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

2. 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)

3. J. Brau, APS NW, May 30, 2003 3 Mysteries We enter the 21st Century with mysteries of monumental significance in particle physics: 20th Century 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? electron spin =1/2 selectron spin = 0

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

5. 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 M  = 0 M W = 80. 426  0.034 GeV/c 2 M Z = 91.188  0.002 GeV/c 2 –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

6. J. Brau, APS NW, May 30, 2003 6 (  ) Complex spin 0 Higgs doublet Electroweak Unification The massless gauge fields are mixed into the massive gauge bosons tan  W = g’/g sin 2  W =g’ 2 /(g’ 2 +g 2 ) e = g sin  W = g’ cos  W e J  (em) A   W  W  Z  () Physical bosons Electroweak symmetry breaking b       () Massless gauge bosons in symmetry limit by the Higgs mechanism

7. 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/c 2 (unitarity arguments) –Strength of Higgs coupling increases with mass fermions: g ffh = m f / vv = 246 GeV gauge boson: g wwh = 2 m Z 2 /v

8. J. Brau, APS NW, May 30, 2003 8 Standard Model Fit M H = 91 GeV/c 2 +58 -37 LEPEWWG

9. J. Brau, APS NW, May 30, 2003 9 (SM) M higgs < 211 GeV at 95% CL. LEP2 limit M higgs > 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 m H = 115.6 GeV with overall significance (4 experiments) ~ 2  Indications for a Light Standard Model-like Higgs

10. 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 Quark 1968 - 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 Z 0 measurements Higgs boson ???? - Electroweak theory and experiments

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

12. J. Brau, APS NW, May 30, 2003 12 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) Establishing Standard Model Higgs

13. 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 M H < 200 GeV (but theoretically ugly - h’archy prob.) Minimal Supersymmetric Standard Model (MSSM) Higgs expect M h < ~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

14. J. Brau, APS NW, May 30, 2003 14 The Next Linear Collider Acceleration of electrons in a circular accelerator is plagued by Nature’s resistance to acceleration –Synchrotron radiation –  E = 4  /3 (e 2  3  4 / R) per turn (recall  = E/m, so  E ~ E 4 /m 4 ) –eg. LEP2  E = 4 GeV Power ~ 20 MW electronspositrons For this reason, at very high energy it is preferable to accelerate electrons in a linear accelerator, rather than a circular accelerator

15. J. Brau, APS NW, May 30, 2003 15 Therefore –Cost (circular) ~ a R + b  E ~ a R + b (E 4 /m 4 R) Synchrotron radiation –  E ~ (E 4 /m 4 R) Cost Advantage of Linear Colliders cost Energy Circular Collider Optimization R ~ E 2  Cost ~ c E 2 Linear Collider –Cost (linear) ~ a  L, where L ~ E At high energy, linear collider is more cost effective R m,E

16. J. Brau, APS NW, May 30, 2003 16 The Linear Collider A plan for a high-energy, high- luminosity, electron-positron collider (international project) –E cm = 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 Warm X-band version 25 KM expanded horizontal scale

17. 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 Z 0 measurements A LR = 0.1513  0.0021 (SLD) asymmetry in Z 0 production with L and R electrons –established Linear Collider concepts

18. J. Brau, APS NW, May 30, 2003 18 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) Superconducting Room T Room T RF cavities structures structures L design (10 34 ) 3.4  5.8 0.43 2.2  3.4 E CM (GeV) 500  800 500 500  1000 Eff. Gradient (MV/m) 23.4  35 34 65 RF freq. (GHz) 1.3 5.7 11.4  t bunch (ns) 337  176 2.8 1.4 #bunch/train 2820  4886 72 190 Beamstrahlung (%) 3.2  4.4 4.6  8.8 * US and Japanese X-band R&D cooperation, but machine parameters may differ There will only be one in the world ILC-Technical Review Committee The “next” Linear Collider

19. J. Brau, APS NW, May 30, 2003 19 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) The “next” Linear Collider

20. J. Brau, APS NW, May 30, 2003 20 Elementary interactions at known E cm * 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. R beampipe  1 cm and  hit  3  m Calorimetry with Jet Energy Flow  E /E  30-40%/  E * beamstrahlung must be dealt with, but it’s manageable Special Advantages of Experiments at the Linear Collider

21. J. Brau, APS NW, May 30, 2003 21 NLC a TESLA Linear Collider Detectors The Linear Collider provides very special experimental conditions (eg. superb vertexing and jet calorimetry) CCD Vertex Detectors Silicon/Tungsten Calorimetry 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 SLD’s VXD3 NLC TESLA

22. J. Brau, APS NW, May 30, 2003 22 For M H = 140 GeV, 500 fb -1 @ 500 GeV Mass Measurement  M H  60 MeV  5 x 10 -4 M H Total width      3 % Particle couplings tt  needs higher  s for 140 GeV, except through H  gg) bb  g  bb / g  bb  2 % cc  g  cc / g  cc  22.5 %      g   / g    5 % WW *  g  ww / g Hww  2 % ZZ  g  / g HZZ  6 % gg  g  gg / g  gg  12.5 %  g  / g   10 % Spin-parity-charge conjugation establish J PC = 0 ++ Self-coupling  HHH / HHH  32 % (statistics limited) If Higgs is lighter, precision is often better Example of Precision of Higgs Measurements at the Next Linear Collider

