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Top Quark Production at Hadron Colliders

Top Quark Production at Hadron Colliders. Fermi National Laboratory Wilson Fellow Seminar February 15, 2006. Joao Guimaraes da Costa Harvard University. How many top quarks are we making?. Top Mass. Higgs Search. Top Cross Section. Top Properties. Event Kinematics (New Physics?).

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Top Quark Production at Hadron Colliders

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  1. Top Quark Production at Hadron Colliders Fermi National Laboratory Wilson Fellow Seminar February 15, 2006 Joao Guimaraes da Costa Harvard University Top Quark Production at Hadron Colliders - Wilson Fellow Joao Guimaraes

  2. How many top quarks are we making? Top Mass Higgs Search Top Cross Section Top Properties Event Kinematics (New Physics?) The Top quark cross section measurement is the cornerstone to all analysis in the top sample

  3. The Top Quark Fermions: Top discovered in 1995 mtop = 172.7  2.9 GeV/c2 • 1989-1995: ~110 pb-1 (Run I) • A few dozen events Mass Lingering Questions: • Any “New Physics” in the top quark sample? • Is the event excess ONLY from top production? • What are the top quark properties? • Top mass, charge, spin, lifetime, branching fractions Force Carriers:

  4. Top in radiative corrections Electromagnetic constant: measured in atomic transitions, e+e- machines Weinberg angle: measured at LEP/SLC Fermi constant: measured in muon decay Radiative corrections

  5. Top Factories Tevatron highest energy collider today LHC highest energy collider starting 2007 1.96 TeV X 7 14 TeV 1-4 x 10-32 X 30-50 10-23 10-34 Today: 318 pb-1 (~ 3x run I dataset) New Results Soon: ~1 fb-1

  6. Top Quark Production at Hadron Colliders Proton Hard scattering cross-section

  7. Parton Distribution Functions TeV LHC Parton distribution function: xF(x,2) Effective center of mass energy LHC Gluon parton distribution function diverges at low x Tevatron

  8. Top Quark Pair Production LHC Tevatron 85% 10% 15% 90%

  9. Theoretical Cross Section (tt) (pb) 1000 LHC 100 10 Tevatron 1 100 1.0 10 • Theoretical uncertainty: ~ 15% • PDFs • Renormalization/factorization scale Mtop = 175 GeV/c2 NLO = 833 pb Rate ~ 700000 tt/day ~ 120x = 6.7 pb Rate ~ 60 tt/day Cacciari et al. JHEP 0404:068 (2004) Kidonakis & Vogt PRD 68 114014 (2003)

  10. Single Top Production Wt-channel t-channel s-channel TeV (√s=1.96 TeV): 0.88 ± 0.11 pb LHC(√s= 14 TeV): 10.6 ± 1.1 pb 1.98 ± 0.25 pb 246.6 ± 11.8 pb <0.1 pb 62.0+16.6-3.6 pb Tevatron Limit: D0 < 5.0 pb < 4.4 pb Harris PRD 66 (02) 054024 Cao hep-ph/0409040 Campbell PRD 70 (04) 094012 Tait PRD 61 (00) 034001 Belyaev PRD 63 (01) 034012 Campbell hep-ph/0506289

  11. Top Quark Decay FCNC SM BR: O(10-14) Top decay Real W Mtop > MW + Mb BR(tqZ) < 13% @ 95% C.L. (LEP) - decay Mtop ~ 175 GeV Virtual W Br(t  Wb) ~ 100% in the SM top 1 GeV top 10-25 seconds ctop < 52.5 m @ 95% C.L. (CDF)

  12. Top Quark Decay (2 x) Br(t  Wb) ~ 100% in the SM All-hadronic: BR largest (45%) but large QCD bkg 6 jets Dilepton: BR small (5%) and little kinematic constraints 2 jets + 2 lep + ETmiss Lepton+Jets: BR larger (30%) 4 jets + 1 lep + ETmiss Always: 2 jets are b-quark jets

  13. Top Event Display from CDF: Tagging b-quarks B-jet  B-jet  Jet 3 Jet 4 b-quarks have long lifetime (c = 460 m) d = c B mesons travel few mm before decaying Displaced Vertex Tagging b  cl (BR  20%) c  sl (BR  20%) Soft Lepton Tag 4x lower efficiency 7x larger fake rate

  14. The CDF Run II Detector • Silicon detectors • L00, SVX, ISL • |h|<2 • Central Outer Tracker • |h|<1 • spT~ 0.15% pT2 • EM Calorimeter • sE/E ~ 14%/E1/2 • Had Calorimeter • sE/E ~ 80%/E1/2 • Muon Chambers • |h|<1.5

