Toward an Understanding of
Hadron-Hadron Collisions
From Feynman-Field to the LHC
Rick Field
University of Florida
Outline of Talk
Outgoing Parton
PT(hard)
 Before Feynman-Field.
Initial-State Radiation
Proton
AntiProton
Underlying Event
 Feynman-Field Phenomenology.
Outgoing Parton
Underlying Event
Final-State
Radiation
University of Florida
November 19. 2007
 CDF Run 2.
 Looking forward to the LHC.
CDF Run 2
University of Florida SPS
November 19, 2007
Rick Field – Florida/CDF/CMS
CMS at the LHC
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 hadronhadron collisions.
PT(hard)
Initial-State Radiation
Proton
AntiProton
Underlying Event
Outgoing Parton
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November 19, 2007
st
Rick Field – Florida/CDF/CMS
Underlying Event
Final-State
Radiation
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Before Feynman-Field
Rick Field 1968
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Before Feynman-Field
Rick & Jimmie
1968
Rick & Jimmie
1970
Rick & Jimmie
1972 (pregnant!)
Rick & Jimmie at CALTECH 1973
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Rick Field – Florida/CDF/CMS
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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!
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Rick Field – Florida/CDF/CMS
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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”
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Rick Field – Florida/CDF/CMS
Page 6
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.
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Rick Field – Florida/CDF/CMS
Quark Fragmentation Functions
determined from e+e- annihilations
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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!
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Rick Field – Florida/CDF/CMS
Page 8
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
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Page 10
Letter from Feynman Page 1
Spelling?
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Letter from Feynman Page 3
It is fun!
Onward!
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Napkin from Feynman
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Feynman Talk at Coral Gables
(December 1976)
1st transparency
Last transparency
“Feynman-Field
Jet Model”
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Rick Field – Florida/CDF/CMS
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QCD Approach: Quarks & Gluons
Quark & Gluon Fragmentation
Functions
Q2 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
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Rick Field – Florida/CDF/CMS
Page 15
Monte-Carlo Simulation
of Hadron-Hadron Collisions
 Color singlet proton collides
with a color singlet antiproton.
 A red quark gets knocked out of
the proton and a blue antiquark
gets knocked out of the
antiproton.
 At short times (small distances) the color forces
are weak and the outgoing partons move away
from the beam-beam remnants.
Jet
quark-antiquark
pairs
color string
Proton
Beam
Beam Beam
Remnants
Remnants
Remnants
AntiProton
Beam
Beam
Beam
Remnants
Remnants
Remnants
color string
quark-antiquark
pairs
Jet
 At long times (large distances) the color
forces become strong and quarkantiquark pairs are pulled out of the
vacuum and hadrons are formed.
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Rick Field – Florida/CDF/CMS
 The resulting event consists of
hadrons and leptons in the form
of two large transverse
momentum outgoing jets plus
the beam-beam remnants.
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A Parameterization of
the Properties of Jets
Field-Feynman 1978
Secondary Mesons
(after decay)
continue
 Assumed that jets could be analyzed on a “recursive”
principle.
(bk) (ka)
 Let f(h)dh be the probability that the rank 1 meson leaves
fractional momentum h to the remaining cascade, leaving
Rank 2
Rank 1
quark “b” with momentum P1 = h1P0.
 Assume that the mesons originating from quark “b” are
distributed in presisely the same way as the mesons which
(cb)
(ba)
Primary Mesons
came from quark a (i.e. same function f(h)), leaving quark
“c” with momentum P2 = h2P1 = h2h1P0.
cc pair bb pair
Calculate F(z)
from f(h) and b i!
Original quark with
flavor “a” and
momentum P0
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November 19, 2007
 Add in flavor dependence by letting bu = probabliity of
producing u-ubar pair, bd = probability of producing ddbar 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.
Rick Field – Florida/CDF/CMS
Page 17
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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Rick Field – Florida/CDF/CMS
Page 18
Monte-Carlo Simulation
of Hadron-Hadron Collisions
FF1-FFF1 (1977)
“Black-Box” Model
F1-FFF2 (1978)
QCD Approach
FFFW “FieldJet” (1980)
QCD “leading-log order” simulation
of hadron-hadron collisions
the past
today
FF2 (1978)
Monte-Carlo
simulation of “jets”
ISAJET
HERWIG
(“FF” Fragmentation)
(“FW” Fragmentation)
tomorrow
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SHERPA
“FF” or “FW”
Fragmentation
PYTHIA
PYTHIA 6.3
Rick Field – Florida/CDF/CMS
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Fermilab
Collider Detector Facility
Proton
CDF
1 mile
AntiProton
 At Fermi National Laboratory
(Fermilab) near Chicago, Illinois
there is a Proton-Antiproton
Collider.
 CDF is one of the two collider
detectors at Fermilab (the other is
called DØ).
Proton
2 TeV
AntiProton
 Protons collide with antiprotons at a center-of-mass energy of 2 TeV.
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Rick Field – Florida/CDF/CMS
Page 20
High Energy Physics
Proton-antiproton collisions at 2 TeV.
 Define EH to be the amount of energy
required to light a 60 Watt light bulb for
1 second (EH = 60 Joules). 1 TeV = 1012
ev = 1.6×10-7 Joules and hence EH =
3.75×108 TeV.
Proton
 A proton-antiproton collisions at 2 TeV is
equal to about 3.2×10-7 Joules which
corresponds to about 1/200,000,000 EH!
The energy is not high in every day
standards but it is concentrated at a
small point (i.e. large energy density).
 The mass energy of a proton is about 1 GeV and the
mass energy of a pion is about 140 MeV. Hence 2
TeV is equavelent to about 2,000 proton masses or
about 14,000 pion masses and lots of hadrons are
produced in a typical collision.
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Rick Field – Florida/CDF/CMS
-7
3.2x10
2 TeV J
AntiProton
Lots of outgoing hadrons
Display of charged
particles in the CDF
central tracker
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Collider Coordinates
xz-plane
x-axis
x-axis
Beam Axis
Proton
P
cm
AntiProton
z-axis
Proton
“Transverse”
xy-plane
y-axis
AntiProton z-axis
 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).
 Use h and  to determine the direction of an
outgoing particle, where h is the “pseudo-rapidity”
defined by h = -log(tan(cm/2)).
Rick Field – Florida/CDF/CMS
Azimuthal
Scattering Angle
y-axis
 The z-axis is defined to be the beam axis with
the xy-plane being the “transverse” plane.
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Center-of-Mass
Scattering Angle
PT

x-axis
h
cm
0
90o
1
40o
2
15o
3
6o
4
2o
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CDF Run II DiJet Event
July 2002
ETjet1 = 403 GeV
ETjet2 = 322 GeV
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Raw ET values!!
Rick Field – Florida/CDF/CMS
Page 23
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.”
University of Florida SPS
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Rick Field – Florida/CDF/CMS
Page 24
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!
University of Florida SPS
November 19, 2007
Rick Field – Florida/CDF/CMS
Page 25
Higgs Production
The next great challenge is to find
the Higgs Boson at the collider.
 Look for b-quark jets and
missing transverse energy.
“Higgs” Production


W
Proton
AntiProton
H
b
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b
Rick Field – Florida/CDF/CMS
Page 26
The LHC at CERN
Me at CMS!
6 miles
CMS at the LHC
Darin
Proton
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November 19, 2007
14 TeV
Proton
Rick Field – Florida/CDF/CMS
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