1. Ênergy frontieR: the There and back Again or Breese quinN University M ississippi of

2. Quarknet Workshop 2008B. Quinn University of Mississippi 2 The Standard modeL EM Strong Weak } up/down1968 SLAC strange1964 BNL charm1974 SLAC/BNL bottom1977 Fermilab top1995 Fermilab D0/CDF photon1905 Planck/Einstein gluon1979 DESY W/Z1983 CERN electron1897 Thomson e-neutrino1956 Reactor muon1937 Cosmic Rays mu-neutrino1962 BNL tau1976 SLAC tau-neutrino 2000 Fermilab u dd d u u electron neutron proton. electron neutrino

3. Quarknet Workshop 2008B. Quinn University of Mississippi 3 The Standard modeL This model has successfully described or predicted almost everything we’ve seen in almost 100 years of particle physics. However it does have some weaknesses Too many free parameters Predictive powers wane as we move past the Electroweak (EW) regime towards the TeV scale and beyond EM Strong Weak }

4. Quarknet Workshop 2008B. Quinn University of Mississippi 4 The Energy FrontieR It takes higher and higher energy to probe smaller and smaller distance scales Higher energy = Earlier time We’re looking back in time to the early universe Accelerators have now gotten us to about 10 -12 seconds, or equivalently, close to the TeV energy scale This is the energy frontier!

5. Quarknet Workshop 2008B. Quinn University of Mississippi 5 What might lie beyond the frontier? Where does mass come from? Is the SM just a low-energy effective theory masking higher more fundamental symmetries? Where does gravity fit in? The Energy FrontieR What might lie beyond the frontier?

6. Quarknet Workshop 2008B. Quinn University of Mississippi 6 how Do we get TherE?

7. Quarknet Workshop 2008B. Quinn University of Mississippi 7 the Fermilab TevatroN The world’s most powerful particle accelerator …until LHC at CERN, 14 TeV, 2008 Main Injector (new) Tevatron DØCDF Chicago   p source Booster Run I 1.8 TeV 1992-1996 Run II 1.96 TeV 2001-? p  p Linac

8. Quarknet Workshop 2008B. Quinn University of Mississippi 8 A Generic detectoR How do we “see” the events? Observe, identify, and measure the decay particles Charged particle trajectories, vertices Charged particle momentum e ,  energy p, n,  ,etc. energy   identification Infer missing energy ( ) <

9. Quarknet Workshop 2008B. Quinn University of Mississippi 9 A Specific detectoR: DØ Silicon Microstrip Tracker 900 silicon devices, 1M channels Central Fiber Tracker 16 layers, 80k channels, Calorimeter, 50k Channels Liquid argon calorimeter with uranium absorber Muon Scintillators Muon Chambers Borg DØ separated at birth?

10. Quarknet Workshop 2008B. Quinn University of Mississippi 10 the DØ collectivE A collaboration of >650 physicists from more than 80 institutions in 19 countries CollaboratioN

11. Quarknet Workshop 2008B. Quinn University of Mississippi 11 24/7 Data collectioN Proton-antiprotons collide at 7MHz or seven million times per second Tiered electronics pick successively more interesting events Level 1 2 kHz Level 2 1 kHz About 100 crates of electronics readout the detectors and send data to a Level 3 farm of 100+ CPUs that reconstruct the data Level 3: 50 events or 12.5 Mbytes of data to tape per second Per year: 500 million events

12. Quarknet Workshop 2008B. Quinn University of Mississippi 12 A Common EvenT A sample Z  e + e - event Collect many such events and measure the Z mass from the distribution of calculated masses for each event Very important calibration sample

13. Quarknet Workshop 2008B. Quinn University of Mississippi 13 Something a little more interestinG? The top quark - it’s HUGE!

