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Particles, Mysteries, and Linear Colliders

Particles, Mysteries, and Linear Colliders. Jim Brau APSNW 2003 Reed College May 30, 2003. Particles. Particle Physics left the 20th Century with a triumphant model of the fundamental particles and interactions - the Standard Model quarks, leptons, gauge bosons mediating gauge interactions.

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Particles, Mysteries, and Linear Colliders

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  1. Particles,Mysteries,and Linear Colliders Jim Brau APSNW 2003 Reed College May 30, 2003 J. Brau, APS NW, May 30, 2003

  2. Particles • Particle Physics left the 20th Century with a triumphant model of the fundamental particles and interactions - the Standard Model • quarks, leptons, gauge bosons mediating gauge interactions • thoroughly tested • no confirmed violations* • * neglecting neutrino mixing e+e- W+W- (LEP) J. Brau, APS NW, May 30, 2003

  3. selectron spin = 0 electron spin =1/2 20th Century Particle Physics Mysteries • We enter the 21st Century with mysteries of monumental significance in particle physics: • Physics behind Electroweak unification? • The top quark mass • Ultimate unification of the interactions? • Hidden spacetime dimensions? • Supersymmetry? - doubling Nature’s fundamental particles • Cosmological discoveries? • What is dark matter? • What is dark energy? J. Brau, APS NW, May 30, 2003

  4. The First Linear Collider future Linear Collider SLAC Linear Collider (SLC) built on existing SLAC linac Operated 1989-98 500 GeV - 1 TeV and beyond could operate by 2015 3 KM 25 KM expanded horizontal scale Linear Colliders • The electron-positron Linear Collider is a critical tool in our probe of these secrets of Nature J. Brau, APS NW, May 30, 2003

  5. Electroweak Symmetry Breaking • One of the major mysteries in particle physics today is the origin of Electroweak Symmetry Breaking • Weak nuclear force and the electromagnetic force unified • SU(2) x U(1)Y with massless gauge fields • Why is this symmetry hidden? • The physical bosons are not all massless • Mg = 0 MW = 80. 4260.034 GeV/c2 MZ = 91.1880.002 GeV/c2 • The full understanding of this mystery appears to promise deep understanding of fundamental physics • the origin of mass • supersymmetry and possibly the origin of dark matter • additional unification (strong force, gravity) and possibly hidden space-time dimensions J. Brau, APS NW, May 30, 2003

  6. ( ) 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 Electroweak Unification by the Higgs mechanism • The massless gauge fields are mixed into the massive gauge bosons tanqW = g’/g sin2qW=g’2/(g’2+g2) e Jm(em) Am e = g sinqW = g’ cosqW J. Brau, APS NW, May 30, 2003

  7. The Higgs Boson • The quantum(a) of the Higgs Mechanism is(are) the Higgs Boson or Bosons • Minimal model - one complex doublet  4 fields • 3 “eaten” by W+, W-, Z to give mass • 1 left as physical Higgs • This spontaneously broken local gauge theory is renormalizable - t’Hooft (1971) • The Higgs boson properties • Mass < ~ 800 GeV/c2 (unitarity arguments) • Strength of Higgs coupling increases with mass • fermions: gffh = mf / v v = 246 GeV • gauge boson: gwwh = 2 mZ2/v J. Brau, APS NW, May 30, 2003

  8. Standard Model Fit +58 -37 • MH = 91 GeV/c2 LEPEWWG J. Brau, APS NW, May 30, 2003

  9. Indications for a Light Standard Model-like Higgs (SM) Mhiggs < 211 GeV at 95% CL. LEP2 limit Mhiggs > 114.4 GeV. Tevatron discovery reach ~180 GeV W mass ( 80.426  0.034 MeV) and top mass ( 174.3  5.1 GeV) agree with precision measures and indicate low SM Higgs mass LEP Higgs search – Maximum Likelihood for Higgs signal at mH = 115.6 GeV with overall significance (4 experiments) ~ 2s J. Brau, APS NW, May 30, 2003

