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W and Z properties from the Tevatron

Detailed presentation on the properties of W and Z bosons at the Tevatron collider, including mass measurements, charge asymmetry, and experimental observables. Lepton energy scale calibration, recoil modeling, and QCD tests are explored.

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W and Z properties from the Tevatron

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  1. W and Z properties from the Tevatron Rainer Wallny University of California, Los Angeles on behalf of the CDF and D0 collaborations HCP 2010 24. August 2010 Many thanks to my CDF and DO colleagues who helped to prepare this talk!

  2. Tevatron Luminosity Luminosity delivered ~ 9 fb-1 Luminosity on tape ~ 7.5 fb-1 /experiment ~600k Z’s, ~6 Mio W’s per experiment Expected delivered Luminosity in Run II (by end of 2011) ~ 12 fb-1 “Run III” (2012-14) being considered ~ 2.5 fb-1/year => Darien Wood’s talk on Friday Rainer Wallny -W and Z properties from the Tevatron

  3. QCD W/Z production at the Tevatron (QCD LO) Proton-antiproton collider : s = 1.96 TeV (ppW l) ~ 2700 pb (ppZ0 l+l-) ~ 250 pb • Test QCD (up to NNLO) in production • Hard and soft gluon emission • sensitive to parton distribution functions • Extract electroweak parameters • - sin θw, Mw, quark-boson couplings Rainer Wallny -W and Z properties from the Tevatron

  4. W/Z detection at DØ/CDF CDF • Z events: • pair of charged leptons (+- or e+e-) • - high pT • - isolated • - opposite charge • W events: • single charged lepton • - high pT • - isolated • missing ET from neutrino (W or e). • - pT is inferred • . |e(trk)|<2.8, ||<1 DØ • Muons:central tracker, muon detectors • Electrons: central tracker, calorimeter |e(trk)|<3.2, ||<2 Rainer Wallny -W and Z properties from the Tevatron

  5. Overview Active and rich research program on W/Z properties at Tevatron in Run II Presented in this talk: DØ W Mass, 1.0 fb-1 ,  PRL 103, 141801 (2009) DØ W Width, 1.0 fb-1, PRL 103, 231802 (2009). CDF W Mass 0.2 fb-1 PRL 99, 151801 (2007); PRD 77, 112001 (2008) CDF W Width 0.4 fb-1 PRL 100 071801 (2008) CDF and DØ W Mass Combination, up to 1.0 fb-1, arXiv:/0908.1374 (hep-ex) (2009) DØ Z/γ transverse momentum 1.0 fb-1 PRL 100, 102002 (2008), 7.3 fb-1 Preliminary 2010 CDF W(→eν) charge asymmetry 1.0 fb-1 PRL 102, 181801 (2009); Method PRD 79 031101 (2009) also preliminary lepton charge re-analysis DØ ElectronCharge Asymmetry , 0.70 fb-1 , PRL 101, 211801 (2008) DØ Muon Charge Asymmetry, 4.9 fb-1, Preliminary(2009) CDF Afb4.1 fb-1 Preliminary (2009) DØ Afb 1.1 fb-1 PRL 101, 91801 (2008) CDF Z rapidity 2.1 fb-1 hep-ex/0908.3914 (2009) Rainer Wallny -W and Z properties from the Tevatron

  6. W Mass + Width Rainer Wallny -W and Z properties from the Tevatron

  7. SM Consistency Check Derive W boson mass from preciselymeasured electroweak quantities (Summer ’10) known to 0.015% MZ known to 0.002% known to 0.0009% Δr: - large radiative corrections - dominated by tb and Higgs loops - sensitive to new physics mtop=(173.3 ± 1.1) GeV (0.6%) mW =(80.399±0.023) GeV (0.028%) ΔmW ~ 0.006 x δmtop ~ 7 MeV for equal weights in Higgs limits NB: New Tevatron mtop combination => Prediction of the Higgs boson mass and consistency check of SM Rainer Wallny -W and Z properties from the Tevatron

  8. W-Mass Measurement at the Tevatron • LEP legacy: MW=80.367±0.033 GeV (0.04%) • At Tevatron: mainly qq’ annihilation • Main ingredients lepton pT(~10-4) and hadronic recoil (~1%) parallel to lepton u|| • Z→ ll superb calibration sample • - Z (CDF) and Zee (CDF, D0) events to derive recoil model • - most systematic uncertainties limited by size of Z sample (10x less Z than W) precise charged lepton measurement is the key Recoil measurement allows inference of neutrino ET Rainer Wallny -W and Z properties from the Tevatron

