Exploring the Terascale: The ILC Frontier

1. P. Grannis Stony Brook University, DOE Fermilab, Oct. 18, 2006 To the Terascale – The ILC opportunity We are confident that new understanding of matter, energy, space and time can be gained through experiments at the TeV scale Outline: 1. Scientific context 4. ILC accelerator 2. Some ILC physics goals 5. International organization 3. Detector needs 6. Conclusions

2. 43 Terascale Bill Gates’ spell check for “Terascale”: Treacle … Erasable Teacake Websters dictionary: Treacle 1: a medicinal compound formerly in wide use as a remedy against poison2 (chiefly British) : MOLASSES

3. 42 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.

4. 41 The Standard Model Over 30 years, the SM has been assembled and tested with 1000’s of precision measurements. No significant departures at the particle level. Strong and unified EM and Weak forces transmitted by carriers – gluons, photon and W/Z. Though very different at everyday energies, EM and Weak forces are similar at very high energy and merge to a single Electroweak force. The SM breaks the symmetry by introducing a Higgs field that gives mass to the W and Z bosons (and quarks and leptons). A single Higgs particle survives with mass ~115 – 200 GeV, waiting to be found.

5. 40 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 ~ 10-13 of Planck mass requires extreme fine tuning (hierarchy problem) – or new physics at Terascale. • Strong and EW forces 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.

6. 39 The Standard Model is flawed 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 !

7. 38 The LHC Mt. Blanc The 14 TeV (ECM), 27 km circumference LHC proton-proton Collider at CERN on the Swiss-French border – complete in 2008. The LHC will be the highest energy accelerator for many years. Lake Geneva But … The protons are bags of many quarks and gluons (partons) sharing the proton momentum. Parton collisions have a wide range of energies – up to ~5000 GeV. Initial angular momentum state is not fixed. parton momentum fraction, x →

8. 37 Proton collisions 2 partons within the protons scatter Two protons approach each other, each with 7 TeV of energy The partons fragment into ‘jets’ of observed particles Each carries only a fraction of the proton energy

9. 36 The International Linear Collider Collide e+ and e- beams with fixed energy, tuneable up to 250 GeV (upgrade to 500 GeV); Ecm =2Ebeam. Two linear 10 (20) km long linear accelerators. 90% polarized electron source; positrons formed by g’s from e-in an undulator, creating e+ (could be 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

10. 35 Scientific case for the ILC The ILC will be very expensive and thus the scientific justification must be very strong. The “Quantum Universe” report gives nine key questions. LHC and ILC will illuminate most of them. • 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.

11. W WW Higgs 34 Revealing the Higgs (1) 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 is somewhat like the Bunraku puppeteers, dressed in black to be ‘invisible’, manipulating the players in the drama. A SM Higgs is experimentally ruled out by LEP below 115 GeV. Their virtual effects on W, top quark masses and Z decays rule out SM Higgs above ~200 GeV. mW Tevatron has a chance! mtop

12. Z e+ e- Higgs Z e+ Higgs e- Higgs 33 Revealing the Higgs (2) LHC can discover Higgs with any mass to >1 TeV. The ILC “sees” the Higgs in unbiassed manner by observing the recoiling Z. (Measure Z) (Infer Higgs) The LHC will likely not determine Higgs spin and parity. ILC can. Rare process e+e-→ ZHH measurable at ILC, yielding Higgs coupling to itself – a crucial test of SM. Final state is 6 jets. Isolating this process from background places very stringent requirements on the jet energy resolution in the calorimeter.

13. 32 Revealing the Higgs (3) 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 what the real model is. In the clean environment of the ILC, can distinguish Higgs decays to b, c, and light quarks; e, m, t; and W, Z . And can measure the Higgs coupling to itself. 2 sample non-SM models String inspired supersymmetry 1.2 SM prediction Coupling to Higgs → 1 0.8 Ratios of BRs to SM Measuring the Higgs BRs set a key criterion for ILC detectors – a very finely grained Si vertex pixel detector at small radius.

14. 31 Decoding Supersymmetry (1) By introducing fermion and boson partners, Supersymmetry theoretically solves many of the SM defects: hierarchy problem, possible unification of EW and Strong, low mass Higgs – and has a good dark matter candidate. There is no experimental confirmation at present! LHC will discover Supersymmetry if it has anything to do with EWSB. Solving these SM ills comes at a price – Supersymmetry itself is a broken symmetry (there is no spin 0 electron partner at 0.511 MeV). Understanding the Supersymmetry model and symmetry breaking will require the ILC. Particles and sparticles – same Q#s, but one is spin 0 and other is spin ½.

15. ~ e+ g,Z m+ ~ m- e- 30 Decoding Supersymmetry (2) ILC can measure sparticle masses to very high precision, particularly partners of leptons, W,Z,g. e.g. Pair produce the partners of muons, with decay m → mc0. (c0 is neutralino – typically the lightest, stable Susy particle –DM candidate). ~ The sharp edges in decay m energy distribution pin down the c0 and m mass to 0.05% accuracy. Their spins (the key Susy signature) are also determined. ~ Two sample Susy breaking models – different patterns. These precise masses and LHC information allow extrapolate Susy parameters to high energy and infer the Susy-breaking mechanism. Energy →

16. 29 Decoding Supersymmetry (3) About 80% of matter in universe is dark – possibly a heavy relic particle from the Big Bang. c0 is an excellent candidate. Planck satellite will measure DM density accurately. ILC (and LHC) can measure DM mass and density. 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. Perhaps the neutralino and its partners violate CP symmetry to the extent needed for baryon-antibaryon asymmetry in the universe. ILC could uncover this.

