1. We are confident that new understanding of matter, energy, space and time can be gained through experiments at the TeV (E cm = 10 12 eV) scale P. Grannis Michigan State, Feb. 23, 2006 Exploring the Terascale with the International Linear Collider

2. 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.

3. 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. The Standard Model 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.

4.  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  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 Standard Model is flawed The SM can’t be the whole story:

5. The Terascale terrain 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! There is non-SM physics in the universe at large:

6. The LHC The 14 TeV (E CM ), 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. Mt. Blanc 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 ~2000 GeV. Initial angular momentum state is not fixed.

7. The International Linear Collider Collide beams with energy tuneable up to 250 GeV (upgrade to 500 GeV); E cm =2E beam. Two identical linear 10 (20) km long linear accelerators. 90% polarized electron source; positrons formed by  ’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. Layout of electron arm

8. 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.

9. The Quantum Universe Questions II. The particle world 5.New particles? 6.What is dark matter? 7.What do neutrinos tell us? III. Birth of universe 8.How did the universe start? 9.Where is the antimatter? The “Quantum Universe” report gives nine key questions in three major areas. 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. I. Einstein’s dream 1.Undiscovered principles, new symmetries? 2.What is dark energy? 3.Extra space dimensions? 4.Do all forces become the same?

10. 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 The Higgs boson is somewhat like the Bunraku puppeteers, dressed in black to be ‘invisible’, manipulating the players in the drama. provides one new particle (the Higgs boson).

11. Revealing the Higgs 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. The Tevatron or LHC will discover the Higgs (unless it decays invisibly). 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 LHC can discover (>5  ) SM Higgs to >1 TeV

12. The LHC will not determine Higgs properties (spin, parity). The ILC will do this unambigously from threshold cross sections and angular distributions. collision energy interaction rate 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. Revealing the Higgs Curves denote different Higgs boson spins; ILC data cleanly discriminate. e + e  → Z H (Z → ee,  three sample H masses

13. 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, ,  ; 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. Coupling to Higgs → Particle mass → Yukawa coupling

14. supersymmetry baryogenesis SM values Revealing the Higgs Understanding the Higgs could give insight into Dark Energy 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

15. Revealing the Higgs  error = 20 – 30% in 1000 fb -1 The Higgs interacts with itself; measuring this self-coupling is a key question for elucidating the Higgs character. 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. V(  ) =  (  2 – ½ v 2 ) (v ~ 246 GeV) m Higgs = 4 v 2 Comparing the Higgs mass and the self- coupling is a crucial consistency check of the character of the Higgs.

16. 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.

17. 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.

18. 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.

19. 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.

20. Understanding dark matter e-e- e+e+  ~  ~ ,Z ILC would copiously produce the partners of leptons, such as  pairs. Decay  →   0. (  0 is neutralino – typically the lightest, stable Susy particle). Measuring the  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. ~~

21. Understanding dark matter An aside: at the LHC, the mass of the neutralino and its heavier cousins (such as the  2 0 ) are entangled. LHC cannot measure the higher mass states accurately as it does not see the   . 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.  2 0 mass neutralino mass  2 0 mass error with ILC help  2 0 mass error with no ILC help LHC measurement

22. 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. 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.

23. 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).

24. 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. Finding extra spatial dimensions 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.

25. collision energy (TeV ) → production rate → 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. The ILC with fixed (but tuneable) energy of electron- positron collisions can disentangle the size and number of dimensions individually. Finding extra spatial dimensions Different curves are for different numbers of extra dimensions

26. Wavefunctions trapped inside a ‘box’ of extra dimensions yields a series of resonance states that decay into e + e - or  +  -. (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 this particle interacts with electrons. The colored regions indicate the expectation of three possible theories; the ILC can tell us which is correct! axial coupling vector coupling dimuon mass production rate Finding extra spatial dimensions ILC error

27. 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 heresense whats happening here

28. 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! force strength energy With supersymmetry, ILC and LHC can find force unification! g3g3 g3g3 g2g2 g2g2 g1g1 g1g1

29. 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.

