperipheral
models, etc.). We shall
Parton-Parton Scattering Outgoing Parton
assume
direction as initial proton
andthat the high PT particles arise from
“Soft” constituent
Collision (no large transverse momentum)
direct hard collisions between
antiproton.
quarks in the incoming particles, which
Hadron
Hadron
 Occasionally there will
be a large
fragment
or cascade down
into several hadrons.”
transverse momentum meson.
Question: Where did it come from?
 We assumed it came from quark-quark
elastic scattering, but we did not know
how to calculate it!
Outgoing Parton
high PT meson
“Black-Box Model”
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 4
Quark-Quark Black-Box Model
No gluons!
Quark Distribution Functions
determined from deep-inelastic
lepton-hadron collisions
FF1 1977 (preQCD)
Feynman quote from FF1
“Because of the incomplete knowledge of
our functions some things can be predicted
with more certainty than others. Those
experimental results that are not well
predicted can be “used up” to determine
these functions in greater detail to permit
better predictions of further experiments.
Our papers will be a bit long because we
wish to discuss this interplay in detail.”
Quark-Quark Cross-Section
Unknown! Deteremined from
hadron-hadron collisions.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Quark Fragmentation Functions
determined from e+e- annihilations
Page 5
Quark-Quark Black-Box Model
Predict
particle ratios
FF1 1977 (preQCD)
Predict
increase with increasing
CM energy W
“Beam-Beam
Remnants”
Predict
overall event topology
(FFF1 paper 1977)
7 GeV/c p0’s!
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 6
QCD Approach: Quarks & Gluons
Quark & Gluon Fragmentation
Functions
2
Q dependence predicted from QCD
Parton Distribution Functions
Q2 dependence predicted from
QCD
FFF2 1978
Feynman quote from FFF2
“We investigate whether the present
experimental behavior of mesons with
large transverse momentum in hadron-hadron
collisions is consistent with the theory of
quantum-chromodynamics (QCD) with
asymptotic freedom, at least as the theory
is now partially understood.”
Quark & Gluon Cross-Sections
Calculated from QCD
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 7
High PT Jets
CDF (2006)
Feynman, Field, & Fox (1978)
Predict
large “jet”
cross-section
30 GeV/c!
Feynman quote from FFF
600writing,
GeV/c Jets!
“At the time of this
there is
still no sharp quantitative test of QCD.
An important test will come in connection
with the phenomena of high PT discussed here.”
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 8
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
+ 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
The “hard core” component
contains both “hard” and
“soft” collisions.
“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
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 9
No-Bias vs Min-Bias
Charged Particle Density: dN/dh
Charged Particle Density: dN/dh
5
5
No Trigger
900 GeV Generated
pyDWT DD NoTtrig
4
pyDW HC Mbtrig
Charged Particle Density
Charged Particle Density
pyDWT HC NoTrig
pyDWT SD NoTrig
3
2
1
CDF Min-Bias Trigger
900 GeV Generated
pyDW DD MBtrig
4
pyDW SD MBtrig
3
2
What you see for
“Min-Bias”
1
depends on your
triggger!
By comparing
different
0
-4
-2
0
2
4
6
8
-8
-6
-4
-2
0
2
4
“Min-Bias”
triggers
one
can
PseudoRapidity h
PseudoRapidity h
learn about the components!
Charged Particle Density: dN/dh
Charged Particle Density: dN/dh
Charged Particles (all PT)
Charged Particles (all PT)
0
-8
-6
5
8
5
No Trigger
900 GeV Weighted
pyDWT HC NoTrig
4
pyDWT Sum MBtrig
Charged Particle Density
pyDWT Sum NoTrig
Charged Particle Density
6
pyDWT DD NoTtrig
pyDWT SD NoTrig
3
2
1
Charged Particles (all PT)
0
CDF Min-Bias Trigger
900 GeV Weighted
pyDWT HC MBtrig
4
pyDWT DD MBtrig
pyDWT SD MBtrig
3
2
1
Charged Particles (all PT)
0
-8
-6
-4
-2
0
2
4
6
8
-8
-6
PseudoRapidity h
MCnet07 - Durham - Part 1
April 18-20, 2007
-4
-2
0
2
4
6
8
PseudoRapidity h
Rick Field – Florida/CDF/CMS
Page 10
No-Bias vs Min-Bias
About 2.5 charged particles
per unit h at h = 0.
Charged Particle Density: dN/dh
PYTHIA Tune
Tune DW
DW
Charged Particles
Particles
No-Bias 1.96 TeV
(HC+SD+DD+EL)
3
About 0.9 charged particles (pT >
0.5 GeV/c) per unit h at h = 0.
All
All PT
PT
PT > 0.5 GeV/c
2
Charged Particle Density: dN/dh
2.0
1
0
-10
-8
-6
-4
-2
0
2
4
6
88
10
10
PseudoRapidity h
 Charged particle (all pT) pseudo-rapidity
distribution, dNchg/dhdf, at 1.96 TeV with
no trigger (i.e. no-bias) from PYTHIA
Tune DW.
Charged Particle Density
Charged
Charged Particle Density
4
PYTHIA Tune DW
Charged Particles (PT > 0.5 GeV/c)
Min-Bias 1.96 TeV
(HC+SD+DD+EL)
1.5
No Trigger
CDF Min-Bias
Trigger
1.0
0.5
0.0
-10
-8
-6
-4
-2
0
2
4
6
8
10
PseudoRapidity h
 Charged particle (pT > 0.5 GeV/c) pseudo-
About 1.5 charged particles (pT >
0.5 GeV/c) per unit h at h = 0
with CDF min-bias trigger.
MCnet07 - Durham - Part 1
April 18-20, 2007
rapidity distribution, dNchg/dhdf, at 1.96
TeV with the CDF Min-Bias trigger from
PYTHIA Tune DW.
Rick Field – Florida/CDF/CMS
Page 11
Min-Bias Particle Types
With Stable Particles
With ct = 10mm
This is a bigger effect
than I expected!
