1. Exploring the Terascale with the International Linear Collider
P. Grannis Univ. Maryland, May 9, 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

2. The Terascale frontier49
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 when the EM and Weak forces diverged, 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.

3. 48
The Standard Model
Over 30 years, the SM has been assembled and tested with 1000’s 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 spin 0 Higgs boson doublet (4 fields) is included to fix unitarity violation, allows unification of EM and Weak and then breaks the EW symmetry with the massless photon and W/Z bosons at ~100 GeV. One Higgs particle remains but is as yet undiscovered.

4. The Standard Model is flawed47
The Standard Model is flawed
The SM can’t be the whole story:
Quantum corrections to Higgs mass (& W/Z mass) would naturally drive them to the Planck (or grand unification) scale. Keeping Higgs/W/Z to ~ 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?. If the up quark were heavier than the down quark – no free proton, no H atom, no stars, no us.)
SM provides CP violation, but not enough to explain asymmetry of baryons and antibaryons in the universe.

5. And we now have the tools to get there !46
The Terascale terrain
There is non-SM physics in the universe at large:
Gravity remains outside the SM
Dark Matter is seen in galaxies and is needed to cluster galaxies in the early universe. It appears to be a heavy particle (or particles) left from the Big Bang, with mass in the Teravolt range.
Unexplained 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 puzzles. There are many theoretical alternatives, so experiment is needed to show us the way.
And we now have the tools to get there !

6. 45
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 The LHC will be the highest energy accelerator for many years.
Lake Geneva
But …
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 ~5000 GeV. Initial angular momentum state is not fixed.

7. The International Linear Collider44
The International Linear Collider
Collide e+ and e- beams with fixed 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 helical undulator creating e+e- pairs (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

8. Scientific case for the ILC43
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 … or a new character of space-time … or finding dark matter … or indications of force unification … or insights into matter-antimatter asymmetry or …
The ILC must be justified 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.

9. The Quantum Universe Questions42
The Quantum Universe Questions
The “Quantum Universe” report gives nine key questions in three major areas.
I. Einstein’s 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 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
“Discovering the Quantum Universe” report, unveiled today.

10. 41
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 field is somewhat like the Bunraku puppeteers, dressed in black to be ‘invisible’, manipulating the players in the drama.

11. 40
Revealing the Higgs
A SM Higgs is experimentally ruled out (at LEP) below 115 GeV. The virtual effects on W, top quark masses and Z decays rule out SM Higgs above about 200 GeV.
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.
The LHC (or Tevatron) will discover the Higgs (unless it decays invisibly).
significance
LHC can discover (>5s) SM Higgs to >1 TeV

12. 39
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 with ILC errors.
collision energy
interaction rate
e+e- → 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.

13. 38
Revealing the Higgs
In the SM, Higgs couplings are directly proportional to mass. In extensions to SM, couplings are different. 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.

14. 37
Revealing the Higgs
Different theories predict different types of Higgs couplings. The ILC capability to see deviations from the SM will tell us the type of model for new physics.
String inspired
SM values
supersymmetry
baryogenesis
Errors expected at ILC
SM values
Understanding the Higgs could give insight into Dark Energy

15. 36
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)
m2Higgs = 2 l v2
Dl/l error = 20 – 30% in 1000 fb-1
Measuring the Higgs self-coupling is a crucial consistency check of the character of the Higgs – not possible at LHC.
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.

16. Decoding Supersymmetry35
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 new particles counter the effects from the SM particles that drive the EW scale to the Grand Unification scale, solving the hierarchy problem.
The partner of the spin ½ electron is a spinless ‘selectron’.
The spin 1 W/Z/g/g bosons have spin ½ supersymmetric partners.
etc.

17. Decoding Supersymmetry34
Decoding Supersymmetry
The LHC is guaranteed to see the effects of supersymmetry if it has relevance for extending 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 partners of the lepton, photon, and W/Z, and determine their masses accurately and their quantum numbers.
If the matter-antimatter asymmetry in the universe arises from supersymmetry, the ILC can show this to be the case.

