We are confident that new understanding of matter, energy, space and time can be gained through expe

1
P. Grannis Michigan State, Feb. 23, 2006
Exploring the Terascale with the
International Linear Collider
We are confident that new understanding of
matter, energy, space and time can be gained
through experiments at the TeV (Ecm 1012 eV)
scale
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The Terascale frontier
Increasing energy of particle collisions in
accelerators corresponds to earlier times in the
universe, when phase transitions from symmetry to
asymmetry occurred, and structures like protons,
nuclei and atoms formed. The Terascale (Trillion
electron volts), corresponding to 1 picosecond
after the Big Bang, is special. We expect
dramatic new discoveries there. The ILC and Large
Hadron Collider (LHC) are like telescopes that
view the earliest moments of the universe.
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The Standard Model
Over 30 years, the SM has been assembled and
tested with 1000s of precision measurements.
No significant departures. 3 weak isospin
doublets of quarks and leptons. Strong
and unified EM and Weak forces transmitted by
carriers gluons, photon and W/Z.
A complex Higgs boson doublet (4 fields) is
included to fix unitarity violation, break the EW
symmetry into distinct EM and Weak forces with
massless photon and W/Z bosons at 100 GeV,
give masses to quarks and leptons. One remains
as a particle to be discovered. The Higgs
couplings to W,Z, top quark etc. gives them mass
direct Higgs search and mass measurements now
tell us the SM Higgs mass is 115 200 GeV.
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The Standard Model is flawed
The SM cant be the whole story

• Quantum corrections to Higgs mass ( W/Z) would
  naturally drive them to the Planck (or grand
  unification) scale. Keeping Higgs/W/Z to 10-13
  of Planck mass requires extreme fine tuning
  (hierarchy problem) or new physics at TeV
  scale.
• Strong and EW are just pasted together in SM,
  but are not unified. New Terascale physics could
  fix this.
• 26 bizarre and arbitrary SM parameters are
  unexplained (e.g. why are n masses 10-12 times
  top quark mass, but not zero?)
• SM provides CP violation, but not enough to
  explain asymmetry of baryons and antibaryons in
  the universe.
• Gravity remains outside the SM

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The Terascale terrain
There is non-SM physics in the universe at large
Dark Matter is seen in galaxies and seems needed
to cluster galaxies in the early universe. It
appears to be a heavy particle (or particles)
left over from the Big Bang, whose mass is in the
Teravolt range. Physics beyond the SM gives
natural candidates. Dark Energy is driving the
universe apart it may be due to a spin zero
field, so study of the Higgs boson (the only
other suspected scalar field) may help understand
it.
New physics is needed at the Terascale to solve
or make progress on these puzzle. There are many
theoretical alternatives, so experiment is needed
to show us the way. And we now have the tools to
enable them!
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The LHC
Mt. Blanc
The 14 TeV (ECM), 27 km circumference Large
Hadron proton-proton Collider at CERN on the
Swiss-French border complete in 2007. The
LHC will be the highest energy accelerator for
many years.
Lake Geneva
The protons are bags of many quarks and gluons
(partons) which share the proton beam momentum.
Parton collisions have a wide range of energies
up to 2000 GeV. Initial angular momentum state
is not fixed.
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The International Linear Collider
Collide beams with energy tuneable up to 250 GeV
(upgrade to 500 GeV) Ecm 2Ebeam. Two identical
linear 10 (20) km long linear accelerators. 90
polarized electron source positrons formed by
gs from undulator creating ee- pairs (possibly
polarized to 60) Damping rings to produce very
small emittance beams. Final focus to collide
beams (few nm high) head on.
Layout of electron arm
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Scientific case for the ILC
The ILC will be very expensive and thus the
scientific justification must be very strong. The
physics case rests upon the overwhelming
expectation for new insights at the Terascale
new particles and symmetries, a new character of
space-time, finding dark matter, indications of
force unification or insights into
matter-antimatter asymmetry. The justification
for the ILC must be made in the context of the
LHC. The LHC will make the first explorations of
the new terrain of the Terascale the role of the
ILC is to provide the detailed maps to tell us
what the new physics is and what it means.
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The Quantum Universe Questions
The Quantum Universe report gives nine key
questions in three major areas.

• I. Einsteins dream
• Undiscovered principles, new symmetries?
• What is dark energy?
• Extra space dimensions?
• Do all forces become the same?

• II. The particle world
• New particles?
• What is dark matter?
• What do neutrinos tell us?

• III. Birth of universe
• How did the universe start?
• Where is the antimatter?

