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APS plenary talk Paul Grannis April 7, 2003

APS plenary talk Paul Grannis April 7, 2003. Sailing the uncharted seas beyond the Standard Model.

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APS plenary talk Paul Grannis April 7, 2003

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  1. APS plenary talk Paul Grannis April 7, 2003 Sailing the uncharted seas beyond the Standard Model New findings in experiments at the highest energy will dramatically expand our knowledge of the structure of matter on the shortest scales of distance, and at the earliest times in the expanding universe. The accelerators and experiments at the energy frontier are costly, so we need confidence that they will bring important new understanding.

  2. Map fragment discovered on the previous voyages in Mare SM: Is it a faithful guide for future exploration, or product of a delusional seaman? Grand Unification Gondwandaland EWSB- land Bay of SUSY Cliffs of Dark Matter Planck Dragon Beagle n Oscillations Mare SM Dark Energy Maelstrom Quark mixing n CP B≠B e→m Muong-2 The Flavor Archipeligo GZK Atolls Gravitational Waves Quark-gluon plasma volcano To boldly go … ! 2

  3. In the Mare Standard Model voyages so far, our explorations showed: “Four fundamental forces” QCD(quantum chromodynamics – the strong nuclear force) Electromagnetic Weak Gravity (still no quantum theory) } become the unified Electroweak (EW)force for ECM > 250 GeV QCD and EW forces are Yang Mills gauge theories – a local invariance (at each space-time point) to generalized phase transformations of the matter fields leads to forces mediated by spin-1 (vector) massless gauge bosons. The fundamental forces have a common nature 3

  4. ( ( ( ) ) ) QCD:mediated by massless gluons coupling to ‘color’. Quarks have color. Leptons do not, so do not feel the strong force. red quark Red +yellow gluon 3 pairs of quark flavors, each coming with 3 colors. u c t d s b yellow quark Gluons carry ‘color charge’ also (an octet of colored gluons), so they couple to themselves. (Making QCD much more complex than EM interaction where the photon couples to charge but carries no charge. Color charge neutralizes in observed particles today, but the early universe had unconfined color – Quark Gluon plasma. The details of the phase transition affect the subsequent universe. 4

  5. EM:mediated by massless photons coupling to ‘electric charge’. All quarks and three leptons e, m, t have charge and feel the EM force quark, e, m, t photon, g quark, e, m, t Charged current The underlyingWEAKinteraction is similar – charged and neutral currents mediated by massless isovector ‘w’ and isoscalar ‘b’ bosons that couple to ‘weak isospin charges’ n, u quark w± e, d quark Neutral current n, lepton, quark b0 n, lepton, quark 5

  6. But the range of the observed Weak force is ~ 1 fm, so the physical W± and Z0bosons must be massive. Experiments of the past decade show MW = 80.450 ± 0.034 GeV and MZ = 91.1875 ± 0.0021 GeV. So observed W and Z cannot be the Yang Mills gauge bosons, and EW symmetry is broken. In the Standard Model, we invoke the spontaneous symmetry breaking of the unified EW force: ( ) Massless gauge bosons in symmetry limit b w-w0 w+ ( ) g W- W+ Z0 Physical bosons = ( ) f1 f2 Complex spin 0 Higgs doublet Electroweak symmetry breaking In the symmetry breaking induced by the Higgs fields, 3 of Higgs degrees of freedom go to provide the missing longitudinal polarization state needed by massive vector bosons. Before symmetry breaking: 4x2 gauge boson d.o.f. and 4 Higgs d.o.f. After, 3x3 for W±/Z, 2 for g and 1 Higgs d.o.f. left over 6

  7. t quark t quark Higgs l l In the Standard Model, the 4th Higgs field results in the HIGGS BOSON. All the parameters of the EW interaction are fixed by experiment, except for the Higgs boson mass. Higgs gives mass to W and Z – and quarks & leptons too e.g. generates the top quark mass The more massive the quark, the larger its Yukawa coupling l. Many observables of the Z and W bosons are dependent upon the mass of the Higgs boson. In the context of the SM, the ~100 precision measurements of the properties of Z, W, top quark indicate: 114 < MH< ~200 GeV Of course, Nature may choose some other way than SM to break Electroweak symmetry! 7

  8. But why the up quark (mass = 5 MeV) and the top quark (mass = 174,000 MeV) have such different couplings is still a big mystery ! ‘Who ordered that’ The phase transition that breaks the EW symmetry also governs the evolution of the early universe. We know the energy scale of that transition to be the vacuum expection value of the Higgs field ≈ 250 GeV. Something new must occur at this energy scale, maybe the Higgs or perhaps something else, and experiments should find the footprints and enough clues to figure out how it works. 8

