1 / 55

Physics of Hadron Colliders Lecture 2: Top Physics at CDF

Physics of Hadron Colliders Lecture 2: Top Physics at CDF. Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu. Fermilab Collider Accelerator Complex. see www-ad.fnal.gov/public/index.html. There are 8 accelerators in the chain Proton source (3) Cockroft-Walton Linac Booster

dawson
Télécharger la présentation

Physics of Hadron Colliders Lecture 2: Top Physics at CDF

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Physics of Hadron CollidersLecture 2: Top Physics at CDF Joseph Kroll University of Pennsylvania kroll@hep.upenn.edu

  2. Fermilab Collider Accelerator Complex see www-ad.fnal.gov/public/index.html • There are 8 accelerators in the chain • Proton source (3) • Cockroft-Walton • Linac • Booster • Antiproton source (2) • Debuncher • Accumulator • Main Injector (1) • Recycler (1) • Tevatron (1) Drawing courtesy of Fermilab J. Kroll University of Pennsylvania

  3. Fixed Target Fermilab Aerial View CDF DØ Tevatron Main Injector n.b., objects not to scale Photo courtesy of Fermilab J. Kroll University of Pennsylvania

  4. Fermilab Site (cont) Accumulator Debuncher Booster Linac Cockroft-Walton Photo courtesy of Fermilab Photo courtesy of Fermilab J. Kroll University of Pennsylvania

  5. Photo courtesy of Fermilab Booster 1 GHz 475 m circumference 400 MeV acc. to 8 GeV accelerates protons beam to MiniBoone too Proton Source Photo courtesy of Fermilab Beam from Booster goes to Main Injector accelerated to 120 GeV to make antiprotons Linac 805 MHz 130 m length 3 MV/meter accel. 400 MeV on output also H¯ Cockroft-Walton 750 kV DC Accelerates H¯ Photo courtesy of Fermilab J. Kroll University of Pennsylvania

  6. Antiproton Source – Three Components • Target • 120 GeV p’s hit Ni target • 106 p make » 20 8 GeV “pbars” • focused by Li lens • pbars filtered out by mag. spec. • Debuncher • trade E for t • pbars easier to accept in Accum. • Accumulator • 8 GeV pbars cooled (stacked) • Stochastic cooling • holds pbar “stack” for hours • large stack = 200mamps Accumulator Debuncher Photo courtesy of Fermilab J. Kroll University of Pennsylvania

  7. Stochastic Cooling I said I would try to find out the answers to questions I could not answer. Here’s an answer from Paul Derwent (FNAL) on why we say “stochastic” J. Kroll University of Pennsylvania

  8. Main Injector and Recycler • Main Injector • Biggest change for Run II • 3.3 km circumference • replaced “Main Ring” • commissioned 98-99 • increases pbar prod by 3 • fixed target @ 120 GeV • collider @ 150 GeV • FT & collider simultaneous Recycler • Recycler • 8 GeV pbars from Acc • allows faster stacking • permanent magnets • 1.5kG dipole, 3.7kG/m Quad Photo courtesy of Fermilab Main Injector J. Kroll University of Pennsylvania

  9. After MI Before MI Main Ring Tevatron Tevatron Photo courtesy of Fermilab Photo courtesy of Fermilab • 1st superconducting synchrotron • 6.28 km in circumference • commissioned 1983 • 1000 4.4 T dipoles, 6.4 m long, 4.2o K • Run I: 900 GeV  Run II: 980 GeV 1989 NAS Medal of Technology: Alvin Tollestrup Helen Edwards of Fermilab AT HE J. Kroll University of Pennsylvania