The LHC and ILC will address at least eight of
these. The LHC should show us there
is new physics at the Terascale the ILC should
tell us what it really is. The LHC and ILC are
highly synergistic each benefits from the other.
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Revealing the Higgs
W
W W
The Higgs field pervades all of space,
interacting with quarks, electrons W, Z etc.
Higgs
These interactions slow down the particles,
giving them mass. The Higgs field causes the EM
and Weak forces to differ at low energy. Three of
the four higgs fields give the longitudinal
polarization states required for massive W and
Z. The fourth
provides one new particle (the Higgs boson).
The Higgs boson is somewhat like the Bunraku
puppeteers, dressed in black to be invisible,
manipulating the players in the drama.
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Revealing the Higgs
A SM Higgs is experimentally ruled out (at LEP)
below 115 GeV. The effects on W, top quark
masses and Z decays rule out SM Higgs above about
200 GeV.
And a SM Higgs gt 1 TeV makes no sense, as it is
the Higgs that prevents violation of unitarity in
WW scattering. Something needs to happen by
this scale. The Tevatron or LHC will discover the
Higgs (unless it decays invisibly).
significance
LHC can discover (gt5s) SM Higgs to gt1 TeV
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Revealing the Higgs
The LHC will not determine Higgs properties
(spin, parity). The ILC will do
this unambigously from threshold cross sections
and angular distributions.
Curves denote different Higgs boson spins ILC
data cleanly discriminate.
ee- ? Z H (Z ? ee, mm)
three sample H masses
The ILC sees the Higgs even if it decays to
invisible particles, by observing the recoiling
Z. By selecting events only on basis of Z, have
an unbiassed sample of Higgs bosons.
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Revealing the Higgs
In the SM, Higgs couplings are directly
proportional to mass. Measuring these couplings
is a sensitive test of whether we have only the
SM or some extension.
Yukawa coupling
Coupling to Higgs ?
Particle mass ?
In the clean environment of the ILC, it is
possible to distinguish Higgs decays to b, c,
and lighter quarks e, m, t and W, Z and thus
directly measure these couplings. This
requirement sets one of the key criteria for ILC
detectors a very finely grained Si vertex pixel
detector at small radius.
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Revealing the Higgs
Different theories predict different types of
Higgs couplings. The deviations from the SM tell
us the type of model for new physics.
String inspired
SM values
baryogenesis
supersymmetry
SM values
Understanding the Higgs could give insight into
Dark Energy
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Revealing the Higgs
The Higgs interacts with itself measuring this
self-coupling is a key question for elucidating
the Higgs character.
V(F) l(F2 ½ v2) (v 246 GeV) mHiggs 4 l v2
Dl/l error 20 30 in 1000 fb-1
Comparing the Higgs mass and the self-coupling is
a crucial consistency check of the character of
the Higgs.
The final state ZHH (both Higgs decaying to bb)
gives 6 jets (4 b jets). The cross section is
small. Isolating this process from background
places very stringent requirements on the jet
energy resolution in the calorimeter.
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Decoding Supersymmetry
Supersymmetry overcomes inconsistencies in the
standard model by introducing new fermionic
space-time coordinates. It requires that every
known particle has a supersymmetric counterpart
at the terascale. These particles stabilize the
EW scale to the Terascale solving the hierarchy
problem.
The partner of the spin ½ electron is a spinless
selectron. All quarks also have their partners,
as do the W and Z bosons, etc.
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Decoding Supersymmetry
The LHC is guaranteed to see the effects of
supersymmetry, if it has relevance for fixing the
standard model. The counterparts of quarks and
gluons will be produced copiously, but the LHC
will not be sensitive to the partners of leptons,
the photon, or of the W/Z bosons.
The ILC can produce the lepton, photon, and W/Z
partners, and determine their masses and quantum
properties. If the matter-antimatter asymmetry
in the universe arises from supersymmetry, the
ILC can show this to be the case.
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Decoding Supersymmetry
There are hundreds of variants of SUSY theories
and only detailed measurement of quantum numbers
and masses of SUSY particles can show us which
one is true. The measured partner-particle
masses can be extrapolated to high energy to
reveal the theory at work.
These plots show how the superpartner masses vary
with energy for two theories the quite
different patterns for each can be distinguished.
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Understanding dark matter
Our own and other galaxies are gravitationally
bound by unseen dark matter, predominating over
ordinary matter by a factor of five. Its nature
is unclear, but it is likely to be due to very
massive new particles created in the early
universe. Supersymmetry provides a very
attractive candidate particle, called the
neutralino. All supersymmetric particles decay
eventually to a neutralino. At the LHC the
neutralino cannot be directly observed, but can
be seen at the ILC.
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Understanding dark matter
ILC would copiously produce the partners of
leptons, such as m pairs. Decay m ? m c0.
(c0 is neutralino typically the lightest,
stable Susy particle). Measuring the m energy
and angular distribution allows determination of
the neutralino mass and spin.