18. Decoding Supersymmetry33
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 supersymmetry mass parameters can be extrapolated to high energy to reveal which theory is at work.
These plots show how the superpartner mass parameters vary with energy for two theories – the quite different patterns can be clearly distinguished.

19. Understanding dark matter32
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.
The lightest Supersymmetry particle (the neutralino) provides a very attractive candidate. All supersymmetric particles decay eventually to a neutralino. At the LHC the neutralino cannot be directly observed, but it can be detected at the ILC.

20. Understanding dark matter31
Understanding dark matter
ILC would copiously produce the partners of leptons, such as m pairs. Decay m → m c (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.

21. Understanding dark matter30
Understanding dark matter
ILC and satellite experiments WMAP and Planck provide complementary views of dark matter. The ILC will identify the neutralino density and measure its mass; WMAP/Planck are sensitive to the total density of dark matter. Together they establish the nature of dark matter.
DM mass →
Maybe ILC agrees with Planck; then the neutralino is the only dark matter particle.
DM density →
Maybe ILC disagrees with Planck; this would tell us that there are different forms of dark matter.

22. Finding extra spatial dimensions29
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 a reduced Planck scale at O(TeV).

23. Finding extra spatial dimensions28
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.

24. Finding extra spatial dimensions27
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

25. Finding extra spatial dimensions26
Finding extra spatial dimensions
dimuon mass
prouction rate
Wavefunctions trapped inside a ‘box’ of extra dimensions yields a series of resonance states that decay into e+e- or m+m- (like a new Z boson). But other new physical mechanisms could provide similar final states. LHC will not tell us what the new particle is.
axial coupling
The ILC can measure the two ways (vector and axial vector) this particle interacts with electrons. The colored regions indicate the expectation of 3 possible theories; the ILC can tell us which is correct!
vector coupling
ILC error

26. 25
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. Precision measurements at the LHC and ILC allow a view of this scale.
We dream that at the Planck scale, gravity may join in.
go here
sense whats happening here

27. 24
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 only a near miss!
force strength
energy
g3 from LHC; g1 and g2 from ILC g2 g3 g3 g2
With supersymmetry, there can be force unification! g1 g1

28. The elements of detectors23
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 electrons & photons
Hadron calorimeter for jet energy measurement (Quarks and gluons fragment into collimated jets of many hadrons; Calorimeters measure jet angles and energy)
Muon detectors outside the calorimeter

29. 22
The LHC ATLAS detector
Nested vertex, tracking, EM calorimeter, hadron calorimeter and muon subdetectors

30. The ILC SiD detector concept21
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.

31. ILC vertex detector needs20
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 bremsstrahlung in field of opposing beam).
Hits in vertex detector allow recognition of ‘long-lived’ particles (b, c quarks and t lepton)
SiD vertex detector
design concept
(Norman Graf)
c decay vertex
b decay vertex
primary vertex

32. 19
ILC calorimeter needs
Desire to separate W and Z to 2 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/E=60%/√E
DE/E=30%/√E

33. Experiment environment at LHC18
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.
LHC detectors are very challenging

34. Experiment environment at ILC17
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 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

35. 16
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
Synchrotron light sources are circular
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. Collide the beams just once (but electrons are cheap!)
Energy
cost
Linear Collider
Circular
Collider
we are here

36. 15
ILC layout
~30 km (500 GeV)
~50 km (1 TeV)
2 x 250 GeV linear accelerators using superconducting rf 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 (polarized to ~60%) made from g’s radiated in helical undulator striking a conversion target.
Two interaction points.
Not to scale

37. L = 2 x 1034 cm-2 s-1 ILC parameters Bunch spacing 337 ns14
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 MV/m
Wall plug effic. 23%
Site power (500 GeV) 140 MW
L = 2 x 1034 cm-2 s-1
105 annihilations/sec
A parameter plane: vary bunch charge, # bunches, beam sizes to allow a flexible operating plane.
Source, damping ring
Interaction pt. beam extraction

38. Accelerating the beams13
Accelerating the beams

39. Accelerating structures12
Accelerating structures Ez c
Travelling wave structure; need phase velocity = velectron = c
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. z
SC cavity

40. 11
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 MW pulse power. Need ~700.
The heart of the linac:
Pure Nb 9-cell cavity operated at 2K; ,000 cavities: 31.5 MV/m accel. gradient.

