university of perugia - lecture 1 march 30, 2006 rick field – florida/cdf/cmspage 1 toward an...
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University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 1
Toward an Understanding of Toward an Understanding of Hadron-Hadron CollisionsHadron-Hadron Collisions
Lecture 1: From Field-Feynman to the Tevatron.
Lecture 2: A Detailed Study of the “Underlying Event” at the Tevatron.
From 7 GeV/c 0’s to 600 GeV/c Jets!
Proton AntiProton
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
QCD Monte-Carlo Models (PYTHIA Tune A).
“Min-Bias” Collisions at the Tevatron.
→ extrapolations to the LHC!
QCD Monte-Carlo Models tunes at the Tevatron. → extrapolations to the LHC!
CMS at the LHCUniversity of Perugia
UE&MB@CMSUE&MB@CMS
Florida-Perugia
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 3
“Feynman-Field Jet Model”
FeynmanFeynman-Field-Field PhenomenologyPhenomenology
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).
1973-1980
FW1: “A QCD Model for e+e- Annihilation”, R. D. Field and S. Wolfram, Nucl. Phys. B213, 65-84 (1983).
My 1st graduate student!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 4
Hadron-Hadron Hadron-Hadron CollisionsCollisions
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”
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 5
Quark-QuarkQuark-QuarkBlackBlack--Box ModelBox ModelFF1 1977 (preQCD)Quark Distribution Functions
determined from deep-inelasticlepton-hadron collisions
Quark Fragmentation Functionsdetermined from e+e- annihilationsQuark-Quark Cross-Section
Unknown! Deteremined fromhadron-hadron collisions.
No gluons!
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.”
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 6
Quark-QuarkQuark-QuarkBlack-Box ModelBlack-Box Model
FF1 1977 (preQCD)Predict
particle ratios
Predictincrease with increasing
CM energy W
Predictoverall event topology
(FFF1 paper 1977)
“Beam-Beam Remnants”
7 GeV/c 0’s!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 7
Telagram from FeynmanTelagram from Feynman
July 1976
SAW CRONIN AM NOW CONVINCED WERE RIGHT TRACK QUICK WRITEFEYNMAN
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 8
Letter from FeynmanLetter from FeynmanJuly 1976
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 9
Letter from Feynman:Letter from Feynman:page 1page 1
Spelling?
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 10
Letter from Feynman:Letter from Feynman:page 3page 3
It is fun!
Onward!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 11
Feynman Talk at Coral Feynman Talk at Coral Gables in December 1976Gables in December 1976
“Feynman-Field Jet Model”
1st transparency Last transparency
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 12
QCD ApproachQCD ApproachQuarks & GluonsQuarks & Gluons
FFF2 1978
Parton Distribution FunctionsQ2 dependence predicted from
QCD
Quark & Gluon Fragmentation Functions
Q2 dependence predicted from QCD
Quark & Gluon Cross-SectionsCalculated from QCD
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.”
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 13
High PHigh PTT Jets Jets
30 GeV/c!
Predictlarge “jet”
cross-section
Feynman, Field, & Fox (1978)CDF (2006)
600 GeV/c Jets!Feynman quote from FFF
“At the time of this writing, there is still no sharp quantitative test of QCD.
An important test will come in connection with the phenomena of high PT discussed here.”
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 14
A Parameterization of A Parameterization of the Properties of Jetsthe Properties of Jets
Assumed that jets could be analyzed on a “recursive” principle.
Field-Feynman 1978
Original quark with flavor “a” and momentum P0
bb pair
(ba)
Let f()d be the probability that the rank 1 meson leaves fractional momentum to the remaining cascade, leaving quark “b” with momentum P1 = 1P0.
cc pair
(cb) Primary Mesons
Assume that the mesons originating from quark “b” are distributed in presisely the same way as the mesons which came from quark a (i.e. same function f()), leaving quark “c” with momentum P2 = 2P1 = 21P0.
Add in flavor dependence by letting u = probabliity of producing u-ubar pair, d = probability of producing d-dbar pair, etc.