30. The elements of detectors The basic structure of detectors is the same for LHC and ILC : nested subsystems covering  ~ 4   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 &   Hadron calorimeter for jet energy measurement (Quarks and gluons fragment into collimated jets of many hadrons; Calorimeters measure jet angles and energy)  Muon detection

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

32. 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.

33. ILC vertex detector needs SiD vertex detector design concept (Norman Graf) 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). Hits in vertex detector allow recognition of ‘long-lived’ particles (b, c quarks and  lepton) primary vertex b decay vertex c decay vertex

34. 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.  E/E=60%/√E  E/E=30%/√E  →      (   →  )

35. Experiment environment at LHC LHC Background events due to strong interactions are large:  Total inelastic cross section = 8x10 10 pb  XS x BR for Z (Z →  ) = 2x10 3 pb  XS x BR for 120 GeV Higgs (H →  ) = 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

36.  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 (J P =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

37. 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. Experiment environment at ILC ILC detectors are very challenging

38.  Particle physics colliders to date have all been circular machines (with one exception – SLAC SLC).  Highest energy e + e  collider was LEP2: E CM =200 GeV  Synchrotron light sources are circular Energy cost Linear Collider Circular Collider we are here As energy increases at given radius  E ~ E 4 /  (synchrotron radiation) e.g. LEP  E=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. Why a linear collider?

39. ILC layout ~30 km (500 GeV) ~50 km (1 TeV) 2 x 250 GeV linear accelerators for E CM < 500 GeV aimed at 20 mrad crossing angle. Plan for upgrade to 500 GeV beams (E CM = 1 TeV). Using backscattered laser light, can produce  collisions to ~80% of e + e  energy. Positrons made from  ’s radiated in undulator (can be polarized) striking a conversion target. Two interaction points. Not to scale

40. ILC parameters L = 2 x 10 34 cm -2 s -1 10 5 annihilations/sec 4 parameter sets: vary bunch charge, # bunches, beam sizes to allow a flexible operating plane. Bunch spacing337 ns Bunch train length950  s Train rep rate5 Hz Beam height at collision6 nm Beam width at collision540 nm Accel. Gradient31.5 MV/m Wall plug effic.23% Site power (500 GeV)140 MW Source, damping ring Interaction pt. beam extraction

41. Accelerating the beams

42. Travelling wave structure; need phase velocity = v electron = c Circular waveguide mode TM 01 has v p > c ; no good for acceleration! Need to slow wave down (phase velocity = c) using irises. Bunch sees constant field E z =E 0 cos  Group velocity < c, controls the filling time in cavity. SC cavity c EzEz z Accelerating structures

43. 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. RF distribution The heart of the linac: Pure Nb 9-cell cavity operated at 2K; Iris size = 3.5 cm ~20,000 Cavities

44. 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. Issues for SC accelerating structures SC specification on gradient and Q value. Now exceeding spec, but rather large spread in gradient.

45. 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.) Achieving the luminosity (keeping the beam emittances small)

46. 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. Damping rings

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

48. 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? Making an international project  What kind of organizational structure?  How to set the site selection process?  How to account for costs and apportion them?

49. 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.

50. ICFA FALC Resource Board ILCSC GDE Directorate GDE Executive Committee Global R&D Program RDR Design Matrix GDE R & D Board GDE Change Control Board GDE Design Cost Board The GDE organization

51. 2005 2006 2007 2008 2009 2010 Global Design EffortProject globally coordinated Baseline configuration Reference Design/ initial cost ILC R&D Program Technical Design Siting International Management sample sites ILCSC Hosting The GDE schedule LHC Results – off ramp expression of interest FALC ILC Lab regional

52. 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. ILC cost

53.  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. Conclusions