MCnet07 - Durham - Part 1 April 18-20, 2007 Rick Field – Florida/CDF/CMS Page 1 Physics and Techniques Physics and Techniques of Event Generators of Event Generators Rick Field University of Florida (for the CDF & CMS Collaborations) CDF Run 2 Min-Bias and the Underlying Event at the TEVATRON and the LHC CMS at the LHC UE&MB@CMS UE&MB@CMS 1 st Lecture IPPP Durham, April 18-20, 2007 The early days of event generators. Proton A ntiProton PT(hard) O utgoing Parton O utgoing Parton U nderlying Event U nderlying Event Initial-State R adiation Final-State Radiation “Min-Bias” at the Tevatron. Studying the “underlying event” in Run 1 at CDF. and extrapolations to the LHC.
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MCnet07 - Durham - Part 1 April 18-20, 2007 Rick Field – Florida/CDF/CMSPage 1 Physics and Techniques of Event Generators Rick Field University of Florida.
MCnet07 - Durham - Part 1 April 18-20, 2007 Rick Field – Florida/CDF/CMSPage 3 “Feynman-Field Jet Model” The Feynman-Field Days FF1: “Quark Elastic Scattering as a Source of High Transverse Momentum Mesons”, R. D. Field and R. P. Feynman, Phys. Rev. D15, (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, (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, (1978) FW1: “A QCD Model for e + e - Annihilation”, R. D. Field and S. Wolfram, Nucl. Phys. B213, (1983). My 1 st graduate student!
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MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 1
Physics and Techniques Physics and Techniques of Event Generatorsof Event Generators
Rick FieldUniversity of Florida
(for the CDF & CMS Collaborations)
CDF Run 2
Min-Bias and the Underlying Eventat the TEVATRON and the LHC
CMS at the LHC
UE&MB@CMSUE&MB@CMS1st Lecture
IPPP Durham, April 18-20, 2007
The early days of event generators.
Proton AntiProton
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
“Min-Bias” at the Tevatron.
Studying the “underlying event” in Run 1 at CDF.
and extrapolations to the LHC.
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 2
Toward and Understanding of Toward and Understanding of Hadron-Hadron CollisionsHadron-Hadron Collisions
From 7 GeV/c 0’s to 600 GeV/c Jets. The early days of trying to understand and simulate hadron-hadron collisions.
Feynman-Field Phenomenology
Feynman and Field
Proton AntiProton
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
1st hat!
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 3
“Feynman-Field Jet Model”
The FeynmanThe Feynman-Field -Field DaysDays
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).
1973-1983
FW1: “A QCD Model for e+e- Annihilation”, R. D. Field and S. Wolfram, Nucl. Phys. B213, 65-84 (1983).
My 1st graduate student!
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Rick Field – Florida/CDF/CMS Page 4
Hadron-Hadron CollisionsHadron-Hadron Collisions
What happens when two hadrons collide at high energy?
Most of the time the hadrons ooze through each other and fall apart (i.e. no hard scattering). The outgoing particles continue in roughly the same direction as initial proton and antiproton.
Occasionally there will be a large 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!
Hadron Hadron ???
Hadron Hadron
“Soft” Collision (no large transverse momentum)
Hadron Hadron
high PT meson
Parton-Parton Scattering Outgoing Parton
Outgoing Parton
FF1 1977 (preQCD)
Feynman quote from FF1“The model we shall choose is not a popular one,
so that we will not duplicate too much of thework of others who are similarly analyzing various models (e.g. constituent interchange
model, multiperipheral models, etc.). We shall assume that the high PT particles arise from direct hard collisions between constituent quarks in the incoming particles, which
fragment or cascade down into several hadrons.”
“Black-Box Model”
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 5
QuarkQuark--Quark BlackQuark Black--Box ModelBox ModelFF1 1977 (preQCD)Quark Distribution Functions
determined from deep-inelasticlepton-hadron collisions
Quark Fragmentation Functionsdetermined from e+e- annihilationsQuark-Quark Cross-Section
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.”
