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Electroweak and Top Physics at the Tevatron and LHC

This presentation focuses on the measurements of electroweak and top quark physics at the Tevatron and LHC. Topics covered include W/Z cross-sections, top mass, top cross-section, and single top production. Precision measurements, systematic uncertainties, and the role of PDF uncertainties are discussed.

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Electroweak and Top Physics at the Tevatron and LHC

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  1. From Tevatron to the LHC: W/Z and top physics Craig Buttar University of Glasgow UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  2. Topics Outline Focus on some electroweak and top quark measurements at the Tevatron and LHC, other topics were covered by Emily Can LHC extend precision of measurements What does Tevatron tell us? • W/Z cross-section • Top mass • Top cross-section • Single top UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  3. LHC 14TeV  10TeV Gain at 14TeV (10TeV) • W/Z production LHC ~x8 (x5) Tevatron • Top productionLHC~x100 (x50) Tevatron UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  4. W/Z xsect UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  5. Tevatron W/Z cross-sections Precision measurement of cross-section with statistical errors ~ 0.5-1.7% and systematic errors ~2-3%Acceptance uncertainties dominated by PDF ~1.5% Limiting factor is luminosity ~6% For 8fb-1 statistical error ~ 0.05-0.17% Both luminosity and PDF systematic error are reduced in the ratiostatistical error ~1.3%systematic error ~1.3% NNLO theoretical errors on cross-section at the level of 2%on the ratio error~0.7% as PDF uncertainties cancel PDF error changes with acceptance region CDF cross-sections (pb) for 72pb-1 UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  6. Tag & Probe • Tag and probe methods used to determine reconstruction and trigger efficiencies from data • Improve systematics with increased data Electron identification Muon reconstruction efficiency UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  7. LHC W/Z cross-sections Systematic uncertainty at 1fb-1 dominated by theoretical uncertainties in acceptance: ISR~2.0%, 0.4% KT, UE 0.2%, PDF 0.9% Likely to improve with measurements at LHC – difficult to quantify Uncertainty on efficiencies improve 2-0.4% from 50b-1 to 1fb-1 as efficiencies are based on data eg tag and probe Luminosity ~5-10% at start-up Dedicated experiments eg ALFA will reduce lumi error Remember CDF? statistical errors ~ 0.5-1.7% and systematic errors ~2-3% • Early running • W-channels • Higher statistics • Systematic dominated by background at 50pb-1 • Z-channels • Lower statistics • systematic dominated by efficiency (2-leptons) • background suppressed (2-leptons) UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  8. W/Z cross-section • Tevatron precision measurements dominated by systematics ~2-3% and luminosity ~6% • LHC statistical error at 1fb-1 ~ Tevatron at 8fb-1 • Systematics comparable to Tevatron due to theoretical uncertainty on acceptance • This may improve but difficult to quantify • Tag & Probe allows for robust efficiency estimates with data, scales with luminosity • LHC luminosity ~2-3% using dedicated forward physics expts • Systematics limited by luminosity and the effect of PDF uncertainty on the acceptance • What do measure from W/Z cross-sections: PDFs, luminosity…? UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  9. Top UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  10. Top mass Precision top mass measurement is required for EW fits to predict MH and then confirm consistency of Standard Model • For equal contribution to MH uncertainty: DMt< 2 GeV  DMW < 15 MeV Can get dMH/MH~30% Important cross-check with direct measurements UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  11. Top mass Tevatron • Most precise CDF top mass measurement • 3.2fb-1 using ME and in-situ Wjj 0.3%stat 0.6% syst UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  12. Colour reconnection • Colour reconnection is part of the soft part of the underlying event • Implemented in new PYTHIA MPI model (6.3 onwards) • Not in conventional tevatron UE tunes • Will be critical to tune from dataeg <Nch> vs pt • Will disappear from Tevatron mass measurements? UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  13. Top mass from cross-section • What top mass is measured? • Input to EW fits is the pole mass • Fits from templates and matrix elements are related to MC variables • Not well defined mass, same for all generators? • Can define mass as a function of cross-section in well defined renormalisation scheme,  well defined measurement of pole mass • Current measurements give dmt~4% cf 1% UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  14. How well can the Tevatron do? UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  15. LHC top mass measurement Semi-leptonic Channel with b-tagging L > 1fb-1 Initial JES ~ 5% • b-jet JES systematic ~3.5GeV • Light-jet JES systematic ~ 1GeV Use W-jj to get 1% light jet and model difference to get b JES Ultimately get to ~ 0.2GeV light quark JES ~0.7GeV for b-quark JES (total JES ~ 0.7GeV cf CDF analysis with W->jj in-situ ~0.6GeV Geometric method UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  16. Top mass via J/Y Method measures direction and momentum of b-quark from Y Reconstruct M(Y+l) Uses well measured leptons and avoids JES systematics Limited in statistics Relies on simulation to determine Mt M(Y+l) UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  17. High-pt top PT>200GeV ~2% for stt ~15k events/10fb-1 • Reconstruct collimated hadronic decay top in large cone directly from calorimeter cells ( • Calibrate the mass using W->jj • Sensitive to the underlying event • Can be removed by looking at UE in data • Avoids effects of jet reconstruction but still subject to calibration errors UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  18. LHC Top mass summary Can achieve results comparable to the Tevatron, but need control JES Larger cross-section allows some techniques to be used that avoid JES UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  19. Top mass from cross-section at the LHC Need to measure cross-section ~3% to get mass at 0.6% (1GeV) UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  20. Tevatron Top xsect • CDF combined xsect • Stat 4.3% • Sys 5.7% • Lumi 5.7% • Total ~9% • Sys dominated by • JES • Heavy