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First Run II Measurement of the W Boson Mass with CDF

First Run II Measurement of the W Boson Mass with CDF. Oliver Stelzer-Chilton University of Oxford. on behalf of the CDF Collaboration. Rencontres de Moriond EW 2007 La Thuile , Aosta Valley, Italy , March 11 – 18, 2007. Outline. Motivation W Production at the Tevatron Analysis Strategy

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First Run II Measurement of the W Boson Mass with CDF

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  1. Oliver Stelzer-Chilton - Oxford First Run II Measurement of the W Boson Mass with CDF Oliver Stelzer-Chilton University of Oxford on behalf of the CDF Collaboration Rencontres de Moriond EW 2007 La Thuile, Aosta Valley, Italy, March 11 – 18, 2007

  2. Oliver Stelzer-Chilton - Oxford Outline • Motivation • W Production at the Tevatron • Analysis Strategy • Detector Calibration • Momentum Scale • Energy Scale • Recoil • Event Simulation • Results • Summary/Outlook

  3. Oliver Stelzer-Chilton - Oxford Motivation • Derive W mass from precisely measured electroweak quantities • Radiative corrections r dominated by top quark and Higgs loop allows constraint on Higgs mass Current top mass uncertainty 1.2% (2.1 GeV)  contributes 0.016% (13 MeV) to MW Current W mass uncertainty 0.036% (29 MeV)  Higgs mass predicted: 85+39-28 GeV • Progress on W mass uncertainty now has the biggest impact on Higgs mass constraint • With improved precision also sensitive to possible exotic radiative corrections

  4. Oliver Stelzer-Chilton - Oxford W Production at the Tevatron Quark-antiquark annihilation dominates (80%) precise charged lepton measurement is the key (achieved ~0.03%) Recoil measurement allows inference of neutrino ET (restricted to u<15 GeV) Use Z and Zee events to derive recoil model Combine information into transverse mass:

  5. Oliver Stelzer-Chilton - Oxford Measurement Strategy W mass is extracted from transverse mass, transverse momentum and transverse missing energy distribution Fast Simulation • NLO event generator • Model detector effects W Mass templates Detector Calibration 81 GeV • Tracking momentum scale • Calorimeter energy scale • Recoil 80 GeV Data + Backgrounds Binned likelihood fit W Mass

  6. Oliver Stelzer-Chilton - Oxford CDF Detector • Silicon tracking • detectors • Central drift • chambers (COT) • Solenoid Coil • EM calorimeter • Hadronic • calorimeter • Muon scintillator • counters • Muon drift • chambers • Steel shielding h = 1.0 h = 2.0  h = 2.8

  7. Oliver Stelzer-Chilton - Oxford Tracker Alignment • Internal alignment is performed using a large sample of cosmic rays  Fit hits on both sides to one helix • Determine final track-level curvature corrections from electron-positron E/p difference in We decays • Statistical uncertainty of track-level corrections leads to systematic uncertainty MW= 6 MeV

  8. Oliver Stelzer-Chilton - Oxford Momentum Scale Calibration Exploit large J/ and Upsilon datasets to set tracker scale Tune model of energy loss  J/ independent of muon pT Apply momentum scale to Z’s MW= 17 MeV Z→μμ Υ→μμ good agreement with PDG (91187±2 MeV) • Data • Simulation Tune resolution on width of di-muon mass peaks • Data • Simulation MW= 3 MeV

  9. Oliver Stelzer-Chilton - Oxford Energy Scale Calibration Transfer momentum calibration to calorimeter using E/p distribution of electrons from W decay by fitting peak of E/p Tune number of radiation lengths with E/p radiative tail Correct for calibration ET dependence Tune resolution on E/p and Z mass peak p E Apply energy scale to Z’s W→eν Z→ee good agreement with PDG (91187±2 MeV) • Data • Simulation • Data • Simulation Add Z Mass fit to calibration (30% weight) MW= 30 MeV MW= 9 MeV

  10. Oliver Stelzer-Chilton - Oxford Hadronic Recoil Definition Recoil definition: Vector sum over all calorimeter towers, excluding: - lepton towers - towers near beamline (“ring of fire”) Electrons: Remove 7 towers keystone MW= 8 MeV Muons: Remove 3 towers (MIP) MW= 5 MeV Model tower removal in simulation

  11. Oliver Stelzer-Chilton - Oxford Hadronic Recoil Model Calibration • Use Z balancing to calibrate recoil energy scale and to model resolution • Calibrate scale (R=umeas/utrue) with balance along bisector axis MW= 9 MeV • Resolution has two components -soft (underlying event) -hard (jets) • Calibrate along both axes,  &  MW= 7 MeV • Data • Simulation     u • Data • Simulation

  12. Oliver Stelzer-Chilton - Oxford Recoil Model Checks • Apply model to W sample to check recoil model from Z’s • Recoil projection along lepton u||  directly affects mT fits  Sensitive to lepton removal, scale, resolution, W decay • Data • Simulation • Recoil distribution  sensitive to recoil scale resolution and boson pT • Recoil model validation plots confirm consistency of the model • Data • Simulation

  13. Oliver Stelzer-Chilton - Oxford Boson pT Model • Model boson pT using RESBOS generator [Balazs et.al. PRD56, 5558 (1997)] • Non-pertubative regime at low pT parametrized with g1, g2, g3 parameters • Data • Simulation • g2 parameter determines position of peak in pT distribution • Measure g2 with Z boson data (other parameters negligible) • Find: g2 = 0.685±0.048 MW= 3 MeV • Data • Simulation

