Electroweak Physics at the Tevatron

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1 Electroweak Physics at the Tevatron Adam Lyon / Fermilab for the DØ and CDF collaborations 15 th Topical Conference on Hadron Collider Physics June 2004 Outline Importance Methodology Single Boson Measurements Summary & Outlook W/Z+γ and Diboson Results up next

2 Learning from Electroweak Physics m W, m t, and m H are related Constrain Higgs mass Test of standard model couplings (and see M. Kirby's talk) Study higher order QCD Many uses in detector studies and luminosity determination 2

3 Uncertainties in m W Run 1 uncertainties (from hep-ex/ ) Uncorrelated Uncertainties (MeV/c 2 ) Correlated Systematics (MeV/c 2 ) Source CDF µ CDF e DØ e W statistics Lepton scale Lepton resolution p T (W) Recoil model Selection bias Backgrounds Source CDF DØ PDF & luminosity Radiative corrections Γ W Uncorrelated uncertainties scale with luminosity Correlated systematics improve as theory improves Perhaps can reach 40 MeV/c 2 per channel & exp with 2 fb -1 3

4 Collider: Tevatron for Run II Base goal is 4.4 fb -1 (Design is 8.5 fb -1 ) by end of FY09 4

5 Detectors: CDF Saved from Run I Solenoid Central Calorimeter Central Muon System New/Improved in Run II 8 layer Si tracking ( η < 2) Central Outer Tracker ( η < 1) Plug Calorimeter (1.0 < η < 3.6) Extended muon coverage to η < 1.5 New and improved trigger and DAQ Luminosity ~400 pb -1 on tape Analyses shown here use pb -1 5

6 Detectors: DØ Saved from Run I Hermetic LAr Calorimeter Muon Toroid and proportional drift tubes New in Run II 2T Superconducting Solenoid Inner Tracker (Si Microstrips and Scintillating Fiber tracker) Preshower detectors Upgraded muon system (including better shielding) New and improved trigger and DAQ 6

7 Detectors: DØ Luminosity 370 pb -1 on tape Analysis here use pb -1 7

8 W/Z Production and Event Topology Use clean leptonic decays W ± (energetic lepton + E T ) Z 0 (energetic opposite sign leptons) 8

9 W and Z events are extremely useful Measure cross sections Calibration of detectors, luminosity measurements Lepton universality, W width Measure W and Z properties (p T (W), p T (Z), y(z), lepton angular distributions) Constrain PDFs, fit for couplings, look for new resonances Measure W m T, lepton p T spectra Yields m W, W width W/Z + Jets Backgrounds to Higgs and Top analyses W/Z + γ, Dibosons Probe electroweak gauge structure Backgrounds to New Phenomena searches 9

10 Analysis Methodologies Both DØ and CDF follow similar strategies Triggers: Calorimeter triggers for electrons Track triggers for muons Muon requirements: Track matched to calorimeter MIP trace and/or muon system track Reject cosmics by timing and impact parameter Track and calorimeter isolation Selection: W - a lepton and large missing transverse energy Z - two opposite charge leptons Electron requirements: Isolated EM cluster Shower shape (CDF uses shower max, DØ has finely segmented calorimeter) Track pointing to calorimeter EM cluster Measure identification efficiencies with Z events Measure backgrounds with QCD Dijet events Systematics Luminosity (~6%) PDF (use CTEQ6 and MRST) (1-2%) Lepton ID (~1%) Backgrounds, E scale, Recoil model, Detector Description 10

11 Z ee Cross Section 2 EM objects with p T > 25 GeV/c CDF: central + plug cal ( η < 2.8) DØ: central only Small backgrounds CDF: DØ: QCD Z ττ ± 3.9 stat ± 5.4 ± 15.2 sys lum ± 9 stat ± 9 sys ± 28 lum pb pb 11

12 Z µµcross Section p T cut lowered to GeV/c for muons DØ applies a Drell-Yan correction Very small backgrounds: QCD (b-jets), Z ττ DØ efficient for m µµ > 30 GeV/c ± 5.9 ± 14.9 pb CDF: DØ: stat 6.2 ± sys lum ± 5.0 stat ± 8.9 sys ± 26.2 lum pb 12

13 W eν Cross Section Requirements: 1 electron with E T > 25 GeV E T > 25 GeV (CDF plug analysis used 20 GeV) CDF: central & plug DØ requires η < 1.1 Track match required Backgrounds QCD, Z ee, W τν 13

14 W eν Cross Section CDF (central): CDF (plug): DØ: 2782 ± stat ± 56 ± 167 sys lum pb 2874 ± 34 stat ± 167 sys ± 172 lum 2844 ± 21 stat ± 128 sys ± 284 lum pb pb 14

15 W µνcross Section Require µ p T, E T > 20 GeV Backgrounds: QCD (b-jets), Z µµ, W τν CDF: DØ: 2772 ± stat ± 60 ± 166 sys lum stat ± 100 sys ± pb 3226 ± lum pb 15

16 Cross section comparisons σ Br = ε N N bkg A L dt Experiment Channel # events Purity Lum. (pb -1 ) ε * A η coverage CDF W eν % % 2.8 DØ W eν % % central CDF W µν % % central DØ W µν % % 1.6 CDF Ζ ee % % 2.8 DØ Ζ ee 831 * 98.3% % central CDF Ζ µµ % % central DØ Ζ µµ % % 1.8 * Track match required CDF and DØ are rather similar, except in angular coverage CDF uses plug calorimeter for far e coverage DØ uses forward muon system for far µ coverage 16