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Rick Field – Florida/CDF/CMS Page 6
Quark-Quark Black-Box ModelQuark-Quark Black-Box Model
Using c = 10 mm reduces the charged particle density by almost 10%! Mostly from Ks→+- (68.6%) and →p-
(64.2%).
With c = 10mm With Stable Particles
charged particle density: 10mm vs Stable
This is a bigger effect than I expected! No-Bias at 14 TeV
Proton AntiProton
Primary
CDF Run 2
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Rick Field – Florida/CDF/CMS Page 13
-1 +1
2
0
1 charged particle
dNchg/dd = 1/4 = 0.08
Study the charged particles (pT > 0.5 GeV/c, || < 1) and form the charged particle density, dNchg/dd, and the charged scalar pT sum density, dPTsum/dd.
Charged Particles pT > 0.5 GeV/c || < 1
= 4 = 12.6
1 GeV/c PTsum
dPTsum/dd = 1/4 GeV/c = 0.08 GeV/c
dNchg/dd = 3/4 = 0.24
3 charged particles
dPTsum/dd = 3/4 GeV/c = 0.24 GeV/c
3 GeV/c PTsum
CDF Run 2 “Min-Bias”Observable Average Average Density
Scalar pT sum of Charged Particles(pT > 0.5 GeV/c, || < 1) 2.97 +/- 0.23 0.236 +/- 0.018
Divide by 4
CDF Run 2 “Min-Bias”
Particle DensitiesParticle Densities
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Rick Field – Florida/CDF/CMS Page 14
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 in “Min-Bias” collisions at 1.8 TeV (|| < 1, all pT).
Convert to charged particle density, dNchg/dd by dividing by 2. There are about 0.67 charged particles per unit - in “Min-Bias” collisions at 1.8 TeV (|| < 1, all pT).
= 1
= 1
x = 1
0.67
There are about 0.25 charged particles per unit - in “Min-Bias” collisions at 1.96 TeV (|| < 1, pT > 0.5 GeV/c).
0.25
CDF Run 1 “Min-Bias” DataCDF Run 1 “Min-Bias” DataCharged Particle DensityCharged Particle Density
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Rick Field – Florida/CDF/CMS Page 15
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
-4 -3 -2 -1 0 1 2 3 4
Pseudo-Rapidity
dN/d
d
CDF Min-Bias 630 GeVCDF Min-Bias 1.8 TeV all PT
CDF Published
Shows the center-of-mass energy dependence of the charged particle density, dNchg/dd for “Min-Bias” collisions at = 0. Also show a log fit (Fit 1) and a (log)2 fit (Fit 2) to the CDF plus UA5 data.
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
10 100 1,000 10,000 100,000CM Energy W (GeV)
Cha
rged
den
sity
dN
/d
d
CDF DataUA5 DataFit 2Fit 1
= 0
<dNchg/dd> = 0.51 = 0 630 GeV
What should we expect for the LHC?
<dNchg/dd> = 0.63 = 0 1.8 TeV
LHC?
24% increase
CDF Run 1 “MinCDF Run 1 “Min--Bias” DataBias” DataEnergy DependenceEnergy Dependence
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 16
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
-6 -4 -2 0 2 4 6
Pseudo-Rapidity
dN/d
d
630 GeV1.8 TeV
Herwig "Soft" Min-Bias 14 TeV
all PT
Shows the center-of-mass energy dependence of the charged particle density, dNchg/dd 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/dd, in “Min-Bias” collisions.
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
10 100 1,000 10,000 100,000
CM Energy W (GeV)
Cha
rged
den
sity
dN
/d d
CDF DataUA5 DataFit 2Fit 1HW Min-Bias
= 0
HERWIG “Soft” Min-Bias predicts a 45% rise in dNchg/dd at = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV). 4 charged particles per unit becomes 6.