  9. Experimental Observables pT(e) most affected by pT(W) MT most affected by measurement of missing transverse momentum No PT(W) PT(W) included Detector Effects added Arbitrary linear scale Arbitrary linear scale Also use pT() (CDF, D0) and pT() (CDF) • Generate Monte Carlo templates for likelihood fit to data • Need precise, parameterized and fast simulation • Generator: RESBOS, PHOTOS/WGRAD Rainer Wallny -W and Z properties from the Tevatron

  10. Lepton Energy/Momentum Scale W→eν CDF: • Calibrate lepton momentum scale using Y, J/, Z • Calibrate calorimeter against precision tracker (E/p) and MZ • Data • Simulation • D0: • Calibrate calorimeter using precisely known MZ from LEP • Detailed corrections for un- instrumented regions • Reduce higher order corrections due to ratio W/Z Dominant systematic uncertainty (D0: 34 MeV, CDF: 17/30 MeV e/) Rainer Wallny -W and Z properties from the Tevatron

  11. W-Mass: Recoil Model • Recoil due to : • QCD radiation “recoiling” against W • underlying event • overlapping min bias u|| Use Z →ee (D0 and CDF) + Z →  (CDF) balancing to calibrate recoil energy scale and to model resolution uT DØ 1 fb-1 systematic uncertainty on MW : D0: 6 MeV mT, 12 MeV pT CDF:9 MeV mT, 17 MeV pT GeV Rainer Wallny -W and Z properties from the Tevatron

  12. Z/γ* pT • Vector boson pT spectrum sensitive to parton initial state radiation => stringent QCD test • Low pT spectrum sensitive to multiple soft gluon emmission => requires resummation techniques/models • Recent D0 result (7.3 fb-1) uses new variable Φ*=aT/mll based on the two lepton directions • => less vulnerable to detector resolution limiting precision of pT(Z) measurement ratio to Pythia Perugia tune Z pT Data does NOT support “small-x broadening” (P. Nadolsky, D.R.Stump, C.P. Yuan, Phys. Rev. D 64,114011 (2001) Rainer Wallny -W and Z properties from the Tevatron

  13. W-Mass Results Improve w/ statistics D0 (1 fb-1): mW=80401±21(stat)±38(syst) MeV →Single most precise result CDF (200 pb-1) mW=80413±34(stat)±34(syst) MeV → update w/ 2.4 fb-1 Ultimately limit precision Tevatron Run II precision goal: mW < 25 MeV/experiment Rainer Wallny -W and Z properties from the Tevatron

  14. Tevatron W Mass Combination • New Tevatron combination: • Update previous CDF result tomodern PDFs • Correct to same W • PDF, QED, W uncertainties correlated • More precise than LEP II combination! • New World Average (Summer 2009) mW=80420±31MeV (0.038%) mW=80399 ± 23 MeV Rainer Wallny -W and Z properties from the Tevatron

  15. W-Width w • w is expected to agree with SM almost irrespective of any new physics • The high mT tail contains information on w - Exploit slower falloff of Breit-Wigner compared to Gaussian resolution New world average: W = 2085  42 (stat + syst) MeV Theory: W = 2089 ± 2 MeV Rainer Wallny -W and Z properties from the Tevatron

  16. W-Asymmetry Rainer Wallny -W and Z properties from the Tevatron

  17. W- and Lepton Charge Asymmetry s - s d / dy d / dy ( = » + - W W s + s d / dy d / dy + - W W - u ( x 1 ) d ( x 2 ) d ( x 1 ) u ( x 2 ) + u ( x 1 ) d ( x 2 ) d ( x 1 ) u ( x 2 ) • At the Tevatron, Ws mainlyproduced by valence quarks • On average, u quark carrieshigher momentum than d quarks- W+ boosted in proton direction- W- boosted in anti-proton direction => W asymmetry A(yw) => sensitive to u/d ratio • Lepton (Wl) charge asymmetry A(l)experimentally more accessible: A y ) W = A(yW) ⊗ (V-A) Rainer Wallny -W and Z properties from the Tevatron

