Transcript P. Grannis Michigan State, Feb. 23, 2006 Exploring the Terascale with the International Linear Collider We are confident that new understanding of matter, energy,

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
The Terascale terrain
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.
The Standard Model
Over 30 years, the SM has been assembled
and tested with 100’s of precision
measurements. No significant departures.
3 doublets of quarks and leptons.
Strong and unified EM and Weak forces
transmitted by carriers – gluons, photon
and W/Z.
Two Higgs boson doublets are 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. modify their masses;
direct Higgs search and mass measurements now tell us the SM
Higgs mass is 115 – 200 GeV.
The Standard Model is flawed
The SM can’t 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).
 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?)
 SM allows for CP violation, but not enough to explain
asymmetry of baryons and antibaryons in the universe.
 Gravity remains outside the SM
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 seems 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
0 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!
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.
But …
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
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 g’s from
undulator creating e+e- pairs (possibly polarized to 60%)
Damping rings to produce very small emittance beams.
Final focus to collide beams (few nm high) head on.
pre-accelerator
few GeV
source
KeV
damping
ring
few GeV
few GeV
bunch
compressor
Layout of electron arm
250-500 GeV
main linac
extraction
& dump
final focus
IP
collimation
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.
The Quantum Universe Questions
The “Quantum Universe” report gives nine key questions
in three major areas.
I. Einstein’s dream
II. The particle
III. Birth of
world
1. Undiscovered principles,
universe
new symmetries?
2. What is dark energy?
5. New particles?
3. Extra space dimensions?
6. What is dark
matter?
4. Do all forces become the
same?
7. What do
neutrinos tell us?
8. How did the
universe start?
9. 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.
Revealing the Higgs
The Higgs field pervades all of space,
interacting with quarks, electrons W, Z etc.
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.
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.
significance
And a SM Higgs > 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.
LHC can discover (>5s)
SM Higgs to >1 TeV
The Tevatron or LHC will discover
the Higgs (unless it decays invisibly).
Revealing the Higgs
interaction rate
Curves denote different Higgs
boson spins; ILC data cleanly
discriminate.
The LHC will not determine Higgs
properties (spin, parity).
The ILC will do this unambigously
from threshold cross sections and
angular distributions.
e +e - → Z H
(Z → ee, mm)
three sample H masses
collision energy
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.
Particle mass →
Coupling to Higgs →
Yukawa coupling
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.
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.
Revealing the Higgs
String inspired
SM values
supersymmetry
Different theories predict different
types of Higgs couplings. The
deviations from the SM tell us the
type of model for new physics.
baryogenesis
SM values
Understanding the Higgs could give insight into Dark Energy
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 selfcoupling 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.
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.
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.
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.
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.
Understanding dark matter
e+
e-
g,Z
~
m+
~
m-
ILC would copiously produce the partners of
leptons, such as~
m pairs. Decay~
m → m c 0.
(c0 is neutralino – typically the lightest, stable
Susy particle). Measuring the m energy and
angular distribution allows determination of
the neutralino mass and spin.
The sharp edges in the
lepton energy distribution
pin down the neutralino
mass to 0.05% accuracy.
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
c 1 0.
c 20
mass
c20 mass
error with
ILC help
c20 mass
error with
no ILC help
LHC measurement
neutralino 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.
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 measures 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.
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).
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 which particles can move in them.
LHC and ILC see complementary processes that will help pin
down these attributes.
Finding extra spatial
dimensions
collision energy (TeV )
→
Different curves are
for different numbers
of extra dimensions
production rate
The ILC with fixed (but tuneable)
energy of electron- positron
collisions can disentangle the size
and number of dimensions
individually.
→
The LHC collisions of quarks span a
range of energies, and therefore do
not measure the size and number of
the ‘large’ extra dimensions
separately.
Finding extra spatial
dimensions
The ILC can measure the two ways
this particle interacts with electrons.