Can we believe HERWIG “soft” Min-Bias?
Can we believe HERWIG “soft” Min-Bias? No!
LHC?
Herwig “Soft” Min-BiasHerwig “Soft” Min-Bias
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Rick Field – Florida/CDF/CMS Page 17
Charged Particle Density
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
0 2 4 6 8 10 12 14
PT (GeV/c)C
harg
ed D
ensi
ty d
N/d
d
dPT
(1/G
eV/c
)
||<1CDF Preliminary
CDF Min-Bias Data at 1.8 TeV
HW "Soft" Min-Biasat 630 GeV, 1.8 TeV, and 14 TeV
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
-6 -4 -2 0 2 4 6
Pseudo-Rapidity
dN/d
d
630 GeV1.8 TeV
Herwig "Soft" Min-Bias 14 TeV
all PT
Shows the pT dependence of the charged particle density, dNchg/dddPT, 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.
Shows the energy dependence of the charged particle density, dNchg/dd for “Min-Bias” collisions compared with HERWIG “Soft” Min-Bias.
Lots of “hard” scattering in “Min-Bias”!
HERWIG “Soft” Min-Bias
CDF Run 1 “Min-Bias” DataCDF Run 1 “Min-Bias” DatappTT Distribution Distribution
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 18
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
-4 -3 -2 -1 0 1 2 3 4
Pseudo-Rapidity
dN/d
d
CDF Min-Bias Data Herwig Jet3 Herwig Min-Bias
1.8 TeV all PTHW "Soft" Min-Bias
HW PT(hard) > 3 GeV/c
Charged Particle Density
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
1.0E+01
0 2 4 6 8 10 12 14
PT (GeV/c)C
harg
ed D
ensi
ty d
N/d
d
dPT
(1/G
eV/c
)
Herwig Jet3Herwig Min-BiasCDF Min-Bias Data
1.8 TeV ||<1
CDF Preliminary
HW PT(hard) > 3 GeV/c
HW "Soft" 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!
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?
HERWIG “soft” Min-Bias does not fit the “Min-Bias” data!
CDF Run 1 “Min-Bias” DataCDF Run 1 “Min-Bias” DataCombining “Soft” + “Hard”Combining “Soft” + “Hard” HERWIG diverges!
No easy way to“mix” HERWIG “hard” with HERWIG “soft”.
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Rick Field – Florida/CDF/CMS Page 19
PYTHIA Tune A Min-BiasPYTHIA Tune A Min-Bias“Soft” + ”Hard”“Soft” + ”Hard”
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
-4 -3 -2 -1 0 1 2 3 4
Pseudo-Rapidity
dN/d
d
Pythia 6.206 Set ACDF Min-Bias 1.8 TeV 1.8 TeV all PT
CDF Published
PYTHIA regulates the perturbative 2-to-2 parton-parton cross sections with cut-off parameters which allows one to run with PT(hard) > 0. One can simulate both “hard” and “soft” collisions in one program.
The relative amount of “hard” versus “soft” depends on the cut-off and can be tuned.
Charged Particle Density
1.0E-06
1.0E-05
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
0 2 4 6 8 10 12 14
PT(charged) (GeV/c)C
harg
ed D
ensi
ty d
N/d
d
dPT
(1/G
eV/c
)
Pythia 6.206 Set ACDF Min-Bias Data
CDF Preliminary
1.8 TeV ||<1
PT(hard) > 0 GeV/c
Tuned to fit the CDF Run 1 “underlying event”!
12% of “Min-Bias” events have PT(hard) > 5 GeV/c!
1% of “Min-Bias” events have PT(hard) > 10 GeV/c!
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)!
Lots of “hard” scattering in “Min-Bias” at the Tevatron!
PYTHIA Tune ACDF Run 2 Default
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 20
Use the maximum pT charged particle in the event, PTmax, to define a direction and look at the the “associated” density, dNchg/dd, in “min-bias” collisions (pT > 0.5 GeV/c, || < 1).