Let F(z)dz be the probability of finding a meson (independent of rank) with fractional mementum z of the original quark “a” within the jet.
Rank 2
continue
Calculate F(z) from f() and i!
(bk) (ka)
Rank 1
Secondary Mesons(after decay)
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 15
A Parameterization of A Parameterization of the Properties of Jetsthe Properties of Jets
R. P. Feynman ISMD, Kaysersberg,
France, June 12, 1977
Feynman quote from FF2“The predictions of the model are reasonable
enough physically that we expect it may be close enough to reality to be useful in
designing future experiments and to serve as a reasonable approximation to compare
to data. We do not think of the model as a sound physical theory, ....”
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 16
Monte-Carlo SimulationMonte-Carlo Simulationof Hadron-Hadron Collisionsof Hadron-Hadron Collisions
FF1-FFF1 (1977) “Black-Box” Model
F1-FFF2 (1978) QCD Approach
FF2 (1978) Monte-Carlo
simulation of “jets”
FFFW “FieldJet” (1980) QCD “leading-log order” simulation
of hadron-hadron collisions
ISAJET(“FF” Fragmentation)
HERWIG(“FW” Fragmentation)
PYTHIAtoday
“FF” or “FW” Fragmentationthe past
tomorrow SHERPA PYTHIA 6.3
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 18
Monte-Carlo SimulationMonte-Carlo Simulationof Quark and Gluon Jetsof Quark and Gluon Jets
ISAJET: Evolve the parton-shower from Q2 (virtual photon invariant mass) to Qmin ~ 5 GeV. Use a complicated fragmentation model to evolve from Qmin to outgoing hadrons.
Q2
Field-Feynman
hadrons
5 GeV 1 GeV 200 MeV
HERWIG: Evolve the parton-shower from Q2 (virtual photon invariant mass) to Qmin ~ 1 GeV. Form color singlet clusters which “decay” into hadrons according to 2-particle phase space.
MLLA: Evolve the parton-shower from Q2 (virtual photon invariant mass) to Qmin ~ 230 MeV. Assume that the charged particles behave the same as the partons with Nchg/Nparton = 0.56!
CDF Distribution of Particles in Jets MLLA Curve!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 19
Collider CoordinatesCollider Coordinates
The z-axis is defined to be the beam axis with the xy-plane being the “transverse” plane.
Proton AntiProton
z-axis
y-axis
x-axis
Beam Axis
Proton AntiProton z-axis
xz-plane x-axis Center-of-Mass Scattering Angle
cm
P
x-axis
“Transverse” xy-plane y-axis
Azimuthal Scattering Angle
PT
cm is the center-of-mass scattering angle and is the azimuthal angle. The “transverse” momentum of a particle is given by PT = P cos(cm). cm
0 90o
1 40o
2 15o
3 6o
4 2o
Use and to determine the direction of an outgoing particle, where is the “pseudo-rapidity” defined by = -log(tan(cm/2)).
Proton AntiProton
Proton AntiProton 2 TeV
Lots of outgoing hadrons
The “rapidity” is defined by y = log((E+pz)/(E-pz))/2 and is equal to in the limit E >> mc2.
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 20
Quark & Gluon JetsQuark & Gluon Jets The CDF calorimeter measures energy deposited
in a cell of size x = 0.11x15o, whch is converted into transverse energy, ET = E cos(cm).
Transverse Energy Grid
Transverse Energy Grid
“Jet” is a cluster of transverse energy within rasius R.
“Jets” are defined to be clusters of transverse energy with a radius R in - space. A “jet” is the representation in the detector of an outgoing parton (quark or gluon).
The sum of the ET of the cells within a “jet” corresponds roughly to the ET of the outgoing parton and the position of the cluster in the grid gives the parton’s direction.