  10. History of Anticipated Particles Positron 1932 -Dirac theory of the electron Pi meson 1947 - Yukawa’s theory of strong interaction Neutrino 1955 -missing energy in beta decay Quark1968 - patterns of observed particles Charmed quark 1974 -absence of flavor changing neutral currents Bottom quark 1977 - Kobayashi-Maskawa theory of CP violation W boson 1983 - Weinberg-Salam electroweak theory Z boson 1984 - “ “ Top quark 1997 - Expected once Bottom was discovered Mass predicted by precision Z0 measurements Higgs boson ???? - Electroweak theory and experiments J. Brau, APS NW, May 30, 2003

  11. Tevatron at Fermilab • Proton/anti-proton collisions at Ecm=2000 GeV • Collecting data now • discovery possible by~2008? 2 km The Search for the Higgs Boson • LHC at CERN • Proton/proton collisions at Ecm=14,000 GeV • Begins operation ~2007 8.6 km J. Brau, APS NW, May 30, 2003

  12. Establishing Standard Model Higgs precision studies of the Higgs boson will be required to understand Electroweak Symmetry Breaking; just finding the Higgs is of limited value We expect the Higgs to be discovered at LHC (or Tevatron) and the measurement of its properties will begin at the LHC We need to measure the full nature of the Higgs to understand EWSB The 500 GeV (and beyond) Linear Collider is the tool needed to complete these precision studies References: TESLA Technical Design Report Linear Collider Physics Resource Book for Snowmass 2001 (contain references to many studies) J. Brau, APS NW, May 30, 2003

  13. Some Candidate Models for Electroweak Symmetry Breaking Standard Model Higgs excellent agreement with EW precision measurements implies MH < 200 GeV (but theoretically ugly - h’archy prob.) Minimal Supersymmetric Standard Model (MSSM) Higgs expect Mh< ~135 GeV light Higgs boson (h) may be very “SM Higgs-like” with small differences (de-coupling limit) Non-exotic extended Higgs sector eg. 2HDM Strong Coupling Models New strong interaction The LC will provide critical data to resolve these possibilities J. Brau, APS NW, May 30, 2003

  14. The Next Linear Collider • Acceleration of electrons in a circular accelerator is plagued byNature’s resistance to acceleration • Synchrotron radiation • DE = 4p/3 (e2b3g4 / R) per turn (recall g = E/m, so DE ~ E4/m4) • eg. LEP2 DE = 4 GeV Power ~ 20 MW • For this reason, at very high energy it is preferable to accelerate electrons in a linear accelerator, rather than a circular accelerator electrons positrons J. Brau, APS NW, May 30, 2003

  15. Optimization R ~ E2 Cost ~c E2 • Cost (linear) ~ aL, where L ~ E Circular Collider At high energy, linear collider is more cost effective cost Linear Collider Energy Cost Advantage of Linear Colliders m,E • Synchrotron radiation • DE ~ (E4 /m4 R) R • Therefore • Cost (circular) ~ a R + b DE ~ a R + b (E4 /m4 R) J. Brau, APS NW, May 30, 2003

  16. 25 KM The Linear Collider • A plan for a high-energy, high-luminosity, electron-positron collider (international project) • Ecm = 500 - 1000 GeV • Length ~25 km • Physics Motivation for the LC • Elucidate Electroweak Interaction • particular symmetry breaking • This includes • Higgs bosons • supersymmetric particles • extra dimensions • Construction could begin around 2009 following intensive pre-construction R&D with operation beginning around 2015 expanded horizontal scale Warm X-band version J. Brau, APS NW, May 30, 2003

  17. The First Linear Collider • This concept was demonstrated at SLAC in a linear collider prototype operating at ~91 GeV (the SLC) • SLC was built in the 80’s within the existing SLAC linear accelerator • Operated 1989-98 • precision Z0 measurements • ALR = 0.1513  0.0021 (SLD) asymmetry in Z0 production with L and R electrons • established Linear Collider concepts J. Brau, APS NW, May 30, 2003

