1. Search for New Phenomena in the CDF Top Quark Sample Kevin Lannon The Ohio State University For the CDF Collaboration

2. SMU Seminar 2-5-07 K. Lannon2 Why Look in Top Sample?  Top only recently discovered  Top turned 10 in 2005  Samples still relatively small  Still plenty of “room” for unexpected phenomena  Top is really massive  Comparable to gold nucleus!  Yukawa coupling near unity  Special role in EWSB?  Many models include new physics coupling to top u d s c b t Quark Masses GeV/c 2 5 orders of magnitude between quark masses!

3. SMU Seminar 2-5-07 K. Lannon3 What Might We Find?  It’s not Standard Model top at all!  Charge not 2/3? [Phys.Rev.D59:091503,1999; Phys.Rev.D61:037301,2000]  Spin not 1/2?  It’s not only Standard Model top  Additional heavy particles decaying to high pt leptons, jets and missing energy (t ’) [Phys.Rev.D64:053004,2001; Phys.Rev.D65:053002,2002]  Heavy resonance decaying to tt [Phys.Lett.B266:419,1991]  t  H + b  ttH production [Phys.Rev.D68:034022,2003]  Nothing but the Standard Model....  Not as bad as it sounds  Test our abilities to calculate signal and background properties  Important at the LHC  top becomes background to other searches  Constrains models that put new physics in the top sample [hep-ph/0504221]

4. SMU Seminar 2-5-07 K. Lannon4 The Tevatron and CDF  Tevatron accelerator  Highest energy accelerator in the world (E cm = 1.96 TeV)  World record for hadron collider luminosity (L inst = 2.72E32 cm -2 s -1 )  Only accelerator currently making top quarks Central Cal Plug Cal Central Tracker Silicon Tracker Muon Detectors  CDF Detector  Trigger on high p T leptons, jets and missing E T  Silicon tracking chamber to reconstruct displaced vertices from b decays

5. SMU Seminar 2-5-07 K. Lannon5 Tevatron Performance  Integrated luminosity at CDF  Total delivered: ~2.3 fb -1  Total recorded: ~1.9 fb -1 (~ 17  Run I!)  So far for top analyses, used up to 1 fb -1  More analyses with 1.0-1.2 fb -1 in progress for winter and spring  Doubling time: ~1 year  Future: ~4 fb -1 by 2007, ~8 fb -1 by 2009 Peak Luminosity Today’s Presentation: 200 pb -1 ~ 1 fb -1 Integrated Luminosity Analyzed by Summer

6. SMU Seminar 2-5-07 K. Lannon6 Triggering on Top  Need high efficiency, low fake rate trigger for high p T leptons  Relies on track trigger (XFT)  Fake rate increases with occupancy  Occupancy increases with luminosity  3x higher than original design because Tevatron didn’t reduce bunch spacing (392 ns  132 ns) Z  ee at low lum. 9 add. Int./crossing fake Fake tracks can be made from segments of different real physical tracks. Trigger  for muons without upgrade Missing segments Instrumenting additional layers reduces fake rate. Efficiency stays high.  Upgrade put into operation in October  Efficiency = 96% for high p T tracks  Fake track rejection factor = 5-7 Reduction factor ~ 4

7. SMU Seminar 2-5-07 K. Lannon7 Top Quark Production at Tevatron ~85% ~15%  QCD pair production   NLO = 6.7 pb  First observed at Tevatron in 1995  EWK single-top production  s-channel:  NLO = 0.9 pb  t-channel:  NLO = 2.0 pb  Not observed yet s-channelt-channel  Other?: ??? (and LHC) 833 pb ~13% ~87% 10.6 pb 247 pb Associated tW 62 pb

8. SMU Seminar 2-5-07 K. Lannon8 Top Production Rates  Like finding a needle in a haystack.... One top pair each 10 10 inelastic collisions at  s = 1.96 TeV  Efficient Trigger  ~90% for high p T leptons  Targeted event selection  Distinctive final state  Heavy top mass  Advanced analysis techniques  Artificial Neural Networks Needle in haystack (approx.)