  10. Tevatron Collider Runs and CDF • Run -2 (October 1985) “Engineering” Run • 28 collisions recorded with VTPC • Run -1 (1987-1988) • first physics (» 30 nb^{-1}): W’s, jets, incl. particle distributions,… • Run 0 (1988-1989) • » 5 pb-1 data: Z0 mass, limits on top, EWK, QCD, B’s, exotics,… • Run 1 (1992-1996) • DØ’s first run • peak L = 2.4 £ 1031 cm-2s-1, 6 £ 6 (3.6 sec) • » 120 pb-1 data: top discovery, W mass, sin2,… • Run 2 (2001-2009?) • to date: 500 pb-1 delivered, 400 recorded by CDF • peak L = 7.2 £ 1031 cm-2s-1, 36 £ 36 (396 nsec) J. Kroll University of Pennsylvania

  11. The CDF II Upgrade (1996-2001)* • Actually there have been many CDF upgrades • CDF II refers to the detector built after Run I • Essentially the entire detector rebuilt • Only the Central EM and HAD calorimeter remained • new bunch separation (132 nsec)  all new electronics • new drift chamber (COT) & silicon tracker (L00, SVXII, ISL) • Time of Flight for particle id • new end plug calorimetry & lumi monitor • more muon coverage • new fully digital trigger system with new capabilities (SVT) • new DAQ * Actually the CDF II upgrade began well before 1996 and is still taking place J. Kroll University of Pennsylvania

  12. Muon systems Iron shielding Hadronic Calorimetry Electromagnetic Calorimetry Lumi monitor Silicon tracking Solenoid and TOF Drift chamber CDF II J. Kroll University of Pennsylvania

  13. Running Conditions (Run I versus Run II) Example of a slide from the days before powerpoint Higher luminosity same number of bunches  more interactions/crossing Average number of interactions/crossing about the same at Lmax in Run 1 and Run 2 n.b.,We will not run with 99 bunches (132 nsec) J. Kroll University of Pennsylvania

  14. CDF Run II Data Taking Tevatron Store Number Day since beginning of year Integrated luminosity acquired by CDF per fiscal year (e.g., FY03 is Oct. 2002 to Sep. 2003) Integrated luminosity delivered and acquired by CDF J. Kroll University of Pennsylvania

  15. CDF Run II Data Taking (continued) Initial Luminosity vs. Store Number CDF Data Taking Efficiecny vs. Store # 80% Blue is running average over 20 Stores CDF Averages and Records Not at the LEP or B Factory Level (yet) J. Kroll University of Pennsylvania

  16. The CDF II Silicon Tracker 3 Parts: Layer 00 SVX II ISL J. Kroll University of Pennsylvania

  17. Insertion of the Central Outer Tracker J. Kroll University of Pennsylvania

  18. Tracking System Assembly (continued) J. Kroll University of Pennsylvania

  19. Roll-in of Central Detector J. Kroll University of Pennsylvania

  20. Detector Hardware tracking for pT1.5 GeV 1.7 MHz bunch crossing rate Muon-track matching 46 L1 buffers L1 trigger Electron-track matching Missing ET, sum-ET 30 kHz L1 accept Silicon tracking 4 L2 buffers L2 trigger Jet finding Refined electron/photon finding 300 Hz L2 accept L3 trigger 300 CPU’s Full event reconstruction 70 Hz L3 accept tape >100Hz with data compression CDF II Trigger System courtesy E. Thomson (OSU/Penn) J. Kroll University of Pennsylvania

  21. Run II Physics @ CDF II • Top physics (center piece of Run II physics program) • top is discovered  measure properties (mass, production, decays) • does it have non-standard model decays, production? • Exotic Physics (new particle searches) • at the energy frontier until LHC turns on • Electroweak Physics • W mass, Higgs search, WW, WZ, ZZ production • QCD • inclusive jet cross-section, W/Z + jets, jet correlations, heavy flavor • soft physics (diffraction, double pomeron scattering, etc.) • Heavy Flavor Physics (b and c) • B hadron weak decays: B0s flavor oscillations is the center piece • Charm physics program (completely new for Run II – SVT) J. Kroll University of Pennsylvania