17 Infer the W width (Preliminary) ) Use measured W and Z cross sections and R σ ( pp W l ν ) σ ( pp W ) Γ ( Z ) Γ ( W l R = σ ( pp Z ll ) σ ( pp Z ) Γ ( Z ll ) Γ ( W ) Measured (CDF Preliminary) R = ± 0.18 ± e stat R = ± 0.27 ± µ stat Theory (NNLO, PDG) σ ( p p W ) / σ ( pp Z ) = ± sys sys BR ( W l ν ) = ± LEP Γ ( Z ll ) / Γ ( Z ) = (3.366 ± 0.002)% Γ ( W ) = 2071 ± 40 MeV ν 17

18 Analyses with Taus Reconstructing τ leptons is challenging Must use hadronic decays for ID (1 or 3 charged tracks plus π 0 's) But these are hadronic jets; high QCD background Look for tracks in a narrow 10 cone pointing toward a narrow calorimeter cluster Require 30 cone isolation for tracks Reconstruct π 0 's (in shower max for CDF) Require effective mass of tracks and π 0 's to be < 1.8 GeV/c 2 (m τ + resolution) τ ± ( 1or 3) π ± ν + n π 18 0

19 W τν (CDF Run II Preliminary) Start with track + E T trigger 2345 candidates in 72 pb -1 Require Bkg = 612 ± 61 events τ E T > 25 GeV, E T > 25 GeV ε( ID) A= 1.06 ± % No other jets above 5 GeV σ BR ( W τν ) = (2.62 ± 0.07 stat ± 0.21 sys ± 0.16 lum g = 0.99 ± 0.02 ± τ BR ( W ) / g e = τν BR ( W e ν ) stat sys ) nb 19

20 Z ττ Look for 1-prong decays 0 Z ττ (e or µ) νν π ± ν + 0 nπ Look for other τ via e or µ Understand tau ID Important for searches Proof of principle that ττ resonances are seen at the Tevatron CDF: σ ( * p p γ / Z ττ ) = 242 ± 48 stat ± 26 sys ± 15 pb 20

21 Charge asymmetry in W eν Goal is to improve understanding of PDFs using W charge asymmetry Since u quarks on average carry more of the p momentum than d quarks, W + produced in ud W + are boosted along p W - produced in du W - are boosted along p + A d σ ( W ) / dy d σ ( W ) / = yw + d σ ( W ) / dy + d σ ( W ) / dy dy The e ± from the W decay carries information on the W direction, but true W direction cannot be reconstructed due to unmeasured p z of ν Use the e ± direction to measure A yw convoluted with V-A decay distribution Results are sensitive to ratio of PDFs for u and d Do for low and high E T [NEW APPROACH] (at higher e E T, e dir is closer to W dir; less cancellation with V-A) Sensitivity is best at high η where it is least constrained 21

22 Charge asymmetry in W eν Require ee T and E T > 25 GeV 50 < m T < 100 GeV No other EM object with E T > 25 GeV In forward region, use "calorimeter seeded Si tracking" to utilize new forward Silicon This along with drift chamber can determine charge within η < 2 Measure charge mis-id rate with data using Zs < ~1% within η < 1.5 < ~4% far forward Backgrounds Z [MC], W τν[mc], QCD [data] 22

23 Drell-Yan Forward Backward Asymmetry Interference of γ * and Z f = u, d, e Leads to A FB in A FB = d d σ (cos σ (cos θ θ pp > > 0) 0) f f * + Z / γ e e 2 d σ d cos θ = A (1 + cos θ ) + B cos e - + d d σ (cos σ (cos θ q q θ θ θ < < 0) 0) γ* f f Z f + f f f Depends on uuz, ddz and eez couplings Can probe couplings Near the Z resonance, A FB is related to sin 2 θ W New interactions may modify the SM A FB prediction e + 23

24 Drell-Yan Forward Backward Asymmetry CDF Run II Preliminary Require 2 isolated electrons with p T > 20 GeV/c 5211 candidates in 72 pb -1 No asymmetry seen in dijet background Use Collins-Soper reference frame for measuring electron scattering angle Reduces uncertainty in scattering angle due to p T of incoming partons 24

25 Drell-Yan Forward Backward Asymmetry CDF Run II Preliminary Fit for weak mixing angle sin 2 χ 2 θ W = ± stat ± sys / ndf = 12.71/14.0 Fits for couplings are in good agreement with world averages No evidence of new interactions above the Z pole 25

26 High Mass Drell-Yan Spectrum Sensitive to new physics New gauge bosons (e.g. Z'), extra dimensions Run 1 limits surpassed and new models explored 26

27 Summary Current preliminary results consistent with SM (Theory lines NNLO from Hamberg, van Neerven, Matsuura) 27

28 Outlook 1.96 TeV cross sections nearing publication Tevatron electroweak working group will make combinations Stay tuned for further analyses; > 300 pb -1 on tape Preliminary W mass measurements soon 28

29 EXTRAS 29

30 Z ee Cross Section 30

31 Afb Acceptance 31

32 Uncorrected A fb 32