Shows the data on the dependence of the “associated” charged particle density, dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 1, not including PTmax) relative to PTmax (rotated to 180o) for “min-bias” events. Also shown is the average charged particle density, dNchg/dd, for “min-bias” events.
It is more probable to find a particle accompanying PTmax than it is to
find a particle in the central region!
CDF Run 2 Min-Bias “Associated”CDF Run 2 Min-Bias “Associated”Charged Particle DensityCharged Particle Density
Shows the data on the dependence of the “associated” charged particle density, dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 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.
Transverse Region
Transverse Region
Jet #1
Shows “jet structure” in “min-bias” collisions (i.e. the “birth” of the leading two jets!).
Jet #2
Ave Min-Bias0.25 per unit -
PTmax Direction
“Toward”
“Transverse” “Transverse”
“Away”
PTmax > 0.5 GeV/c
PTmax > 2.0 GeV/c
CDF Run 2 Min-Bias “Associated”CDF Run 2 Min-Bias “Associated”Charged Particle DensityCharged Particle Density Rapid rise in the particle
density in the “transverse” region as PTmax increases!
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 22
Shows the data on the dependence of the “associated” charged particle density, dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 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”).
PTmax > 2.0 GeV/c
PTmax > 0.5 GeV/c
PTmax Direction
“Toward”
“Transverse” “Transverse”
“Away”
Transverse Region Transverse
Region
PY Tune A
CDF Run 2 Min-Bias “Associated”CDF Run 2 Min-Bias “Associated”Charged Particle DensityCharged Particle Density
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 23
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
-6 -4 -2 0 2 4 6
Pseudo-Rapidity
dN/d
d
all PT
CDF Data Pythia 6.206 Set A
630 GeV
1.8 TeV
14 TeV
PYTHIA was tuned to fit the “underlying event” in hard-scattering processes at 1.8 TeV and 630 GeV.
Charged Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
10 100 1,000 10,000 100,000CM Energy W (GeV)
Cha
rged
den
sity
dN
/d
d
Pythia 6.206 Set ACDF DataUA5 DataFit 2Fit 1
= 0
Shows the center-of-mass energy dependence of the charged particle density, dNchg/dd for “Min-Bias” collisions compared with PYTHIA Tune A with PT(hard) > 0.
PYTHIA Tune A predicts a 42% rise in dNchg/dd at = 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 becomes 6.
Shows the center-of-mass energy dependence of the charged particle density, dNchg/dddPT, 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!
1% of “Min-Bias” events have PT(hard) > 10 GeV/c!
12% of “Min-Bias” events have PT(hard) > 10 GeV/c!
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)!
Shows the predictions of PYTHIA Tune A, Tune DW, Tune DWT, and the ATLAS tune for the charged particle pT distribution at 14 TeV (|| < 1) and the average number of charged particles with pT > pT
Shows the average transverse momentum of charged particles (||<1, pT>0.5 GeV) versus the number of charged particles, Nchg, for the CDF Run 2 Min-Bias events.
The charged <PT> rises with Nchg!
Average PT versus Nchg
0.6
0.8
1.0
1.2
1.4
1.6
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
Number of Charged Particles
Ave
rage
PT
(GeV
/c)
CDF Preliminarydata uncorrectedtheory + CDFSIM
PYTHIA Tune A 1.96 TeV
Charged Particles (||<1.0, PT>0.5 GeV/c)
Min-Bias
Charged <PCharged <PTT> versus N> versus Nchgchg
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Rick Field – Florida/CDF/CMS Page 28
Using Pile-Up to Study Min-BiasUsing Pile-Up to Study Min-Bias
The primary vertex is the highest PTsum of charged particles pointing towards it.
Proton AntiProton
60 cm
Primary
Normally one only includes those charged particles which point back to the primary vertex.
Pile-Up
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).
