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

The physical world is composed of Quarks and Leptons interacting via force carriers (Gauge Bosons) Last entries: top-quark 1995 tau-neutrino 2000 What have we learned the last 50 years or Status of the Standard Model

Standard Model Precision measurements (LEP,SLD,Tevatron, NuTeV,…) Standard Model tested to permille level Precise and quantitative description of subatomic physics

Indirect determination of the top mass possible due to precision measurements known higher order electroweak corrections Proves high energy reach through virtual processes Test of the SM at the Level of Quantum Fluctuations Top quark mass LEP indirect

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

HERA ep collider Electroweak Unification 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 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)

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 The next steps M H between 114 and ~200 GeV

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 ● Clean environment collision of point-like particles → low backgrounds ● precise knowledge of cross sections ● Additional options: e - e -, eγ, γγ collisions Machine for Discoveries and Precision Measurements The power of e + e - Colliders q q  LEP(OPAL) e+e+ e-e-

Physics Potential of a Linear Collider (highlights) Higgs bosons Supersymmetry Structure of space-time Precision tests of electroweak interactions top W Z √s: 91…500…~1000 GeV

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)

Dominant production processes at LC: Precision physics of Higgs bosons

model independent measurement Recoil mass spectrum ee -> HZ with Z -> l + l -  ~ 3% m ~ 50 MeV sub-permille precision

 m H = 40 MeV Precision physics of Higgs bosons  m H = 120 GeV ee -> HZ diff. decay channels  m H = 150 GeV  m H = 70 MeV

Reconstructed Higgs Mass (GeV) m H =240 GeV Precision physics of Higgs bosons Δm H = 400 MeV (0.2%) Δ σ (HZ) = 4% Results available for M H up to 320 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 bb2.4% cc8.3% gg5.5% tt6.0% gg23.0% WW5.4% For 500 fb -1 M H = 120 GeV

Standard Model Higgs vs MSSM Higgs Precision physics of Higgs bosons High precision allows sensitivity to new effects e.g. additional heavy Higgs bosons

Reconstruction of the Higgs-potential Φ(H)=λv 2 H 2 + λvH 3 + 1/4λH 4 SM: g HHH = 6λv, fixed by M H g HHH (1 ab -1 )

Precision physics of Higgs bosons 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 Conclusion

Beyond the Higgs Why are electroweak scale (10 2 GeV) and the Planck scale (10 19 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

Mass spectra depend on choice of models and parameters... Supersymmetry well measureable at LHC precise spectroscopy at the Linear Collider

Supersymmetry Production and decay of supersymmetric particles at e + e - colliders charginos s-muons Lightest supersymmetric particle stable in most models candidate for dark matter Experimental signature: missing energy

Energy spectrum of muons Production and decay of smuons: 320 GeV, 160 fb-1 Mass errors (MeV): smuon Χ 1 0 end points: threshold: Supersymmetry Sleptons 3 ‰ 1 ‰

Cross section rises as Shape of X-section -> spin Produced in pairs 350 GeV 160 fb -1  m ~ 50 MeV Easy detection through their decays Supersymmetry Charginos

Di-jet inv mass (500 fb -1, E = 800 GeV)Mass peak (50 fb -1, E = 800 GeV) MSSM: one additional Higgs doublet → h 0,H 0,A 0,H +,H - Supersymmetry HA: 5σ discovery possible up to Σm = √s – 30 GeV

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 Gluino (LHC) SUSY partners of electroweak bosons and Higgs Supersymmetry Extrapolation to GUT scale

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…. W L W L 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 String theory motivates brane models in which our world is confined to a membrane embedded in a higher dimensional space Extra dimensions provide an explanation for the hierarchy problem e.g. large extra dimensions: Emission of gravitons into extra dimensions Experimental signature single photons In how many dimensions do we live?

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) cross section for anomalous single photon production Energy  = # of extra dimensions e+e- ->  G Hidden dimensions

Effects from virtual graviton exchange: can prove Spin-2 exchange! Hidden dimensions

Randall-Sundrum Model cross-section for e + e - →μ + μ - including exchange of a KK-tower of gravitons Direct observation…

Precision electroweak tests σ (pb) Energy scan of top-quark threshold As the heaviest quark, the top-quark could play a key role in the understanding of flavour physics….. …requires precise determination of its properties…. ΔM top ≈ 100 MeV

together with ΔM W = 7 MeV (threshold scan) And ΔM top = 100 MeV high luminosity running at the Z-pole Giga Z (10 9 Z/year) ≈ 1000 x “LEP” in 3 months with e - and e + polarisation Precision electroweak tests ΔsinΘ W =

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. Summary: key scientific points The Linear Collider Report of the Worldwide Physics and Detector Study Group:

The challenges: Luminosity:high charge density (10 10 ), > 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, GeV) To meet these challenges: A lot of R&D on LC’s world-wide different technologies: NLC/JLC…..TESLA……CLIC For E > 200 GeV need to build linear colliders Proof of principle: SLC General layout of a Linear Collider

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

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. Essence :

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 The TESLA Linear Collider

TESLA April 2003: 38 MV/m High power test of electropolished nine-cell cavity The path to higher energies….

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 or How to arrive at a LC as a Global Project International LC Steering Group:

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. Aim at joint selection of one technology in spring 2004 Next steps 1. Technology Recommendation

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 Next steps 2. Global Linear Collider Center

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