  18. CDF direct A(yW) measurement • CDF Weighting Method: • Use W mass constraint to infer pZ • Calculate W rapidity from both two solutions and weight them • Iterate to remove potential theory bias A. Bodek at al. Phys.Rev D 79 031101 (2009) * ¯ P P Fold Precision much better than error band => Improve global fits 18 Rainer Wallny -W and Z properties from the Tevatron

  19. D0 Lepton Charge Asymmetry • New high statistics D0 muon charge asymmetry data confirms previousdeviation from theory • Trend more pronounced for higher pTl bin • Global fitters (MSTW,CTEQ) have problems incorporating D0 lepton charge asymmetry results • Tension with low-x data (see e.g. CTEQ arXiv:1007.2241[hep-ph]) • Preliminary re-analysis of CDF resultA(yW)  A(l) confirms D0 result! • Currently being investigated by theorists and experimental teams (see also H. Schellman, DIS 2010 proceedings, arXiv 1008.1973 [hep-exp]) Rainer Wallny -W and Z properties from the Tevatron

  20. dσ/dy(Zee) Afb Rainer Wallny -W and Z properties from the Tevatron

  21. Z-cross section and Rapidity • Z-Boson rapidity reconstructed from leptonic decays • High rapidity (y) probes high-x parton region (mainly dv) MSTW • Shape described well by NLO QCD • Total cross section |y| <2.9: • =256.00.7(stat)2.0(syst) pb + 6% luminosity error • 236.1±1.93 pb NLO CTEQ6M • 252.6 ±3.1 pb NNLO MRST 2006 • => impact dv in global fits Rainer Wallny -W and Z properties from the Tevatron

  22. Z Forward Backward Asymmetry Afb * * • AFB determines the relative strengths of V-A boson-fermion couplings as well as sin2θW • AFB sensitive to new resonance (f.g Z’) via interference with Z/* Phys. Rev. Lett. 101,191801 (2008) 500 GeV Z’ Rosner et al. PRD 54, 1078 (1996) D0: sin2W = 0.2326 ±0.0018(stat.) ± 0.0006(syst.) World = 0.23153 ±0.00016 Future Tevatron precision ~ 0.0005 Rainer Wallny -W and Z properties from the Tevatron

  23. Conclusions • The Tevatron will have the largest sample of W and Z bosons for still some time • Total Run II statistics of W and Z bosons will be bigger than LHC 1 fb-1 @ 7 TeV • Harvesting precision electroweak results from the Tevatron: • Most precise single measurement of W mass and W width (both D0 in 1 fb-1 ) • Both collaborations working on updates (2.4 fb-1 CDF, 5.0 fb-1 D0) • < 25 MeV single experiment W mass uncertainty possible in Run II => Legacy measurements for years to come! • Novel techniques: • New method to unfold PT(Z) spectrum at low PT (D0) • Direct unfolding of W charge asymmetry (CDF) • W charge and lepton asymmetry present and interesting puzzle • Experimental data agree but difficulties in global fits • Data is quite precise and will constrain pdfs much further • A measurement unique to the Tevatron • Still large potential for more precise electroweak measurements in Run II • Towards a competitive Afb measurement => sin2θW andlight quark axial and vector couplings Rainer Wallny -W and Z properties from the Tevatron

  24. BACKUP Rainer Wallny -W and Z properties from the Tevatron

  25. W Mass from the Tevatron Beyond a few fb-1 overall uncertainty does not improve significantly without better understanding of systematics, but energy scale systematics still statistics limited Goal: δMW< 25 MeV per experiment by the end of Run II Rainer Wallny -W and Z properties from the Tevatron

  26. Lepton Momentum Scale and Resolution (CDF) Systematic uncertainty on Lepton Momentum scale: 0.02%  Zee Z Rainer Wallny -W and Z properties from the Tevatron

  27. d(x)/u(x) in global fits CTEQ6.6M PDF sets at Q=81.4 GeV d(x)/u(x) Rainer Wallny -W and Z properties from the Tevatron

  28. RESBOS + CTEQ 6.6 Predictions • N Lepton PT cut introduces correlation between asymmetry and pT(W) H. Schellman, DIS 2010 proceedings arXiv:1008.1973v1 [hep-ex] Rainer Wallny -W and Z properties from the Tevatron

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