High PT Jet
Primary
MB
CDF Run 2
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Rick Field – Florida/CDF/CMS Page 29
Using Pile-Up to Study Min-BiasUsing Pile-Up to Study Min-BiasCharged Particle Density: dN/d
0
1
2
3
4
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
PseudoRapidity
Cha
rged
Par
ticle
Den
sity
Charged Particles (PT > 0.5 GeV/c)
CDF Pre-PreliminaryMin-Bias at 1.96 TeVPrimary
Charged Particle Density: dN/d
0
1
2
3
4
-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0
PseudoRapidity
Cha
rged
Par
ticle
Den
sity
Charged Particles (PT > 0.5 GeV/c)
CDF Pre-PreliminaryMin-Bias at 1.96 TeV
Pile-Up
Primary
Shows the the charged particle density, dNchg/dfor charged particles (pT > 0.5 GeV/c) pointing to theprimary vertex for “Min-Bias” collisions at 1.96 TeV.
About 2.6 charged particles per unit at = 0.
About 1.6 charged particles per unit at = 0 per pile-up
interaction.
Shows the the charged particle density, dNchg/d(per interaction) for charged particles (pT > 0.5 GeV/c) pointing to thepile-up vertices for “Min-Bias” collisions at 1.96 TeV.
Clearly the pile-up “min-bias” is biased 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”.
MCnet07 - Durham - Part 1 April 18-20, 2007
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Is the Pile-Up Biased?Is the Pile-Up Biased?Pile-Up: Charged Particle Multiplicity
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
0 5 10 15 20 25 30
Number of Charged Particles
Frac
tion
of E
vent
s
Min-Bias Events<Nchg> = 3.2
CDF Pre-Preliminary1.96 TeV
Charged Particles (PT > 0.5 GeV/c, || < 1)
Pile-Up: Charged Particle Multiplicity
1.0E-04
1.0E-03
1.0E-02
1.0E-01
1.0E+00
0 5 10 15 20 25 30
Number of Charged Particles
Frac
tion
of E
vent
s
Min-Bias Events<Nchg> = 3.2
CDF Pre-Preliminary1.96 TeV
PT(jet#1) > 150 GeV/c<Nchg> = 4.2
Charged Particles (PT > 0.5 GeV/c, || < 1)
Shows the the charged particle multiplicity distribution(per interaction)for charged particles (pT > 0.5 GeV/c, || <1) pointing to thepile-up vertices for “Min-Bias” collisions at 1.96 TeV.
Shows the the charged particle multiplicity distribution (per interaction) for charged particles (pT > 0.5 GeV/c, || <1) pointing to thepile-up vertices for high p jet production (PT(jet#1) > 150 GeV/c) at 1.96 TeV.
The pile-up is different for Min-bias collisions and high pT jet production! Amasing!
Warning! This data is verypreliminary and
not “blessed” by CDF.So do not believe it yet!
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 31
Is the Pile-Up Biased?Is the Pile-Up Biased? Jet#1 Direction
Shows the data on the dependence of the charged particle density, dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 1) pointing to theprimary vertex relative to the leading calorimeter jet (rotated to 270o) for 150 < PT(jet#1) < 250 GeV/c |(jet#1)| < 2.
Shows the data on the dependence of the charged particle density, dNchg/dd, for charged particles (pT > 0.5 GeV/c, || < 1) (per interaction) pointing to thepile-up vertices relative to the leading calorimeter jet (rotated to 270o) for 150 < PT(jet#1) < 250 GeV/c |(jet#1)| < 2.
The pile-up knows the direction of the leading high pT jet! Amasing!
The pile-up conspires to help give you what you ask for
(i.e. satisfy your “trigger” or your event selection)!
Warning! This data is verypreliminary and
not “blessed” by CDF.So do not believe it yet!
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 32
Min-Bias SummaryMin-Bias Summary “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.
Proton AntiProton
“Minumum Bias” Collisions
Preliminary results seem to show that pile-up is biased! and that it conspires to help give you what you ask for (i.e. satisfy your “trigger” or your event selection)!