  15. Top Cross Section Measurements CDF σ(tt) results D0 σ(tt) results

  16. Event Selection Top is Massive Large total event transverse energy: jets ET + lepton pT, ET + MET Golden Channel (lepton + jets) (30%) • MT(W) > 20 GeV • HT > 200 GeV • ≥ 1 SecVtx b-tag • ≥ 2 SecVtx b-tags • One high PT electron or muon • ET or PT > 20 GeV • Lepton isolated from jets • Large missing energy from neutrino • MET>20 GeV • ≥ 3 high ET>15 GeV jets or

  17. B-tagging (Secondary Vertex) y x z Start with set of tracks and general location of luminous region JET 30 m

  18. The luminous region at CDF (2002 to 2005) Average location of the pp interaction point per run size magnified 30x (real size 30 m) z = 0 Beam pipe z direction along beampine (proton direction)

  19. B-tagging (Secondary Vertex) y x z Start with set of tracks and general location of luminous region JET Find primary vertex Improved b-tagging efficiency ~ 20% Primary vertex 10 m 30 m

  20. B-tagging (Secondary Vertex) y x z Start with set of tracks and general location of luminous region JET Find primary vertex Improved b-tagging efficiency ~ 20% Select tracks with large impact parameter inside jet Make a seed for secondary vertex and form vertex Iterate: removing tracks with worst chi2 Primary vertex d0

  21. B-tagging (Secondary Vertex) y x z Start with set of tracks and general location of luminous region JET Find primary vertex Improved b-tagging efficiency ~ 20% Select tracks with large impact parameter inside jet Secondary vertex Make a seed for secondary vertex and form vertex L2D Iterate: removing tracks with worst chi2 Primary vertex d0 Got a vertex! Check if L2D is large enough

  22. Updated B-tagging (Tight SecVtx) Start with set of tracks and general location of luminous region Find primary vertex Improved b-tagging efficiency ~ 20% Select tracks with large impact parameter inside jet Make a seed for secondary vertex and form vertex Iterate: removing tracks with worst chi2 Got a vertex! Check if Lxy is large enough y x z Loosen initial track selection More tracks from B decays JET Secondary vertex L2D Primary vertex d0 Tighten secondary vertex quality cuts

  23. Fake rate: Tags in light flavor jets Mistags: Negative tag rate from dijet data parametrized in jet ET,, , track multiplicity and event  ET Corrections for HF in jet data, material interactions, Ks and  Fake tags from resolution (negative tag) JET Primary vertex Lxy Secondary vertex All these are not well simulated Need input from data x y z Mistags: 3x larger in data • Additional mistags: • Interactions in material • Long lived particles: Ks, 

  24. B-Tagging Efficiency Determination: MC Scale Factor bb event Away jet Electron jet Use inclusive low-pt (8 GeV) electron/muon sample Concern: Extrapolate to average jet ET of top events (~ 50 GeV) Fb ~ 25 % Tag away jet Fb ~ 70 % Tag electron jet Improvement from 82% earlier in Run II Scale Factor = Data/MC = 91 +/- 6 %

  25. Multiple Tagging and Loose SecVtx Tags Aim: 1% mistag rate per jet Similar to “typical” LHC taggers What efficiency can we really get on DATA ? New in Run II • Multiple tagging: • Larger datasets  full reconstruction of events • More precise measurement of top mass • Reconstruction of W hadronic decays • (4-jet top events) • New window into new physics: • Higgs (H  bb) • Supersymmetry • (sbottom, stop, charged higgs) 4 b-jets Loose SecVtx algorithm optimized for double tagged analysis Approach: Loosen input track quality selection selection Prove of principle for future improvements to b-tagging

  26. Loose SecVtx Tagging Efficiency • 20% b-jet efficiency increase • 2.5 x fake rate increase Effective luminosity increase: ~45%

  27. Top Cross Section: Tight / Loose Tagger 300% gain since start of run II • Efficiency corrected with data/MC scale factor

  28. Backgrounds • Major backgrounds: • Wbb,Wcc,Wc • Estimated from MC • ALPGEN + HERWIG • Normalized to pretag data • W + light jet + fake b • Estimated from data • Non-W • Estimated from data • Single top, WW, WZ, Z • Small • Estimated from MC • Pythia

  29. Top Cross Section (Single Tag) Signal region Loose Tagger Higgs production

  30. Top Cross Section (Double Tags) Loose Tagger Measured cross section Expectation for mtop = 178 GeV Signal region

  31. Major Systematic Uncertainties Largest systematic } Small improvements possible LHC: Use good prediction from NNLO and higher rate of W and Z to monitor luminosity