No-Bias at 14 TeV
charged particle density: 10mm vs Stable
Charged Particle Density: dN/dh
Charged Particle Density
6
Min-Bias 14 TeV
PY Tune DWT
4
2
pyDWT HC+SD+DD NoTrig
pyDWT HC+SD+DD NoTrig 10mm
Charged Particles (all PT)
0
-8
-6
-4
-2
0
2
4
6
8
PseudoRapidity h
 Using ct = 10 mm reduces the
charged particle density by
almost 10%! Mostly from
Ks→p+p- (68.6%) and L →pp(64.2%).
MCnet07 - Durham - Part 1
April 18-20, 2007
CDF Run 2
Proton
Rick Field – Florida/CDF/CMS
AntiProton
Primary
60 cm
Page 12
Particle Densities
DhDf = 4p = 12.6
2p
f
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-f
dNchg
chg/dhdf = 1/4p
3/4p = 0.08
0.24
13 GeV/c PTsum
0
-1
h
+1
Divide by 4p
dPTsum/dhdf = 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/dhdf, and the charged scalar pT sum density,
dPTsum/dhdf.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 13
CDF Run 1 “Min-Bias” Data
Charged Particle Density
Charged Particle Density: dN/dhdf
Charged Particle Pseudo-Rapidity Distribution: dN/dh
1.0
7
CDF Published
CDF Published
6
0.8
dN/dhdf
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/dhdf> = 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).
DhxDf = 1
Convert to charged particle density, dNchg/dhdf, by dividing by 2p.
Df = 1
There are about 0.67 charged particles per unit h-f 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-f in “Min-Bias”
Dh = 1
collisions at 1.96 TeV (|h| < 1, pT > 0.5 GeV/c).
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 14
CDF Run 1 “Min-Bias” Data
Energy Dependence
Charged Particle Density: dN/dhdf
Charged Particle Density: dN/dhdf
1.4
1.0
CDF Published
CDF Data
UA5 Data
Fit 2
Fit 1
1.2
Charged density dN/dhdf
dN/dhdf
0.8
0.6
0.4
0.2
CDF Min-Bias 630 GeV
CDF Min-Bias 1.8 TeV
1.0
0.8
0.6
0.4
0.2
all PT
h=0
0.0
-4
-3
-2
-1
0
1
2
3
4
0.0
10
Pseudo-Rapidity h
100
1,000
10,000
100,000
CM Energy W (GeV)
LHC?
<dNchg/dhdf> = 0.51
h = 0 630 GeV
24% increase
<dNchg/dhdf> = 0.63
h = 0 1.8 TeV
 Shows the center-of-mass energy dependence of the charged particle density, dNchg/dhdf,

for “Min-Bias” collisions at h = 0. Also show a log fit (Fit 1) and a (log)2 fit (Fit 2) to the
CDF plus UA5 data.
What should we expect for the LHC?
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 15
Herwig “Soft” Min-Bias
Can
Can we
we believe
believe HERWIG
HERWIG
“soft”
Min-Bias?
“soft”
Min-Bias?
No!
Charged Particle Density: dN/dhdf
Charged Particle Density: dN/dhdf
1.4
1.4
14 TeV
Herwig "Soft" Min-Bias
1.2
CDF Data
1.2
Charged density dN/dhdf
UA5 Data
dN/dhdf
1.0
0.8
0.6
0.4
1.8 TeV
0.2
Fit 2
1.0
Fit 1
HW Min-Bias
0.8
0.6
0.4
0.2
630 GeV
all PT
h=0
0.0
0.0
-6
-4
-2
0
2
4
6
10
Pseudo-Rapidity h
100
1,000
10,000
CM Energy W (GeV)
100,000
LHC?
 Shows the center-of-mass energy dependence of the charged particle density, dNchg/dhdf,

for “Min-Bias” collisions compared with the HERWIG “Soft” Min-Bias Monte-Carlo
model. Note: there is no “hard” scattering in HERWIG “Soft” Min-Bias.
HERWIG “Soft” Min-Bias contains no hard parton-parton interactions and describes fairly
well the charged particle density, dNchg/dhdf, in “Min-Bias” collisions.
 HERWIG “Soft” Min-Bias predicts a 45% rise in dNchg/dhdf at h = 0 in going from the
Tevatron (1.8 TeV) to the LHC (14 TeV). 4 charged particles per unit h becomes 6.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 16
CDF Run 1 “Min-Bias” Data
pT Distribution
Lots of “hard” scattering
in “Min-Bias”!
Charged Particle Density: dN/dhdf
Charged Particle Density
1.4
1.0E+01
14 TeV
Herwig "Soft" Min-Bias
1.2
HERWIG “Soft” Min-Bias
|h|<1
1.0E+00
0.8
0.6
0.4
1.8 TeV
0.2
630 GeV
all PT
0.0
-6
-4
-2
0
2
4
6
Pseudo-Rapidity h
 Shows the energy dependence of the
charged particle density, dNchg/dhdf, for
“Min-Bias” collisions compared with
HERWIG “Soft” Min-Bias.
Charged Density dN/dhdfdPT (1/GeV/c)
1.0
dN/dhdf
CDF Preliminary
CDF Min-Bias Data at 1.8 TeV
1.0E-01
1.0E-02
HW "Soft" Min-Bias
at 630 GeV, 1.8 TeV, and 14 TeV
1.0E-03
1.0E-04
1.0E-05
1.0E-06
0
2
4
6
8
10
12
14
PT (GeV/c)
 Shows the pT dependence of the charged particle density, dNchg/dhdfdPT, for “Min-Bias”
collisions at 1.8 TeV collisions compared with HERWIG “Soft” Min-Bias.
 HERWIG “Soft” Min-Bias does not describe the “Min-Bias” data! The “Min-Bias” data
contains a lot of “hard” parton-parton collisions which results in many more particles at
large PT than are produces by any “soft” model.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 17
CDF Run 1 “Min-Bias” Data
Combining “Soft” + “Hard”
No easy way to
“mix” HERWIG “hard”
with HERWIG “soft”.
sHC
Hard-Scattering Cross-Section
Charged
Particle Density
100.00
Charged Particle Density: dN/dhdf
1.6
CTEQ5L
1.8 TeV
Cross-Section (millibarns)
1.0E+01
1.4
Herwig Jet3
Herwig Min-Bias
CDF Min-Bias Data
10.00
CDF Preliminary
1.2
1.0E+00
1.0
HW PT(hard) > 3 GeV/c
0.8
0.6
0.4
0.2
HW "Soft" Min-Bias
1.8 TeV all PT
0.0
-4
-3
-2
-1
0
1
2
3
4
Pseudo-Rapidity h
CDF Min-Bias Data
Herwig Jet3
Herwig Min-Bias
 HERWIG “hard” QCD with PT(hard) > 3
GeV/c describes well the high pT tail but
produces too many charged particles
overall. Not all of the “Min-Bias” collisions
have a hard scattering with PT(hard) > 3
GeV/c!