  22. 10 Years Ago Aside: Have we directly observed all 12 fundamental fermions? J. Kroll University of Pennsylvania

  23. Top Pair Production The dominant source of top is strong (QCD) production top is massive at Tevatron produced centrally quark-antiquark annihilation gluon fusion J. Kroll University of Pennsylvania

  24. Predicted Cross-section M. Cacciari et al., hep-ph/0303085 GeV cross-section in picobarns (pb) Central value is “CTEQ6” structure fcns = 175 GeV • Variation from • pdf’s • s,  pdf uncertainty: from high-x g - see later slide 30% increase s = 1.8 to 1.96 TeV J. Kroll University of Pennsylvania

  25. Comment on Parton Distribution Functions There are many sets of pdf’s based on global fits of various data check out www.durpdg.dur.ac.uk/hepdata/pdf3.html CTEQ is an acronym for a set of structure functions produced by a collaboration called : “Coordinated Theoretical-Experimental Project on QCD” see www.phys.psu.edu/~cteq n.b.,excellent summer school transparencies available there There are others: e.g., MRST Martins, Roberts, Stirling, Thorne, hep-ph/0207067 J. Kroll University of Pennsylvania

  26. Which Process Dominates? Depends on mt and s Parton 4-vectors are (E,pz): Center of mass energy Ecm of partons 1 and 2 Aside: really need more (phase space) mean pT(top) » mt/2 Need at least For x1¼ x2 x > 0.2 Tevatron x > 0.03 LHC J. Kroll University of Pennsylvania

  27. Quarks at Tevatron, Gluons at LHC Tevatron (uncertainty in g at high x  ~ 10% uncertainty on ) LHC g Tevatron LHC u d u J. Kroll University of Pennsylvania

  28. Single Top Production See B.W. Harris et al., Phys. Rev. D 66, 054024 (2002) Electroweak top production also important 0.88 § 0.10 pb-1 1.98 § 0.24 pb-1 negligible @ Tevatron Harder to observe than Difficult background for SM Higgs search J. Kroll University of Pennsylvania

  29. Standard Model Top Anti-Top Signature mt = 175 GeV  real W Vtb¼ 1* BF(t ! Wb) = 100% no top hadrons (t! Wb) = 1.5 GeV, t = 4£10-25 s Classify topologies according to W decay both W decays leptonic (means e or , not ) dilepton lepton + jets One W decay leptonic, other hadronic all hadronic both W decays hadronic dilepton and lepton + jets are the discovery modes * assuming unitarity 0.9990 < Vtb < 0.9993 @ 90% CL (PDG2002) J. Kroll University of Pennsylvania

  30. Use W! e, 10.7% each (add W! 10.7%, !e, 35.2% total) Three tt Signatures Dilepton 4.6% (6.4%) 2 high pT leptons, ET, 2 b-jets Lepton + jets 33.6% (37.6%) 1 high pT lepton, ET, 2 b-jets, 2 light quark jets All hadronic 61.8% (56.0%) 2 b-jets, 4 light quark jets W!, ! hadrons treated separately J. Kroll University of Pennsylvania

  31. Remember Three Signatures (continued) most probable topology All hadronic QCD multijet production several orders of magnitude higher ► need b-jet identification ► must reconstruct top invariant mass ► still very challenging (for trigger too) Lepton+jet also a probable topology Real W production still orders of magnitude higher ►several approaches – described later ►much cleaner than hadronic – especially with b-tag see next slide  Dilepton least probably topology Real WW production comparable see next slide  J. Kroll University of Pennsylvania

  32. Aside: W and Z Production at the Tevatron Dilepton and Lepton+jets signature contain W! e, (for s=1.96 TeV, about 10% lower for s=1.8 TeV) WW production is comparable to top production e.g., see J.M. Cambell & R.K. Ellis, Phys. Rev. D 60, 113006 (1999) J. Kroll University of Pennsylvania