  18. The “next” Linear Collider The next Linear Collider proposals include plans to deliver a few hundred fb-1 of integrated lum. per year TESLA JLC-C NLC/JLC-X * (DESY-Germany) (Japan) (SLAC/KEK-Japan) SuperconductingRoom T Room T RF cavities structures structures Ldesign (1034)3.45.80.432.23.4 ECM (GeV)500  800 500 500  1000 Eff. Gradient (MV/m) 23.4  353465 RF freq. (GHz) 1.35.7 11.4 Dtbunch (ns)337  1762.8 1.4 #bunch/train2820  4886 72 190 Beamstrahlung (%) 3.2  4.4 4.6  8.8 There will only be one in the world ILC-Technical Review Committee * US and Japanese X-band R&D cooperation, but machine parameters may differ J. Brau, APS NW, May 30, 2003

  19. The “next” Linear Collider Standard Package: e+e-Collisions Initially at 500 GeV Electron Polarization  80% Options: Energy upgrades to ~ 1.0 -1.5 TeV Positron Polarization (~ 40 - 60% ?) Collisions e-e-and e-Collisions Giga-Z (precision measurements) J. Brau, APS NW, May 30, 2003

  20. Special Advantages of Experiments at the Linear Collider Elementary interactions at known Ecm* eg. e+e- Z H Democratic Cross sections eg. (e+e -ZH) ~ 1/2 (e+e -d d) Inclusive Trigger total cross-section Highly Polarized Electron Beam ~ 80% Exquisite vertex detection eg. Rbeampipe ~ 1 cm and hit ~ 3 mm Calorimetry with Jet Energy Flow E/E ~ 30-40%/E * beamstrahlung must be dealt with, but it’s manageable J. Brau, APS NW, May 30, 2003

  21. Linear Collider Detectors The Linear Collider provides very special experimental conditions (eg. superb vertexing and jet calorimetry) Silicon/Tungsten Calorimetry CCD Vertex Detectors SLD Lum (1990) Aleph Lum (1993) Opal Lum (1993) Snowmass - 96 Proceedings NLC Detector - fine gran. Si/W Now TESLA & NLD have proposed Si/W as central elements in jet flow measurement NLC a TESLA TESLA NLC SLD’s VXD3 J. Brau, APS NW, May 30, 2003

  22. Example of Precision of Higgs Measurements at the Next Linear Collider For MH = 140 GeV, 500 fb-1 @ 500 GeV Mass Measurement MH  60 MeV  5 x 10-4 MH Total width  H / H  3 % Particle couplings tt(needs higher s for 140 GeV, except through H  gg) bbgHbb / gHbb  2 % ccgHcc / gHcc  22.5 % +- gH / gH    5 % WW* gHww/ gHww  2 % ZZgHZZ/ gHZZ  6 % gg gHgg / gHgg  12.5 % gg gHgg/ gHgg  10 % Spin-parity-charge conjugation establish JPC = 0++ Self-coupling HHH/ HHH 32 % (statistics limited) If Higgs is lighter, precision is often better J. Brau, APS NW, May 30, 2003

  23. Higgs Studies- the Power of Simple Reactions Higgs recoiling from a Z0 (nothing else) known CM energy (powerful for unbiassed tagging of Higgs decays) measurement even of invisible decays • Tag Zl+ l • Select Mrecoil = MHiggs > 10,000 ZH events/year for mH = 120 GeV at 500 GeV Invisible decays are included ( - some beamstrahlung) 500 fb-1 @ 500 GeV, TESLA TDR, Fig 2.1.4 J. Brau, APS NW, May 30, 2003