  14. Oliver Stelzer-Chilton - Oxford Background %(Muons) %(Electrons) Hadronic Jets 0.10.1 0.250.15 Decay in Flight 0.30.2 - Cosmic Rays 0.050.05 - Zll 6.60.3 0.240.04 W 0.890.02 0.930.03 Production, Decay and Backgrounds • QED radiative corrections: - use complete NLO calculation (WGRAD) [Baur et.al. PRD59, 013002 (1998)] - simulate FSR, apply (105)% correction for 2nd MW= 11 (12) MeV for e () • Parton Distribution Functions: - affect kinematics through acceptance cuts - use CTEQ6 ensemble of 20 uncertainty PDFs MW= 11 MeV • Backgrounds: - have very different lineshapes compared to W signal - distributions are added to template - QCD measured with data - EWK predicted with Monte Carlo MW= 8 (9) MeV for e ()

  15. Oliver Stelzer-Chilton - Oxford W Mass Fits Transverse mass fits: Muons Electrons mW = 80417 ± 48 MeV (stat + syst) combination yields P(2) = 7%

  16. Oliver Stelzer-Chilton - Oxford Muon ET fit W Mass Fits Also fit ET and ET distributions in muon and electron channel and combine with transverse mass fits: Electron ET fit mW = 80413 ± 48 MeV (stat + syst) combination of all six fits yields P(2) = 44%

  17. Oliver Stelzer-Chilton - Oxford Systematic Uncertainty Systematic uncertainty on transverse mass fit ⇒Combined Uncertainty: 48 MeV for 200 pb-1

  18. Oliver Stelzer-Chilton - Oxford Results • New CDF result is the world’s most precise single measurement • World average increases: 80392 to 80398 MeV • Uncertainty reduced ~15% (29 to 25 MeV) • Standard Model Higgs (LEPEWWG) constraint: 80+36-26 GeV (previous: 85+39-28 GeV)

  19. Oliver Stelzer-Chilton - Oxford Summary/Outlook • First Run II W mass measurement completed using 200 pb-1 of data • With a total uncertainty of 48 MeV  worlds most precise single measurement • Projection from previous Tevatron measurements • Expect MW < 25 MeV with 1.5 fb-1 already collected

  20. Oliver Stelzer-Chilton - Oxford Backup

  21. Oliver Stelzer-Chilton - Oxford Standard Model Higgs Constraint • Previous SM Higgs fit: - MH = 85+39-28 GeV - MH < 166 GeV (95% CL) - MH < 199 GeV (95% CL) Including LEPII direct exclusion • Updated preliminary SM Higgs fit: - MH = 80+36-26 GeV(M. Grünewald, private communication) - MH < 153 GeV (95% CL) - MH < 189 GeV (95% CL) Including LEPII direct exclusion

  22. Oliver Stelzer-Chilton - Oxford Systematic Uncertainty

  23. Oliver Stelzer-Chilton - Oxford Signed 

  24. W Mass Measurement pTW = 0 pTW ≠ 0 measured mT • Insensitive to pTW to 1st order • Reconstruction of pTν sensitive to hadronic response and multiple interactions pT • Less sensitive to hadronic response modeling • Sensitive to W production dynamics Oliver Stelzer-Chilton - Oxford

  25. Oliver Stelzer-Chilton - Oxford Response and resolution In EM calorimeter Energy loss into hadronic calorimeter Electromagnetic Calorimeter Energy loss in solenoid Track reconstruction In outer tracker Bremsstrahlung and Conversions in silicon Full Electron Simulation

  26. Oliver Stelzer-Chilton - Oxford Consistency of Radiative Material Model • Excellent description of E/p tail • Radiative material tune factor: Smat=1.0040.009stat0.0002bkg • Z mass reconstructed from electron track momenta • Data • Simulation geometry confirmed: Smat independent of || • Data • Simulation Measured value in good agreement with PDG

  27. Oliver Stelzer-Chilton - Oxford Lepton Removal • Estimate removed recoil energy using towers separated in Φ • Model tower removal in simulation Muons: Remove 3 towers (MIP) MW= 5 MeV Electrons: Remove 7 towers keystone (shower) MW= 8 MeV

  28. Oliver Stelzer-Chilton - Oxford Hadronic Recoil Response Calibration • Project vector sum of pT(ll) and u on orthogonal axes defined by lepton directions • Use Z balancing to calibrate recoil energy scale • Mean and RMS of projections as a function of pT(ll) provide information for model parameters Hadronic model parameters tuned by minimizing 2 between data and simulation MW= 9 MeV • Data • Simulation

  29. Oliver Stelzer-Chilton - Oxford Progress since 1995 2007 direct mt and mw 2007 indirect mt and mw 1995 indirect mt and mw 1995 direct mt and mw

  30. Oliver Stelzer-Chilton - Oxford Momentum Scale Calibration Central Outer Tracker: Open-cell drift chamber • Use clean sample of cosmic rays for cell-by-cell internal alignment • Fit COT hits on both sides simultaneously to a single helix • Measure cell tilts and shifts

  31. Oliver Stelzer-Chilton - Oxford Alignment Example Cell shift (microns) Final relative alignment of cells ~5m (initial alignment ~50m)

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