flavour model in MC • B-tagging in MC • lumi UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  21. Top Cross-section at the LHC Semi-leptonic channel Dilepton channel for 10fb-1 UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  22. Top summary and conclusions • Top well understood at Tevatron • Top mass constrained ~1GeV  for EW fits the issue is now Mw • Top mass needs to be understood • LHC with 1fb-1/expt can achieve dmt~3.5GeV with JES 5% (dmt~1GeV JES 1%) • LHC has access to rare methods that may help understand mass better • The issue of what top mass is measured • Cross-section measurements can provide well defined mass measurements • Cross-section errors are too large for precision • Tevatron has given LHC a new precision “standard candle” • Can we use this measure the b-jet JES for other analyses? UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  23. Single top at the Tevatron Use multivariate discriminators to identify different channels Combination gives 5s discovery Key channel for Higgs searches UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  24. Single top observation at Tevatron Use multivariate discriminators to identify different channels Combination gives 5s discovery UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  25. Single top at LHC • Background are: • W+jets • Tt • As at Tevatron require multivariate analysis to reduce backgrounds ln+2b+X Sensitive to NP ln+b+jets tt-like ln+b+jets UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  26. Single top at LHC • t-channel results for 1fb-1 • Principal systematic, background from tt background • Use BDT UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  27. Single top at the LHC • s-channel • Most challenging, small signal • W+jet and tt background • t-channel • tt-like signal UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  28. Single Top summary • Tevatron has observed single top making a combined measurement of s and t channels and using multivariate analysis • At LHC can observe individual channels, with varying degrees of precision • LHC has carried over multivariate analysis techniques UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  29. Summary and conclusions • Increased cross-sections help with • Rare processes: Single top • Avoiding JES: top mass from high PT and M(Yl) • Tevatron has provided LHC with another “standard candle” -- top • Mass well known • Can LHC use it to measure b-JES • Cross-section measurements may be needed to determine the mass • Tevatron has observed single top with combined measurement • LHC can observe individual channels, with varying precision • Many LHC systematics currently based on uncertainties in models: ISR, UE etc, likely to come down with data UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  30. Good ideas help UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  31. Backup slides UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  32. Principal References • Tevatron References: • CDF public pages: http://wwwcdf.fnal.gov/physics/physics.html • D0 public pages: http://wwwd0.fnal.gov/Run2Physics/WWW/results.htm • LHC • ATLAS: Expected performance of the ATLAS experiment: detector, trigger and physics: arXiv 0901.0512 (All results for 14TeV unless otherwise stated) • CMS: Physics TDR UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  33. Determining the jet energy scale Determine jet-energy scale (JES) uncertainty using in-situ methods • Z-jets10GeV<Pt<100-200GeV1% statistical uncertainty on JES with 300pb-1Systematics: ISR/FSR+UE ~5-10% at low Pt, reducing to 1-2% for Pt~100-200GeV • g-jets100-200<Pt<500GeV1-2% statistical uncertainty on JES with 100pb-1systematics from physics effects: ISR/FSR+UE ~ 1-2% UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  34. DIS09 top review UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  35. W and Z inclusive production • Well understood theoretically • Dominant uncertainty is due to PDFs • For 1fb-1 • Ds/s(ppZ+Xmm+X)=0.13±2.3±10% • Ds/s(ppW+Xmn+X)=0.04±3.3±10% Tracker efficiency PT (LONLO) Muon efficiency Trigger efficiency MET PT(LONLO) Stat sys lumi Equivalently can use to evaluate luminosity at the level of 6-7% UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  36. Z-afb UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  37. Measurement of Afb in Z-decays and determination of sin2θefflept(MZ2) AFB = b { a - sin2θefflept( MZ2) } Measure Afb with leptons in Z0 DY events Can fit with Mt to constrain MH a, b calculated to NLO QED and QCD. Need to define direction At the Tevatron -- well defined qq pdfs  low z-boost Match q+l+ q qbar • At LHC no asymmetry wrt beam • Assume that there is a • Q-qbar collision  large Z-boost • quark direction from y(ll) • Requires measurement at high y(ll) Q qbar UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  38. Why measure Afb • Precision measurement of Afb can give precison measurement of sintheta – which contains higher order terms – , together with a precison measurement of mt, this provides a constraint on the Higgs mass UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  39. D0 Run-II Afb result and sin2θefflept(MZ2) UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  40. ATLAS study of Afb • 100fb-1 measurement • Not a day-1 measurement • 2 classes • C-C central electrons with tracker • C-F central electron and forward electron • Need forward electrons for statistics • 2.5<|h|<3.2 • No tracking information Select only |h|>1 to reduce Sq-Sqbar background Q qbar UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  41. ATLAS sinthetaW C-F one central electron |h|<2.5 + forward electron |h|<4.9 C-C two central electrons |h|<2.5 Statistical error for LHC with 100fb-1 (1yr at 1034cm-2s-1) x10 better than Tevatron UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  42. Effect of underlying event in jet reconstruction Z+jets Events Fragmentation reduces the amount of energy in jet cone UE adds energy to the hadron level jet • Underlying event and fragmentation have the opposite effect • Precise behaviour depends on the jet algorithm used • Frag. corrections for Cone DR=0.7 jets smaller than for Cone DR=0.4 jets, UE corrections larger due to the larger cone size • KT D=0.4 shows the lowest combined corrections (Frag. and UE effects cancel out). • KT D=0.6 jets is comparable to Cone DR=0.4 jets. • (Except for Cone DR=0.7 jets), non-perturbative effects are negligible for jets with pT>40 GeV (PYTHIA). UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