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!
Start with the perturbative 2-to-2 (or sometimes 2-to-3) parton-parton scattering and add initial and final-state gluon radiation (in the leading log approximation or modified leading log approximation).
Hard Scattering
PT(hard)
Outgoing Parton
Outgoing Parton
Initial-State Radiation
Final-State Radiation
Hard Scattering
PT(hard)
Outgoing Parton
Outgoing Parton
Initial-State Radiation
Final-State Radiation
Proton AntiProton
Underlying Event Underlying Event
Proton AntiProton
Underlying Event Underlying Event
“Hard Scattering” Component
“Jet”
“Jet”
“Underlying Event”
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 and final-state radiation.
“Jet”
The “underlying event” is an unavoidable background to most collider observables 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 34
Charged Jet #1Direction
“Transverse” “Transverse”
“Toward”
“Away”
“Toward-Side” Jet
“Away-Side” Jet
Look at charged particle correlations in the azimuthal angle relative to the leading charged particle jet.
Define || < 60o as “Toward”, 60o < || < 120o as “Transverse”, and || > 120o as “Away”. All three regions have the same size in - space, x = 2x120o = 4/3.
Look at the charged particle density in the “transverse” region!“Transverse” region
very sensitive to the “underlying event”!
CDF Run 1 Analysis
CDF Run 1: Evolution of Charged JetsCDF Run 1: Evolution of Charged Jets“Underlying Event”“Underlying Event”
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 35
Compares the average “transverse” charge particle density with the average “Min-Bias” charge particle density (||<1, pT>0.5 GeV). Shows how the “transverse” charge particle density and the Min-Bias charge particle density is distributed in pT.
Run 1 Charged Particle DensityRun 1 Charged Particle Density “Transverse” p“Transverse” pTT Distribution Distribution
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 36
Plot shows average “transverse” charge particle density (||<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).
Beam-BeamRemnants
ISAJETCharged Jet #1Direction
“Toward”
“Transverse” “Transverse”
“Away”
“Hard”Component
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 5 10 15 20 25 30 35 40 45 50
PT(charged jet#1) (GeV/c)
"Tra
nsve
rse"
Cha
rged
Den
sity
CDF Run 1Datadata uncorrectedtheory corrected
1.8 TeV ||<1.0 PT>0.5 GeV
Isajet
"Remnants"
"Hard"
ISAJET 7.32ISAJET 7.32“Transverse” Density“Transverse” Density
ISAJET uses a naïve leading-log parton shower-model which does
not agree with the data!
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 37
Plot shows average “transverse” charge particle density (||<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).
Beam-BeamRemnants
HERWIG
Charged Jet #1Direction
“Toward”
“Transverse” “Transverse”
“Away”
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 5 10 15 20 25 30 35 40 45 50
PT(charged jet#1) (GeV/c)
"Tra
nsve
rse"
Cha
rged
Den
sity
CDF Run 1Datadata uncorrectedtheory corrected
1.8 TeV ||<1.0 PT>0.5 GeV
Herwig 6.4 CTEQ5LPT(hard) > 3 GeV/c
Total "Hard"
"Remnants"
“Hard”Component
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 5 10 15 20 25 30 35 40 45 50
PT(charged jet#1) (GeV/c)
"Tra
nsve
rse"
Cha
rged
Den
sity
CDF Run 1Datadata uncorrectedtheory corrected
1.8 TeV ||<1.0 PT>0.5 GeV
Isajet
"Remnants"
"Hard"
HERWIG uses a modified leading-log parton shower-model which
does agrees better with the data!
HERWIG 6.4HERWIG 6.4“Transverse” Density“Transverse” Density
Compares the average “transverse” charge particle density (||<1, pT>0.5 GeV) versus PT(charged jet#1) and the pT distribution of the “transverse” density, dNchg/dddPT 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.