e

g,Z
m

m-
e-
The sharp edges in the lepton energy distribution
pin down the neutralino mass to 0.05 accuracy.
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Understanding dark matter
An aside at the LHC, the mass of the neutralino
and its heavier cousins (such as the c20) are
entangled. LHC cannot measure the higher mass
states accurately as it does not see the c10.
c20 mass error with ILC help
c20 mass
The precise ILC neutralino mass measurement
allows the LHC to pin down the other particle
mass a typical example of the synergy of the
ILC and LHC. Measurements at one accelerator
enable improvements at the other.
c20 mass error with no ILC help
LHC measurement
neutralino mass
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Understanding dark matter
ILC and satellite experiments WMAP and Planck
provide complementary views of dark matter. The
ILC will identify the dark matter particle and
measure its mass WMAP/Planck are sensitive just
to the total density of dark matter. Together
they establish the nature of dark matter.
Maybe ILC agrees with Planck then the neutralino
is likely the only dark matter particle.
Maybe ILC disagrees with Planck this would tell
us that there are different forms of dark matter.
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Finding extra spatial dimensions
String theory requires at least 6 extra spatial
dimensions (beyond the 3 we already know). The
extra dimensions are curled up like spirals on a
mailing tube. If their radius is large (1
attometer billionth of an atomic diameter) or
larger, they could unify all forces (including
gravity) at lower energy than the Planck mass.
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Finding extra spatial dimensions
If a particle created in an energetic collision
goes off into the extra dimensions, it becomes
invisible in our world and the event shows
missing energy and total momentum imbalance.
There are many possibilities for the number of
large extra dimensions, their size and metric,
and which particles can move in them. LHC and
ILC see complementary processes that will help
pin down these attributes.
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Finding extra spatial dimensions
collision energy (TeV ) ?
The LHC collisions of quarks span a range of
energies, and therefore measure a combination of
the size and number of the large extra
dimensions. The ILC with fixed (but tuneable)
energy of electron- positron collisions can
disentangle the size and number of dimensions
individually.
production rate ?
Different curves are for different numbers of
extra dimensions
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Finding extra spatial dimensions
Wavefunctions trapped inside a box of extra
dimensions yields a series of resonance states
that decay into ee- or mm-. (But other new
physical mechanisms could provide similar final
states.) LHC will not tell us what an observed
new resonance is.
The ILC can measure the two ways (vector and
axial vector) this particle interacts with
electrons. The colored regions indicate the
expectation of three possible theories the ILC
can tell us which is correct!
ILC error
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Seeking Unification
At everyday energy scales, the four fundamental
forces are quite distinct.
At the Terascale, the Higgs field unifies the EM
and Weak forces. LHC and ILC together will map
the unified Electroweak force.
The Strong force may join the Electroweak at the
Grand Unification scale. The ILC precision
allows a view of this. We dream that at the
Planck scale, gravity may join in.
go here
sense whats happening here
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Seeking Unification
Present data show that the three forces (strong,
EM, weak) have nearly the same strength at very
high energy indicating unification?? A closer
look shows its a near miss!
force strength
energy
g2
g3
g3
With supersymmetry, ILC and LHC can find force
unification!
g2
g1
g1
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Seeking Unification
Einsteins greatest dream was finding unification
of the forces. ILC will provide the precision
measurements to tell us if grand unification of
forces occurs. The ILC can provide a connection
to the string scale where gravity may be brought
in. Precision measurements at the ILC provide
the telescope for charting the very high energy
character of the universe instants after the Big
Bang.
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The elements of detectors
The basic structure of detectors is the same for
LHC and ILC nested subsystems covering DW 4p

• Fine segmentation Si pixel/strip detectors to
  measure displaced decay vertices (b and c quark
  identification)
• Tracking detectors in B-field to measure charged
  particle momenta
• EM calorimeter to identify, locate and measure
  energy of e g
• Hadron calorimeter for jet energy measurement
  (Quarks and gluons fragment into
  collimated jets of many hadrons Calorimeters
  measure jet angles and energy)
• Muon detection