  43. PYTHIA Params • max. mass: • parp(61)=0.384, mstp(70)= 0 and parp(62)=1.0, parj(81)=0.07 • min. mass: • parp(61)=0.096, mstp(70)=0 and parp(62)=3.0, parj(81)=0.28. MC-level Plots For semi-leptonic tt events (Cone DR=0.4 truth jets) _ Mtop [GeV] Mtop [GeV] - Top Physics • Main goal, so far, has been to estimate uncertainties on reconstructed top parameters from UE (MPI) and ISR/FSR (coupled together) • variations on UE, ISR/FSR affect observables on which selections cuts are applied: jet multiplicity, particles pT etc. • potentially a serious impact on top reconstructed parameters (e.g. Mtop, stT) • ISR and FSR PYTHIA parameters have been varied to give smallest and largest values of reconstructed top mass • Max ISR, Min FSR (LISR*2, ISR cutoff -0.5*ISR cutoff, LFSR*0.5)→ Max Mtop • Min ISR, Max FSR (LISR*0.5, ISR cutoff +0.5*ISR cutoff, LFSR*2)→ Min Mtop • up to ~10% change in the Selection Efficiency from Min-Max Mtop samples • contributing ~10% on syst. uncertainty on early data stT • visible effect on reconstructed Mtop: • MC-Truth: ~5 GeV (hadronic Mtop) and ~1-2 GeV (leptonic Mtop) AcerMC+PYTHIA AcerMC+PYTHIA MC-Truth MC-Truth UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

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