Toward an Understanding of HadronHadron Collisions

1
Toward an Understanding ofHadron-Hadron
Collisions
From Feynman-Field to the LHC
Rick Field University of Florida
Outline of Talk
LBNL January 15, 2009

• Before Feynman-Field Phenomenology.

• The early days of Feynman-Field Phenomenology.

• Studying min-bias collisions and the
  underlying event at CDF.

• Extrapolations to the LHC.

CDF Run 2
CMS at the LHC
2
Before Feynman-Field
My Ph.D. advisor!
R. D. Field University of California, Berkeley,
1962-66 (undergraduate) University of California,
Berkeley, 1966-71 (graduate student)
Rick Field 1964
My sister Sally!
me
Chris Quigg
Bob Cahn
me
J.D.J
The very first Berkeley Physics Course!
3
Before Feynman-Field
Rick Jimmie 1970
Rick Jimmie 1968
Rick Jimmie 1972 (pregnant!)
Rick Jimmie at CALTECH 1973
4
Toward and Understanding of Hadron-Hadron
Collisions
1st hat!
Feynman
and
Field

• From 7 GeV/c p0s to 600 GeV/c Jets. The early
  days of trying to understand and simulate
  hadron-hadron collisions.

5
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 ee- Annihilation, R. D.
  Field and S. Wolfram, Nucl. Phys. B213, 65-84
  (1983).

My 1st graduate student!
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Hadron-Hadron Collisions
FF1 1977 (preQCD)

• What happens when two hadrons collide at high
  energy?

Feynman quote from FF1 The model we shall choose
is not a popular one, so that we will not
duplicate too much of the work 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.

• 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!

Black-Box Model
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Quark-Quark Black-Box Model
No gluons!
FF1 1977 (preQCD)
Quark Distribution Functions determined from
deep-inelastic lepton-hadron collisions
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 Fragmentation Functions determined from
ee- annihilations
Quark-Quark Cross-Section Unknown! Deteremined
from hadron-hadron collisions.
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Quark-Quark Black-Box Model
FF1 1977 (preQCD)
Predict increase with increasing CM energy W
Predict particle ratios
Beam-Beam Remnants
Predict overall event topology (FFF1 paper 1977)
7 GeV/c p0s!
9
Telagram from Feynman
July 1976
SAW CRONIN AM NOW CONVINCED WERE RIGHT TRACK
QUICK WRITE FEYNMAN
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Letter from Feynman
July 1976
11
Letter from Feynman Page 1
Spelling?
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Letter from Feynman Page 3
It is fun!
Onward!
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Feynman Talk at Coral Gables (December 1976)
1st transparency
Last transparency
Feynman-Field Jet Model
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QCD Approach Quarks Gluons
Quark Gluon Fragmentation 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.
Parton Distribution Functions Q2 dependence
predicted from QCD
Quark Gluon Cross-Sections Calculated from QCD
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A Parameterization of the Properties of Jets
Field-Feynman 1978
Secondary Mesons (after decay)

• Assumed that jets could be analyzed on a
  recursive principle.

• Let f(h)dh be the probability that the rank 1
  meson leaves fractional momentum h to the
  remaining cascade, leaving quark b with
  momentum P1 h1P0.

Rank 2
Rank 1

• 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(h)), leaving quark c with momentum
  P2 h2P1 h2h1P0.

Primary Mesons
continue

• Add in flavor dependence by letting bu
  probabliity of producing u-ubar pair, bd
  probability of producing d-dbar pair, etc.

Calculate F(z) from f(h) and bi!

• 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.