Charged Density dN/dhdfdPT (1/GeV/c)
dN/dhdf
HERWIG diverges!
1.0E-01
1.0E-02
1.00
1.8 TeV |h|<1
0.10
PYTHIA
HERWIG
HW PT(hard) > 3 GeV/c
0.01
0
2
4
6
8
10
12
14
16
18
PYTHIA cuts off
the divergence.
HW "Soft" Min-Bias
Can run
PT(hard)>0!
1.0E-03
1.0E-04
1.0E-05
1.0E-06
0
2
4
6
8
10
12
14
PT (GeV/c)
HERWIG “soft”
Min-Bias does not fit
the “Min-Bias” data!
 One cannot run the HERWIG “hard” QCD Monte-Carlo with PT(hard) < 3 GeV/c because
the perturbative 2-to-2 cross-sections diverge like 1/PT(hard)4?
MCnet07 - Durham - Part 1
April 18-20, 2007
20
Hard-Scattering Cut-Off PTmin
Rick Field – Florida/CDF/CMS
Page 18
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/dhdf
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
P“Min-Bias”
can simulate both “hard”
theOne
Tevatron!
T(hard) >at0.
and “soft” collisions in one program.
Charged Density dN/dhdfdPT (1/GeV/c)
dN/dhdf
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)!
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 19
CDF Run 2 Min-Bias “Associated”
Charged Particle Density
“Associated” densities do
not include PTmax!
Highest pT
charged particle!
Charged Particle Density: dN/dhdf
PTmax Direction
PTmax Direction
0.5
Df
Correlations in f
Charged Particle Density
CDF Preliminary
Associated Density
PTmax not included
data uncorrected
0.4
Df
Charge Density
0.3
0.2
0.1
Min-Bias
Correlations
in f
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
Df (degrees)
 Use the maximum pT charged particle in the event, PTmax, to define a direction and

is “associated”
more probable
to finddN
a chg
particle
look at the It
the
density,
/dhdf, in “min-bias” collisions (pT > 0.5
accompanying
PTmax
than
it
is to
GeV/c, |h| < 1).
find a particle in the central region!
Shows the data on the Df dependence of the “associated” charged particle density,
dNchg/dhdf, 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/dhdf, for “min-bias” events.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 20
CDF Run 2 Min-Bias “Associated”
Charged Particle Density Rapid rise in the particle
density in the “transverse”
region as PTmax increases!
Associated Particle Density: dN/dhdf
PTmaxDirection
Direction
PTmax
Df
“Toward”
“Transverse”
“Transverse”
Correlations in f
“Away”
Associated Particle Density
Jet #1
Df
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
Df (degrees)
Ave Min-Bias
0.25 per unit h-f
PTmax > 0.5 GeV/c
 Shows the data on the Df dependence of the “associated” charged particle density,
dNchg/dhdf, 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!).
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 21
CDF Run 2 Min-Bias “Associated”
Charged Particle Density
PY Tune A
PTmax > 2.0 GeV/c
PTmax Direction
Direction
PTmax
Df
“Toward”
“Transverse”
“Transverse”
Correlations in f
“Away”
PTmax > 2.0 GeV/c
Associated Particle Density
Df
Associated Particle Density: dN/dhdf
1.0
CDF Preliminary
PY Tune A
0.8
data uncorrected
theory + CDFSIM
PTmax > 0.5 GeV/c
PY Tune A
Transverse
Region
0.6
PY Tune A 1.96 TeV
Transverse
Region
0.4
0.2
PTmax
PTmax not included
(|h|<1.0, PT>0.5 GeV/c)
0.0
0
30
60
90
120
PTmax > 0.5 GeV/c
150
180
210
240
270
300
330
360
Df (degrees)
 Shows the data on the Df dependence of the “associated” charged particle density,
dNchg/dhdf, 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 GeV/c and PTmax >
2.0 GeV/c compared with PYTHIA Tune A (after CDFSIM).
 PYTHIA Tune A predicts a larger correlation than is seen in the “min-bias” data (i.e.
Tune A “min-bias” is a bit too “jetty”).
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 22
PYTHIA Tune A
LHC Min-Bias Predictions
Charged Particle Density: dN/dhdf
Charged Particle Density: dN/dhdf
1.4
1.4
Pythia 6.206 Set A
CDF Data
14 TeV
Charged density dN/dhdf
1.0
dN/dhdf
Pythia 6.206 Set A
CDF Data
UA5 Data
Fit 2
Fit 1
1.2
1.2
1.8 TeV
0.8
0.6
0.4
0.2
0.8
0.6
0.4
0.2
all PT
630 GeV
1.0
h=0
0.0
-6
-4
-2
0
Pseudo-Rapidity h
2
4
6
LHC?
0.0
10
100
1,000
10,000
100,000
CM Energy W (GeV)
 Shows the center-of-mass energy dependence of the charged particle density, dNchg/dhdf,
for “Min-Bias” collisions compared with PYTHIA Tune A with PT(hard) > 0.
 PYTHIA was tuned to fit the “underlying event” in hard-scattering processes at 1.8 TeV
and 630 GeV.
 PYTHIA Tune A predicts a 42% rise in dNchg/dhdf at h = 0 in going from the Tevatron (1.8
TeV) to the LHC (14 TeV). Similar to HERWIG “soft” min-bias, 4 charged particles per
unit h becomes 6.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 23
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/dhdfdPT (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
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
dependence of the charged particle density,
dNchg/dhdfdPT, 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!
