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

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

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

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

Tevatron W/Z cross-sections sW(m) 2768±16±64±166 sW(e) 2780±14±60±167 sW(e+m) 2775±10±53±167 sW(NLLO) 2687±54 sZ(m) 248.0±5.9±7.6±14.9 sZ(e) 255.8±3.9±5.5±15.4 sZ(e+m) 254.9±3.3±4.6±15.2 sZ(NLLO) 251.3±5.0 R(m) 11.12±0.27±0.18 R(e) 10.82±0.18±0.16 R(e+m) 10.92±0.15±0.14 R(NNLO) 10.69±0.08 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 ratio statistical 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

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

LHC W/Z cross-sections 50pb-1 1fb-1 sW(m) ±0.2%±3% ±0.04%±2.3% sW(e) ±0.2%±5% ±0.04%±2.5% sZ(m) ±0.7%±4% ±0.2%±2.4% sZ(e) 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) 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 UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

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

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

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

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

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 data eg <Nch> vs pt Will disappear from Tevatron mass measurements? UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

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

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

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

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

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 dMt ISR 0.1 FSR b-fragmentation 0.3 UE estimate 1.3 Mass scale calibration 0.9 1.6GeV UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009

LHC Top mass summary dMt GeV Dominant error Semileptonic (kinematic fit) ~1 (~3.5GeV) FSR+light and b-jet energy scales~1% (5%) Semileptonic high pt 1.6 Calibration+UE Di-leptons PDFs (statistical~0.3GeV) Multijet 3.0 JES ISR/FSR J/Y 1.5 Statistics 50fb-1+theoretical errors Semileptonic channels we have already discussed. Di-leptons are characterised by tow high pt isolated leptons, large Et-miss and two b-jets. Get ~400k events for 10fb-1 Cuts are: two opposite leptons with pt>35Gev and 25Gev in eta<2.5, et-miss>40GeV and two jets with pt>25GeV. Get 80K signal with a S/B~10 Backgrounds are Drell-Yan, Z->tautau+jets, WW+jets and bbbar production. To find top mass do kinematic fit using various input top masses. The weights of the best solution for a given top mass are found. For each top mass the mean weight over all events is found, the maximum average weight corresponds to the measured mass. Efficiency-purity is 97.6%-73%. Constraints are conservation of pt in ttbar system assuming pt=0; lnu systems are constrained to Mw; lnuj systems are constrained to Mtop, used as an input. Multi-jet channel, S/B=3x10-8 at production. Kinematic cuts get to S/B=1/19 and after kinematic fit and x-sq cut get 1/2.6, and finally limiting the mass window to 130-200GeV, get 6/1. The efficiency for ttbar is 0.18% but large statisitcs allow for this still giving 6660 events/10fb-1. The top mass can be measured in a number of different ways, that mostly have different dominant systematic errors so that combinations of these measurements, and combinations of the expts should certainly allow the top mass error to get below ~1 GeV. 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

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

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

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

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

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

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

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

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

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

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

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

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

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

Principal References Tevatron References: LHC 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

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

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

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

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

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

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

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

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

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

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

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) Mtop [GeV] 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. AcerMC+PYTHIA AcerMC+PYTHIA MC-Truth MC-Truth MC-level Plots For semi-leptonic tt events (Cone DR=0.4 truth jets) _ UK HEP Forum: From the Tevatron to the LHC, Cosners House, May 2009