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

K. McFarland, W Charge Asymmetry Outline Introduction and Analysis Technique Signal, Backgrounds and Corrections Uncertainties Preliminary results 8 April 2008 K. McFarland, W Charge Asymmetry

W Charge Asymmetry and PDFs At Tevatron, W± are produced primarily by uproton (danti-proton) and uanti-proton (dproton) W charge Asymmetry u d u quarks carry more momentum than d quarks 8 April 2008 K. McFarland, W Charge Asymmetry

Lepton Charge Asymmetry CDFII, 170 pb-1 Previous work from TeVatron has measured the charge asymmetry vs. lepton η in W→ℓν This observable is a convolution of the W charge asymmetry and V-A W decay angular distribution Lepton charge asymmetry W charge asymmetry 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Lepton and W Rapidity Lepton prefers to decay against boost 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry 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 charge asymmetry can’t measure !!! Probability of angular distribution Differential W cross section 8 April 2008 K. McFarland, W Charge Asymmetry

Complications: Detector Effects true rapidity weighting factor response matrix 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 Response matrix to correct for detector acceptance, smearing and final state effects QED, W→τν→eννν 8 April 2008 K. McFarland, W Charge Asymmetry

Complications: W Production from the sea Sign of V-A angular bias flips when W± is produced from anti-quarks take this fraction as an input ratio of two angular distributions at each rapidity 8 April 2008 K. McFarland, W Charge Asymmetry

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 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Outline Introduction and Analysis Technique Signal, Backgrounds and Corrections Uncertainties Preliminary results 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Summary of Data Issues Require one high ET electron and missing ET to tag the neutrino ETe>25(20) GeV in central (plug) detector missing ET>25 GeV Detector response, including missing ET, tuned on Z→e+e- sample Highlight backgrounds (primarily jets faking electrons) and charge mismeasurement also, trigger and detector acceptance and smearing 8 April 2008 K. McFarland, W Charge Asymmetry

Data and Simulation Kinematic Distributions Red : MC Blue : data Scale and resolution tuned on Z→e+e- 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry 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 8 April 2008 K. McFarland, W Charge Asymmetry

Electron Charge Identification Charge identification is crucial for this measurement Forward tracking has fewer points at shorter lever arm Determine directly from (background subtracted) 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Outline Introduction and Analysis Technique Signal, Backgrounds and Corrections Uncertainties Preliminary results 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry 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 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry 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 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Outline Introduction and Analysis Technique Signal, Backgrounds and Corrections Uncertainties Preliminary results 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Uncertainties Unfolding correlates (strongly) the statistical errors in nearby bins Systematics also strongly correlated… PDF fitters, please exercise caution… 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry 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% 8 April 2008 K. McFarland, W Charge Asymmetry

CDF Preliminary Result (1fb-1) Positive and negative yW agree, so fold Compare to NNLO (MRST) NLO error PDFs (CTEQ) 8 April 2008 K. McFarland, W Charge Asymmetry

CDF Preliminary Result (1fb-1) Compare CTEQ6M and MRST2006 with PDFs and their uncertainties 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Conclusions First direct measurement of W charge asymmetry despite additional complication of multiple solutions, it works! appears that it will have impact on d/u of proton Looking forward to working with PDF fitting groups to incorporate 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Outline Introduction and Analysis Technique Signal, Backgrounds and Corrections Uncertainties Preliminary results Backup 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Results 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Systematics 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Acceptance 8 April 2008 K. McFarland, W Charge Asymmetry

Plug Electron Tracking Efficiency 8 April 2008 K. McFarland, W Charge Asymmetry

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) 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry f(PT) and g(PT) 8 April 2008 K. McFarland, W Charge Asymmetry

NNLO K-factor: (dσNNLO/dyW)/(dσLO/dyW) NNLO dσ±/dyW (mrst2002 PDFs) from theoretical prediction. 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry NNLO K-factor W charge asymmetry measurement using K-factor. 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry 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. 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry 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. 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Q(yW,PWT) (cont.) 10 < PT and 10 < PT < 20 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Q(yW,PWT) (cont.) 20 < PT < 40 and 40 < PT < 60 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Q(yW,PWT) (cont.) 60 < PT < 80 and 80 < PT < 200 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry 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. 8 April 2008 K. McFarland, W Charge Asymmetry

K. McFarland, W Charge Asymmetry Q(yW,PWT) using MC@NLO W charge asymmetry measurement using NLO Q factor Compare it with previous result using LO Q factor 8 April 2008 K. McFarland, W Charge Asymmetry