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W Charge Asymmetry at CDF

W Charge Asymmetry at CDF. Kevin McFarland University of Rochester on behalf of CDF collaboration Ph.D. thesis of Bo-Young Han DIS 2008, UC-London, 8 April 2008. Outline. Introduction and Analysis Technique Signal, Backgrounds and Corrections Uncertainties Preliminary results.

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W Charge Asymmetry at CDF

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  1. W Charge Asymmetry at CDF Kevin McFarland University of Rochester on behalf of CDF collaboration Ph.D. thesis of Bo-Young Han DIS 2008, UC-London, 8 April 2008

  2. Outline • Introduction and Analysis Technique • Signal, Backgrounds and Corrections • Uncertainties • Preliminary results K. McFarland, W Charge Asymmetry

  3. At Tevatron, W± are produced primarily by uproton (danti-proton) and uanti-proton(dproton) u quarks carry more momentum than d quarks W Charge Asymmetry and PDFs W charge Asymmetry u d K. McFarland, W Charge Asymmetry

  4. Lepton charge asymmetry W charge asymmetry Lepton ChargeAsymmetry CDFII, 170 pb-1 • Previous workfrom TeVatron has measured the charge asymmetry vs. lepton η in W→ℓν • This observable is aconvolution of the Wcharge asymmetryand V-A W decayangular distribution K. McFarland, W Charge Asymmetry

  5. Lepton and W Rapidity • Lepton prefers to decay against boost K. McFarland, W Charge Asymmetry

  6. Analysis Technique • Measure W± rapidity • Use W mass constraint solve eqn. answer : • Weight the two solutions • This method must be iterated to remove input bias • shown it does not depend on assumed chargeasymmetry can’t measure !!! Probability of angular distribution Differential W cross section K. McFarland, W Charge Asymmetry

  7. Complications:Detector Effects true rapidity weighting factor response matrix • Response matrix to correct for detector acceptance, smearing and final state effects • QED, W→τν→eννν Y1 Y2 wt1 wt2 YW YW FSR depends on physics input →should be iterated doesn’t depends on physics input →do not need to be iterated K. McFarland, W Charge Asymmetry

  8. Complications:W Production from the sea • Sign of V-A angular bias flipswhen W± is produced fromanti-quarks • take this fraction as an input ratio of two angulardistributions at each rapidity K. McFarland, W Charge Asymmetry

  9. What is input, and what is measured? • Inputs from theory: • and • Output from iteration: method documented in B.Y.Han et al., arXiv:hep-ph/0711.2859 K. McFarland, W Charge Asymmetry

  10. Outline • Introduction and Analysis Technique • Signal, Backgrounds and Corrections • Uncertainties • Preliminary results K. McFarland, W Charge Asymmetry

  11. Summary of Data Issues • Require one high ETelectron and missing ETto tag the neutrino • ETe>25(20) GeV incentral (plug) detector • missing ET>25 GeV • Detector response, including missing ET,tuned on Z→e+e- sample • Highlight backgrounds (primarilyjets faking electrons) and charge mismeasurement • also, trigger and detector acceptance and smearing K. McFarland, W Charge Asymmetry

  12. Data and Simulation Kinematic Distributions • Scale and resolution tuned on Z→e+e- Red : MC Blue : data K. McFarland, W Charge Asymmetry

  13. Backgrounds • Measure jet backgrounds directly in data • use extra energy “isolation” around electron to separate, and fit shape to background fraction • Illustrative fit (one of many)shown at right • use jet sample to predict measured“yW” and charge from this sample • uncertainty is ~0.15% of total sample • A number of minor backgrounds(real Ws) from simulation electron K. McFarland, W Charge Asymmetry

  14. Electron ChargeIdentification • Charge identification is crucial for this measurement • Forward tracking has fewer points at shorter lever arm • Determine directly from (background subtracted) K. McFarland, W Charge Asymmetry

  15. Outline • Introduction and Analysis Technique • Signal, Backgrounds and Corrections • Uncertainties • Preliminary results K. McFarland, W Charge Asymmetry

  16. Systematic Effects • Detector response • energy scale and smearing for electron and recoil • efficiency to find electron and pass missing ET cut • Inputs • PDF uncertainties (CTEQ6 PDF error sets) for total W production and quark/anti-quark fractions K. McFarland, W Charge Asymmetry