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The LHC ATLAS detector
Nested vertex, tracking, EM calorimeter, hadron
calorimeter and muon subdetectors
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The ILC SiD detector concept
Broadly the LHC and ILC detectors are similar.
But the details vary considerably to meet the
specific challenges and physics goals at the two
colliders.
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ILC vertex detector needs
Silicon pixel and strip detectors arranged in
barrels and disks, starting at about 15 mm from
the beam line (have to stay outside the intense
flood of ee- pairs from beamsstrahlung).
Hits in vertex detector allow recognition of
long-lived particles (b, c quarks and t lepton)
c decay vertex
b decay vertex
primary vertex
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ILC calorimeter needs
Desire to separate W and Z to jets at ILC
requires very good energy resolution. Do this by
using magnetic measurement of charged particle
energy and calorimetric measure of neutrals.
Need to separate the energy clusters for charged
and neutral in calorimeter fine segmentation.
r ? p p0 (p0 ? g g )
DE/E60/vE
DE/E30/vE
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Experiment environment at LHC

• LHC Background events due to strong interactions
  are large
• Total inelastic cross section 8x1010 pb
• XS x BR for Z (Z ? mm) 2x103 pb
• XS x BR for 120 GeV Higgs (H ? gg) 0.07 pb
• Signal to background for interesting events is
  small.
• Require sophisticated trigger to select
  interesting events.
• 100s of particles produced event reconstruction
  is a challenge.
• Large event rate gives event pileup and large
  radiation dose.

LHC detectors are very challenging
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Experiment environment at ILC

• In the ILC the beam e and e- are the colliding
  partons, so the collision energy is the full ee-
  energy and can be accurately controlled . But
  require different energy settings for producing
  different particles.
• Initial state is fixed (JP1-). The e can be
  polarized, thus enhancing or suppressing signal
  or background reactions.
• Small angle region contains intense flux of ee-
  pairs radiated by the EM fields of the beams.
• Can place detectors close to the beams.

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Experiment environment at ILC

• Rate of collisions is rather low (good for
  backgrounds, bad for high statistics studies),
  and number of produced particles is typically
  small.
• Total ee- annihilation XS (500 GeV) 5 pb
• ee- ? ZZ cross section 1 pb
• ee- ? ZH cross section 0.05 pb
• Signal to background for interesting events is
  large.
• Precision studies at ILC require excellent jet
  energy and spatial resolution, and precise
  measurement of long lived decay vertices.

ILC detectors are very challenging
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Why a linear collider?

• Particle physics colliders to date have all been
  circular machines (with one exception SLAC
  SLC).
• Highest energy ee- collider was LEP2 ECM200
  GeV
• Synchrotron light sources are circular

As energy increases at given radius DE E4/r
(synchrotron radiation) e.g.
LEP DE4 GeV/turn P20 MW High energy in a
circular machine becomes prohibitively expensive
large power or huge tunnels. Go to long single
pass linacs to reach desired energy.
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ILC layout
30 km (500 GeV) 50 km (1 TeV)
2 x 250 GeV linear accelerators for ECM lt 500 GeV
aimed at 20 mrad crossing angle. Plan for upgrade
to 500 GeV beams (ECM 1 TeV). Using
backscattered laser light, can produce gg
collisions to 80 of ee- energy. Positrons
(polarized to 60) made from gs radiated in
undulator striking a conversion target. Two
interaction points.
Not to scale
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ILC parameters
Bunch spacing 337 ns Bunch train length 950
ms Train rep rate 5 Hz Beam height at
collision 6 nm Beam width at collision 540
nm Accel. Gradient 31.5 MV/m Wall plug
effic. 23 Site power (500 GeV) 140 MW
L 2 x 1034 cm-2 s-1 105 annihilations/sec
4 parameter sets vary bunch charge, bunches,
beam sizes to allow a flexible operating plane.
Source, damping ring
Interaction pt. beam extraction
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Accelerating the beams
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Accelerating structures
Ez
c
Travelling wave structure need phase velocity
velectron c Circular waveguide mode TM01 has
vpgt c no good for acceleration! Need to
slow wave down (phase velocity c) using irises.
Bunch sees constant field EzE0 cosf Group
velocity lt c, controls the filling time in cavity.
z
SC cavity
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RF distribution
Modulator (switching circuit) turns AC line power
into HV DC pulse. Multibeam klystron (RF power
amplifier) makes 1.4 ms pulses at 1.3 GHz. 10
MW pulse power. Need 600.
The heart of the linac Pure Nb 9-cell cavity
operated at 2K Iris size 3.5 cm
20,000 Cavities
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Issues for SC accelerating structures
Learning how to prepare smooth pure Nb surfaces
to get the design gradient was a decade-long
effort, now achieved. Recent advance uses
electropolishing instead of chemical polishing
for smooth surface. Alternate cavity shapes
have reached gt 50 MV/m. One still worries about
reproducibility and field emission from
imperfections on the surface that lead to current
draw, and unacceptable loads on cryogenic systems.
SC specification on gradient and Q value. Now
exceeding spec, but rather large spread in
gradient.
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Achieving the luminosity
(keeping the beam emittances small)
Create small emittance beams in damping rings
before the main linacs allow synchrotron
radiation to reduce all three components of
particle energy restore longitudinal momentum
with RF acceleration. (To keep the DR
circumference small (6km) the 300 km long bunch
train is folded on itself.)
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Damping rings
Must keep very careful control of magnet
alignment, stray B fields, vacuum, instabilities
induced by electron cloud (in e rings) or
positive ions (in e- ring) to avoid emittance
dilution. Need a very fast kicker to inject and
remove bunches from the train to send to the
linacs.
Damping ring has been built in KEK (Japan) and
achieved necessary emittance. The 6ns kickers
now exist.
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Wake fields
Wakefields Off axis beam particles induce image
currents in cavity walls these cause deflections
of the tail of the same bunch, and perhaps on
subsequent bunches. Betatron oscillation in
head of bunch creates a wakefield that resonantly
drives the oscillation of the tail of same bunch.
Can be cured by reducing tail energy quads
oversteer and compensate for beam size growth.
amplitude
Wakefield effects on subsequent bunches die out
in the long bunch time interval (337 ns), so not
a problem.
z?
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Making an international project
Herding cats how do we organize the ILC so that
all regions of the world feel that they are full
partners and gain from participation?