  9. g1 g2 g3 The gauge couplings vary with the size of the probe (or momentum transfer q2). The QCD coupling decreases with q2while EM and Weak couplings increase. Were they to converge at a common point, we would have unification of the gauge forces. In the SM, the couplings come close ataround 1016 GeV but do not unify 9

  10. The flavor archipelago has many exotic islands: • Particle-antiparticle (CP) symmetry is violated for the quarks; the SM prescription fails however to explain the baryon-antibaryon asymmetry in the universe. • Quarks ‘ mix ’ (i.e. the quark QCD eigenstates differ from the weak states): a linear combination of down, strange and bottom quarks couple to the up quark in producing b decay. • Neutrinos have mass, mix (hence flavor species oscillate). They could have CP-violation as well. The mixing pattern is bizarre. • The difference of fermion masses from the lightest neutrino at about 10-3 eV to the heaviest quark above 1011 eV is a mystery! • We do not know if quarks and leptons are immutable – and thus if protons are stable. The energy scale at which fundamental new insights will emerge is less clear for the flavor issues than for Electroweak Symmetry breaking. 10

  11. The SM explains much, but seems flawed: • Failure to unify Strong, Electromagnetic and Weak forces • The masses (W, Z, Higgs) are unstable to quantum corrections and should rise to the Planck scale (1019 GeV) if not protected (the “hierarchy problem”) • Gravity is left out • Baryon-antibaryon asymmetry of the universe is not explained by SM sources of CP violation • There is no good dark matter candidate in the SM • The ad hoc mass and mixing parameters have no explanation and are puzzling Our map fragment from the SM experiments of the past two decades gives some guidance of what we may find, but is not a clear blueprint for the new discoveries on the coming voyages of exploration. 11

  12. electron spin =1/2 Possible New Physics – Supersymmetry Postulate extension to Poincare group to include a symmetry between bosonic (commuting) and fermionic (anticommuting) space-time coordinates selectron spin = 0 For every SM boson there is a supersymmetry fermion partner with all other quantum numbers the same (color, charges, chirality …) and a superpartner boson for SM fermions. Partner masses in the TeV range. Susy expands the Higgs sector to 5 physical Higgs states, one with mass likely below 130 GeV. • String theories have supersymmetry as a necessary ingredient • Cancellation of quantum corrections between boson and fermion partners prevents mass renormalizations to Planck scale • Lightest Susy particle (LSP) stable and non-interacting: an excellent candidate for dark matter • Potential for CP violations in supersymmetry sector to explain B≠B • A large spectrum of new particles to discover and measure 12

  13. Possible New Physics – Large Extra Dimensions If the 7 extra spatial dimensions needed in string theory are curled up, not at the Planck length, but at mm or fm scales, one could perhaps cure the hierarchy problem by reducing the true energy (Planck) scale of gravity to few TeV. • Possible signatures include: • Production of mini-black holes when collision energy exceeds the inverse extra dimension size (mini-BH’s decay democratically to all particles) • Resonances from ‘standing wave nodes’ between two branes in extra dimensions – Kaluza Klein states resemble excited Z bosons • Apparent mono-photon production when graviton escapes into extra dimension (qq or e+e-→ g [unseen graviton] ) • Modifications to e+e- or qq scattering at high energy Many model variants exist, depending on the number & size of large extra dimensions, and the particles that penetrate into them. 13

  14. Possible New Physics – Strong Coupling • A new interaction patterned on QCD gauge theory, in which there is a new spectrum of fundamental particles above the TeV scale. Condensates of the new particles can form scalar particles that generate EW symmetry breaking and give mass to W and Z . • Observe the Goldstone boson condensates, measure their properties (different from SM Higgs) • Seek the new fundamental particles at higher energy • Measure modifications to W/Z/g couplings and anomalous form factors of the top quark • Measure deviations to e+e- or qq scattering at high energies • Detectable differences in precision Z/W properties from SM Past precision W,Z, top measurements constrain Strong Coupling models tightly 14

  15. The voyages of exploration now planned or proposed: 18 16 14 Base 12 Stretch 10 Projection Integratef fb-1 8 6 4 2 0 FY02 FY03 FY04 FY05 FY06 FY07 FY08 FY09 FY10 End FY The Fermilab Tevatron: CDF DØ Counter-rotating p and p, colliding at 1.96 TeV. In effect the Tevatron is a quark-antiquark collider with qq energy up to ≈ 1 TeV. Two experiments CDF and DØ will operate until the LHC program is producing physics results (2009?) 2 km Present luminosity is 4x1031cm-2s-1; expect to reach 3x1032cm-2s-1 . Total accumulation of 10 – 15 fb-1 by the end of the program. 15