  32. Cross Section Mass Dependence This analysis: 16% relative error Recall Run I:  = 5.1  1.5 pb (30% relative error) Early Run II (before b-tagging improvements)  = 5.6  1.5 pb (27% relative error) mtop = 172.7  2.9 GeV/c2

  33. TOP MASS MEASUREMENT

  34. Top Mass Measurements Summary

  35. Top Mass Reconstruction Lepton + Jets Kinematical Fit PT balance mt1 = mt2 ml = mW mjj = mW 4 Jets x 2 neutrino Pz solutions

  36. Top Mass Reconstruction Herwig MC: Mtop = 175 GeV Resolution of reconstructed mass is dominated by incorrect combinations

  37. Top Mass Reconstruction Lepton + Jets Kinematical Fit PT balance mt1 = mt2 ml = mW mjj = mW 4 Jets x 2 neutrino Pz solutions

  38. W Mass Reconstruction: JES Lepton + Jets mjj = mW 4 Jets

  39. W Reconstruction: Effect from b-Tagging Mtop = 175 GeV, JES nominal Resolution of reconstructed mass is dominated by incorrect combinations Measure JES Mjj templates by varying JES 1 

  40. CDF L+jets Template Method (3) Top Mass with Jet Energy Scale Calibration Likelihood fit for top mass and JES 318 pb-1 Mtop = 173.5 +2.7/-2.6 (stat.)  2.5 (JES)  1.3 (syst.) GeV/c2 compared to 3.1 GeV wo/ in situ calibration

  41. Effect on Higgs Mass Expectations mtop= 178.0 ± 4.3 GeV mH = 114 GeV mH < 260 GeV @ 95% C.L. +69 -45 +4.1 mtop= 173.5 GeV mH = 94 GeV mH < 208 GeV @ 95% C.L. -4.0 +54 -33 • Using only CDF Run II Top Mass mtop = 2.5% mH = 18% World Average: mtop = 172.7  2.9 GeV/c2 • mtop< 1.5 GeV/c2 Future Prospects: • mW< 25 MeV/c2

  42. Physics at CMS

  43. New Physics Measurements at LHC • Standard Model Higgs • Low mass region:Htt ! bbbbWW • Supersymmetric (SUSY) Higgs • Charge Higgs (H+):tt ! bH+ bW !bbW, tH+! btt ! bbbWW, tbH+! bbtt ! bbbbWW • Heavy Neutral Higgs (H/A):bbH/A !bb • SUSY squarks • Stop: tt ! bb ± ±!bbWW0 0 tt ! tt 0 0!bbWW0 0 • Sbottom: gg ! bb bb !bbbb0 0 Essential for the understanding of the nature of new discoveries at LHC ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ • b-quarks in final state • Backgrounds from tt ! bbWW production Common to signatures:

  44. Searching for new physics with double-tags Precise test of SM Top is a major background for most new physics • Identification of high-PT b-quarks (b-tagging) • Develop algorithms • Measure efficiency • Top cross section • LHC is a top quark factory • New physics to explore • Light Higgs (Htt) • SUSY Higgs (H+, H/A) • Third generation squarks Signature based analysis >= 2 b-jets + leptons + missing energy (8 million tt events in first year)

  45. _ _ _ Light Higgs Search: ttH  ttbb Likelihood based CMS study • Good b-tagging essential • eb  60% • Backgrounds: • ttbb, ttjb, ttjj • Reduced by reconstructing both top quarks • Complementary to H , • Best channel to measure H  bb coupling MH < 130 GeV/c2 4 b-jets _ _ _ _

  46. Summary Large top quark sample are now available Top Cross Section (single b-tag): Top Cross Section (double b-tag): (54 events) Top Mass: 172.7  2.9 GeV/c2 High precision measurements coming next! 1 fb-1 results in Summer 2006 The LHC is a top factory Calibration tool Background Probe for new physics Top quark

  47. Backup Slides

  48. Increasing B-Tagging Efficiency from tuning Add’l signal • Include event-by-event primary vertex (20%) • Re-optimize tagger parameters (15%) • Add L00 tracks (5%) • Overall 44% increase of efficiency

  49. Measuring B-Tagging Mistag Rate • Use negative L2D tags in jet data to predict mistags • Parameterize negative tag rate in • Jet ET • Number of tracks in jet • Jet h • Jet f • Event  ET • Correct for HF in negative tail and long-lived LF (aLF)

  50. Controlling B-Tagging Mistag Rate Vertex x vs y (cm) Beam Spot • Reduced azimuthal asymmetry due to beamline offset • Reduced tags due to conversions and material interactions by 50% • Maintained mistag rate ~0.5% per jet Center of SVX

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