9. SMU Seminar 2-5-07 K. Lannon9 SM Top Quark Decays  Particular analysis usually focuses on one or two channels  New physics can impact different channels in different ways  Comparisons between channels important in search for new physics BR(t  Wb) ~ 100%

10. SMU Seminar 2-5-07 K. Lannon10 Top Signatures Electron or muon: p T > 20 GeV Neutrino: Missing E T > 20-25 GeV Jet: E T > 15-20 GeV cone = 0.4 b-jet: identified with secondary vertex tag DileptonLepton + JetsAll Hadronic

11. SMU Seminar 2-5-07 K. Lannon11 Top Event Yields  To give an idea of CDF sample sizes....  Based on top cross section of 6.7 pb  Background and signal numbers based on event yields from current analyses, scaled by luminosity  Assume no changes in event selection, efficiency, etc. Luminosity1 fb -1 4 fb -1 Total Top Events670026,800 Decay ModeDil.L + JL + J (b-tag)Dil.L + JL + J (b-tag) Before Event Selection330198513257940 Selected Signal Events5048029019019101140 Expected Background4022901601509150670  L+J: ~2k signal events with 4 fb -1 (signal:background ~ 1 : 5)  L+J (b-tag): ~1k signal events with 4 fb -1 (signal:background ~ 2:1)

12. SMU Seminar 2-5-07 K. Lannon12 Searching for New Physics  Precision study of top properties  Non-SM behavior from top quark  Evidence of something other than top in sample  Direct search for new phenomena in top sample  Resonant production  Non-SM decays  New particles with “top-like” signature  New particles produced in association with top V tb

13. SMU Seminar 2-5-07 K. Lannon13 Top Properties Working Group  Studying all properties of top quark (except mass)  ~ 150 faculty, postdocs, students  ~15 papers (so far)  ~50 active analyses V tb

14. SMU Seminar 2-5-07 K. Lannon14 Precision Study: Cross Section  Cross section  Measured in different final states  New physics can affect different final states differently  Different techniques used in same final state  Results combined at end for most precise answer  tt production calculated to NLO  Central value: 6.7 pb — 6.8 pb  Uncertainties: 5.8pb — 7.4 pb  For m top = 175 GeV/c 2  Combined result:  7.3  0.9 pb N Top = N obs - N background, or from fit

15. SMU Seminar 2-5-07 K. Lannon15 Two Best Measurements  Both in Lepton + Jets Channel  Vertex Tag (weight = 0.50, pull = + 0.88)  Uses b-tagging to increase ratio of signal to background  Counting experiment  Count W+jets events with a b-tag  Subtract expected background  Excess attributed to top  Kinematic Artificial Neural Net (weight = 0.32, pull = -1.14)  Uses kinematic variables to separate signal from background  Combines several variables in a neural network to increase sensitivity  Fit for the number of top events  Does not use b-tagging (lower signal to background ratio)

16. SMU Seminar 2-5-07 K. Lannon16 B-Tagging  b-tagging: Identifying jets containing a b quark  Take advantage of long b lifetime  Look at precision tracking information for tracks within jet  Reconstruct secondary vertices displaced from primary  Efficiency  Per jet  40% for b jet  9% for c jet  0.5% for light jet  Per event (tt )  60% for single tag  15% for double tag

17. SMU Seminar 2-5-07 K. Lannon17 Sample Composition Number of events with an identified W +  1 jets Signal regionControl region 695 pb -1 Backgrounds that produce W + jets signature Excess of data over background attributed to top production Agreement between data and background checks accuracy of background estimate

18. SMU Seminar 2-5-07 K. Lannon18 Lepton + Jets Vertex Tag Result  One Tag + H T Cut  8.2 ± 0.6 (stat.) ± 1.0 (sys.) pb  Two tags, no H T Cut  Cross check  8.8 +1.2 -1.1 (stat.) +2.0 -1.3 (sys.) pb H T = scalar sum of lepton, jet, and missing ET

19. SMU Seminar 2-5-07 K. Lannon19 Using Kinematics to Identify Top  Look for central, spherical events with large transverse energy  Signal: PYTHIA tt monte carlo  Background: ALPGEN + HERWIG W + 3p monte carlo Normalized to unit area H T  scalar sum of lepton, jet, and missing E T Aplanarity uses lepton, jet and missing E T Max jet  uses 3 highest E T jets; all others use 5 highest