Original quark with flavor a and momentum P0
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Feynman-Field Jet Model
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, ....
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Monte-Carlo Simulationof Hadron-Hadron Collisions
FF1-FFF1 (1977) Black-Box Model
FF2 (1978) Monte-Carlo simulation of jets
F1-FFF2 (1978) QCD Approach
FFFW FieldJet (1980) QCD leading-log order
simulation of hadron-hadron collisions
FF or FW Fragmentation
the past
ISAJET (FF Fragmentation)
HERWIG (FW Fragmentation)
PYTHIA
today
tomorrow
SHERPA
PYTHIA 6.4
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High PT Jets
CDF (2006)
Feynman, Field, Fox (1978)
Predict large jet cross-section
30 GeV/c!
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.
600 GeV/c Jets!
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CDF DiJet Event M(jj) 1.4 TeV
ETjet1 666 GeV ETjet2 633 GeV Esum 1,299
GeV M(jj) 1,364 GeV
M(jj)/Ecm 70!!
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The Fermilab Tevatron
CDF SciCo Shift December 12-19, 2008
My wife Jimmie on shift with me!
Acquired 4728 nb-1 during 8 hour owl shift!

• I joined CDF in January 1998.

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Proton-AntiProton Collisionsat the Tevatron
The CDF Min-Bias trigger picks up most of the
hard core cross-section plus a small amount of
single double diffraction.
stot sEL sIN
stot sEL sSD 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
The hard core component contains both hard
and soft collisions.
Beam-Beam Counters 3.2 lt h lt 5.9
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QCD Monte-Carlo ModelsHigh Transverse Momentum
Jets
Underlying Event

• 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).

• 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 an unavoidable
background to most collider observables and
having good understand of it leads to more
precise collider measurements!

• Of course the outgoing colored partons fragment
  into hadron jet and inevitably underlying
  event observables receive contributions from
  initial and final-state radiation.

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Particle Densities
Charged Particles pT gt 0.5 GeV/c h lt 1
CDF Run 2 Min-Bias
DhDf 4p 12.6

• Study the charged particles (pT gt 0.5 GeV/c, h
  lt 1) and form the charged particle density,
  dNchg/dhdf, and the charged scalar pT sum
  density, dPTsum/dhdf.

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CDF Run 1 Min-Bias AssociatedCharged Particle
Density
Associated densities do not include PTmax!
Highest pT charged particle!

• Use the maximum pT charged particle in the event,
  PTmax, to define a direction and look at the the
  associated density, dNchg/dhdf, in min-bias
  collisions (pT gt 0.5 GeV/c, h lt 1).

It is more probable to find a particle
accompanying PTmax than it is to 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 gt 0.5
  GeV/c, h lt 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.

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CDF Run 1 Min-Bias AssociatedCharged Particle
Density
Rapid rise in the particle density in the
transverse region as PTmax increases!
PTmax gt 2.0 GeV/c
Transverse Region
Transverse Region
Ave Min-Bias 0.25 per unit h-f
PTmax gt 0.5 GeV/c

• Shows the data on the Df dependence of the
  associated charged particle density,
  dNchg/dhdf, for charged particles (pT gt 0.5
  GeV/c, h lt 1, not including PTmax) relative to
  PTmax (rotated to 180o) for min-bias events
  with PTmax gt 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!).

26
CDF Run 1 Evolution of Charged JetsUnderlying
Event
Charged Particle Df Correlations PT gt 0.5 GeV/c
h lt 1
Look at the charged particle density in the
transverse region!
Transverse region very sensitive to the
underlying event!
CDF Run 1 Analysis

• Look at charged particle correlations in the
  azimuthal angle Df relative to the leading
  charged particle jet.
• Define Df lt 60o as Toward, 60o lt Df lt 120o
  as Transverse, and Df gt 120o as Away.
• All three regions have the same size in h-f
  space, DhxDf 2x120o 4p/3.

27
Run 1 Charged Particle Density Transverse pT
Distribution
PT(charged jet1) gt 30 GeV/c Transverse
ltdNchg/dhdfgt 0.56
Min-Bias
CDF Run 1 Min-Bias data ltdNchg/dhdfgt 0.25

• Compares the average transverse charge particle
  density with the average Min-Bias charge
  particle density (hlt1, pTgt0.5 GeV). Shows how
  the transverse charge particle density and the
  Min-Bias charge particle density is distributed
  in pT.