17. 28 Finding extra spatial dimensions (1) 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 = 10-9 of atomic diameter), they could unify all forces (including gravity) at a reduced Planck scale at O(TeV). 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 – detectable in LHC or ILC experiments. Our 3-d world

18. 27 Finding extra spatial dimensions (2) 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. 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. 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.

19. dimuon mass prouction rate 26 Finding extra spatial dimensions (3) 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

20. 25 Seeking Unification go here sense whats happening here Present data show that the three forces (strong, EM, weak) have nearly the same strength at very high energy – indicating unification?? Closer look shows it’s only a near miss! g2 g3 Supersymmetry at TeV scale allows forces to unify at GUT scale. g1

21. 24 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 • Muon detectors outside the calorimeter

22. 23 The LHC CMS and ILC SiD detectors To theorists and general public, the detectors look pretty much alike. To the experimenters, like proud parents, each is unique and lovely. SiD concept And the ILC detectors present some special challenges.

23. SiD vertex detector design concept (Norman Graf) 22 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) c decay vertex b decay vertex primary vertex

24. 21 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. DE/E=60%/√E DE/E=30%/√E r +→ p+ p0 (p0 → g g ) Particle flow calorimetry has yet to be demonstrated experimentally.

25. 20 Experiment environment at LHC • LHC Background events due to strong interactions are large: • Total inelastic cross section = 8x1010 pb • XS x BR for 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

26. 19 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

27. ILC is here cost Circular Collider Linear Collider Energy 18 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!)

28. Not to scale ~31 km 14mr ML ~10km (G = 31.5MV/m) RTML ~1.6km BDS 5km 14mr e+ undulator @ 150 GeV (~1.2km) R = 955m E = 5 GeV 17 ILC baseline configuration Footprint as of 7/06 2 x 250 GeV linear accelerators using superconducting rf (31.5 MV/m). Positrons (upgrade to polarized e+) made from g’s radiated in undulator, striking a conversion target. 6 km circumference Damping Rings to provide small emittance. Two interaction points; 6 nm high beams. Plan for upgrade to 500 GeV beams (ECM = 1 TeV). With backscattered laser light, can produce ggcollisions ~80% of e+e-energy. Baseline is evolving under change control

29. 16 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) ~200 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

30. 15 Accelerating the beams

31. 14 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 to phase velocity = c, using irises. Bunch sees constant field Ez=E0cosf Group velocity < c, controls the filling time in cavity. z Electrons surf the wave SC cavity

32. 13 SCRF systems 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 ~700. Waveguide transmission to coupler and cavity; need flexible distribution to adjust phase and power delivered. The heart of the linac: Pure Nb 9-cell cavity operated at 1.8K; 17,000 cavities: 31.5 MV/m accel. gradient. ~ 1m

33. 12 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 (rather than?) 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. Not all make it; large spread BCP EP A good cavity: exceed goal

34. 11 Learning to make reliable cavities Weld free cavity forming Chemical / electropolish Rinse, bake Intensive R&D; extensive test facilities Electropolish Chemical Polish DESY photos String test Vertical / horizontal test Cryomodule assembly

35. 10 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, decreasing relative transverse momenta. (To keep the DR circumference small (6km) the 300 km long bunch train is folded on itself.)

36. 9 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 (few ns) 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.

37. tail head Beam growth due to single bunch wakefield 8 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 big problem. z→

38. 7 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?

39. 6 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 2003. FALC is discussing the organizational model, rules for site selection, timetable for government consideration of the full ILC project.

40. 5 ILC cost The ILC cost is not a well defined term; each nation has its own costing rules (include labor? contingency? overheads? R&D? escalation?) 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 ‘ILC consensus document’) and by 25 years for building + initial operation project duration: Cost per physicist/year = $150,000 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.

41. 4 Reference design and cost • No one knows how high a cost is too much. It is clear nevertheless that finding cost reductions is necessary. • Current GDE work is • Trying to squeeze component costs (optimize civil construction elements, uniform magnet designs, vacuum system simplification etc.) • Looking for design optimization (e.g. e+ and e- DR in one tunnel, replace 2mr crossing with 14mr) • Considering possible scope changes (reduce design luminosity cushion , 1 vs.2 IRs) Expect Reference Design and cost early in 2007. Should do international review (FALC?) Proceed to Engineering level design.

42. 3 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 R&D Program regional expression of interest Siting Hosting sample sites International Management ILCSC ILC Lab FALC

43. 2 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. 2006 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.

44. Conclusions • We know the terascale (treacle?) is fertile ground for new discoveries about matter, energy, space and time. We believe there is a new playing field at the terascale – but we don’t know yet who the players are, or rules of the game. • The ILC allows precision measurements that will tell us the true nature of the new phenomena seen at LHC. The ILC and the LHC together provide the binocular vision needed to see the new physics in perspective. • There are real technical challenges in the ILC, but the proofs of principle exist. • We are entering new territory for international cooperation.