Calorimeter Jets
Charged Particle Jet Can also construct jets from the charged particles!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 22
Proton-AntiProton CollisionsProton-AntiProton Collisionsat the Tevatronat the Tevatron
Elastic Scattering Single Diffraction
M
tot = ELSD DD HC
Double Diffraction
M1 M2
Proton AntiProton
“Soft” Hard Core (no hard scattering)
Proton AntiProton
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
“Hard” Hard Core (hard scattering)
Hard Core
1.8 TeV: 78mb = 18mb + 9mb + (4-7)mb + (47-44)mb
The CDF “Min-Bias” trigger picks up most of the “hard
core” cross-section plus a small amount of single & double
diffraction.
The “hard core” component contains both “hard” and
“soft” collisions.
Beam-Beam Counters
3.2 < || < 5.9
CDF “Min-Bias” trigger1 charged particle in forward BBC
AND1 charged particle in backward BBC
tot = ELIN
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 23
Proton-AntiProton Collisions Proton-AntiProton Collisions at the Tevatronat the Tevatron
“Hard core” does not imply that a “hard” parton-parton collision has occured?
Proton AntiProton
“Soft” Collision (no hard scattering)
Proton AntiProton
“Hard” Scattering
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
90% of “hard core” collisions are “soft hard core” and the proton and antiproton ooze through each other and fall apart (i.e. no hard scattering, PT(hard) < 5 GeV/c). The outgoing particles continue in roughly the same direction as initial proton and antiproton.
10% of the “hard core” collisions arise from a “hard” parton-parton collision (PT(hard) > 5 GeV/c) resulting in large transverse momentum outgoing partons.
About 0.3% of all parton-parton collisions produce a b-bbar quark pair (about 1/1,000 of all interactions).
Proton AntiProton
“Flavor Creation” b-quark
b-quark
q or g q or g
Proton AntiProton
“Flavor Creation” b-quark
b-quark
Underlying Event Underlying Event
Initial-State Radiation
Hard Core
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 24
CDF “Min-Bias” DataCDF “Min-Bias” DataCharged Particle DensityCharged Particle Density
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).
Charged Particle Pseudo-Rapidity Distribution: dN/d
0
1
2
3
4
5
6
7
-4 -3 -2 -1 0 1 2 3 4
Pseudo-Rapidity
dN
/d
CDF Min-Bias 1.8 TeV
CDF Min-Bias 630 GeV all PT
CDF Published
<dNchg/d> = 4.2
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 GeV
CDF Min-Bias 1.8 TeV all PT
CDF Published
<dNchg/dd> = 0.67
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).
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 25
-1 +1
2
0
1 charged particle
dNchg/dd = 1/4 = 0.08
Particle DensitiesParticle Densities
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
AverageAverage Density
per unit -
NchgNumber of Charged Particles
(pT > 0.5 GeV/c, || < 1) 3.17 +/- 0.31 0.252 +/- 0.025
PTsum
(GeV/c)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”
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 26
CDF “Min-Bias” DataCDF “Min-Bias” DataEnergy DependenceEnergy Dependence
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 GeV
CDF 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 10,000 100,000
CM Energy W (GeV)
Ch
arg
ed d
ensi
ty d
N/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
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 27
Herwig “Soft” Min-BiasHerwig “Soft” Min-BiasCharged 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)
Ch
arg
ed d
ensi
ty d
N/d
d
CDF Data
UA5 Data
Fit 2
Fit 1
HW 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?
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 28
CDF “Min-Bias” DataCDF “Min-Bias” DataPPTT Dependence Dependence
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
har
ged
Den
sity
dN
/d d
dP
T (
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 contain 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”!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 29
Min-Bias: CombiningMin-Bias: Combining“Hard” and “Soft” Collisions“Hard” and “Soft” Collisions
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
har
ged
Den
sity
dN
/d
d d
PT
(1/
GeV
/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!
No easy way to“mix” HERWIG “hard” with HERWIG “soft”.
Hard-Scattering Cross-Section
0.01
0.10
1.00
10.00
100.00
0 2 4 6 8 10 12 14 16 18 20
Hard-Scattering Cut-Off PTmin
Cro
ss
-Se
cti
on
(m
illi
ba
rns
)
PYTHIA
HERWIG
CTEQ5L1.8 TeV
HC
HERWIG diverges!
