1. Why a Linear Collider Now? S. Dawson, BNL October, 2002  Asian, European, and American communities all agree  High Energy Linear Collider is next large accelerator  WHY???

2. Where are we going? US high energy community just completed long range planning process 20 year roadmap for the future HEPAP subpanel: We recommend that the highest priority of the U.S. program be a high-energy, high-luminosity, electron- positron linear collider, wherever it is built in the world

3. Linear Collider Basics Initial design, e + e - at  s=500 GeV Luminosity  10 34 cm 2 /sec  300 fb -1 /yr 80% e - polarization Energy upgrade to.8-1.2 TeV in future Physics in  2012

4. The international accelerator community believes that a TeV-scale linear collider can be successfully built NLC High Power Klystron TESLA Superconducting Cavity JLC Accelerator Test Facility

5. TESLA Preliminary designs for Linear Colliders NLC

6. ????? What are the big questions we want to answer? Why do we think we can predict where we want to go? –What do we know now? –What do we expect to learn from the Tevatron and LHC? –What questions will remain unanswered?

7. What is particle physics? Study of Space, Time, Matter Bagger/Barish report

8. The Big Questions? What is the origin of mass? Do protons decay? Do forces unify at a large scale? Are there more than four dimensions? Why are there 4 forces? No unification of couplings in SM

9. Cosmic Connections What is dark matter? How are particle physics & cosmology connected? What is dark energy? Where did the anti- matter go?

10. Planning for the Future Based on Success of last 20 years…. Model of electroweak physics verified at.1% level The problem of mass remains W and Z bosons discovered at CERN in 1983 Masses not zero….or even small

11. Why is Mass a Problem? Lagrangian for gauge field (spin 1): L=-¼ F  F  F  =   A -  A  L is invariant under transformation: A  (x)  A  (x)-    (x) Gauge invariance is guiding principle Mass term for gauge boson ½ m 2 A  A  Violates gauge invariance So we understand why photon is massless

12. Simplest possibility for Origin of Mass is Higgs Boson Higgs mechanism gives gauge invariant masses for W , Z Requires physical, scalar particle, H, with unknown mass Observables predicted in terms of: –M Z =91.1875 .0021 GeV –G F =1.16639(1) x 10 -5 GeV -2 –  =1/137.0359895(61) –M h Higgs and top quark enter into quantum corrections,  M t 2, log(M h )

13. Precision Measurements sensitive to top quark before it was discovered!

14. Large number of measurements fit electroweak predictions

15. Indirect Indications for Light Higgs Mass Direct measurements of M W, M t agree well with indirect measurements Prefer Higgs in 100- 200 GeV range ASSUMES no new physics

16. Where is the Higgs boson? Higgs couplings of fixed Production rates at LEP, Tevatron, LHC fixed in terms of mass Direct search limit from LEP: Higgs contributions to precision measurements calculable Precision measurements: G. Mylett, Moriond02

17. Tantalizingly close….. Direct limit: M h >114.1 GeV Indirect limit: M h <193 GeV  New Physics is just around the corner!  Fits assume Standard Model….if Standard Model incorrect, even more exciting new physics….

18. Higgs mass and scale of new physics correlated….. Sensible theory here 130 < M h < 170 GeV

19. Fermilab Tevatron at  s=2 TeV May discover Higgs if very lucky Requires light Higgs and high luminosity Physics in 2002-2008

20. CDF D0 Upgraded Detectors for RunII Enhanced capabilities for b tagging aid Higgs search

21. CERN Large Hadron Collider (LHC) pp interactions at  s =14 TeV LHC will discover Higgs boson if it exists Sensitive to M h from 100- 1000 GeV Higgs signal in just a few channels Physics circa 2008 ATLAS TDR

22. Discovery isn’t enough…. Is this a Higgs or something else? Linear Collider can answer critical questions –Does the Higgs generate mass for the W,Z bosons? –Does the Higgs generate mass for fermions? –Does the Higgs generate its own mass?

23. Is it a Higgs? How do we know what we’ve found? Measure couplings to fermions & gauge bosons Measure spin/parity Measure self interactions

24. Coupling Constant Measurements Zeppenfeld, hep-ph/0203123 LHC measures combinations of coupling constants Typical accuracy, 10-20% Only some subset of couplings Assumptions necessary to get couplings L=200 fb -1

25. Linear Collider is Higgs Factory! e + e -  Zh produces 40,000 Higgs/year Clean initial state gives precision Higgs mass measurement M h 2 =s-2  sE Z +M Z 2 Model independent Higgs branching ratios WWh vertex ZZH vertex

26. Higgs mass measurements LC: LHC: Direct reconstruction of LC @ 350 Gev Conway, hep-ph/0203206

27. Precision Measurements of Higgs Couplings Dots are experimental error 1-2% measurement Measure ALL Higgs couplings Bands are theory error –Larger than experiment –Largest error from m b Battaglia & Desch, hep-ph/0101165

28. Higgs measurements test model! Couplings to fermions very different in SUSY models LC can distinguish SM from SUSY up to M A =600 GeV Standard Model