20. SMU Seminar 2-5-07 K. Lannon20 Statistical Sensitivity  Evaluate expected fit fractional error using MC-based pseudo experiments  Single variable fits: fit signal fraction using distributions of a single kinematic variable  Plotted  Points: median fit fractional error  Error bars: 68% interval

21. SMU Seminar 2-5-07 K. Lannon21 Multivariate Approach: Neural Nets  Structure  Composed of nodes modeled after neurons in nervous system  Organized into layers  Input layer: initialized by input variables  Hidden layer: takes information from each input node and passes to output layer  Output node: new discriminating variable with range [0,1]  Training  Neural net output determined by exposure to training data  Iteratively adjust parameters to minimize error:  Training accomplished through JETNET program (Peterson et al. CERN-TH/7135-94) 7 kinematic variables  7 input nodes Output node—range [0,1]—signal = 1 1 hidden layer, 7 hidden nodes Information flow

22. SMU Seminar 2-5-07 K. Lannon22 Statistical Sensitivity  Evaluate expected fit fractional error using MC-based pseudo experiments  Single variable fits: fit signal fraction using distributions of a single kinematic variable  NN: fit NN output of data to NN templates  Plotted  Points: median fit fractional error  Error bars: 68% interval  NN Fit performs significantly better than single variable fits

23. SMU Seminar 2-5-07 K. Lannon23 Using NN to Fit Data  Basic Approach  Train NN to distinguish tt signal from backgrounds  PYTHIA tt MC as signal model  ALPGEN + HERWIG W + 3p MC as background model  Use this NN to make templates for fitting the data  Use same signal model as above  Also extract QCD multijet template from data  Supplement electroweak template with contributions from other processes: WW,WZ, Z + jets, single top  Fit templates to NN distribution from data  Binned maximum likelihood fit  Three component fit  Signal and electroweak float  QCD constrained to value estimated using isolation vs missing E T method

24. SMU Seminar 2-5-07 K. Lannon24 Lepton + Jets Kinematic ANN Result SampleEventsFitted tt  (tt ) W +  3 Jets2102324.6  31.66.0  0.6  0.9 pb W +  4-Jet461166.0  22.15.8  0.8  1.3 pb

25. SMU Seminar 2-5-07 K. Lannon25 Kinematics of b-Tagged Events  Looks like top!

26. SMU Seminar 2-5-07 K. Lannon26 Systematic Uncertainties  Main Systematic Uncertainties uncorrelated  Lepton + Jets Vertex Tag  b-tagging efficiency: 6.5%  Background estimation: 3.4%  Kinematic ANN  Background shape modeling: 10.2%  Jet Energy Scale: 8.3%  For both results, uncertainty dominated by systematics  Both are working to reduce for 1.2 fb -1 publications

27. SMU Seminar 2-5-07 K. Lannon27 Search for t  H + b  Compare top yield in four different channels  Measurements consistent with SM  Consider correlated effect of t  H + b decays on four channels  Exclude when changes make expectation inconsistent with data  Limits for 6 sets of MSSM parameters and less model-specific scenarios Varying model parameters changes: BR(t  H + b) BR(H +   ) BR(H+  cs) BR(H+  t*b) BR(H+  W + h 0 ) BR(H+  W + A 0 ) Shown here: Variations as a function of tan  particular set of MSSM parameters Phys.Rev.Lett. 96 (2006) 042003

28. SMU Seminar 2-5-07 K. Lannon28 MSSM Limits  Calculate BR(t  H + b) and H + BR’s as a function of M H+ and tan(  )  Use 6 different MSSM “benchmarks”  Results for “Benchmark #1” shown below

29. SMU Seminar 2-5-07 K. Lannon29 Less Model Dependent Limit  “Tauonic Higgs” Model  Assume BR(H +   ) = 1  i.e. MSSM with high tan(  )  “Worst” Limit  Find arbitrary combination of H + BR’s that give least stringent limit

