P Grannis Stony Brook University DOE Fermilab Oct
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 Te. V scale Outline: 1. Scientific context 2. Some ILC physics goals 3. Detector needs 4. ILC accelerator 5. International organization 6. Conclusions
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 poison 2 (chiefly British) : MOLASSES
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. 42
The Standard Model 41 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 Ge. V, waiting to be found.
The Standard Model is flawed 40 The SM can’t be the whole story: v 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. v Strong and EW forces are just pasted together in SM, but are not unified. New Terascale physics could fix this. v 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. ) v SM provides CP violation, but not enough to explain asymmetry of baryons and antibaryons in the universe.
The Standard Model is flawed v Gravity remains outside the SM 39 There is non-SM physics in the universe at large: v 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. v 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 !
38 The LHC Mt. Blanc The 14 Te. V (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. parton momentum fraction, x → 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 Ge. V. Initial angular momentum state is not fixed.
37 Proton collisions Two protons approach each other, each with 7 Te. V of energy 2 partons within the protons scatter The partons fragment into ‘jets’ of observed particles Each carries only a fraction of the proton energy
The International Linear Collider 36 Collide e+ and e- beams with fixed energy, tuneable up to 250 Ge. V (upgrade to 500 Ge. V); Ecm =2 Ebeam. Two linear 10 (20) km long linear accelerators. 90% polarized electron source; positrons formed by g’s from ein 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
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 II. The particle III. Birth of world universe 1. Undiscovered principles, 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 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.
34 Revealing the Higgs (1) W W W The Higgs field pervades all of space, Higgs 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 Ge. V. Their virtual effects on W, top quark masses and Z decays rule out SM Higgs above ~200 Ge. V. Tevatron has a chance! m. W mtop
33 Revealing the Higgs (2) LHC can discover Higgs with any mass to >1 Te. V. The ILC “sees” the Higgs in unbiassed manner by observing the recoiling Z. Z (Measure Z) + e e- Higgs (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. e+ Z e- Isolating this process from background places very stringent requirements on the jet energy resolution in the Higgs
Revealing the Higgs (3) 32 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. Coupling to Higgs → 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 String inspired supersymmetry non-SM models 1. 2 SM prediction 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
Decoding Supersymmetry (1) 31 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 Me. V). Particles and sparticles – same Q#s, but one is spin 0 and other is spin ½. Understanding the Supersymmetry model and symmetry breaking will require the ILC.
Decoding Supersymmetry (2) ILC can measure sparticle masses to very high precision, particularly partners of leptons, W, Z, g. e. g. Pair produce ~ m→ the partners of muons, with decay m c 0. (c 0 is neutralino – typically the lightest, stable Susy particle –DM candidate). The sharp edges in decay m energy distribution pin 30 e+ g, Z e- ~ m+ ~ m- ~ mass to 0. 05% accuracy. Their down the c 0 and m 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 Energy →
Decoding Supersymmetry (3) 29 About 80% of matter in universe is dark – possibly a heavy relic particle from the Big Bang. c 0 is an excellent candidate. Planck satellite will measure DM density accurately. ILC (and LHC) can measure DM mass and density. DM density → DM mass → Maybe ILC agrees with Planck; then the neutralino is the only dark matter particle. 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.
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 (>1 attometer = 10 -9 of atomic diameter), they could unify all ‘large’ forces (including gravity) at a reduced Planck scale at O(Te. V). Our 3 -d world 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. 28
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. 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. Different curves are for different numbers of extra dimensions production rate → collision energy (Te. V ) →
26 Finding extra spatial dimensions (3) prouction 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- (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. 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! dimuon mass ILC error
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! g 2 g 3 Supersymmetry at Te. V scale allows forces to unify at GUT scale. g 1
The elements of detectors The basic structure of detectors is the same for LHC and ILC : nested subsystems covering DW ~ 4 p v Fine segmentation Si pixel/strip detectors to measure displaced decay vertices (b and c quark identification) v Tracking detectors in B-field to measure charged particle momenta v EM calorimeter to identify, locate and measure energy of electrons & photons v Hadron calorimeter for jet energy measurement v Muon detectors outside the calorimeter 24
The LHC CMS and ILC Si. D detectors 23 To theorists and general public, the detectors look pretty much alike. To the experimenters, like proud parents, each is unique and lovely. And the ILC detectors present some special challenges. Si. D concept
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’ Si. D vertex detector particles (b, c quarks and t design concept lepton) (Norman Graf) c decay vertex b decay vertex primary vertex
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 + p 0 (p 0 → g g ) Particle flow calorimetry has yet to be demonstrated experimentally.
