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The Electron-Positron Linear Collider Probing the Secrets of the Universe R.-D. Heuer (Univ. Hamburg) Colloquium Brookhaven, May 25, 2003 History of the Universe LHC, LC RHIC,HERA ● Particle Physics today ● The case for the Linear Collider ● Status of the TESLA project ● The LC as a global project What have we learned the last 50 years or Status of the Standard Model The physical world is composed of Quarks and Leptons interacting via force carriers (Gauge Bosons) Last entries: top-quark 1995 tau-neutrino 2000 Standard Model Precision measurements 1990-2000 (LEP,SLD,Tevatron, NuTeV,…) Standard Model tested to permille level Precise and quantitative description of subatomic physics Top quark mass LEP indirect Test of the SM at the Level of Quantum Fluctuations Indirect determination of the top mass possible due to • precision measurements • known higher order electroweak corrections ( Mt 2 M ) , ln( h ) MW MW Proves high energy reach through virtual processes Higgs boson mass LEP indirect Test of the SM at the Level of Quantum Fluctuations Indirect determination of the Higgs mass possible due to • precision measurements • known higher order electroweak corrections Mt 2 Mh ( ) , ln( ) MW MW Electroweak Unification HERA ep collider Weak and electromagnetic Interactions: Similar magnitude beyond ~ 100 GeV Open questions Standard Model • What is the origin of mass Open questions Ultimate Unification • Do the forces unify, at what scale • Why is gravity so different • Are there new forces • • • Open questions Hidden Dimensions • Are there more than four space-time dimensions • What is the quantum theory of gravity • • • Open questions Cosmic Connections • What is dark matter • What is dark energy • What happened to antimatter • • • Particle Physics and Cosmology Particle Physics and Cosmology both point to New Physics at the TeV scale Electroweak unification Dark Matter Dark Energy Inflation Neutrino Masses CP Violation The next steps There are two distinct and complementary strategies for gaining new understanding of matter, space and time at future particle accelerators HIGH ENERGY direct discovery of new phenomena i.e. accelerators operating at the energy scale of the new particle HIGH PRECISION interference of new physics at high energies through the precision measurement of phenomena at lower scales Both strategies have worked well together → much more complete understanding than from either one alone ex: top quark , prediction of Higgs boson mass range (LEP/Tevatron) The next steps We know enough now to predict with great certainty that fundamental new understanding of how forces are related, and the way that mass is given to all particles, will be found with a Linear Collider operating at an energy of at least 500 GeV. Experimental limits on the Higgs boson mass indirect direct MH between 114 and ~200 GeV The power of e+e- Colliders Electron-Positron Linear Collider offers ● well defined initial state collision energy √s well defined collision energy √s tuneable precise knowledge of quantum numbers polarisation of e- and e+ possible e+ e- LEP(OPAL) ● Clean environment collision of point-like particles → low backgrounds ● precise knowledge of cross sections ● Additional options: e-e- , eγ , γγ collisions qqmm Machine for Discoveries and Precision Measurements Physics Potential of a Linear Collider (highlights) √s: 91…500…~1000 GeV • Higgs bosons • Supersymmetry • Structure of space-time • Precision tests of electroweak interactions top W Z Precision physics of Higgs-Bosons Discovery and first measurements at the LHC (perhaps at Tevatron?) The Higgs boson is a new form of matter a fundamental scalar a new force coupling to mass Therefore, need to establish Higgs mechanism as the mechanism responsible for giving mass to elementary particles breaking of the electroweak symmetry Task of the Linear Collider: Precision measurements to determine mass(es) quantum numbers (spin zero) couplings (proportional to masses of bosons, quarks, leptons) self-coupling (→ reconstruction of Higgs potential) Precision physics of Higgs bosons Dominant production processes at LC: Precision physics of Higgs bosons Recoil mass spectrum ee -> HZ with Z -> l+l- Ds ~ 3% model independent measurement Dm ~ 50 MeV sub-permille precision Precision physics of Higgs bosons mH = ee -> HZ diff. decay channels 120 GeV DmH = mH = 40 MeV 150 GeV DmH = 70 MeV Precision physics of Higgs bosons mH=240 GeV e e ZH qqqq ΔmH = 400 MeV (0.2%) Δ σ (HZ) = 4% Results available for