  16. The LHC at CERN Mt. Blanc The Large Hadron Collider (LHC) at CERN will collide protons with protons at 14 TeV. This will provide collisions of the constituent quarks and gluons to about 5 TeV. General purpose experiments ATLAS and CMS. First collisions are expected in 2007; first physics run in 2008 and first results in 2009?? Lake Geneva ATLAS 8.6 km CMS Luminosity should reach 1x1034 cm-2 s-1 The LHC will reach the energy scale where current experiments tell us that new physics should surely exist – LHC is the primary discovery vessel 16

  17. The e+e- Linear Collider (proposed) • The first phase of the LC should collide e+ and e- at energies up to 500 GeV. Luminosity up to a few x 1034 cm-2 s-1. Electrons polarized to above 80%. • First operation in 2015 ??? • Upgrades and options: • energy increase to about 1 TeV • Polarized gg collisions (backscattered laser light); also e-g and e-e- collisions) • Polarized positrons ~30 km Two technology proposals exist – the TESLA proposal (Germany) using superconducting rf cavities, and the room temperature rf proposals of Japan (JLC) and US (NLC). Both judged feasible, but expensive (~$5B), so world cooperation to build is necessary. R&D continues on 5 TeV linear collider (CLIC at CERN). US version of the Linear Collider 17

  18. The discovery voyages Tevatron: operating now with seasoned detector collaborations. Mainly qq collisions at high energy. Energy is limited however and will access only a part of the terra incognito where new physics can lurk. We need to complete this program and discover what we can. LHC: being built and fully funded, has the largest energy reach so should span the TeV scale new physics regime. The colliding quarks and gluons within the protons have a range of energies, and the initial state quantum numbers are not fixed. The collision rates are very high (Giga Hz) and the backgrounds from SM and new physics processes are large; experiments are challenging. LC: proposed, with technical and political challenges remaining to be solved. 500 GeV energy is large enough to explore the EW symmetry breaking (Higgs) physics and some part of the new physics (SUSY etc.), but not all. However, the initial state has a fixed cm energy and well-defined quantum state. The processes are simple, and rates and backgrounds are low. The LC will provide the detailed and precise information to sort out the new physics. 18

  19. What will the different voyages tell us? Higgs boson and EW symmetry breaking Past experiments at the CERN LEP collider, the SLAC SLC and the Tevatron have constrained the SM Higgs boson to have a mass below about 200 GeV through precision measurements of the Z, W bosons and top quark. LEP measurements set a lower limit for Higgs mass at 114 GeV Only if the Higgs mass is in the range 140 – 180 GeV can the SM be a valid theory up to the Planck scale. If we find the Higgs expected in SM or SUSY will require new physics! 19

  20. excluded by LEP Higgs boson and EW symmetry breaking now Tevatron will seek Higgs via qq → WH or ZH with H → bb (for MH below about 135 GeV) or gg → H with H → WW above 135 GeV. Can obtain 3s evidence for Higgs over much of this range, or rule out SM Higgs for MH < 185 GeV. with Tevatron Run 2 from precision W and top mass Tevatron experiments can discover the Higgs, measure its mass to a few %, determine its dominant decay mode and branching fraction times cross section to 10’s of percent. 20

  21. Higgs boson and EW symmetry breaking LHC will be able to discover SM-like Higgs boson (> 5s) from the current limit up to 1000 GeV. Low mass region favored in SM is hardest; only H → gg observed. Determine Higgs mass to fraction of %. Can measure width if MH > 200 GeV. Determine the ratio of branching fractions of Higgs for some decay channels to ~25%. 1 yr run at full design luminosity Susy Higgs states: can always observe at least 1, typically 2 or more, but require several years at full luminosity. 21

  22. SM value (decoupling limit) b c W Allowed MA Possible BR measurements t g Susy models Higgs boson and EW symmetry breaking Higgs of several possible mass values seen as recoil to Z LC produces Higgs from e+e-→ ZH or Hnn. Seeing Higgs recoil from Z gives ‘bias free’ Higgs laboratory in which one can measure Higgs branching ratios (bb, cc, t+t-, gg, W+W-) to a few %. These BRs are crucial for establishing whether the Higgs seen is SM, Susy or other model. The LC will establish the spin-parity of the Higgs state and its width; measure the ttH coupling; measure the Higgs self-coupling gHHH which is related to the shape of the Higgs potential and to the Higgs mass, thus is a crucial constraint on the model. Tevatron or LHC discover the Higgs: LC tells us what it really is 22