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ISAJET 7.32Transverse Density
ISAJET uses a naïve leading-log parton
shower-model which does not agree with the data!
ISAJET
Hard Component
Beam-Beam Remnants

• Plot shows average transverse charge particle
  density (hlt1, pTgt0.5 GeV) versus PT(charged
  jet1) compared to the QCD hard scattering
  predictions of ISAJET 7.32 (default parameters
  with PT(hard)gt3 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).

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HERWIG 6.4Transverse Density
HERWIG uses a modified leading-log parton
shower-model which does agrees better with the
data!
HERWIG
Hard Component
Beam-Beam Remnants

• Plot shows average transverse charge particle
  density (hlt1, pTgt0.5 GeV) versus PT(charged
  jet1) compared to the QCD hard scattering
  predictions of HERWIG 5.9 (default parameters
  with PT(hard)gt3 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).

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MPI Multiple PartonInteractions

• 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.

• 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).

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Tuning PYTHIAMultiple Parton Interaction
Parameters
Hard Core
Determine by comparing with 630 GeV data!
Affects the amount of initial-state radiation!
Take E0 1.8 TeV
Reference point at 1.8 TeV
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PYTHIA 6.206 Defaults
MPI constant probability scattering
PYTHIA default parameters

• Plot shows the Transverse charged particle
  density versus PT(chgjet1) compared to the QCD
  hard scattering predictions of PYTHIA 6.206
  (PT(hard) gt 0) using the default parameters for
  multiple parton interactions and CTEQ3L, CTEQ4L,
  and CTEQ5L.

Default parameters give very poor description of
the underlying event!
Note Change PARP(67) 4.0 (lt 6.138) PARP(67)
1.0 (gt 6.138)
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Run 1 PYTHIA Tune A
CDF Default!
PYTHIA 6.206 CTEQ5L
Run 1 Analysis

• Plot shows the transverse charged particle
  density versus PT(chgjet1) 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)
Old PYTHIA default (more initial-state radiation)
New PYTHIA default (less initial-state radiation)
New PYTHIA default (less initial-state radiation)
34
Run 1 vs Run 2 Transverse Charged Particle
Density
Transverse region as defined by the leading
charged particle jet
Excellent agreement between Run 1 and 2!

• Shows the data on the average transverse charge
  particle density (hlt1, pTgt0.5 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.

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).

35
PYTHIA Tune A Min-BiasSoft Hard
These are old PYTHIA 6.2 tunes! There are
new 6.4 tunes by Arthur Moraes (ATLAS) Hendrik
Hoeth (MCnet) Peter Skands (Tune S0)
Tuned to fit the CDF Run 1 underlying event!
PYTHIA Tune A CDF Run 2 Default
Tune B
Tune AW
Tune BW
Tune A
12 of Min-Bias events have PT(hard) gt 5 GeV/c!
1 of Min-Bias events have PT(hard) gt 10 GeV/c!
Tune DW

• PYTHIA regulates the perturbative 2-to-2
  parton-parton cross sections with cut-off
  parameters which allows one to run with PT(hard)
  gt 0. One can simulate both hard and soft
  collisions in one program.

Tune D6
Tune D
Tune D6T
Lots of hard scattering in Min-Bias at the
Tevatron!

• 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) gt 5 GeV/c
  (1 with PT(hard) gt 10 GeV/c)!

36
Min-Bias Correlations
New

• Data at 1.96 TeV on the average pT of charged
  particles versus the number of charged particles
  (pT gt 0.4 GeV/c, h lt 1) for min-bias
  collisions at CDF Run 2. The data are corrected
  to the particle level and are compared with
  PYTHIA Tune A at the particle level (i.e.
  generator level).

