WZ and top physics at ATLAS and CMS Ellie Dobson With main focus on W/Z inclusive cross sections

Ingredients for the measurement Results shown are on data collected between March and June Analyses presented today (ICHEP and HCP) have processed between 10 nb -1 and 1pb -1 (with 11% uncertainty on luminosity) 100 nb -1 corresponds to…. – ~ 2000 leptonic W events – ~ 200 leptonic Z events – ~ 5 semi leptonic top events – ~ 1 fully leptonic top event Of course to decrease once selection cuts are applied!

Event cleaning After initial good run selection, additional cleaning cuts trained on data to remove suspicious events: Events seen to reduce the non Gaussian tails in EtMiss without loss of core resolution - must ensure that cuts do not remove any MC noise bursts coherent noise out of time jets beam halo cosmics beam scrape

Electrons for analysis Common cut variables L1 Electron/photon trigger, track-cluster matching, shower shape, conversion veto ATLAS specific Transition radiation veto to reject conversions and pions Forward electrons also used with alternate clustering alg CMS specific High Level Trigger also implemented Isolation criteria implemented (ΔR=0.3) Electron sources W/Z decays Heavy flavour decays Conversions Fakes from charged hadrons Reconstruction algs cut on variables to separate signal from background First data used to validate these variables

Muons for analysis Common cut variables L1 muon trigger, tracking and muon detector information, isolation cuts, originating from IP ATLAS specific Wider Zμμ peak in data than expected - widened resolution in muon endcap track seen wrt ID track, hinting at alignment issues CMS specific HLT implemented on L1 candidates Additional punch-through veto Both inside out and outside in reconstruction req Muon sources W/Z decays Heavy flavour decays pi/K decays in flight Punch through Reconstruction algs cut on variables to separate signal from background First data used to measure efficiency and response (compare ID and Sp info)

MEt for analysis Common MEt reconstruction techniques ATLAS specific Sum over 3D topological clusters over threshold (with a correction for muon P T ) Apply calibration for objects associated with jets, dead material, out of cone deposit… CMS specific Particle Flow MEt (reconstructs objects and calibrates accordingly) used Tracking based MEt also considered MEt sources W decays Badly measured jet events Cosmic rays Punch through In top and W analysis, cut on MEt to separate signal from background First data used to measure MEt response and train calibration algorithms

Reconstructed using anti K T algorithm with R=0.4/0.5 Use 3-D noise-suppressed clusters of cells as input Simple calibration determined from MC Jets for early analysis

WZ physics programme at the LHC 100μb -1 1nb -1 10nb nb -1 1pb -1 10pb pb -1 1fb -1 and beyond…. WZ candidate hunting Inclusive cross sections Differential cross sections Boson + jets cross sections Ratios: W/Z, W+/W- Lumi measurement Theory model testing (low x) Calibration and alignment Background to BSM physics Boson + jets candidate hunting PDF constraints

Hunting the…..W ATLAS specific Remove events where cluster falls into dead calorimeter region (5% acceptance loss) QCD MC after preselection seen to overestimate data by a factor ~2: normalise MC to this factor Drell Yan veto in electron channel (larger calorimeter acceptance) Common cut variables Single lepton trigger, primary vertex with N tracks, tight lepton selection, MEt>25, M T >40

Hunting the Z ATLAS specific Medium lepton selection (as opposed to tight as in the W case) 66<Mz<112 CMS specific Looser quality cuts applied on the second muon than the first Electron selection looser than in Wenu 60<Mz<120 Common cut variables Single lepton trigger, primary vertex with N tracks, two leptons of opposite charge

Estimating background: electrons MC used to estimate EW contribution CMS specific Fit MET with signal and QCD background shapes where absolute normalisation is floated but shapes are taken from MC ATLAS specific Template fit to electron isolation distribution with loose-tight scaling factor from simulation - QCD Background to Z in ATLAS estimated by measuring with loose electron requirements and applying scaling factor loose-medium 1.1±0.2±0.4 QCD events (out of 46 Wenu candidates)

Estimating background: muons MC used to estimate EW BG QCD BG to Z ATLAS specific ‘ABCD’ method in MEt/track isolation - sensitive to bad reco & pion/kaon decays Also study reversing isolation cuts and normalise using MEt distribution 0.9±0.3±0.6 QCD events (72 Wmunu candidates) CMS specific Template binned likelihood fit in M T - shapes obtained by using a reversed isolation cut

Acceptance (generator level) ATLAS specific PYTHIA with MRSTLO* PDF Systematic uncertainty of 3%: compare to datasets with CTEQ6.6 and HERAPDF1.0 (dominated by differences) CMS specific POWHEG NLO + CTEQ 6.6 (NLO) Systematic uncertainty of ~3%: compare to datasets with CTEQ6.6, MSTW08NLO, NNPDF2.0 and treatment of ISR, FSR, and scale (dominated by PDF uncertainty) Number of events at Born level passing fiducial requirements (MEt, lepton P T and η) Other tools used FEWZ : complete NLO, NNLO XS ResBos : NNLL resummation + NNLO k- factor HORACE : full 1-loop EW corrections PHOTOS : final-state QED showering

Detection efficiency in ATLAS C factor calculated from MC but scale factors (~0.98) applied for data-MC discrepancy in muons - includes trigger, reconstruction, detector response for leptons and MEt, charge misID, additional selection cuts In W analysis electron efficiency lower in data than in MC (10% systematic assigned in Z XS) - due to bad description of some electron identification variables Systematic evaluation and scale factors on C factor Trigger efficiency (muons): change matching tolerance and compare different data streams Reconstruction efficiency: - material, dead calo regions and ID variables (electrons) - residual pi/K (muons) - compare muon tracks seen in inner and muon detector Lepton response: smear with measured lepton response MEt response: vary energy scale, smear with resolution, pile-up, dead calorimeter regions