  23. Supersymmetry Tevatron can sense the presence of Susy through such processes as pair production of partners of W and Z, leading to multiple lepton final states, or squark/gluino production with decays into ordinary quark/gluon jets plus missing energy carried by the LSP. LHCwill see Susy if it exists and has anything to do with EWSB. Primarily produce the strongly interacting squarks and gluinos, but can have a range of particles in the decay chains of these. LHC can measure the masses of Susy particles, but which ones and the precisions depend on the nature of the Susy model. The nature of the mass spectrum will give reasonable indication of the type of Susy model. Rate vs. sum of 4 leading jet transverse energies and missing transverse energy: Solid points are for SM processes only;Openpoints include the production of supersymmetric squarks and gluinos. An order of magnitude enhancement. 23

  24. Supersymmetry LC can make precision measurements of Susy particles that are light enough to be produced. • Kinematic distributions and threshold scans determine Susy masses to typically O(0.1 %) • Electron beam polarization and angular distributions allow determination of spin, parity, chirality of observed states. • Accurate masses & cross sections will give the mixing matrix angles and phases for the states of similar quantum numbers (e.g. 4 partners of Z, g and neutral higgs). These measurements, together with the LHC determinations of squark and gluino, allow extrapolation of the Susy parameters to very high energy, and should indicate the type of Susy model Nature chooses, without model assumptions. Connect to string theories? 24

  25. Large Extra Dimensions If there are additional large (> Planck length) dimensions, new phenomena appear which depend on the size and number of extra dimensions, and the fields (gravitons, fermions, gauge bosons) that move in them. Fundamental Planck scale M* is lowered to the TeV region. Tevatron: Gravitons moving in mm sized ED’s would modify the cross section for pp → e+e- or gg at high mass and small angles. Tevatron Sensitive to M* to about 2 TeV, depending on the number of extra dimensions. 25

  26. g q q Gn Our 4-d world (brane) Large Extra Dimensions LHC : qq → g Gn , where Gn is a graviton escaping into extra dimensions results in a monojet event. The LHC will be sensitive to such processes for fundamental Planck scales, M*, up to ~ 8 TeV. Gravity propagating in usual 3+1 dim. brane PLUS N extra (small) bulk dimensions. n=2 Mini Black Hole production n=7 If collision energy exceeds the reduced Planck scale, can produce mini-black holes of mass MBH > MPlanck . If the real Planck scale is several TeV, then mini-black hole production at LHC is very large for BH mass up to >10 TeV. LHC would be a Black Hole factory. g+X Drell-Yan 26

  27. Large Extra Dimensions Hawking radiation from mini-black holes is very rapid. Since the coupling is to mass/energy, there is a democracy in the particles produced, so get sprays of particles including W,Z bosons, Higgs bosons, top quarks in equal abundance with ordinary light quarks. Gives an alternate way forLHCto produce Higgs bosons (copiously) s = 15 nb MP = 1 TeV, 1 LHC-hour (!) Example spectra of two jets in a multijet event from black hole evaporation, for MPlanck = 1 TeV. Peaks show the W/Z, 130 GeV Higgs and top quark (unresolved jets from W/Z). Tagging b-quarks improves the cleanliness but is not necessary. t h W/Z 27

  28. Large Extra Dimensions s(ee gGn) LC: The process e+e- → g Gn and the qq → g Gn process at LHC have comparable reach for effective Planck scale for 500 GeV LC (1 TeV LC is better). These measurements depend both on M* and on d = # extra dimensions. Varying the energy of the LC determines d. d=6 5 4 3 d=2 400 800 600 ECM In the case of TeV-1 sized extra dimensions with a warped metric, resonances that resemble excited Z bosons (KK states) appear and can be seen directly at LC or LHC. e+e- → m+m- mini Black Hole evaporation event at 5 TeV CLIC 28

  29. The LHC has higher energy The LC with precision measurements can indirectly sense new of its colliding partons, phenomena at very large larger backgrounds and energy. The detailed a less well controlled measurements of initial quantum state couplings and quantum than the LC. numbers of new The LHC is thus particles adds much to more sensitive to our understanding of the direct discovery of new new physics, and the nature phenomena at highmass of the uncharted territory at but with less incisive detail. even higher energy. The complementarity of the programs LC LHC As for past programs with e+e- and hadron collisions, the LHC and LC offer a complementary view of Nature at the energy frontier. The two operating together is more than the sum of the individual programs. 29

  30. Conclusions The two main paths of forthcoming voyages into new waters will help triangulate the terra incognito that we have now glimpsed only darkly. The richness of the program can give us a huge leap in understanding: • The way Nature unifies its forces (or doesn’t) • How the underlying symmetric theory of EM and weak forces is broken into the pattern that we observe • Point to the way the universe was from 10-32 to 10-12 seconds old when our future fate was sealed • See the dark matter • Quite possibly transform our understanding of space and time itself

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