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 24
PYTHIA 6.2 Tunes
LHC Min-Bias Predictions
Charged Particle Density: dN/dY
Charged Particle Density: dN/dh
12
pyA
pyDW
pyDWT
ATLAS
Generator Level
14 TeV
8
Charged Particle Density
Charged Particle Density
10
6
4
2
pyA
pyDW
pyDWT
ATLAS
Generator Level
14 TeV
10
8
6
4
2
Charged Particles (all pT)
Charged Particles (all pT)
0
0
-10
-8
-6
-4
-2
0
2
4
6
8
10
-10
-8
-6
-4
PseudoRapidity h
-2
0
2
4
6
8
10
Rapidity Y
 Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for
the charged particle density dN/dh and dN/dY at 14 TeV (all pT).
 PYTHIA Tune A and Tune DW predict about 6 charged particles per unit h at h = 0, while
the ATLAS tune predicts around 9.
 PYTHIA Tune DWT is identical to Tune DW at 1.96 TeV, but extrapolates to the LHC using
the ATLAS energy dependence.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 25
PYTHIA 6.2 Tunes
LHC Min-Bias Predictions
Average Number of Charged Particles vs PTmin
Charged PT Distribution
20
100.0
Generator Level
Min-Bias 14 TeV
pyA <PT> = 641 MeV/c
Generator Level
Min-Bias 14 TeV
pyDW <PT> = 665 MeV/c
15
pyA
pyDW
pyDWT
ATLAS
<Nchg>
1/Nev dN/dPT (1/GeV/c)
pyDWT <PT> = 693 MeV/c
ATLAS <PT> = 548 MeV/c
10.0
10
5
Charged Particles (|h|<1.0, PT>PTmin)
1.0
0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Minimum PT (GeV/c)
Charged Particles (|h|<1.0)
0.1
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Charged Particle PT (GeV/c)
 Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for
the charged particle pT distribution at 14 TeV (|h| < 1) and the average number of charged
particles with pT > pTmin (|h| < 1).
 The ATLAS tune has many more “soft” particles than does any of the CDF Tunes. The
ATLAS tune has <pT> = 548 MeV/c while Tune A has <pT> = 641 MeV/c (100 MeV/c more
per particle)!
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 26
Charged <PT> versus Nchg
The charged <PT>
rises with Nchg!
Average PT versus Nchg
1.6
CDF Preliminary
Average PT (GeV/c)
PYTHIA Tune A 1.96 TeV
data uncorrected
theory + CDFSIM
1.4
Min-Bias
1.2
1.0
0.8
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.6
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
Number of Charged Particles
 Shows the average transverse momentum of charged particles (|h|<1, pT>0.5 GeV)
versus the number of charged particles, Nchg, for the CDF Run 2 Min-Bias events.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 27
Using Pile-Up to Study Min-Bias
High PT Jet
CDF Run 2
Proton
AntiProton
Pile-Up
Primary
60 cm
MB
 The primary vertex is the highest PTsum of charged particles pointing towards it.
 Normally one only includes those charged particles which point back to the primary
vertex.
 However, the primary vertex is presumably the collision that satisfied the trigger
and is hence biased.
 Perhaps the pile-up is not biases and can serve as a new type of “Min-Bias” trigger.
 This assumes that the pile-up is not affected by the trigger (i.e. it is the same for all
primary processes).
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 28
Using Pile-Up to Study Min-Bias
About 2.6 charged particles
per unit h at h = 0.
Charged
Charged Particle
Particle Density:
Density: dN/dh
dN/dh
Charged Particle
Particle Density
Density
Charged
44
CDF
CDF Pre-Preliminary
Pre-Preliminary
Primary
Primary
Min-Bias
Min-Bias at
at 1.96
1.96 TeV
TeV
33
22
11
Pile-Up
00
-2.0
-2.0
-1.5
-1.5
-1.0
-1.0
Charged
Charged Particles
Particles (PT
(PT >> 0.5
0.5 GeV/c)
GeV/c)
-0.5
-0.5
0.0
0.0
0.5
0.5
1.0
1.0
1.5
1.5
2.0
2.0
PseudoRapidity
PseudoRapidity hh
About 1.6 charged particles per
unit h at h = 0 per pile-up
interaction.
 Shows the the charged particle density, dNchg/dh, for  Clearly the pile-up “min-bias” is biased
charged particles (pT > 0.5 GeV/c) pointing to the
primary vertex for “Min-Bias” collisions at 1.96
TeV.
 Shows the the charged particle density, dNchg/dh,
(per interaction) for charged particles (pT > 0.5
GeV/c) pointing to the pile-up vertices for “MinBias” collisions at 1.96 TeV.
MCnet07 - Durham - Part 1
April 18-20, 2007
because there must to be some particles
in the central region to form a vertex
(e.g. elestic scattering does not
contribute), but it is less biased than
CDF “min-bias”.
Rick Field – Florida/CDF/CMS
Page 29
Is the Pile-Up Biased?
Pile-Up: Charged Particle Multiplicity
1.0E+00
1.0E+00
Fraction
Fraction of
of Events
Events
Charged Particles
Particles
Charged
(PT >> 0.5
0.5 GeV/c,
GeV/c, |h|
|h| << 1)
1)
(PT
1.0E-01
1.0E-01
The pile-up is different for
Min-bias collisions and high
pT jet production! Amasing!
CDF Pre-Preliminary
1.96 TeV
TeV
1.96
PT(jet#1) > 150 GeV/c
<Nchg> = 4.2
1.0E-02
1.0E-02
1.0E-03
1.0E-03
Min-Bias Events
Events
Min-Bias
<Nchg> == 3.2
3.2
<Nchg>
1.0E-04
1.0E-04
00
55
10
10
15
15
20
20
25
25
30
30
Number of Charged Particles
 Shows the the charged particle multiplicity
distribution (per interaction) for charged particles
(pT > 0.5 GeV/c, |h| <1) pointing to the pile-up
vertices for “Min-Bias” collisions at 1.96 TeV.
Warning! This data is very
preliminary and
not “blessed” by CDF.
So do not believe it yet!
 Shows the the charged particle multiplicity
distribution (per interaction) for charged particles
(pT > 0.5 GeV/c, |h| <1) pointing to the pile-up
vertices for high pT jet production (PT(jet#1) > 150
GeV/c) at 1.96 TeV.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 30
Is the Pile-Up Biased?
Jet#1 DirectionThe pile-up knows the
Correlations in f The

Charged
Particle
Density
Charged
PTsum
Density
(GeV/c)
Charged
Particle
Density
Df
direction of the leading
100.0
100.0
1000.0
high pT jet! Amasing!