PYTHIA cuts off the divergence.
Can run PT(hard)>0!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 30
Monte-Carlo SimulationMonte-Carlo Simulationof Hadron-Hadron Collisionsof Hadron-Hadron Collisions
The underlying event in a hard scattering process has a “hard” component (particles that arise from initial & final-state radiation and from the outgoing hard scattered partons) and a “soft?” component (“beam-beam remnants”).
Proton AntiProton
“Hard” Collision
initial-state radiation
final-state radiation outgoing parton
outgoing parton
Clearly? the “underlying event” in a hard scattering process should not look like a “Min-Bias” event because of the “hard” component (i.e. initial & final-state radiation).
+
“Soft?” Component “Hard” Component
initial-state radiation
final-state radiation outgoing jet
Beam-Beam Remnants
“Soft?” Component
Beam-Beam Remnants
Hadron Hadron
“Min-Bias” Collision
However, perhaps “Min-Bias” collisions are a good model for the “beam-beam remnant” component of the “underlying event”.
Are these the same?
The “beam-beam remnant” component is, however, color connected to the “hard” component so this comparison is (at best) an approximation.
color string
color string
Maybe not all “soft”!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 31
MPI: Multiple PartonMPI: Multiple PartonInteractionsInteractions
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).
+
“Semi-Hard” MPI “Hard” Component
initial-state radiation
final-state radiation outgoing jet Beam-Beam Remnants
or
“Soft” Component
Proton AntiProton
“Hard” Collision
initial-state radiation
final-state radiation outgoing parton
outgoing parton
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 32
PYTHIA 6.2: Multiple PartonPYTHIA 6.2: Multiple PartonInteraction ParametersInteraction Parameters
Pythia uses multiple partoninteractions to enhancethe underlying event.
Parameter Value
Description
MSTP(81) 0 Multiple-Parton Scattering off
1 Multiple-Parton Scattering on
MSTP(82) 1 Multiple interactions assuming the same probability, with an abrupt cut-off PTmin=PARP(81)
3 Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a single Gaussian matter distribution, with a smooth turn-off PT0=PARP(82)
4 Multiple interactions assuming a varying impact parameter and a hadronic matter overlap consistent with a double Gaussian matter distribution (governed by PARP(83) and PARP(84)), with a smooth turn-off PT0=PARP(82)
Hard Core
Multiple parton interaction more likely in a hard
(central) collision!
and now HERWIG
!
Jimmy: MPIJ. M. Butterworth
J. R. ForshawM. H. Seymour
Proton AntiProton
Multiple Parton Interactions
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying EventUnderlying Event
Same parameter that cuts-off the hard 2-to-2 parton cross sections!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 33
Tuning PYTHIA 6.2:Tuning PYTHIA 6.2:Multiple Parton Interaction ParametersMultiple 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.
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-off
PT0 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 10,000 100,000
CM Energy W (GeV)
PT
0
(Ge
V/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!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 34
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)
Tuned PYTHIA 6.206Tuned PYTHIA 6.206
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)).
PYTHIA 6.206 CTEQ5L"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
nsv
erse
" C
har
ged
Den
sity
1.8 TeV ||<1.0 PT>0.5 GeV
CDF Preliminarydata uncorrectedtheory corrected
CTEQ5L
PYTHIA 6.206 (Set A)PARP(67)=4
PYTHIA 6.206 (Set B)PARP(67)=1
CDF Default!
Run 1 Analysis
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 35
PYTHIA Min-BiasPYTHIA 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 A
CDF 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
har
ged
Den
sity
dN
/d d
dP
T (
1/G
eV/c
)
Pythia 6.206 Set A
CDF Min-Bias Data
CDF Preliminary
1.8 TeV ||<1
PT(hard) > 0 GeV/c
Tuned to fit the “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”!