30. SMU Seminar 2-5-07 K. Lannon30 t ’ Production  Consider possible contribution to “top” sample from heavier particles with “top-like” signature (t’)  Examples  4 th chiral generation consistent with precision EWK data [Phys. Rev. D64, 053004 (2001)]  “Beautiful Mirrors” Model: additional generation of quarks that mix with 3 rd generation [Phys. Rev. D65, 053002 (2002)]  Consider decay of t’  Wq  Happens when m t’ < m b’ + m W  Precision EWK data suggests mass splitting between b’ and t ’ small  Search for by fitting H T vs M reco  H T = sum of transverse momenta of all objects in event  M reco = Wq invariant mass reconstructed with a  2 fitter (same technique used in top mass reconstruction)

31. SMU Seminar 2-5-07 K. Lannon31 t ’ Search Results  No evidence for t ’ observed  Set 95% confidence level limits on  t’  BR(t’  Wq) 2  Exclude m t’ < 258 GeV for BR(t’  Wq) = 100%  Interesting behavior in high mass tails

32. SMU Seminar 2-5-07 K. Lannon32 Resonant top production: No evidence seen Exclude Leptophobic Z’ with M z’ < 725 GeV/c 2 Top Quark Lifetime (~10 -24 s in SM) Result: c  < 52.5  m at 95% confidence level Consistent with detector resolution. W Helicity in Top Decay: SM: F 0 = 0.7, F - = 0.3, F + = 0.0 Result: F 0 = 0.61  0.13, F + < 0.09 Summary There are many more CDF results than I could show here. Top Mass measured to 2.4 GeV/c 2 (1.4%) uncertainty!  Even More results on the public webpage http://www-cdf.fnal.gov/physics/new/top/top.html  No deviations from Standard Model so far  Many results statistically limited  More results with 1-1.2 fb -1 coming soon  Results for ~2fb -1 by this summer  Many new and updated analyses in progress  Improved cross section measurements  Single-top  Top charge  Flavor changing neutral currents  Direct search for t  H + b http://www-cdf.fnal.gov/physics/new/top/top.html

33. SMU Seminar 2-5-07 K. Lannon33 The Future: Top at LHC  “Top physics will be easy at the LHC”  Top cross section increases by factor of ~ 100  Background cross sections increase by factor of ~10  Probe for new Physics  M tt distribution  Associated Higgs production: ttH  Even used for LHC detector calibrations  High precision results from Tevatron important  Discover new physics  ~ 1-2 GeV/c 2 precision on mass  Production and decay well understood Looks a little like B physics at the Tevatron precision physics

34. SMU Seminar 2-5-07 K. Lannon34 Extra Slides

35. SMU Seminar 2-5-07 K. Lannon35 Top Cross Section vs Mass

36. SMU Seminar 2-5-07 K. Lannon36 Search for Resonant Production  Motivation  Some models predict particles decaying to top pairs  Should be visible as resonance in tt invariant mass spectrum  Example model: Topcolor assisted technicolor  Extension to technicolor that includes new strong dynamics  Couples primarily to 3 rd generation  Includes new massive gauge bosons: topgluons and Z’

37. SMU Seminar 2-5-07 K. Lannon37 Search for Resonant Production  Look for generic, spin 1 resonance (X 0 ) decaying to top pairs  Assume  X0 = 1.2%  M X0  Test masses between 450 GeV and 900 GeV in 50 GeV increments  Results  No evidence for resonance  Set 95% confidence level limit for  X0 at each mass  Exclude leptophobic Z’ with M z’ < 725 GeV

38. SMU Seminar 2-5-07 K. Lannon38 W Helicity in Top Decay V-A Forbidden W 0 Longitudinal fraction F 0 W - Left-Handed fraction F - t b W +1/2 -1/2 +1 W + Right-Handed fraction F + t W b +1/2 +1 -1/2  Helicity of W determined by V-A structure of EWK interaction  70% longitudinal  30% left-handed  Right handed forbidden t W +1/2 0 W b

39. SMU Seminar 2-5-07 K. Lannon39 W Helicity in Top Decay  Can be tested by measuring W helicity angle:  *   * = angle of the lepton relative to negative the direction of the top in the W rest frame.  Can also use M lb 2  0.5(m t 2 -m W 2 )cos  *