MH up to 320 GeV Reconstructed Higgs Mass (GeV) Precision physics of Higgs bosons Determination of quantum numbers Spin from threshold measurement CP-quantum numbers from H,Z angular distributions or polarisation analysis of Higgs decays to taus Precision physics of Higgs bosons Higgs field responsible for particle masses → couplings proportional to masses Precision analysis of Higgs decays ΔBR/BR bb cc gg tt gg WW 2.4% 8.3% 5.5% 6.0% 23.0% 5.4% For 500 fb-1 MH = 120 GeV Precision physics of Higgs bosons High precision allows sensitivity to new effects e.g. additional heavy Higgs bosons Standard Model Higgs vs MSSM Higgs Reconstruction of the Higgs-potential gHHH Φ(H)=λv2H2 + λvH3 + 1/4λH4 SM: gHHH = 6λv, fixed by MH D 20% (1 ab-1) Precision physics of Higgs bosons Conclusion The precision measurements at the Linear Collider are crucial to establish the Higgs mechanism responsible for the origin of mass and for revealing the character of the Higgs boson If the electroweak symmetry is broken in a more complicated way then foreseen in the Standard Model the LC measurements strongly constrain the alternative model Beyond the Higgs Why are electroweak scale (102 GeV) and the Planck scale (1019 GeV) so disparate ? Are there new particles ? → supersymmetry new forces ? → strong interactions hidden dimensions ? Supersymmetry ● unifies matter with forces for each particle a supersymmetric partner (sparticle) of opposite statistics is introduced ● allows to unify strong and electroweak forces ● provides a link to string theories Supersymmetry ● Predicts • light Higgs boson ( + additional heavier Higgs bosons) • spectrum of sparticles (→doubling number of particles) ● Contains • many new parameters connected to SUSY breaking ● High precision measurements of • masses • couplings • quantum numbers needed to • extract fundamental parameters (few) • determine the way Supersymmetry is broken i.e the underlying supersymmetric model Supersymmetry Mass spectra depend on choice of models and parameters... well measureable at LHC precise spectroscopy at the Linear Collider Supersymmetry charginos Production and decay of supersymmetric particles at e+e- colliders s-muons Lightest supersymmetric particle stable in most models candidate for dark matter Experimental signature: missing energy Supersymmetry Sleptons Production and decay of smuons: 320 GeV, 160 fb-1 Mass errors (MeV): smuon Χ1 0 end points: 300 100 threshold: 90 50 3‰ 1‰ Energy spectrum of muons Supersymmetry Charginos Produced in pairs Easy detection through their decays 350 GeV 160 fb-1 Dm ~ 50 MeV Cross section rises as Shape of X-section -> spin Supersymmetry MSSM: one additional Higgs doublet Di-jet inv mass (500 fb-1, E = 800 GeV) → h0,H0,A0,H+,H- Mass peak (50 fb-1, E = 800 GeV) HA: 5σ discovery possible up to Σm = √s – 30 GeV Supersymmetry Gluino (LHC) Extrapolation to GUT scale Extrapolation of SUSY parameters from weak to GUT scale (within mSUGRA) Gauge couplings unify at high energies, Gaugino masses unify at same scale Precision provided by LC for slepton, charginos and neutralinos will allow to test if masses unify at same scale as forces SUSY partners of electroweak bosons and Higgs Supersymmetry Conclusions The Linear Collider will be a unique tool for high precision measurements ● model independent determination of SUSY parameters ● determination of SUSY breaking mechanism ● extrapolation to GUT scale possible but what if …… No Higgs boson(s) found…. WLWL scattering: Standard Model mathematically inconsistent unless new physics at about 1.3 TeV Experimental consequence: New strong interaction measurable in triple and quartic gauge boson couplings Sensitivity at a TeV Linear Collider: ~ 8 TeV (TGC) ~ 3 TeV (QGC) Hidden dimensions In how many dimensions do we live? Extra dimensions provide an explanation for the hierarchy problem String theory motivates brane models in which our world is confined to a membrane embedded in a higher dimensional space e.g. large extra dimensions: Emission of gravitons into extra dimensions Experimental signature single photons Hidden dimensions cross section for anomalous single photon production d = # of extra dimensions e+e- -> gG measurement of cross sections at different energies allows to determine number and scale of extra dimensions (500 fb-1 at 500 GeV, 1000 fb-1 at 800 GeV) Energy Hidden dimensions Effects from virtual graviton exchange: can prove Spin-2 exchange! Hidden dimensions Randall-Sundrum Model Direct observation… cross-section for e+e-→μ+μ- including exchange of a KK-tower of