23. J. Brau, APS NW, May 30, 2003 23 Higgs recoiling from a Z 0 (nothing else) known CM energy  (powerful for unbiassed tagging of Higgs decays) measurement even of invisible decays Tag Z  l + l  Select M recoil = M Higgs 500 fb -1 @ 500 GeV, TESLA TDR, Fig 2.1.4 Invisible decays are included Higgs Studies - the Power of Simple Reactions > 10,000 ZH events/year for m H = 120 GeV at 500 GeV (  - some beamstrahlung)

24. J. Brau, APS NW, May 30, 2003 24 Higgs Couplings - the Branching Ratios 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. bb  g  bb / g  bb  2 % cc  g  cc / g  cc  22.5 %      g   / g    5 % WW *  g  ww / g Hww  2 % ZZ  g  / g HZZ  6 % gg  g  gg / g  gg  12.5 %  g  / g   10 % SM predictions

25. J. Brau, APS NW, May 30, 2003 25 H  or   H rules out J=1 and indicates C=+1 Higgs Spin Parity and Charge Conjugation (J PC = 0 ++ ) LC Physics Resource Book, Fig 3.23(a) Threshold cross section ( e + e   Z H) for J=0 , while for J > 0, generally higher power of  (assuming n = (-1) J P) TESLA TDR, Fig 2.2.8 Also e  e  e  e  Z Han, Jiang Production angle (  ) and Z decay angle in Higgs-strahlung reveals J P (e + e   Z H  ffH) J P = 0 + J P = 0  d  /dcos  sin 2  (1 - sin 2  ) d  /dcos  sin 2  (1 +/- cos  ) 2  is angle of the fermion, relative to the Z direction of flight, in Z rest frame

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

27. J. Brau, APS NW, May 30, 2003 27 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 eg. selectron pair production e + e -  e + e -    LC Resource Book, Fig 4.3

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

29. 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  /M A wedge. Directly observed strong WW/ZZ resonances at LHC are understood from asymmetries at Linear Collider Analyze extra neutral gauge bosons Giga-Z constraints

30. J. Brau, APS NW, May 30, 2003 30 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 Political Developments 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......

31. J. Brau, APS NW, May 30, 2003 31 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 Conclusion

32. J. Brau, APS NW, May 30, 2003 32

33. J. Brau, APS NW, May 30, 2003 33 Is This the Standard Model Higgs? 1.) Does the hZZ coupling saturate the Z coupling sum rule?  g hZZ = M Z 2 g ew 2 / 4 cos 2  W eg. g hZZ = g Z M Z sin(  -  ) g HZZ = g Z M Z cos(  -  )g Z = g ew /2 cos  W 2.) Are the measured BRs consistent with the SM? eg. g hbb = g hbb (-sin  / cos  )  - g hbb (sin(  -  ) - cos(  -  ) tan  ) g h  = g h  (-sin  / cos  )  - g h  (sin(  -  ) - cos(  -  ) tan  )  g htt = g htt (-cos  / sin  )  g htt (sin(  -  ) + cos(  -  ) / tan  ) (in MSSM only for smaller values of M A will there be sensitivity, since sin(  -  as M A grows -decoupling) 3.) Is the width consistent with SM? 4.) Have other Higgs bosons or super-partners been discovered? 5.) etc. MSSM

34. J. Brau, APS NW, May 30, 2003 34 Large Extra Dimensions In addition to the three infinite spatial dimensions we know about, it is assumed there are n new spatial dimensions of finite extent R Some of the extra dimensions could be quite large The experimental limits on the size of extra dimensions are not very restrictive –to what distance has the 1/r 2 force law been measured? –extra dimensions could be as large as 0.1 mm, for example –experimental work is underway now to look for such large extra dimensions

35. J. Brau, APS NW, May 30, 2003 35 Large Extra Dimensions Particles and the Electroweak and Strong interactions are confined to 3 space dimensions Gravity is different: –Gravitons propagate in the full (3 + n)- dimensional space (see Large Extra Dimensions: A New Arena for Particle Physics, Nima Arkani-Hamed, Savas Dimopoulos, and Georgi Dvali, Physics Today, February, 2002) If there were only one large extra dimension, its size R would have to be of order 10 10 km to account for the weakness of gravity. But two extra dimensions would be on the order of a millimeter in size. As the number of the new dimensions increases, their required size gets smaller. –For six equal extra dimensions, the size is only about 10 -12 cm Explaining the weakness of gravity

36. J. Brau, APS NW, May 30, 2003 36 Cosmic connections Big Bang Theory GUT motivated inflation dark matter accelerating universe dark energy

37. J. Brau, APS NW, May 30, 2003 37 The Large Hadron Collider (LHC) The LHC at CERN, colliding proton beams, will begin operation around 2007 This “hadron-collider” is a discovery machine, as the history of discoveries show discoveryfacility offacility of discoverydetailed study charmBNL + SPEARSPEAR at SLAC tauSPEARSPEAR at SLAC bottomFermilabCornell Z 0 SPPS LEP and SLC The “electron-collider” (the LC) will be essential to sort out the LHC discoveries