29. Angular correlations of decay products distinguish scalar/pseudoscalar Miller, hep-ph/0102023 Threshold behavior measures spin [20 fb -1 /point] Higgs spin/parity in e + e -  Zh

30. Measuring Higgs Self Couplings g hhh, g hhhh completely predicted by Higgs mass Must measure e + e -  Zhh Small rate (.2 fb for M h =120 GeV), large background Large effects in SUSY Lafaye, hep-ph/0002238

31. Problem with this picture… Fundamental Higgs is not natural Quantum corrections to M h are quadratically divergent  M h 2  2 So enormous fine-tuning needed to keep Higgs light  M h 2 \M h 2  M W 2 \M pl 2  10 -32

32. Solution is Supersymmetry Quadratic contributions to Higgs mass cancel between scalars and fermions To make cancellation hold to all orders need symmetry Bose-Fermi symmetry….supersymmetry

33. Do the forces unify? Coupling constants change with energy Coupling constants unify in supersymmetric models Hint for new physics?

34. New particles in SUSY Theory Spin ½ quarks  spin 0 squarks Spin ½ leptons  spin 0 sleptons Spin 1 gauge bosons  spin ½ gauginos Spin 0 Higgs  spin ½ Higgsino Experimentalists dream….many particles to search for! What mass scale? Supersymmetry is broken….no scalar with mass of electron

35. Supersymmetry Can we find it? Can we tell what it is? Masses of new particles depend on mechanism for breaking Supersymmetry Couplings of new particles predicted in terms of few parameters Simplest version has 105 new parameters

36. Simplifying Assumption: Assume masses unify at same scale as couplings Everything specified in terms of scalar/fermion masses at high scale and 3 parameters Predictive anzatz…..

37. LHC/Tevatron will find SUSY Discovery of many SUSY particles is straightforward Untangling spectrum is difficult  all particles produced together SUSY mass differences from cascade decays;eg M  0 limits extraction of other masses Catania, CMS

38. Light SUSY consistent with Precision Measurements SUSY predicts light Higgs SUSY predicts 5 scalars For M A , SUSY Higgs sector looks like SM Can we tell them apart? Higgs BR are different in SUSY

39. LHC Find all the Higgs Bosons Carena, hep-ph/9907422 Tevatron

40. Into the wedge with a LC  s>2M H e + e -  H + H -, H 0 A 0 observable to M H =460 GeV at  s=1 TeV  s<2M H e+e-  H +, H +  tb L=1000 fb -1,  s=500 GeV, 3  signal for M H  250 GeV

41. LC can step through Energy Thresholds Run-time Scenario for L=1000 fb -1 Year124567  L (fb -1 ) 1040150200250 SUSY masses to.2-.5 GeV from sparticle threshold scans  M  0 /M  0  7% (Combine with LHC data) 445 fb -1 at  s=450-500 GeV 180 fb -1 at  s=320-350 GeV (Optimal for Higgs BRs) Higgs mass and couplings measured, g bbh  1.5% Top mass and width measured,  M t  150 MeV Battaglia, hep-ph/0201177

42. How do we know it’s SUSY? Need to measure masses, couplings Observe SUSY partners, eg Polarization can help separate states Discovery is straightforward e  energies measure masses LC Study, hep-ex/0106056  m e  1 GeV L=50 fb -1

43. SUSY Couplings: Compare rates at NLO: Lowest order, Super-oblique corrections sensitive to higher scales Masses from endpoints Assume Tests coupling to 1% with 20 fb -1

44. What is the universe made of? Stars and galaxies are only 0.1% Neutrinos are ~0.1–10% Electrons and protons are ~5% Dark Matter ~25% Dark Energy ~70% H. Murayama

45. Supersymmetry provides understanding of dark matter? Lightest SUSY particle (LSP) could be dark matter candidate! LSP is weakly interacting, neutral, and stable LSP in range of LC/LHC LC can determine LSP mass; check dark matter predictions LSP is dark matter M h =115 GeV g-2 Drees, hep-ph/0210142 M 0 (GeV) M 1/2

46. Standard Model Needs Top Quark Top quark completes 3 rd generation –Why are there 3 generations, anyways? Theory inconsistent without top

47. Top Quark discovery at Fermilab in 1995 CDF top event D0 top event Why is M t (=175 GeV)>>M b (=5 Gev)??

48. Understanding the Top Quark Why is ? Kinematic reconstruction of tt threshold gives pole mass at LC Compare LHC Groote, Yakovlov, hep-ph/0012237 QCD effects well understood NNLO ~20% scale uncertainty 2M t (GeV) 

49. Top Yukawa coupling tests models tth coupling sensitive to strong dynamics Above tth threshold e + e  tth Theoretically clean  s=700 GeV, L=1000 fb -1 Large scale dependence in tth rate at LHC L=300 fb -1 Baer, Dawson, Reina, hep-ph/9906419 Juste, Merino, hep-ph/9910301 Reina, Dawson, Orr, Wackeroth Beenacker, hep-ph/0107081

50. Exciting physics ahead LHC/Tevatron finds Higgs   LC makes precision measurements of couplings to determine underlying model LHC finds evidence for SUSY, measures mass differences  LC untangles spectrum, finds sleptons  LC makes precision measurements of couplings and masses etc