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Adventures at the Terascale: Opportunities and Challenges

This presentation discusses the current state of particle physics, the importance of the terascale, and the challenges and opportunities faced by researchers. It covers topics such as electroweak unification, the Higgs boson, and the search for dark matter. The presentation emphasizes the need for new physics beyond the Standard Model and the potential for discoveries at the Terascale.

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Adventures at the Terascale: Opportunities and Challenges

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  1. Adventures at the Terascale: Opportunities and Challenges Sally Dawson Fall, 2006 BNL

  2. Outline • Where is particle physics today? • What is the terascale and why is it important? • Planning for the Future • EPP2010 • European Strategy Committee

  3. Electroweak Unification: A Successful Model • Glashow , Salam, & Weinberg realized that the field responsible for the electromagnetic force (the photon) • And the fields responsible for the Weak force (the then undiscovered W+ and W-) • Could be described by a single theory if another field (an undiscovered heavy neutral boson (Z)) were to exist

  4. Desire for Unification is a Guiding Theme • Charged and neutral • currents unify at 100 GeV HERA • Experimental evidence for the unification of the weak and electromagnetic forces Model requires Higgs boson or something like it to explain W,Z, fermion masses

  5. 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 m2 AA • Violates gauge invariance • So we understand why photon is massless

  6. 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: • MZ=91.1875.0021 GeV • GF=1.16639(1) x 10-5 GeV-2 • =1/137.0359895(61) • Mh • Higgs and top quark enter into quantum corrections,  Mt2, log(Mh)

  7. Electroweak Theory is Precision Theory 2006 We have a model…. And it works to the 1% level Gives us confidence to predict the future!

  8. Quantum Consistency of model tells us where the Higgs is • Mh < 166 GeV (precision measurements) • Mh < 199 GeV if direct search (yellow band) included • Limits have moved around with top quark quark mass • Now Mt=171.4  2.1GeV New from ICHEP, 2006

  9. Quantum Corrections are sensitive to the Higgs Mass • Direct observation of W boson and top quark (blue) • Inferred values from precision measurements (pink) New from ICHEP, 2006

  10. Can the Tevatron discover the Higgs? 2009 2006 This relies on statistical combination of multiple weak channels

  11. Fermilab looks for the Higgs in Many Channels • 2006: D0, CDF combined results, New from ICHEP 2006

  12. Where is the Higgs ? • We need to find the Higgs to understand mass • We didn’t find it at LEP • We haven’t found it at Fermilab • The end is in sight…..if we don’t find it at the LHC, the Standard Model as it stands cannot be the whole story (because precision measurements would be inconsistent)

  13. A Decade of Discovery • Electroweak Theory • Neutrino flavor oscillations • Three separate neutrino species • Understanding QCD • Discovery of top quark • B meson decays violate CP • Quarks and leptons structureless at TeV scale

  14. Even if we find a Higgs…. • We know the Standard Model is incomplete • It leaves too many open questions • A few (but not all) of the unanswered questions follow

  15. We live in special times 2006 Nobel Prize for COBE: The first survey of dark matter in the universe We have a census of the universe

  16. The Universe has an Energy Budget Crisis • Stars and galaxies are only ~0.5% • Neutrinos are ~0.3–10% • Rest of ordinary matter (electrons and protons) are ~5% • Dark Matter ~30% • Dark Energy ~65%

  17. Is Dark Matter a Particle? Can we produce dark matter in a collider and study all its properties?

  18. The Cosmic Questions • What is Dark Matter? • If it’s a particle, there is no candidate in the Standard Model • What is Dark Energy? • Standard Model can’t explain this either These questions connect particle physics and cosmology in an inescapable way …. And tell us that the Standard Model can’t be the whole story

  19. Discoveries of last decade point to new discoveries • Incredibly successful model • Our model cannot explain dark matter, dark energy, neutrino masses, why the top quark is so heavy…… • It points to an energy scale of 1 TeV as place where physics explaining our questions might lurk WE HAVE THE TOOLS TO ANSWER OUR QUESTIONS!

  20. Quantum Corrections Connect Weak and Planck Scales Quantum corrections drag weak scale to Planck scale Tevatron/LHC Energies Weak GUT Planck 102 GeV 1019 GeV 1016

  21. Why 1 TeV (the Terascale)? H • Higgs mass grows with high scale,  (a priori =Mpl) Points to 1 TeV as scale of new physics MH 200 GeV requires  ~ TeV

  22. Experimental Opportunities • Particle physicists employ three general sets of tools for addressing the open questions • High-energy beams • High-intensity beams • Nature’s particle sources

  23. Livingstone Plot—The March of Progress • Electron machines access full energy of collisions • Quark and gluon interactions in a hadron machine access some fraction of total collision energy

  24. Science Timeline Tevatron LHC LHC Upgrade ILC 2006 2007 2012

  25. proton-proton collider at CERN (2007) 14 TeV energy 7 mph slower than the speed of light cf. 2TeV @ Fermilab ( 307 mph slower than the speed of light) Typical energy of quarks and gluons 1-2 TeV Large Hadron Collider (LHC)

  26. Stored Energy of Beams unprecedented • Ebeam=1.5 Giga Joule • LHC beams have same kinetic energy as aircraft carrier at 15 knots! • Largest scientific project ever attempted!