Charged
Charged
Particle
Density:dPT/dhdf
dN/dhdf
ChargedPTsum
ParticleDensity:
CDFPreliminary
Preliminary
CDF
Preliminary
CDF
1.96TeV
TeV
1.96
TeV
1.96
100.0
10.0
10.0
Primary
Primary
Primary
150 <150
PT(jet#1)
< PT(jet#1)
< 250< GeV/c
250 GeV/c
Transverse
Pile-Up/Interaction
Region
Pile-Up/Interaction
10.0
1.0
1.0
1.0
pile-up conspires
to help
Warning!
This data is very
Charged
Charged Particles (PT > 0.5 GeV/c, |h| <1)
give you
what0.1
you
0.1
0.1
preliminary
andask for
30 60
60 90
90 120
120 150
150 180
180 210
210 240
240 270 300 330
000 30
330 360
30
60
90
150
360
(i.e. satisfy
your by
“trigger”
or120
not “blessed”
CDF.
Df (degrees)
(degrees)
Df
Df
So doevent
not believe
it yet!
your
selection)!
Shows the data on the Df dependence of the charged particle density, dNchg/dhdf, for
charged particles (pT > 0.5 GeV/c, |h| < 1) pointing to the primary vertex relative to the
leading calorimeter jet (rotated to 270o) for 150 < PT(jet#1) < 250 GeV/c |h(jet#1)| < 2.
 Shows the data on the Df dependence of the charged particle density, dNchg/dhdf, for
charged particles (pT > 0.5 GeV/c, |h| < 1) (per interaction) pointing to the pile-up vertices
relative to the leading calorimeter jet (rotated to 270o) for 150 < PT(jet#1) < 250 GeV/c
|h(jet#1)| < 2.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 31
Min-Bias Summary
“Minumum Bias” Collisions
 “Min-Bias” is not well defined. What you
see depends on what you trigger on! Every
trigger produces some biases. We learn
about “min-bias” by comparing different
“low bias” triggers.
If true this means the pile-up is not the
same for all processes. It is process (i.e.
trigger) dependent! This would have big
implications for the LHC!
AntiProton
Leading Jet
Pile-Up Charged PTsum Density: dPT/dhdf
10.0
Charged PTsum Density (GeV/c)
 Preliminary results seem to show that pileup is biased! and that it conspires to help
give you what you ask for (i.e. satisfy your
“trigger” or your event selection)!
Proton
CDF Preliminary
1.96 TeV
Min-Bias
35 < PT(jet#1) < 80 GeV/c
150 < PT(jet#1) < 250 GeV/c
1.0
Charged Particles (PT > 0.5 GeV/c, |h| <1)
0.1
0
30
60
90
120
150
180
210
240
270
300
330
360
Df (degrees)
I must double check my analysis
and get it “blessed”!
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 32
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!
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 33
CDF Run 1: Evolution of Charged Jets
“Underlying Event”
Charged Particle Df Correlations
PT > 0.5 GeV/c |h| < 1
Charged Jet #1
Direction
“Transverse” region
very sensitive to the
“underlying event”!
Look at the charged
particle density in the
“transverse” region!
2p
“Toward-Side” Jet
Df
“Toward”
CDF Run 1 Analysis
Away Region
Charged Jet #1
Direction
Df
Transverse
Region
“Toward”
“Transverse”
f
Leading
Jet
“Transverse”
Toward Region
“Transverse”
“Transverse”
Transverse
Region
“Away”
“Away”
Away Region
“Away-Side” Jet
0
-1
h
+1
 Look at charged particle correlations in the azimuthal angle Df relative to the leading charged
particle jet.
 Define |Df| < 60o as “Toward”, 60o < |Df| < 120o as “Transverse”, and |Df| > 120o as “Away”.
 All three regions have the same size in h-f space, DhxDf = 2x120o = 4p/3.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 34
Run 1 Charged Particle Density
“Transverse” pT Distribution
"Transverse" Charged Particle Density: dN/dhdf
Charged Particle Density
Charged Particle Jet #1
Direction
"Transverse"
PT(chgjet#1) > 5 GeV/cDf
1.0E+00
CDF Min-Bias
CDF Run 1
CDF JET20
data uncorrected
0.75
0.50
Factor of 2!
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)
PT(charged jet#1) > 30 GeV/c
“Transverse” <dNchg/dhdf> = 0.56
“Min-Bias”
50
Charged Density dN/dhdfdPT (1/GeV/c)
"Transverse" Charged Density
1.00
CDF Run 1
data uncorrected
1.0E-01
“Toward”
"Transverse"
PT(chgjet#1) > 30 GeV/c
1.0E-02
“Transverse”
“Transverse”
1.0E-03
“Away”
1.0E-04
Min-Bias
1.0E-05
1.8 TeV |h|<1 PT>0.5 GeV/c
1.0E-06
CDF Run 1 Min-Bias data
<dNchg/dhdf> = 0.25
0
2
4
6
8
10
12
14
PT(charged) (GeV/c)
 Compares the average “transverse” charge particle density with the average “Min-Bias”
charge particle density (|h|<1, pT>0.5 GeV). Shows how the “transverse” charge particle
density and the Min-Bias charge particle density is distributed in pT.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 35
ISAJET 7.32
“Transverse” Density
ISAJET uses a naïve leading-log
parton shower-model which does
not agree with the data!
Charged Jet #1
Direction
1.00
Df
“Transverse”
“Transverse”
“Away”
CDF Run 1Data
"Transverse" Charged Density
“Toward”
ISAJET
"Transverse" Charged Particle Density: dN/dhdf
Isajet
data uncorrected
theory corrected
0.75
"Hard"
0.50
0.25
“Hard”
Component
"Remnants"
1.8 TeV |h|<1.0 PT>0.5 GeV
Beam-Beam
Remnants
0.00
0
5
10
15
20
25
30
35
40
45
50
PT(charged jet#1) (GeV/c)
 Plot shows average “transverse” charge particle density (|h|<1, pT>0.5 GeV) versus PT(charged
jet#1) compared to the QCD hard scattering predictions of ISAJET 7.32 (default parameters with
PT(hard)>3 GeV/c) .