• What kind of organizational structure?
• How to set the site selection process?
• How to account for costs and apportion them?

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Organizing the alphabet soup

• International Linear Collider Steering Committee
  (ILCSC) formed 2002
• Set basic physics specifications (2003)
• Made choice among competing technologies (for SC
  RF) (2004)
• Established Global Design Effort (GDE) virtual
  world lab to do design, manage RD, cost estimate
  (started in 2005).
• GDE has now established the baseline design
  parameters, will make conceptual design and cost
  in 2006.
• Funding Agencies Linear Collider (FALC) is
  science minister level group formed in 2003.
  FALC is discussing the organizational model,
  rules for site selection, timetable for
  government consideration of the full ILC project.

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The GDE organization
FALC
ICFA
FALC Resource Board
ILCSC
GDE Directorate
GDE Executive Committee
GDE R D Board
GDE Change Control Board
GDE Design Cost Board
Global RD Program
RDR Design Matrix
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The GDE schedule
LHC Results off ramp
2005 2006 2007 2008
2009 2010
Global Design Effort
Project
Baseline configuration
Reference Design/ initial cost
Technical Design
globally coordinated
ILC RD Program
regional
expression of interest
Siting
Hosting
sample sites
International Management
ILCSC
ILC Lab
FALC
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ILC cost
The ILC cost is not a well defined term each
nation has its own costing rules (include labor?
overhead? Inflation?) and materials and labor
costs vary. Lets take the estimate for the 500
GeV TESLA project which was 3.1B (4B) (not
including salaries of professionals). Translate
to 8B in US terms Divide by 3000 physicists
(those signing the consensus document) and by 20
years for building initial operation project
duration Cost per physicist/year
130,000 ILC cost will be done as for ITER in
terms of value units basic materials and some
value of manpower. Host country takes 50
other nations bid for their desired pieces
apportioned by value share.
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Conclusions

• We know the terascale is fertile ground for new
  discoveries about matter, energy, space and
  time.
• We strongly believe new phenomena will be seen
  there, but dont know yet which they will be.
• The ILC allows precision measurements that will
  tell us the true nature of the new phenomena.
• The ILC and the LHC together provide the
  binocular vision needed to see the new physics in
  perspective and view the terrain at much higher
  energies, and thus earlier times in the universe.

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Revealing the Higgs
Higgs self couplings a key feature of the SM or
its extensions. Sombrero plot and HHH coupling
diagram and limits. Sets the other key
requirement for ILC detectors on jet energy
resolution PFA (separate slide). Top Yukawa
coupling at 500 GeV, LHC measures the rate of
Htt with H to bb. ILC adds the bb BR so
together they get the top coupling. At 1000 GeV,
ILC directly measures the ttH to give xx
precision.
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