PYTHIA Tune ACDF Run 2 Default
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 36
Min-BiasMin-Bias “Associated” “Associated”Charged Particle DensityCharged Particle Density
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).
PTmax Direction
Correlations in
Charged Particle Density: dN/dd
0.0
0.1
0.2
0.3
0.4
0.5
0 30 60 90 120 150 180 210 240 270 300 330 360
(degrees)
Ch
arg
ed
Pa
rtic
le D
en
sit
yPTmax
Associated DensityPTmax not included
CDF Preliminarydata uncorrected
Charged Particles (||<1.0, PT>0.5 GeV/c)
Charge Density
Min-Bias
“Associated” densities do not include PTmax!
Highest pT charged particle!
PTmax Direction
Correlations in
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!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 37
Min-BiasMin-Bias “Associated” “Associated”Charged Particle DensityCharged Particle Density
Associated Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
0 30 60 90 120 150 180 210 240 270 300 330 360
(degrees)
As
so
cia
ted
Pa
rtic
le D
en
sit
y
PTmax > 2.0 GeV/c
PTmax > 1.0 GeV/c
PTmax > 0.5 GeV/c
CDF Preliminarydata uncorrected
PTmaxPTmax not included
Charged Particles (||<1.0, PT>0.5 GeV/c)
Min-Bias
PTmax Direction
Correlations in
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
Rapid rise in the particle density in the “transverse” region as PTmax increases!
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 40
Min-BiasMin-Bias “Associated” “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 GeV/c and PTmax > 2.0 GeV/c compared with PYTHIA Tune A (after CDFSIM).
PTmax Direction
Correlations in
Associated Particle Density: dN/dd
0.0
0.2
0.4
0.6
0.8
1.0
0 30 60 90 120 150 180 210 240 270 300 330 360
(degrees)
As
so
cia
ted
Pa
rtic
le D
en
sit
y
PTmax > 2.0 GeV/c
PY Tune A
PTmax > 0.5 GeV/c
PY Tune A
CDF Preliminarydata uncorrectedtheory + CDFSIM
PTmaxPTmax not included (||<1.0, PT>0.5 GeV/c)
PY Tune A 1.96 TeV
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
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 42
PYTHIA Tune APYTHIA Tune ALHC PredictionsLHC Predictions
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 10,000 100,000
CM Energy W (GeV)
Ch
arg
ed
de
ns
ity
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.
LHC?
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 43
PYTHIA Tune APYTHIA Tune ALHC PredictionsLHC Predictions
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)
Ch
arg
ed D
ensi
ty d
N/d
d d
PT
(1/
GeV
/c)
CDF Data
||<1
630 GeV
Pythia 6.206 Set A
1.8 TeV
14 TeV
Hard-Scattering in Min-Bias Events
0%
10%
20%
30%
40%
50%
100 1,000 10,000 100,000
CM Energy W (GeV)
% o
f E
ve
nts
PT(hard) > 5 GeV/c
PT(hard) > 10 GeV/c
Pythia 6.206 Set A
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!
LHC?
University of Perugia - Lecture 1 March 30, 2006
Rick Field – Florida/CDF/CMS Page 44
LHC Min-Bias LHC Min-Bias PredictionsPredictions
Tevatron LHC
Both HERWIG and the tuned PYTHIA Tune A predict a 40-45% rise in dNchg/dd at = 0 in going from the Tevatron (1.8 TeV) to the LHC (14 TeV). 4 charged particles per unit at the Tevatron becomes 6 per unit at the LHC.
Proton AntiProton
PT(hard)
Outgoing Parton
Outgoing Parton
Underlying Event Underlying Event
Initial-State Radiation
Final-State Radiation
12 times more likely to find a 10 GeV
“jet” in “Min-Bias” at the LHC!
The tuned PYTHIA Tune A predicts that 1% of all “Min-Bias” events at the Tevatron (1.8 TeV) are the result of a hard 2-to-2 parton-parton scattering with PT(hard) > 10 GeV/c which increases to 12% at LHC (14 TeV)!