  24. Higgs Couplings - the Branching Ratios bbgHbb / gHbb  2 % ccgHcc / gHcc  22.5 % +- gH / gH    5 % WW* gHww/ gHww  2 % ZZgHZZ/ gHZZ  6 % gg gHgg / gHgg  12.5 % gg gHgg/ gHgg  10 % SM predictions Measurement of BR’s is powerful indicator of new physics e.g. in MSSM, these differ from the SM in a characteristic way. Higgs BR must agree with MSSM parameters from many other measurements. J. Brau, APS NW, May 30, 2003

  25. Higgs Spin Parity and Charge Conjugation (JPC = 0++) Threshold cross section (e+ e- Z H)for J=0 s ~ b , while for J > 0, generally higher power of b (assuming n = (-1)J P) Production angle (q) and Z decay angle in Higgs-strahlung reveals JP (e+ e- Z H ffH) JP = 0+ JP = 0- ds/dcosq sin2q (1 - sin2q ) ds/dcosf sin2f (1 +/- cosf )2 f is angle of the fermion, relative to the Z direction of flight, in Z rest frame LC Physics Resource Book, Fig 3.23(a) Also e+e-  e+e-Z Han, Jiang TESLA TDR, Fig 2.2.8 H  or   H rules out J=1 and indicates C=+1 J. Brau, APS NW, May 30, 2003

  26. Is This the Standard Model Higgs? Z vs. W b vs. c Arrows at: MA = 200-400 MA = 400-600 MA = 600-800 MA = 800-1000 HFITTER output conclusion: for MA < 600, likely distinguish b vs. tau b vs. W J. Brau, APS NW, May 30, 2003 TESLA TDR, Fig 2.2.6

  27. eg. selectron pair production e+e- e+e-   LC Resource Book, Fig 4.3 Supersymmetry • Supersymmetry • all particles matched by super-partners • super-partners of fermions are bosons • super-partners of bosons are fermions • inspired by string theory • high energy cancellation of divergences • could play role in dark matter (stable neutral particle) • many new particles (detailed properties at LC) Arkani-Hamed, Dimopoulos, Dvali J. Brau, APS NW, May 30, 2003

  28. g e+ e- Gn Our 4-d world (brane) e+e- + - e+e-  Gn LC Resource Book, Fig 5.17 LC Resource Book, Fig 5.13 Extra Dimensions • Extra Dimensions • string theory predicts them • solves hierarchy problem (Mplanck >> MEW) if extra dimensions are large (or why gravity is so weak) • large extra dimensions would be observable at LC J. Brau, APS NW, May 30, 2003

  29. Adding Value to LHC measurements • The Linear Collider will enhance the LHC • measurements (“enabling technology”) • How this happens depends on the Physics: • Add precision to the discoveries of LHC • eg. light higgs measurements • Measure superpartner masses • SUSY parameters may fall in the tan  /MA wedge. • Directly observed strong WW/ZZ resonances at LHC • are understood from asymmetries at Linear Collider • Analyze extra neutral gauge bosons • Giga-Z constraints J. Brau, APS NW, May 30, 2003

  30. Political Developments • In US, HEPAP subpanel endorsed LC as the highest priority future project for the US program (2002) • DOE Off. of Science 20 year • Roadmap for new facilities(2003) • HEP Facilities Committee • LC gets top marks for science and feasibility • Recommended Japanese Roadmap Report (2003) German Science Council (2001) requests gov’t consent German Government (2003) formal statement - supports project - wait for int’l plan OECD Global Science Forum Report strongly endorses LC project as next facility in Elem. Particle Physics (2002) Discussions between governmental representatives from countries interested in the LC have been active recently and are continuing . . . . . . J. Brau, APS NW, May 30, 2003

  31. Conclusion The Linear Collider will be a powerful tool for studying Electroweak Symmetry Breaking and the Higgs Mechanism, as well as the other possible scenarios for TeV physics Current status of Electroweak Precision measurements strongly suggests that the physics at the LC will be rich. We can expect these studies to further our knowledge of fundamental physics in unanticipated ways J. Brau, APS NW, May 30, 2003

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