gravitons Precision electroweak tests As the heaviest quark, the top-quark could play a key role in the understanding of flavour physics….. …requires precise determination of its properties…. σ (pb) Energy scan of top-quark threshold ΔMtop ≈ 100 MeV Precision electroweak tests high luminosity running at the Z-pole Giga Z (109 Z/year) ≈ 1000 x “LEP” in 3 months with e- and e+ polarisation ΔsinΘW = 0.000013 together with ΔMW = 7 MeV (threshold scan) And ΔMtop = 100 MeV Summary: key scientific points The Linear Collider Report of the Worldwide Physics and Detector Study Group: We know enough now to predict with very high confidence that the Linear Collider, operating at energies up to 500 GeV, will be needed to understand how forces are related and the way mass is given to all particles. We are confident that the new physics that we expect beyond the standard model will be illuminated by measurements at both the LHC and the LC, through an intimate interplay of results from the two accelerators. The physics investigations envisioned at the LC are very broad and fundamental, and will require a leading edge program of research for many years. General layout of a Linear Collider For E > 200 GeV need to build linear colliders Proof of principle: SLC The challenges: Luminosity: high charge density (1010), > 10,000 bunches/s very small vertical emittance (damping rings, linac) tiny beam size (5x500 nm) (final focus) Energy: high accelerating gradient (> 25 MV/m, 500 - 1000 GeV) To meet these challenges: A lot of R&D on LC’s world-wide different technologies: NLC/JLC…..TESLA……CLIC The TESLA Linear Collider superconducting Nb cavities Decisions of the German Ministry for Education and Research concerning the TESLA Linear Collider 5 February 2003 ● Today no German site for the TESLA linear collider will be put forward. ● This decision is connected to plans to operate this project within a world-wide collaboration ● DESY will continue its research work on TESLA in the existing international framework, to facilitate and assure German participation in a future global project ● DESY will remain a world-wide leading centre of particle physics. ● The decision to not propose a site today is not meant as a reduction of the importance of particle physics in Germany Essence: The statement by the German government • is positive on a linear collider in general, • approves continued R&D on TESLA, • encourages the German participation in a global project, • but leaves the site selection open for the time being. The TESLA Linear Collider Routine production of cavities exceeding 25 MV/m (TESLA goal for 500 GeV) New surface treatment, gradients of > 40 MV/m (single cells) -> clear energy upgrade TESLA The path to higher energies…. High power test of electropolished nine-cell cavity April 2003: 38 MV/m Next steps or How to arrive at a LC as a Global Project International LC Steering Group: 1. unite first behind one project with all its aspects, including the technology choice, and then 2. approach all possible governments in parallel in order to trigger the decision process and site selection. Next steps 1. Technology Recommendation Aim at joint selection of one technology in spring 2004 How: • Gather a committee of wise persons, who use criteria to be developed by the ILCSG, to recommend a technology choice to the ILCSC. • The regional steering committees will each nominate 4 persons from which the ILCSG will choose three from each list for a total of 9 wise persons. First discussion of the make-up of the committee in August. Next steps 2. Global Linear Collider Center The ILCSG agrees that it would be highly desirable to form a precursor to the Global Linear Collider Center: Core group to begin making an international design, based on accumulated work to date, but reexamined in a completely international context. In parallel to the work of the design group: preparation of political decision, definition of organisational structure, site analysis Aim at approval of LC around 2006/2007 Conclusion We have a convincing scientific case and a world consensus on the importance of a Linear Collider and on its timing w.r.t. the LHC LC and LHC offer complementary view of Nature at energy frontier We have the technology/ies for the LC at hand We are developing detector technologies to do the physics at the LC We have a great dynamics in the international coordination and are gaining political attention We have an exciting and promising future for discoveries and for understanding the universe and its origin Let’s make it happen