14. Quarknet Workshop 2008B. Quinn University of Mississippi 14 Why Study the Top? The Standard Model (SM) predicts all top properties given m t In the SM, the top and W mass constrain the mass of the Higgs Boson via EW radiative corrections In 1964, Peter Higgs postulated a physics mechanism which gives all particles their mass. This mechanism is a field which permeates the universe and is mediated by a particle called the Higgs boson. WW t WW H

15. Quarknet Workshop 2008B. Quinn University of Mississippi 15 Why Study the Top? The Standard Model (SM) predicts all top properties given m t In the SM, the top and W mass constrain the mass of the Higgs Boson via EW radiative corrections Since the top is so heavy, it should have particularly strong coupling to the Higgs Likely to play a significant role in EW Symmetry Breaking (m W, m Z ) Top decay time (τ ~ 4  10 -25 s) < hadronization time Opportunity to study bare quarks In general, quarks do not exist as free particles. qq pairs are pulled from the vacuum to produce stable hadrons with 2 quarks (mesons) or 3 quarks (baryons) This process is called hadronization Since the top quark decays before that happens, we can study quark properties such as spin polarization here and no where else

16. Quarknet Workshop 2008B. Quinn University of Mississippi 16 Run II, the Top Quark & DØ Most all that we knew about the top quark before Run II came from the DØ and CDF Run I data 1992-1996: ~100 events / experiment Top mass and production cross section at  s = 1.8 TeV m t = 174.3 ± 5.1 GeV (DØ and CDF combined) σ tt = 5.7 ± 1.6 pb (DØ); σ tt = 6.5 +1.7 -1.4 pb (CDF) At this point in Run II we have 40 times more data, with a few thousand top quark events. Should yield:  m t  ±3 GeV, along with  m W  ±40 MeV Constrain the Higgs mass:  m H  40%m H At  s = 1.96 TeV,  σ tt = 10%σ tt Standard Model: σ tt = 8.8 pb Larger than SM: new physics (resonance production, anomalous couplings) Smaller than SM: non-SM decays, e.g. t  Hb

17. Quarknet Workshop 2008B. Quinn University of Mississippi 17 Production: Cross Sections Top events are very rare One collision out of every 3  10 9 produced a tt pair To study processes with small cross sections, one needs High luminosity to produce enough interesting events Methods for distinguishing those events from more copious backgrounds

18. Quarknet Workshop 2008B. Quinn University of Mississippi 18 Top Physics at DØ: Decays BR(t  Wb) ~ 100% Significant deviation would indicate new physics Top decays before hadronization Can study polarization of a free quark 21% 15% 1.3% 2.6% 1.3% 44% τ +X  +jets e+jets e+e e+  ++ all hadronic Jets: showers of particles produced from quarks bbbbb qq l - W-W- t bbbbb qq l + qq l + W+W+ t lepton+jets { dilepton { all jets

19. Quarknet Workshop 2008B. Quinn University of Mississippi 19 Decay: What Does a Top Event Look Like? BR(t  Wb) ~ 100% W  qq or W  l  So top events should have either 6 jets from quarks 4 jets, 1 charged lepton, 1 neutrino 2 jets, 2 charged leptons, 2 neutrinos 2 jets must come from b quarks These jets can be distinguished from light quark jets Powerful background rejection tool

20. Quarknet Workshop 2008B. Quinn University of Mississippi 20 b-tagging Lifetime 1.5 ps  c   0.5 mm Displaced secondary vertex Requires precise tracking near the primary collision point: silicon trackers, new for DØ in Run II! Flight Length ~ few mm Collision Impact Parameter Decay Vertex B Decay Products

21. Quarknet Workshop 2008B. Quinn University of Mississippi 21  pt48 GeV MEt55 GeV W pt51 GeV JetEt154 GeV Apla0.160 Ht517 GeV Run II:  +jets Candidate 2 jets are tagged as b -jets passes topological selection tt  jjjj candidate

22. Quarknet Workshop 2008B. Quinn University of Mississippi 22 Run II:  +jets Candidate 2 jets tagged with displaced secondary vertices Track in the calorimeter and muon tracker

23. Quarknet Workshop 2008B. Quinn University of Mississippi 23 Run II, the Top Quark & DØ What we’ve measured at this point: top mass

24. Quarknet Workshop 2008B. Quinn University of Mississippi 24 Run II, the Top Quark & DØ What we’ve measured at this point: cross section

25. Quarknet Workshop 2008B. Quinn University of Mississippi 25 is there Something a bit more exotiC? At the frontier will we find… The origin of mass? The higgß ParticlE Higher symmetry? SupersymmetrY - SUSY A place for gravity? ExtrA dimensionß

26. Quarknet Workshop 2008B. Quinn University of Mississippi 26 the Higgß Peter Higgs showed that Electroweak unification implied the existence of a molasses-like field (the Higgs field), which gives particles their mass. Predicts at least one Higgs particle – not yet discovered. The strength of a particle’s interaction with the Higgs particle determines its mass. e t  Higgs Field H