The colored regions indicate the
expectation of three possible
theories; the ILC can tell us which is
correct!
production rate
axial coupling
vector coupling
Wavefunctions trapped inside a ‘box’
of extra dimensions yields a series of
resonance states that decay into e+eor m+m-. (But other new physical
mechanisms could provide similar
final states.) LHC will not tell us what
an observed new ‘resonance’ is.
dimuon mass
ILC error
Seeking Unification
At everyday energy scales, the 4
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
force strength
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 it’s a
near miss!
energy
g2
g3
g1
With
supersymmetry,
ILC and LHC can
find force
unification!
g3
g2
g1
Seeking Unification
Einstein’s 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.
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
The LHC ATLAS detector
Nested vertex, tracking, EM
calorimeter, hadron calorimeter
and muon subdetectors
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.
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 e+e- pairs from beamsstrahlung).
SiD vertex detector
design concept
(Norman Graf)
Hits in vertex detector allow
recognition of ‘long-lived’
particles (b, c quarks and t
lepton)
c decay vertex
b decay vertex
primary vertex
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.
DE/E=60%/√E
DE/E=30%/√E
r → p+ p0
(p0 → g g )
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.
100’s of particles produced: event reconstruction is a challenge.
Large event rate gives event pileup and large radiation dose.
All processes occur for one energy setting.
LHC detectors are very challenging
Experiment environment at ILC
 In the ILC the beam e+ and e- are the colliding partons, so
the collision energy is the full e+e- energy and can be
accurately controlled . But require different energy settings
for producing different particles.
 Initial state is fixed (JP=1-). The e± can be polarized, thus
enhancing or suppressing signal or background reactions.
 Small angle region contains intense flux of e+e- pairs
radiated by the EM fields of the beams.
 Can place detectors close to the beams.
Experiment environment at ILC
Rate of collisions is low (good for backgrounds, bad for high
statistics studies), and number of produced particles is
typically small.
 Total e+e- annihilation XS (500 GeV) = 5 pb
 e+e- → ZZ cross section
= 1 pb
 e+e- → 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
Why a linear collider?
 Particle physics colliders to date have all been circular
machines (with one exception – SLAC SLC).
 Highest energy e+e- collider was LEP2: ECM=200 GeV
As energy increases at given radius
DE ~ E4/r (synchrotron radiation)
e.g. LEP DE=4 GeV/turn; P~20 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.
cost
 Synchrotron light sources are circular
we are here
Circular
Collider
Linear Collider
Energy
ILC layout
~30 km (500 GeV)
~50 km (1 TeV)
2 x 250 GeV linear accelerators for
ECM < 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
e+e- energy.
Positrons made from g’s radiated in
undulator (can be polarized) striking
a conversion target.
Two interaction points.
Not to scale
ILC parameters
L = 2 x 1034 cm-2 s-1
105 annihilations/sec
Source,
damping ring
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
Interaction pt.
beam extraction
4 parameter sets: vary
bunch charge, # bunches,
beam sizes to allow a
flexible operating plane.
Accelerating the beams
Accelerating structures
Ez
Travelling wave structure; need phase
velocity = velectron = c
c
z
Circular waveguide mode TM01 has
vp> c ; no good for acceleration!
Need to slow wave down (phase
velocity = c) using irises.
Bunch sees constant field Ez=E0 cosf
Group velocity < c, controls the filling
time in cavity.
SC cavity
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
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 > 50 MV/m. One still worries about 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.
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.)
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.
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.
amplitude
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.
tail
head
z→
Beam growth due to single
bunch wakefield
Wakefield effects on subsequent
bunches die out in the long
bunch time interval (337 ns), so
not a problem.
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?
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 R&D, 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.
The GDE organization
FALC
ICFA
FALC
Resource Board
ILCSC
GDE
Directorate
GDE
Executive Committee
GDE
R & D Board
GDE
Change Control Board
Global
R&D Program
GDE
Design Cost Board
RDR
Design Matrix
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
regional
ILC R&D Program
globally coordinated
Siting
sample sites expression of interest
ILCSC
FALC
ILC Lab
Hosting
International
Management
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.
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 don’t 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.