40. SMU Seminar 2-5-07 K. Lannon40 W Helicity Results  Two CDF results with 955 pb -1  Use different kinematic fitters to reconstruct tt system: cos  *  Very consistent measurements of F 0 and limits on F +  F 0 = 0.61  0.12(stat)  0.04 (syst) and F + < 0.11 at 95% C.L.  F 0 =0.59  0.12(stat) +0.07 -0.06 (syst) and F + < 0.10 at 95% C.L.  One measurement with 750 pb -1  Uses M lb and measures fraction of V+A  F V+A < 0.29 at 95% C.L.  Assuming F 0 = 0.7  F + < 0.09 at 95% C.L.

41. SMU Seminar 2-5-07 K. Lannon41 Top Quark Lifetime  Measure impact parameter of lepton from Lepton + Jets top decay  Evidence of displaced top suggests  Production via decay of long-lived particle  New long-lived particle in top sample  Anomalous top lifetime Templates for SM processes Result: c  < 52.5  m at 95% confidence level

42. SMU Seminar 2-5-07 K. Lannon42 Sample Composition W+light flavor: From pretag using mistag matrix W+heavy flavor: From pretag using MC for HF fraction and b-tagging eff. Single Top and Diboson: Estimated using theoretical cross section Non-W QCD: Estimated from MET and lepton isolation side-bands Difference between observed and predicted background attributed to top Event count before applying b-tagging Number of events with an identified W +  1 jets

43. SMU Seminar 2-5-07 K. Lannon43 The Search for Single Top  Standard Model  Rate  |V tb | 2  Spin polarization probes V-A structure  Background for other searches (Higgs)  Beyond the Standard Model  Sensitive to a 4 th generation  Flavor changing neutral currents  Additional heavy charged bosons  W ’ or H +  New physics can affect s-channel and t-channel differently Tait, Yuan PRD63, 014018(2001)

44. SMU Seminar 2-5-07 K. Lannon44 Signal and Backgrounds W + Heavy Flavor W + Light Flavor (Mistags) Multi-jet QCD tt Other EWK Total Background: 646  96 events Expected Single-Top: 28  3 events Signal / Background ~ 1/20 e or  : p T > 20 GeV : MET> 20 GeV 2 jets: E T > 15 GeV,  1 b-tag Single-top Signature Backgrounds Must use multivariate, kinematic techniques to separate signal from background

45. SMU Seminar 2-5-07 K. Lannon45 Multivariate Discriminants  Improve signal discrimination by combining several variables into a multivariate discriminant  Neural Network and multivariate likelihood function both used  Variables: ℓ b and dijet invariant masses, H T, Q , angles, jet E T and , W-boson , kinematic fitter quantities, NN b-tag output ZOOM

46. SMU Seminar 2-5-07 K. Lannon46 Single Top Multivariate Likelihood Result  Best fit result for s- and t-channel separately  s-channel:  t-channel:  95% CL upper limit on combined s- + t-channel:

47. SMU Seminar 2-5-07 K. Lannon47 Single Top Neural Network Result  Combined search:  s-channel + t-channel combined in SM ratio  Best fit:  95% CL Limit:  Separate search  s- and t-channel vary separately  Best Fit:  t-channel:  s-channel:  95% CL Limit:  t-channel:  s-channel:

48. SMU Seminar 2-5-07 K. Lannon48 Single Top Matrix Element Result Best fit result:

49. SMU Seminar 2-5-07 K. Lannon49 Summary  This is an exciting time to be at the Tevatron  1.2 fb -1 sample currently in hand and being analyzed  Top sample has grown from ~30 events in Run I to ~ several hundred  Larger samples coming soon (almost 2 fb -1 ) by summer  Analysis techniques becoming increasingly mature and sophisticated  Look forward to  1 fb -1 publications this winter  No evidence for new physics in top sample so far  Have many more top measurements than covered in this talk (see CDF public results webpage)  Increasing precision continues to test consistency of measurements in different channels  Many new analyses on their way (as well as updates of current results)  Improved cross section measurements  Single-top  Top charge  Flavor changing neutral currents  Direct search for t  H + b