  33. Dilepton Signature Pair of opp. charge, high pT leptons: e+e-, e+-& e-+, +- Substantial ET from two ’s Two high pT b-jets • Background from real high pT lepton pairs (“physics backgrounds”) • Drell-Yan and Z0! ee, (no real ET) • Z0! (real ET too) • WW production (real ET too) • Background from “fake” leptons too • W + jets, W! e, & jet! fake lepton Jet requirement greatly reduces these backgrounds J. Kroll University of Pennsylvania

  34. Lepton + Jets Signature High pT lepton: e or  Substantial ET from  Two high pT b-jets Two high pT light quark jets • Physics background • W + jets • Reduce backgrounds with • kinematic criteria • identifying b jets (b-tags) Run I results published in CDF Collaboration, T. Affolder et al., Phys. Rev. D 63, 072003 (2001) J. Kroll University of Pennsylvania

  35. Digression: Jet Reconstruction at CDF Quarks and gluons do not exist as “free” objects (colored) fragment or hadronize into “jets” of particles Recall results from UA2 in Lecture 1 jet reconstruction  get back to the parton (q or g) 4-vector to compare to theory or reconstruct mass e.g., W! qq0 Many possible approaches used at e+e- and hadron colliders CDF: uses fixed cone algorithm in - space follows UA1 J. Kroll University of Pennsylvania

  36. CDF Jet - Cone Algorithm see CDF Collaboration F. Abe et al., Phys. Rev. D 45 1448 (1992) • Start with calorimeter cells – define energy momentum vector • vector points from origin to centroid of cell: (px,py,pz,E), where E = |p| • ET2 = px2 + py2 • Select “seed” cells: ETcell > seed threshold (e.g., 1 GeV) • Form seed “clusters” • Add vectors of all seed cells within R (ranked in ET) • typical values R: 0.4, 0.7, 1.0 top search uses R = 0.4 • centroid of cluster determined by ET weighting • changes as seed clusters added - iterate • After all seeds merged, add in remaining calorimeter cells • require E_T > noise threshold (e.g., 100 MeV) • Jets defined this way have mass (partons are massless) J. Kroll University of Pennsylvania

  37. Azimuthal Energy Flow in 2 Jet Events From CDF two jet data CDF Collaboration F. Abe et al., Phys. Rev. D 45 1448 (1992) Distribution of calorimeter energy around jet axes away jet leading jet leading jet leading jet has <ET> » 40 GeV Cone size 0.4, 0.7, 1.0 all reasonable top: R=0.4 optimal for counting jets J. Kroll University of Pennsylvania

  38. Jets formed from “raw” calorimeter energies Jet Energy Corrections Detector Effects Calibrate central calorimeter (||<1) in situ with spectrometer • nonlinear calorimeter response • to low energy hadrons • B field bends low pT particles • out of cone (or do not reach Cal) • cracks and transition regions • of calorimeter • different response of EM & Had Balance calorimeter response out to ||=2.4 using dijet data Check jet energy scale with  vs. jet data Physics Effects Typical correction: increase raw ET by 30% • extra E from “underlying event” • & multiple interactions • fragmentation effects & soft g rad. •  and  J. Kroll University of Pennsylvania

  39. CDF Jet Corrections Have Several Levels Run II: use absolute E correction from Run I Top analysis uses Level 5 jets J. Kroll University of Pennsylvania

  40. Focus 1st on Lepton + Jets Channel • This was the discovery channel in Run I • Used to measure top production and mass • Signature is a leptonic W decay & four jets (2 are b’s) • Jets not all in detector acceptance  3 or 4 jets • Discovery relied on identifying at least one b jets • B hadron relatively long lived – use secondary vertex tag • Exploit B semileptonic decays – soft lepton tag (soft ≠ W decay) • Can also isolate top signal using kinematic criteria • top is heavy – harder more central jets than initial state parton radiation • neural nets give even better discrimination J. Kroll University of Pennsylvania