Experiment environment at LHC 20 LHC Background events due to strong interactions are large: v Total inelastic cross section = 8 x 1010 pb v XS x BR for Z → mm = 2 x 103 pb v XS x BR for 120 Ge. V 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
Experiment environment at ILC 19 Rate of collisions is rather low (good for backgrounds, bad for high statistics studies), and number of produced particles is typically small. v Total e+e- annihilation XS (500 Ge. V) = 5 pb v e+e- → ZZ cross section = 1 pb v 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
18 Why a linear collider? v Particle physics colliders to date have all been circular machines (with one exception – SLAC SLC). v Highest energy e+e- collider was LEP 2: ECM=200 Ge. V As energy increases at given radius DE ~ E 4/r (synchrotron radiation) e. g. LEP DE=4 Ge. V/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!) cost v Synchrotron light sources are circular ILC is here Circular Collider Linear Collider Energy
ILC baseline configuration Not to scale 17 ~31 km Footprint as of 7/06 14 mr ML ~10 km (G = 31. 5 MV/m) RTML ~1. 6 km 14 mr R = 955 m E = 5 Ge. V BDS 5 km e+ undulator @ 150 Ge. V (~1. 2 km) 2 x 250 Ge. V 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 Ge. V beams (ECM = 1 Te. V). With backscattered laser light, can produce gg collisions ~80% of e+e- energy. Baseline is evolving under change control
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 Ge. V) ~200 MW Source, damping ring Interaction pt. beam 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.
Accelerating the beams 15
Accelerating structures Ez 14 Travelling wave structure; need phase velocity = velectron = c c z Electrons surf the wave Circular waveguide mode TM 01 has vp> c ; no good for acceleration! Need to slow wave down to phase velocity = c, using irises. Bunch sees constant field Ez=E 0 cosf Group velocity < c, controls the filling time in cavity. SC cavity
SCRF systems 13 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: ~ 1 m Pure Nb 9 -cell cavity operated at 1. 8 K; 17, 000 cavities: 31. 5 MV/m accel. gradient.
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. BCP Not all make it; large spread EP A good cavity: exceed goal
Learning to make reliable cavities Weld free cavity forming Intensive R&D; extensive test facilities Chemical / electropolish Chemical Polish Rinse, bake Electropolish DESY photos String test Cryomodule assembly 11 Vertical / horizontal test
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 (6 km) the 300 km long bunch train is folded on itself. ) 10
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 6 ns kickers now exist. 9
Wake fields 8 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 big 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? v What kind of organizational structure? v How to set the site selection process? v How to account for costs and apportion them? 7
Organizing – the alphabet soup 6 International Linear Collider Steering Committee (ILCSC) (2002): v Set basic physics specifications (2003) v Made choice among competing technologies (for SC RF) (2004) v 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
ILC cost 5 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 Ge. V TESLA project of $3. 1 B€; add salaries, contingency, overheads, detectors to get >$10 B 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.
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 a) Trying to squeeze component costs (optimize civil construction elements, uniform magnet designs, vacuum system simplification etc. ) b) Looking for design optimization (e. g. e+ and e- DR in one tunnel, replace 2 mr crossing with 14 mr) c) 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. 4
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 regional ILC R&D Program globally coordinated Siting sample sites expression of interest ILCSC FALC ILC Lab Hosting International Management
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. 2
Conclusions v 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. v 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. v There are real technical challenges in the ILC, but the proofs of principle exist. v We are entering new territory for international cooperation.