 The predictions of ISAJET are divided into two categories: charged particles that arise from the
break-up of the beam and target (beam-beam remnants); and charged particles that arise from the
outgoing jet plus initial and final-state radiation (hard scattering component).
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 36
HERWIG 6.4
“Transverse” Density
Df
“Toward”
“Transverse”
“Transverse”
“Away”
1.00
1.00
CDF Run 1Data
CDF
"Transverse" Charged Density
Charged Jet #1
Direction
HERWIG uses a modified leadinglog parton shower-model which
does agrees better with the data!
"Transverse"
"Transverse"Charged
ChargedParticle
ParticleDensity:
Density:dN/dhdf
dN/dhdf
Isajet
Total
"Hard"
data uncorrected
theory corrected
0.75
0.75
"Hard"
0.50
0.50
0.25
0.25
"Remnants"
"Remnants"
Beam-Beam
Remnants
HERWIG
Herwig 6.4 CTEQ5L
PT(hard) > 3 GeV/c
1.8TeV
TeV|h|<1.0
|h|<1.0PT>0.5
PT>0.5GeV
GeV
1.8
0.00
0.00
0
5
10
10
15
15
20
20
25
25
30
30
3535
PT(chargedjet#1)
jet#1) (GeV/c)
(GeV/c)
PT(charged
4040
4545
5050
“Hard”
Component
 Plot shows average “transverse” charge particle density (|h|<1, pT>0.5 GeV) versus PT(charged
jet#1) compared to the QCD hard scattering predictions of HERWIG 5.9 (default parameters with
PT(hard)>3 GeV/c).
 The predictions of HERWIG are divided into two categories: charged particles that arise from the
break-up of the beam and target (beam-beam remnants); and charged particles that arise from the
outgoing jet plus initial and final-state radiation (hard scattering component).
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 37
HERWIG 6.4
“Transverse” PT Distribution
HERWIG has the too steep of a pT
dependence of the “beam-beam remnant”
"Transverse" Chargedcomponent
Particle Density:
dN/dhdf
of the
“underlying event”!
"Transverse" Charged Particle Density
Charged Jet #1
Direction
CDF Data
"Hard"
Total
data uncorrected
theory corrected
0.75
1.0E+00
Herwig 6.4 CTEQ5L
PT(hard) > 3 GeV/c
Df
0.50
0.25
"Remnants"
1.8 TeV |h|<1.0 PT>0.5 GeV
0.00
0
5
10
CDF Data
PT(chgjet#1) > 5 GeV/c
15
20
25
30
35
40
45
PT(charged jet#1) (GeV/c)
Herwig PT(chgjet#1) > 30 GeV/c
“Transverse” <dNchg/dhdf> = 0.51
50
Charged Density dN/dhdfdPT (1/GeV/c)
"Transverse" Charged Density
1.00
data uncorrected
theory corrected
1.0E-01
“Toward”
1.8 TeV |h|<1 PT>0.5 GeV/c
1.0E-02
“Transverse”
1.0E-03
“Transverse”
“Away”
1.0E-04
1.0E-05
PT(chgjet#1) > 30 GeV/c
Herwig 6.4 CTEQ5L
1.0E-06
Herwig PT(chgjet#1) > 5 GeV/c
<dNchg/dhdf> = 0.40
0
2
4
6
8
10
12
14
PT(charged) (GeV/c)
 Compares the average “transverse” charge particle density (|h|<1, pT>0.5 GeV) versus
PT(charged jet#1) and the pT distribution of the “transverse” density, dNchg/dhdfdPT with the
QCD hard scattering predictions of HERWIG 6.4 (default parameters with PT(hard)>3
GeV/c. Shows how the “transverse” charge particle density is distributed in pT.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 38
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).
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 39
Tuning PYTHIA:
Multiple Parton Interaction Parameters
Parameter
Default
Description
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.
Multiple Parton Interaction
Color String
Color String
PARP(86)
PARP(89)
PARP(90)
PARP(67)
0.33
0.66
1 TeV
0.16
1.0
Probability that the MPI produces two gluons
with color connections to the “nearest neighbors.
Multiple PartonDetermine
Interactionby comparing
with 630 GeV data!
Probability that the MPI produces two gluons
either as described by PARP(85) or as a closed
gluon
loop.
remaining
fraction consists of
Affects
the The
amount
of
quark-antiquark
pairs.
initial-state radiation!
Color String
Hard-Scattering Cut-Off PT0
5
Determines the reference energy E0.
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.
PYTHIA 6.206
e = 0.25 (Set A))
4
PT0 (GeV/c)
PARP(85)
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
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 40
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/dhdf
CDF Data
Pythia 6.206 (default)
MSTP(82)=1
PARP(81) = 1.9 GeV/c
data uncorrected
theory corrected
0.75
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)
MCnet07 - Durham - Part 1
April 18-20, 2007
Default parameters give
very poor description of
the “underlying event”!
Rick Field – Florida/CDF/CMS
Page 41
Run 1 PYTHIA Tune A
CDF Default!
PYTHIA 6.206 CTEQ5L
"Transverse" Charged Particle Density: dN/dhdf
Parameter
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
"Transverse" Charged Density
1.00
CDF Preliminary
0.75
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)
MCnet07 - Durham - Part 1
April 18-20, 2007
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
PARP(86)
PYTHIA 6.206 (Set A)
PARP(67)=4
data uncorrected
theory corrected
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/CMS
Page 42
Run 1 vs Run 2: “Transverse”
Charged Particle Density
“Transverse” region as
defined by the leading
“charged particle jet”
"Transverse"
"Transverse" Charged
Charged Particle
Particle Density:
Density: dN/dhdf
dN/dhdf
"Transverse"
Charged
Particle
Density:
dN/dhdf
"Transverse"
Charged
Particle
Density:
dN/dhdf
Charged Particle Jet #1
Direction
Df
“Toward”
“Transverse”
“Transverse”
“Away”
"Transverse"
ChargedDensity
Density
"Transverse"Charged
Charged
Density
"Transverse"
"Transverse"
Charged
Density
1.25
1.25
1.25
CDF Run 1 Min-Bias
CDF Run 1 Min-Bias
CDF
Run
11Published
CDF
Run
JET20
CDF
Run
1 Published
CDF
Run
1 JET20
CDF Run 2 Preliminary
CDF Run 2 Preliminary
PYTHIA Tune A
CDF Run 2
CDFPreliminary
Run 1 Data
CDF
CDF
Preliminary
CDF
Preliminary
data
uncorrected
1.00
1.00
1.00
data
uncorrected
data
uncorrected
data
uncorrected
theory corrected
0.75
0.75
0.75
0.50
0.50
0.50
0.25
0.25
0.25
|h|<1.0
PT>0.5
GeV/c
|h|<1.0
PT>0.5
GeV/c
1.8
TeV
|h|<1.0
|h|<1.0
PT>0.5PT>0.5
GeV GeV
0.00
0.00
0.00
0.00
000
0
10
20
10
10 5 20
20
30
30
10
30
40
50
40
4015 50
50
60
70 2580
60
20
60 70
70 80
80
PT(charged
jet#1)
PT(charged jet#1)
90
10035110
120
140 150
90
130
30
40 130
50
90 100
100 110
110 120
120
13045140
140 150
150
(GeV/c)
PT(charged jet#1) (GeV/c)
(GeV/c)
 Shows the
Excellent agreement
between
Run average
1 and 2!