  41. Electron Selection Muon Selection ET > 20 GeV, ||<1 (central) pT > 20 GeV/c, ||<1 • Selection criteria based on • Ehad/EEM • E/p • Shower shape in Calo. • track match with shower max det. • shape in shower max det. • Selection criteria based on • minimum ionizing in EM and Had • match  chambers and track Efficiency: 90% Efficiency: 80% W Selection see e.g., CDF Collaboration F. Abe et al., Phys. Rev. D 50 p. 2966 (1994) Start with event sample collected with inclusive high pT lepton trigger Lepton (e or ) must be isolated Reject dileptons, Z0! e+e-, +- ET > 20 GeV J. Kroll University of Pennsylvania

  42. Do Selected Events Look Like W’s? Transverse Mass Distributions CDF Collaboration F. Abe et al., Phys. Rev. D 50 p. 2966 (1994) From ‘94 top “evidence” PRD, Run II selection very similar J. Kroll University of Pennsylvania

  43. Jet Requirements and HT Top signal sample: ≥ 3 Jets ET>15 GeV, ||<2.0 R=0.4 contains 70% E @ this stage tt efficiency is » 8%  40-60 events in 100 pb-1, S:B»1:4 Jets mt measurement: require 4th jet ET>8 GeV, ||<2.4 HT Run II: may add HT>200 GeV HT´ ET of lepton, jets, ET Simulation Top is heavy  larger HT on average than W+jets background J. Kroll University of Pennsylvania

  44. Identifying (tagging) b quark Jets CDF Collaboration F. Abe et al., Phys. Rev. D 50 p. 2966 (1994) Displaced tracks or secondary vertex B hadron lifetime ~ 1.5 psec Significant Lorentz boost  measurable displacement Simulation: top mass = 160 GeV pT(b) Semileptonic decays: Not isolated and softer than W!l  “soft lepton tag” or SLT displacement in transverse plane 5 mm J. Kroll University of Pennsylvania

  45. Illustration of Displaced Tracks and Vertex J. Kroll University of Pennsylvania

  46. B decay product Underlying event B fragmentation product Jet Axis d = impact parameter d Secondary Vertex (displaced vertex) Interaction point (primary vertex) Illustration of Displaced Tracks and Vertex in plane transverse to beam axis J. Kroll University of Pennsylvania

  47. Primary vertex: pp interaction point Definition of Terms Impact parameter d: distance of closest approach of track to vertex Primary vertex follows Gaussian distribution in x, y, & z Unless specified otherwise, “impact parameter” means in the plane transverse to the beam line (xy or rφ) Secondary vertex: decay/interaction point displaced from the primary vertex by a distance that is experimentally measurable. † at the most narrow point (waist) – transverse size varies with z J. Kroll University of Pennsylvania

  48. Rely on impact parameter d& error d Impact parameter significance: d/d Methods of Identifying Long Lived Particles includes 30m from beamspot • Associate Tracks with jety • count number of significantly displaced tracks: d/d > parameter • 1st used at Mark II (SLC) for Z0! bb (R. Jacobsen) • determine probability tracks originated from PV: “jet probability” • developed at LEP (א – Dave Brown) – later used by CDF • correlations between “d” and “φ” (used by CDF in “top evidence”) • reconstruct secondary vertex • from J/ (pT>1.5 GeV) with SVXII inner-most layer • d should include • uncertainty in track parameters • uncertainty in vertex position J. Kroll University of Pennsylvania † jet may be calorimeter jet or track based jet found with - algorithm

  49. Lxy < 0 Lxy > 0 Decay Distance in plane transverse to beam axis Jet axis Generic jets: symmetric distribution around 0 in Lxy b-jets: very asymmetric distribution, biased towards Lxy>0 J. Kroll University of Pennsylvania

  50. CDF Displaced Vertex Algorithm (SECVTX) J. Kroll University of Pennsylvania

More Related