Detection efficiency in CMS C factor calculated from MC but scale factors (~0.98) applied for data-MC discrepancy - includes lepton trigger, reconstruction, response, isolation, charge MisID for leptons - other factors (MEt) applied as additional systematic Systematic evaluation and scale factors on C factor Trigger efficiency: compare leptons triggered by different trigger (jet, tau, MB) Reconstruction efficiency: - comparison with Z tag and probe - compare tracks seen in inner and muon detector Isolation: Random cone technique (see next slide) Charge symmetry: Study photon conversions MEt response: template fitting of hadronic recoil (see next slide)

Systematic uncertainty case study I MET shape uncertainty in CMS - Convolve recoil response model with MC W PT spectrum and fit to data Method gives best-fit recoil parameters & error Indicate that response discrepancies up to 10% cannot be excluded (although small impact on XS) Findings consistent with photon+jet studies

Systematic uncertainty case study II Build eta/phi cones around MC leptons and measure activity ‘behind’ lepton Build cones in data (ignoring lepton direction) Find bias (~0.5%) in activity Random cone technique in CMS - Data driven correction to isolation cut

Systematic uncertainty case study III MS Hit method in ATLAS (similar in CMS): - Orthogonal measurement of efficiency to tag and probe in Z Select a control sample of tagged ID tracks Extrapolate each track to a muon tube hit in the muon spectrometer Define efficiency as the fraction of selected tracks matched to a muon hit To remove decay in flight muons, use templates of hit residuals for prompt and decay in flight (single pion) samples.

Summary of systematic uncertainties I ATLAS, ~17-200nb -1

Summary of systematic uncertainties II CMS, ~200nb -1

Cross section extraction channel (lumi)N cand N background cross section (nb) Wenu (17 nb -1 )462.6 ± ± 1.3 (stat) ± 0.7 (sys) ± 0.9 (lum) Wmunu (17 nb -1 )725.3 ± ± 1.3 (stat) ± 0.8 (sys) ± 1.1 (lum) Zee (219 nb -1 ) ± ± 0.11 (stat) ± 0.10 (sys) ± 0.08 (lum) Zmumu (229 nb -1 ) ± ± 0.10 (stat) ± 0.07 (sys) ± 0.10 (lum) channel (lumi)cross section (nb) Wenu (198 nb -1 ) 9.34 ± 0.36 (stat) ± 0.70 (sys) ± 1.03 (lumi) Wmunu (198 nb -1 ) 9.14 ± 0.33 (stat) ± 0.58 (sys) ± 1.00 (lumi) Zee (198 nb -1 ) (stat) (sys) ± 0.10 (lumi) Zmumu (198 nb -1 ) (stat) (sys) ± 0.10 (lumi) ATLAS CMS Numbers already beginning to look systematics limited!

All cross sections on the lower side of expectation but are consistent with SM prediction Comparison with theory: ATLAS Reference cross sections NNLO in QCD using FEWZ with MSTW2008 PDF Uncertainty of 4% estimated using PDF error eigenvectors at 90% CL, NNLO HERA PDF1.0 α s variations and normalisation and scale variation.

Comparison with theory: CMS Reference cross sections FEWZ (NNLO) with MSTW 2008 used to calculate reference cross sections Uncertainty of ~4% evaluated All cross sections on the lower side of expectation but are consistent with SM prediction

W asymmetry Yields information about PDFs (W+ favoured in proton-proton collisions) Measurements requires correction for reconstruction for + and - leptons Results seen in ATLAS and CMS both consistent with MC expectations

To the future…WZ+jets Analysis thus far still at the observation phase Differential distributions for numbers of events measured Results seen in ATLAS and CMS both consistent with MC expectations

Top physics programme at the LHC 100μb -1 1nb -1 10nb nb -1 1pb -1 10pb pb -1 1fb -1 and beyond…. Top candidate hunting Top cross sections b tag commissioning Theory model testing Background to BSM physics Cross calibrate JES

Hunting the top Selection (preselection as in WZ) Semi leptonic channel - 1 medium isolated lepton with b layer hit - >=4 jets (>=1 b tag) - MEt> 30 GeV Leptonic - 2 medium isolated lepton with b layer hit - >= 2 jets - MEt> 20 GeV - Z boson veto using mass cuts At HCP…. ATLAS: 2 (7) (semi) leptonic top candidates (295nb -1 ) CMS: 4 (7) (semi) leptonic top candidates (840pb -1 ) Muon Pt=60 GeV Electron Pt=80 GeV 2 jets, 1 b-tag MET=49 GeV

Background and b tagging Using b tagging reduces greatly the background (although severely reduces stats)

Background estimation methods - W+jets estimated from MC (in future will use W+i/W+i+1 jet ratio) - QCD estimated by using fake rates in a QCD enhanced control (low MET or non-isolated) region and extrapolating to signal region - Drell Yan background outside Z veto region estimated using events inside region (CMS) Extrapolating QCD measured in non isolated region to that in isolated region Main backgrounds from W+jets and QCD (and Drell Yan for leptonic channel)

Conclusions WZ cross sections and asymmetry have been measured - Values consistent with SM expectations WZ measurement already approaching a systematics limited one First top candidates have been seen Observed number of top candidates consistent with expectation