HERWIG has the too steep of a pT dependence of the “beam-beam remnant”
component of the “underlying event”! Charged Jet #1Direction
“Toward”
“Transverse” “Transverse”
“Away”
HERWIG 6.4HERWIG 6.4“Transverse” P“Transverse” PTT Distribution Distribution
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”.
Proton AntiProton
Multiple Parton Interaction
initial-state radiation
final-state radiation outgoing parton
outgoing parton
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).
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.
PARP(85) 0.33 Probability that the MPI produces two gluons with color connections to the “nearest neighbors.
PARP(86) 0.66 Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop. The remaining fraction consists of quark-antiquark pairs.
PARP(89) 1 TeV Determines the reference energy E0.
PARP(90) 0.16 Determines the energy dependence of the cut-offPT0 as follows PT0(Ecm) = PT0(Ecm/E0) with = PARP(90)
PARP(67) 1.0 A scale factor that determines the maximum parton virtuality for space-like showers. The larger the value of PARP(67) the more initial-state radiation.
Hard Core
Multiple Parton Interaction
Color String
Color String
Multiple Parton Interaction
Color String
Hard-Scattering Cut-Off PT0
1
2
3
4
5
100 1,000 10,000 100,000CM Energy W (GeV)
PT0
(GeV
/c)
PYTHIA 6.206
= 0.16 (default)
= 0.25 (Set A))
Take E0 = 1.8 TeV
Reference pointat 1.8 TeV
Determine by comparingwith 630 GeV data!
Affects the amount ofinitial-state radiation!
Tuning PYTHIA:Tuning PYTHIA:Multiple Parton Interaction ParametersMultiple Parton Interaction Parameters
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 41
"Transverse" Charged Particle Density: dN/dd
0.00
0.25
0.50
0.75
1.00
0 5 10 15 20 25 30 35 40 45 50
PT(charged jet#1) (GeV/c)"T
rans
vers
e" C
harg
ed D
ensi
ty
CTEQ3L CTEQ4L CTEQ5L CDF Min-Bias CDF JET20
1.8 TeV ||<1.0 PT>0.5 GeV
Pythia 6.206 (default)MSTP(82)=1
PARP(81) = 1.9 GeV/c
CDF Datadata uncorrectedtheory corrected
Default parameters give very poor description of the “underlying event”!
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.
Old PYTHIA default(more initial-state radiation)New PYTHIA default
(less initial-state radiation)
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
PARP(86) 1.0 0.95
PARP(89) 1.8 TeV 1.8 TeV
PARP(90) 0.25 0.25
PARP(67) 1.0 4.0
Old PYTHIA default(more initial-state radiation)New PYTHIA default
(less initial-state radiation)
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)).
Shows the data on the average “transverse” charge particle density (||<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 uncertainties.
CDF Run 1 PublishedCDF Run 2 PreliminaryPYTHIA Tune A
||<1.0 PT>0.5 GeV/c
CDF Preliminarydata uncorrectedtheory corrected
PYTHIA Tune A was tuned to fit the “underlying event” in Run I!
Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after CDFSIM).
Run 1 vs Run 2: “Transverse” Run 1 vs Run 2: “Transverse” Charged Particle DensityCharged Particle Density“Transverse” region as defined by the leading “charged particle jet”
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 44
Shows the data on the average “transverse” charged PTsum density (||<1, pT>0.5 GeV) as a function of the transverse momentum of the leading charged particle jet from Run 1.
"Transverse" Charged PTsum Density: dPTsum/dd
0.00
0.25
0.50
0.75
1.00
1.25
0 5 10 15 20 25 30 35 40 45 50
PT(charged jet#1) (GeV/c)"T
rans
vers
e" P
Tsum
Den
sity
(GeV
) CDF JET20CDF Min-Bias
CDF Run 1 Datadata uncorrected
1.8 TeV ||<1.0 PT>0.5 GeV
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 uncertainties.