27. Quarknet Workshop 2008B. Quinn University of Mississippi 27 Past Higgß searches and current limitS Over the last decade or so, experiments at LEP or the European e + e – collider have been searching for the Higgs. Direct searches for Higgs production, similar to our Z mass measurement exclude m H < 114 GeV. Precision measurements of electroweak parameters combined with DØ’s new* Run I top quark mass measurement, favor m H = 117 GeV with an upper limit of m H = 251 GeV. * Nature 10 June 2004

28. Quarknet Workshop 2008B. Quinn University of Mississippi 28 Search for hw productioN One very striking and distinctive signature Look for an electron = track + EM calorimeter energy neutrino = missing transverse energy two b quarks = two jets each with a secondary vertex from the long lived quarks. p p W* q q’q’ H W e b b

29. Quarknet Workshop 2008B. Quinn University of Mississippi 29 a Higgß candidatE Two events found, consistent with Standard Model Wbb production 12.5 pb upper cross section limit for pp  WH where H  bb m H =115 GeV. By the end of Run II and combining all channels, we should have sensitivity to ~130 GeV.

30. Quarknet Workshop 2008B. Quinn University of Mississippi 30 SM is “ugly” – it requires too much fine tuning of too many free parameters. May only be an effective theory valid to some energy scale beyond which higher symmetries may manifest as new particles and forces. Supersymmetry, or SUSY is the leading candidate. Every particle and force carrier has a massive super-partner (squark, gluino, etc.) Theoretically attractive: SUSY closely approximates SM at low energies Allows unification of forces at much higher energies Provides a path to incorporate gravity and string theory: Local Supersymmetry = Supergravity Lightest stable particle cosmic dark matter candidate Masses expected to be 100 GeV - 1 TeV SupersymmetrY ?

31. Quarknet Workshop 2008B. Quinn University of Mississippi 31 the Golden tri-leptoN SUSY SignaturÊ In one popular model the charged and neutral partners of the gauge and Higgs bosons, the charginos and neutralinos, are produced in pairs Decay into fermions and the Lightest Supersymmetric Particle (LSP), a candidate for dark matter. The signature is particularly striking: Three leptons = track + EM calorimeter energy or tracks + muon tracks (could be eee, ee , e , , ee , etc… ). neutrino= missing transverse energy

32. Quarknet Workshop 2008B. Quinn University of Mississippi 32 Tri-lepton search Resultß In four tri-lepton channels three events total found. Consistent with Standard Model expectation of 2.9 events. Here is a like-sign muon candidate

33. Quarknet Workshop 2008B. Quinn University of Mississippi 33 Extra dimensionS Gravity (in particular, its weakness) does not fit into the SM. It can be accommodated in a higher dimensional world (t + 3D + “n” extra spatial dim.). Only gravity can propagate in the extra dimensions which are hidden to us because we are confined to the 4-D surface, or brane. Gravity would therefore be as strong as the other forces, but since it spreads its influence in the other dimensions, it appears weakened or diluted from our viewpoint. 4-D Universe extra dimensions q graviton q

34. Quarknet Workshop 2008B. Quinn University of Mississippi 34 Extra dimensionS Gravitons could be produced in collisions, leave our 3- D world, go into the other dimensions… …come back and decay into two photons or electrons that appear to come from nowhere. An unexpectedly high rate of such pairs at high energies would signal the presence of extra dimensions. p p G q q’q’ e e

35. Quarknet Workshop 2008B. Quinn University of Mississippi 35 High mass candidate eventß ee pair  pair

36. Quarknet Workshop 2008B. Quinn University of Mississippi 36 Extra dimension limitS Di-electrogmagnetic objects are collected and the mass calculated (just as in our Z plot a few minutes ago). The observed mass spectrum is compared to a linear combination of SM signals Instrumental backgrounds Extra Dimension Signals No evidence is found for hidden dimensions, @ 95%CL n = 2, 170  m n = 3, 1.5 nm n = 4, 5.7 pm n = 5, 0.2 pm n = 6, 21 fm n = 7, 4.2 fm Note the long mass tail

37. Quarknet Workshop 2008B. Quinn University of Mississippi 37 We’ve just begun to explorE All of these results represent at most a quarter of our data