  27. Requires Detectors of Unprecedented Scale • Two large multi-purpose detectors • CMS is 12,000 tons (2 x’s ATLAS) • ATLAS has 8 times the volume of CMS

  28. LHC Status • Initial operation at ECM=900 GeV to debug machine and detectors at end of 2007 • 14 TeV physics run in 2008 • Initially run at low luminosity (2 x 1033 cm-2 s-1 ) • Ramp to full luminosity in 2010 (1034 cm-2 s-1 )

  29. Detectors • ATLAS and CMS will be ready for pilot physics run in August, 2007 ATLAS, 9/06 CMS

  30. Initial Physics Program at the LHC • Large numbers of events even at low LHC luminosity ECM (TeV)

  31. W  e Z  ee First Physics • Standard Model processes with new detectors and the LHC energy • W,Z, and top production (well understood theoretically) • pp collisions at √s=900GeV • end of 2007 • Luminosity around 1029 cm-2s-1

  32. √s=14 TeV-- the first 10 pb-1 Similar statistics to CDF, D0 ~10 pb-1 1 month at 1030 and < 2 weeks at 1031,=50% • LHC is a W,Z, top factory • Small statistical errors in precision measurements • Search for rare processes • Large samples for studies of systematic effects

  33. LHC Will find SM Higgs if it exists LHC will find Standard Model Higgs Consistency of SM REQUIRES a Higgs Boson or something like it

  34. LHC will discover Higgs boson if it exists Sensitive to Mh from 100-1000 GeV Higgs signal in just a few channels LHC and the Higgs

  35. Measure couplings to fermions & gauge bosons Measure spin/parity Measure self interactions Is it a Higgs?

  36. Discovery isn’t Enough • Is this a Higgs or something else? • We must 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?

  37. Two Paths to Discovery • High Energy • Operating at the energy frontier • Direct discovery of new particles • Tevatron and LHC • High Precision • Infering new physics effects from high energy scales through precision measurements at low energy Combining both stategies gives much more complete understanding than either one alone

  38. Linear Collider is Next • Initial design, • Luminosity •  15 miles long • International project • 80% e- polarization • Physics arguments for 1 TeV energy scale Energy upgrade a must! e+e- collisions are pointlike

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

  40. Progress on the International Front • International Team recommended cold technology in August, 2004 • Global Design Effort (GDE) for International Linear Collider (ILC) • Barry Barish, Director • Regional Centers in Asia, Europe, North America • Site independent design • Cost by end of 2006 • Optimistic time frame has construction decision in 2010, physics in 2015 LHC results before construction decision

  41. e+e-Zh produces 40,000 Higgs/yr Clean initial state gives precision Higgs mass measurement Mh2=s-2sEZ+MZ2 Model independent Higgs branching ratios Clean probe of underlying model Linear Collider is a Higgs Factory

  42. Does the Higgs Generate Mass? Linear Collider is the place to measure Higgs couplings!

  43. Measuring the spin of the Higgs Threshold behavior measures spin [20 fb-1 /point] Linear collider can change initial state energy to do energy scans Very hard to do at the LHC

  44. Where do we go from here? • Great scientific opportunities • Tevatron / Babar / CESR shut down 2009-2010 • The energy frontier moves to Europe when LHC turns on DOES IT MATTER?

  45. Revealing the Hidden Nature of Space and Time Final Report of the Committee on Elementary Particle Physics in (the First Decades of) the 21st Century May 5, 2006

  46. Context of the Report • The report examines and is framed by • The nature of the scientific opportunities • The current status of the U.S. program • An articulation of a set of strategic principles • Evaluation of alternative sets of priorities • Reasonable budget assumptions • (The ongoing national discussion of competitiveness, innovation, and the future position of U.S. science and technology)

  47. The “EPP2010” Committee • National Academies convened this committee in response to an informal request from NSF and DOE to • Identify the compelling questions that define the current particle physics agenda • Recommend a 15-year implementation plan with realistic, ordered priorities to address them

  48. Unusual Features of this Report • Over the past 10 years, many committees have examined the future of elementary particle physics • What makes this assessment by the National Academies ANY different?

  49. Committee membership was extraordinary in its breadth and its depth • Over half of the committee members were drawn from outside particle physics, bringing expertise in astronomy, astrophysics, condensed-matter physics, AMO science, even genetics, aerospace engineering, and economics • Report reflects the efforts of a broad group of experienced individuals to place the particle physics agenda in a larger context in order to understand the significance of the current opportunities

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