41. Issues for SC accelerating structures10
Issues for SC accelerating structures
Learning how to prepare smooth pure Nb surfaces to get the high gradient was a decade-long effort. Recent advance uses electropolishing as well as chemical polishing for smooth surface. Alternate cavity shapes have reached >50 MV/m. But the process is not under good control. One still worries about field emission from surface imperfections giving large dark current.
SC specification on gradient and Q value. Now exceeding spec, but large spread in gradient and poor reproducibility.

42. Achieving the luminosity (keeping the beam emittances small)9
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.)

43. 8
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 in the damping rings.
Prototype damping ring has been built in KEK (Japan) and achieved necessary emittance. The 6ns kickers now exist.

44. 7
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.
head
tail
Beam growth due to single bunch wakefield
amplitude
Wakefield effects on subsequent bunches die out in the long bunch time interval (337 ns), so not a problem. z→

45. Making an international project6
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?

46. Organizing – the alphabet soup5
Organizing – the alphabet soup
International Linear Collider Steering Committee (ILCSC) (2002):
Set basic physics specifications (2003)
Made choice among competing technologies (for SC RF) (2004)
Established Global Design Effort =GDE (2005) – virtual world lab with balanced Asian, European, Americas participation to do design, manage R&D, cost estimate. Barry Barish is Director.
GDE established the baseline design parameters in 2005; is preparing Reference Design and cost estimate during 2006.
Funding Agencies Linear Collider (FALC) is science minister level group formed in FALC is discussing the organizational model, rules for site selection, timetable for government consideration of the full ILC project.

47. expression of interest4
The GDE schedule
LHC Results – off ramp
Global Design Effort
Project
Baseline configuration
Reference Design/ initial cost
Technical Design
globally coordinated
regional
ILC R&D Program
expression of interest
Siting
sample sites
Hosting
International Management
ILCSC
FALC
ILC Lab

48. The ILC in the US context3
The ILC in the US context
ILC is US highest priority for new initiative (HEPAP); DOE put ILC at top of list for intermediate term, and expressed interest in hosting ILC at a site near Fermilab.
Administration’s ACI initiative would double DOE SC, NSF, NIST core research in 10 years, with focus on areas of maximum economic impact. But even for basic research, the outlook has brightened.
National Academy panel (Apr report “Revealing the Hidden Nature of Space and Time”) with significant participation of non-physicists concludes: US should be a leader in high energy physics, and advocates an optimum strategy that pursues vigorous R&D on ILC and seeks to host in US.

49. 2
ILC cost
The ILC cost is not a well defined term; each nation has its own costing rules (include labor? contingency? overheads? R&D? inflation?) and materials and labor costs vary. Taking the estimate for the 500 GeV TESLA project of $3.1B€; add salaries, contingency, overheads, detectors to get ≈$10B in US terms:
Divide by 3000 physicists (those signing the consensus document) and by 25 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.

50. Conclusions
We know the terascale is fertile ground for new discoveries about matter, energy, space and time.
We strongly believe there is a new playing field where there are new phenomena but we don’t know yet the players or rules of the game.
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 thus probe the earliest times in the universe.

53. Experiment environment at ILC18
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.

54. 25
Seeking Unification
Einstein’s greatest dream was finding unification of the forces.
The LHC and ILC together 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 Terascale provide the telescope for charting the very high energy character of the universe, instants after the Big Bang.

55. 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

56. 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
R&D Program
RDR
Design Matrix

59. 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.