CDF Run 1 PublishedCDF Run 2 PreliminaryPYTHIA Tune A
CDF Preliminarydata uncorrectedtheory corrected
||<1.0 PT>0.5 GeV/c
Shows the prediction of PYTHIA Tune A at 1.96 TeV after detector simulation (i.e. after CDFSIM).
PYTHIA Tune A was tuned to fit the “underlying event” in Run I!
Run 1 vs Run 2: “Transverse” Run 1 vs Run 2: “Transverse” Charged PTsum DensityCharged PTsum Density
“Transverse” region as defined by the leading “charged particle jet”
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 45
Compares the average “transverse” charge particle density (||<1, pT>0.5 GeV) versus PT(charged jet#1) with the pT distribution of the “transverse” density, dNchg/dddPT. Shows how the “transverse” charge particle density is distributed in pT.
Compares the Run 2 data (Min-Bias, JET20, JET50, JET70, JET100) with Run 1.
Run 1 Min-Bias PreliminaryRun 2 PreliminaryRun 1 Published
CDF Preliminarydata uncorrected
Charged Particles || < 1.0
Min-Bias
"Transverse"PT(chgjet#1) > 30 GeV/c
Excellent agreement between Run 1 and 2!
Charged Particle DensityCharged Particle Density “Transverse” p “Transverse” pTT Distribution Distribution
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 46
JetClu Jet #1 Direction
“Transverse” “Transverse”
“Toward”
“Away”
“Toward-Side” Jet
“Away-Side” Jet
Look at charged particle correlations in the azimuthal angle relative to the leading JetClu jet.
Define || < 60o as “Toward”, 60o < || < 120o as “Transverse”, and || > 120o as “Away”. All three regions have the same size in - space, x = 2x120o = 4/3.
Perpendicular to the plane of the 2-to-2 hard scattering
“Transverse” region is very sensitive to the “underlying event”!
JetClu Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
-1 +1
2
0
Leading Jet
Toward Region
Transverse Region
Transverse Region
Away Region
Away Region
Look at the charged particle density in the “transverse” region!
““Underlying Event”Underlying Event”as defined by “Calorimeter Jets”as defined by “Calorimeter Jets”
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 47
Shows the data on the average “transverse” charge particle density (||<1, PT>0.5 GeV) as a function of the transverse energy of the leading JetClu jet (R = 0.7, |(jet)| < 2) from Run 2.
JetClu Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
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.
““Transverse” Transverse” Charged Particle DensityCharged Particle Density
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 48
Shows the data on the average “transverse” charged PTsum density (||<1, PT>0.5 GeV) as a function of the transverse energy of the leading JetClu jet (R = 0.7, |(jet)| < 2) from Run 2.
JetClu Jet #1 Direction
“Toward”
“Transverse” “Transverse”
“Away”
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.
Charged Particles (||<1.0, PT>0.5 GeV/c) ChgJet#1 R = 0.7
JetClu Jet#1 (R = 0.7,|(jet)|<2)
"Transverse" Charged PTsum Density: dPTsum/dd
0.0
0.5
1.0
1.5
0 25 50 75 100 125 150 175 200 225 250
PT(chgjet#1) or ET(jet#1) (GeV)
"Tra
nsve
rse"
PTs
um D
ensi
ty (G
eV/c
) CDF Preliminarydata uncorrectedtheory corrected
Charged Particles (||<1.0, PT>0.5 GeV/c) ChgJet#1 R = 0.7
JetClu Jet#1 (R = 0.7,|(jet)|<2)
PYTHIA Tune A 1.96 TeV
““Transverse” Transverse” Charged PTsum DensityCharged PTsum Density
MCnet07 - Durham - Part 1 April 18-20, 2007
Rick Field – Florida/CDF/CMS Page 49
Shows the ratio of PT(chgjet#1) to the “matched” JetClu jet ET versus PT(chgjet#1).
Shows the “matched” JetClu jet ET versus the transverse momentum of the leading “charged particle jet” (closest jet within R = 0.7 of the leading chgjet).