37
Min-Bias Average PT versus Nchg

• Beam-beam remnants (i.e. soft hard core) produces
  low multiplicity and small ltpTgt with ltpTgt
  independent of the multiplicity.

• Hard scattering (with no MPI) produces large
  multiplicity and large ltpTgt.

• Hard scattering (with MPI) produces large
  multiplicity and medium ltpTgt.

This observable is sensitive to the MPI tuning!



The CDF min-bias trigger picks up most of the
hard core component!
38
Average PT versus Nchg

• Data at 1.96 TeV on the average pT of charged
  particles versus the number of charged particles
  (pT gt 0.4 GeV/c, h lt 1) for min-bias
  collisions at CDF Run 2. The data are corrected
  to the particle leveland are compared with PYTHIA
  Tune A, Tune DW, and the ATLAS tune at the
  particle level (i.e. generator level).

• Particle level predictions for the average pT of
  charged particles versus the number of charged
  particles (pT gt 0.5 GeV/c, h lt 1, excluding the
  lepton-pair) for for Drell-Yan production (70 lt
  M(pair) lt 110 GeV) at CDF Run 2.

39
Average PT versus Nchg
No MPI!

• Z-boson production (with low pT(Z) and no MPI)
  produces low multiplicity and small ltpTgt.

• High pT Z-boson production produces large
  multiplicity and high ltpTgt.

• Z-boson production (with MPI) produces large
  multiplicity and medium ltpTgt.

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Average PT(Z) versus Nchg
No MPI!

• Predictions for the average PT(Z-Boson) versus
  the number of charged particles (pT gt 0.5 GeV/c,
  h lt 1, excluding the lepton-pair) for for
  Drell-Yan production (70 lt M(pair) lt 110 GeV) at
  CDF Run 2.

• Data on the average pT of charged particles
  versus the number of charged particles (pT gt 0.5
  GeV/c, h lt 1, excluding the lepton-pair) for
  for Drell-Yan production (70 lt M(pair) lt 110 GeV)
  at CDF Run 2. The data are corrected to the
  particle level and are compared with various
  Monte-Carlo tunes at the particle level (i.e.
  generator level).

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Average PT versus Nchg
PT(Z) lt 10 GeV/c
No MPI!
Remarkably similar behavior! Perhaps indicating
that MPI playing an important role in both
processes.

• Predictions for the average pT of charged
  particles versus the number of charged particles
  (pT gt 0.5 GeV/c, h lt 1, excluding the
  lepton-pair) for for Drell-Yan production (70 lt
  M(pair) lt 110 GeV, PT(pair) lt 10 GeV/c) at CDF
  Run 2.

• Data the average pT of charged particles versus
  the number of charged particles (pT gt 0.5 GeV/c,
  h lt 1, excluding the lepton-pair) for for
  Drell-Yan production (70 lt M(pair) lt 110 GeV,
  PT(pair) lt 10 GeV/c) at CDF Run 2. The data are
  corrected to the particle level and are compared
  with various Monte-Carlo tunes at the particle
  level (i.e. generator level).

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UEMB_at_CMS
UEMB_at_CMS

• Min-Bias Studies Charged particle distributions
  and correlations. Construct charged particle
  jets and look at mini-jet structure and the
  onset of the underlying event. (requires only
  charged tracks)

Study the underlying event by using charged
particles and muons! (start as soon as possible)
Shapes of the pT(mm-) distribution at the
Z-boson mass.

• Underlying Event Studies The transverse
  region in leading Jet and back-to-back
  charged particle jet production and the central
  region in Drell-Yan production. (requires
  charged tracks and muons for Drell-Yan)

ltpT(mm-)gt is much larger at the LHC!

• Drell-Yan Studies Transverse momentum
  distribution of the lepton-pair versus the mass
  of the lepton-pair, ltpT(pair)gt, ltpT2(pair)gt,
  ds/dpT(pair) (only requires muons). Event
  structure for large lepton-pair pT (i.e. mm
  jets, requires muons).