  17. Evaluation • Derive result with shifted parameters • Systematics dominate only if yW<0.2 or >2.6 largest detector effect: energy scale largest PDF effect: qbar/q largest selection effect: elec. cuts charge fake rate uncertainty K. McFarland, W Charge Asymmetry

  18. Outline • Introduction and Analysis Technique • Signal, Backgrounds and Corrections • Uncertainties • Preliminary results K. McFarland, W Charge Asymmetry

  19. Uncertainties • Unfolding correlates (strongly) the statistical errors innearby bins • Systematics also strongly correlated… • PDF fitters, please exercise caution… K. McFarland, W Charge Asymmetry

  20. Input PDFs • We are in the process of documenting how result depends on input PDFs • PDF fitters can explicitly put this in (or ignore if small) effect of increasing valence u+d by +5% effect of increasing sea u+d by +5% K. McFarland, W Charge Asymmetry

  21. CDF Preliminary Result (1fb-1) • Positive and negative yW agree, so fold • Compare to NNLO (MRST) • NLO error PDFs (CTEQ) K. McFarland, W Charge Asymmetry

  22. CDF Preliminary Result (1fb-1) • Compare CTEQ6M and MRST2006 with PDFs and their uncertainties K. McFarland, W Charge Asymmetry

  23. Conclusions • First direct measurement of W charge asymmetry • despite additionalcomplication of multiplesolutions, it works! • appears that it will haveimpact on d/u of proton • Looking forward toworking with PDF fitting groups to incorporate K. McFarland, W Charge Asymmetry

  24. Outline • Introduction and Analysis Technique • Signal, Backgrounds and Corrections • Uncertainties • Preliminary results • Backup K. McFarland, W Charge Asymmetry

  25. Results K. McFarland, W Charge Asymmetry

  26. Systematics K. McFarland, W Charge Asymmetry

  27. Acceptance K. McFarland, W Charge Asymmetry

  28. Plug Electron Tracking Efficiency K. McFarland, W Charge Asymmetry

  29. QCD higher order corrections • Our weight factor is initialized by one prediction. • The parameterization of angular distribution : • The ratio of anti-quark and quark in proton : Q(yW,PWT) using MC@NLO • Differential cross-sections : dσ±/dyW • KNNLO = (dσNNLO/dyW)/(dσLO/dyW) K. McFarland, W Charge Asymmetry

  30. f(PT) and g(PT) K. McFarland, W Charge Asymmetry

  31. NNLO K-factor: (dσNNLO/dyW)/(dσLO/dyW) • NNLO dσ±/dyW (mrst2002 PDFs) from theoretical prediction. K. McFarland, W Charge Asymmetry

  32. NNLO K-factor • W charge asymmetry measurement using K-factor. K. McFarland, W Charge Asymmetry

  33. Z PT at LO (Pythia) • check if LO (Pythia) is tuned by DATA. • Using Zee samples : zewk6d(Pythia) vs bhel0d(data) • Looks MC agrees with data. K. McFarland, W Charge Asymmetry

  34. W Pt tune at MC@NLO • Comparison of Pt distribution between NLO(Herwig) and LO(Pythia) • Using W→eν samples • Obtain the re-weight factor from the ratio of both • We are going to re-weight the event of NLO. K. McFarland, W Charge Asymmetry

  35. Q(yW,PWT) (cont.) • 10 < PT and 10 < PT < 20 K. McFarland, W Charge Asymmetry

  36. Q(yW,PWT) (cont.) • 20 < PT < 40 and 40 < PT < 60 K. McFarland, W Charge Asymmetry

  37. Q(yW,PWT) (cont.) • 60 < PT < 80 and 80 < PT < 200 K. McFarland, W Charge Asymmetry

  38. Q factor + K-factor • Even if QCD higher order correction makes small effect on the asymmetry, we believe that it describes better differential cross-section and angular distribution. K. McFarland, W Charge Asymmetry

  39. Q(yW,PWT) using MC@NLO • W charge asymmetry measurement using NLO Q factor • Compare it with previous result using LO Q factor K. McFarland, W Charge Asymmetry

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