data
on the
“transverse” charge particle density (|h|<1, pT>0.5 GeV) as
a function of the transverse momentum of the leading charged particle jet from Run 1.
 Compares the Run 2 data (Min-Bias, JET20, JET50, JET70, JET100) with Run 1.

The errors on the (uncorrected) Run 2 data include both statistical
and Tune
correlated
PYTHIA
A was tuned to fit
the “underlying event” in Run I!
systematic uncertainties.
Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after
CDFSIM).
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 43
Run 1 vs Run 2: “Transverse”
Charged PTsum Density
“Transverse” region as
defined by the leading
“charged particle jet”
“Toward”
“Transverse”
“Transverse”
“Away”
1.25
1.25
1.25
"Transverse"
PTsum
Density
(GeV)
"Transverse"
"Transverse"PTsum
PTsumDensity
Density(GeV/c)
(GeV)
Charged Particle Jet #1
Direction
Df
"Transverse" Charged PTsum Density: dPTsum
sum/dhdf
sum
CDFPreliminary
Preliminary
CDF
CDF
Run
1 Data
CDF JET20
CDF Min-Bias
data
uncorrected
data
datauncorrected
uncorrected
1.00
1.00
1.00
theory corrected
0.75
0.75
0.75
CDF Run
1Run
Published
CDF
2
CDF Run
1 Published
CDF Run 2 Preliminary
CDF
CDF
RunJET20
2 Preliminary
PYTHIA Tune A
CDF Min-Bias
0.50
0.50
0.50
0.25
0.25
0.25
|h|<1.0
PT>0.5
|h|<1.0GeV
PT>0.5GeV
GeV/c
1.8 TeV |h|<1.0 PT>0.5
0.00
0.00
000
10 5 20
20
10
30
30
10
40
4015 50
50
60
60
20
70
70 2580
80
90
140
90
10035110
110 120
120
130 45
140 150
150
30 100
40 130
50
PT(charged
PT(charged jet#1)
jet#1) (GeV/c)
(GeV/c)
 Shows the
Excellent agreement
between
Run average
1 and 2!
data on the
“transverse” charged PTsum density (|h|<1, pT>0.5 GeV)
as a function of the transverse momentum of the leading charged particle jet from Run 1.
 Compares the Run 2 data (Min-Bias, JET20, JET50, JET70, JET100) with Run 1. The
errors on the (uncorrected) Run 2 data include both statistical and
correlated
systematic
PYTHIA
Tune A was
tuned to fit
the “underlying event” in Run I!
uncertainties.
 Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after
CDFSIM).
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 44
Charged Particle Density
“Transverse” pT Distribution
"Transverse" Charged Particle Density: dN/dhdf
Charged Particle Density
CDF Run 1 Min-Bias
CDF
Run
11
Published
CDF
Run
JET20
CDF Run 2 Preliminary
CDF Run 2
CDF Preliminary
Preliminary
CDF
datauncorrected
uncorrected
data
1.00
0.75
0.50
0.25
|h|<1.0
PT>0.5
|h|<1.0
PT>0.5
GeV GeV/c
0.00
0
10
20
30
40
1.0E+00
1.0E+00
50
60
70
80
90 100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
 Compares the average “transverse”
charge particle density (|h|<1, pT>0.5
GeV) versus PT(charged
jet#1)agreement
with the
Excellent
pT distribution of the “transverse”
between Run 1 and 2!
density, dNchg/dhdfdPT. Shows how the
“transverse” charge particle density is
distributed in pT.
MCnet07 - Durham - Part 1
April 18-20, 2007
"Transverse"
PT(chgjet#1) > 30 GeV/c
1.0E-01
1.0E-01
Charged Density
(1/GeV/c)
Density dN/dhdfdPT
dN/dhdfdPT (1/GeV/c)
Charged
"Transverse"
"Transverse" Charged
Charged Density
Density
1.25
Run 1
Preliminary
CDF CDF
uncorrected
datadata
uncorrected
uncorrected
data
"Transverse"
Run 2 Min-Bias Preliminary
PT(chgjet#1) > 30 GeV/c
Run 1 Min-Bias Preliminary
1.0E-02
1.0E-02
Run 2 Preliminary
Run 1 Published
1.0E-03
1.0E-03
1.0E-04
1.0E-04
1.0E-05
1.0E-05
Min-Bias
1.0E-06
1.0E-06
Charged
Charged Particles
Particles |h|
|h| << 1.0
1.0
1.0E-07
1.0E-07
00
22
44
66
88
10
10
12
12
14
14
16
16
20
20
18
18
PT(charged) (GeV/c)
 Compares the Run 2 data (Min-Bias,
JET20, JET50, JET70, JET100) with
Run 1.
Rick Field – Florida/CDF/CMS
Page 45
“Underlying Event”
as defined by “Calorimeter Jets”
Charged Particle Df Correlations
JetClu Jet #1
Direction
pT > 0.5 GeV/c |h| < 1
“Transverse” region is
2p
very sensitive to the
JetClu
Jet
#1
“Toward-Side” Jet
“underlying event”!
Direction
Df
“Toward”
Look at the charged
particle density in the
“transverse” region!
Away Region
Df
Transverse
Region
“Toward”
f
“Transverse”
“Transverse”
“Transverse”
Leading
Jet
“Transverse”
Toward Region
“Away”
Transverse
Region
“Away”
“Away-Side” Jet
Away-side “jet”
(sometimes)
Away Region
Perpendicular to the plane of the
2-to-2 hard scattering
0
-1
h
+1
 Look at charged particle correlations in the azimuthal angle Df relative to the leading


JetClu jet.
o
o
o
o
Define |Df| < 60 as “Toward”, 60 < |Df| < 120 as “Transverse”, and |Df| > 120 as
“Away”.
o
All three regions have the same size in h-f space, DhxDf = 2x120 = 4p/3.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 46
“Transverse”
Charged Particle Density
Direction
“Transverse” region as
defined by the leading
“calorimeter jet”
Df
“Toward”
“Toward”
“Transverse”
“Transverse”
“Transverse”
“Transverse”
“Away”
“Away”
"Transverse"
Charged Particle
Particle Density: dN/dhdf
"Transverse" Charged
1.00
1.00
1.00
Df
Density
"Transverse"
"Transverse" Charged
Charged Density
Density
JetClu Jet #1
or ChgJet#1
Direction
JetClu Jet #1
CDF
CDF
Preliminary
CDFPreliminary
CDF
data Preliminary
uncorrected
data
data uncorrected
uncorrected
data uncorrected
theory
theorycorrected
corrected
0.75
0.75
0.75
PYTHIA Tune A
JetCluJetClu
Jet#1 (R
= 0.7,
Jet#1
(R |h(jet)|<2)
= 0.7,|h(jet)|<2)
CDF Run 2 Preliminary
0.50
0.50
ChgJet#1 R = 0.7
PYTHIA
Tune A 1.96
JetClu (R
= 0.7, |h(jet#1)|
< 2)TeV
ChgJet#1 R = 0.7
0.25
0.25
Charged
Particles
(|h|<1.0,
PT>0.5
GeV/c)
Charged
Particles
(|h|<1.0,
PT>0.5
GeV/c)
Charged
Particles
(|h|<1.0,
PT>0.5
GeV/c)
0.00
0.00
00
25
25
50
50
75
75
100
100
125
125
150
150
175
175
200
225
250
ET(jet#1)
(GeV) (GeV)
PT(chgjet#1)
or ET(jet#1)
 Shows the data on the average “transverse” charge particle density (|h|<1, PT>0.5 GeV)
as a function of the transverse energy of the leading JetClu jet (R = 0.7, |h(jet)| < 2)
from Run 2., compared with PYTHIA Tune A after CDFSIM.
 Compares the “transverse” region of the leading “charged particle jet”, chgjet#1, with
the “transverse” region of the leading “calorimeter jet” (JetClu R = 0.7), jet#1.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 47
“Transverse”
Charged PTsum Density
Direction
“Transverse” region as
defined by the leading
“calorimeter jet”
"Transverse" Charged PTsum Density: dPTsum/dhdf
Df
Df
“Toward”
“Toward”
“Transverse”
“Transverse”
“Transverse”
“Transverse”
“Away”
“Away”
1.5
"Transverse"
"Transverse" PTsum
PTsum Density
Density (GeV/c)
(GeV/c)
JetClu Jet #1
or ChgJet#1
Direction
JetClu
Jet #1
CDF Preliminary
CDF
Preliminary
data uncorrected
data
uncorrected
theory
corrected
1.0
JetClu Jet#1 (R = 0.7,|h(jet)|<2)
JetClu Jet#1 (R = 0.7,|h(jet)|<2)
0.5
PYTHIA Tune A
ChgJet#1 RR= =0.7
0.7
CDF ChgJet#1
Run 2 Preliminary
PYTHIA Tune A 1.96 TeV
JetClu (R = 0.7, |h(jet#1)| < 2)
Charged Particles
Particles (|h|<1.0,
(|h|<1.0, PT>0.5
PT>0.5 GeV/c)
GeV/c)
Charged
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.0
0
25
50
75
100
125
150
175
200
225
250
PT(chgjet#1)
or ET(jet#1)
ET(jet#1)
(GeV) (GeV)
 Shows the data on the average “transverse” charged PTsum density (|h|<1, PT>0.5
GeV) as a function of the transverse energy of the leading JetClu jet (R = 0.7, |h(jet)| <
2) from Run 2., compared with PYTHIA Tune A after CDFSIM.
 Compares the “transverse” region of the leading “charged particle jet”, chgjet#1, with
the “transverse” region of the leading “calorimeter jet” (JetClu R = 0.7), jet#1.
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 48
Relationship Between
“Calorimeter” and “Charged Particle” Jets
PT(chgjet#1)/ET(matched jet) vs PT(chgjet#1)
ET(matched jet) vs PT(charged jet#1)
1.2
160
CDF Preliminary
140
data uncorrected
theory corrected
120
PYTHIA Tune A
100
CDF Run 2 Preliminary
80
60
PT(chgjet#1)/ET(matched jet)
Matched Jet ET (GeV)
180
1.0
0.8
PYTHIA Tune A
CDF Run 2 Preliminary
0.6
In lecture 2 I will show
you
CDF Preliminary
A more detailed study of the
“underlying event” in
Run 2 at CDF!
 Shows the “matched” JetClu jet ET
 Shows the ratio of PT(chgjet#1) to the
JetClu (R = 0.7, |h(jet#1)| < 2)
40
JetClu (R = 0.7, |h(jet#1)| < 2)
0.4
data uncorrected
theory corrected
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
20
Charged Particles (|h|<1.0, PT>0.5 GeV/c)
0.2
0
0
10
20
30
40
50
60
70
80
90
100 110 120 130 140 150
0
10
20
30
40
50
60
70
80
90
100 110 120 130 140 150
PT(charged jet#1) (GeV/c)
PT(charged jet#1) (GeV/c)
versus the transverse momentum of the
leading “charged particle jet” (closest
jet within R = 0.7 of the leading chgjet).
“matched” JetClu jet ET versus
PT(chgjet#1).
The leading chgjet comes from a
JetClu jet that is, on the average,
about 90% charged!
MCnet07 - Durham - Part 1
April 18-20, 2007
Rick Field – Florida/CDF/CMS
Page 49