W, Z and Drell-Yan Production II Asymmetries

1. W, Z and Drell-Yan Production II Asymmetries Susan Blessing Florida State University For the DØ and CDF Collaborations ICHEP 2006 July 27, 2006

2. W production charge asymmetry W mn (DØ) and W  en (CDF) direct method in W  en (CDF) Z  ee forward/backward asymmetry (CDF) Summary Outline Susan Blessing

3. u quarks typically carry more of a proton’s momentum than d quarks W+ goes in the proton direction W- in the antiproton direction Use this difference to get information about the proton’s u and d distributions – PDFs dσ/dy (nb) √s = 1.96 TeV Rapidity y ds ds ds ds - + (W+) (W-) (W+) (W-) dy dy dy dy - u u u u + - (xp) (xp) (xp) (xp) ≈ d d d d - W boson production charge asymmetry A(yW) = Susan Blessing

4. CDF, W  en DØ, W mn MW e±y Q2 ≈ MW2, x = W √s Q2, x reach Q2, x coverage for CDF, DØ, HERA and fixed target experiments Traditionally, PDFs are measured in deep inelastic scattering – high energy electron-nucleon interactions. W asymmetry measurements: for |yW| < 2 (W mn, DØ) 0.005 < x < 0.3 for |yW| < 2.5 (W  en, CDF) x = momentum fraction of parton Q2 = square of momentum transfer 0.003 < x < 0.5 Susan Blessing

5. W asymmetry difficult to measure neutrino longitudinal momentum Lepton pseudorapidity is available Lepton asymmetry is a combination of the W asymmetry and V-A interaction from decay at higher lepton transverse momentum, V-A contribution is smaller, A(yl) is larger at higher lepton rapidity, V-A contribution is larger, A(yl) is smaller ds ds ds ds (l-) (l-) (l+) (l+) + - dh dh dh dh A(hl) = Lepton charge asymmetry For all muon momenta Susan Blessing

6. L = 230 pb-1 pT > 20 GeV |h| < 2.0ET > 20 GeV MT > 40 GeV L = 170 pb-1 ET > 25 GeV |h| < 2.5ET > 25 GeV50 < MT < 100 GeV m e charge misid ≈10-4 for W mn ≈10-2 for W  en / / 230 pb-1 + Bkgd W mn (DØ) and W  en (CDF) W mn W  en Tight selections to reduce charge and event misidentification Analyses done bin-by-bin DØ transverse mass distribution CDF charge misid vs pseudorapidity PRD 71, 051104(R) (2005) Susan Blessing

7. W mn W  en L≈230 pb-1 m pT > 20 GeV MRST02 Statistical and total uncertainties CTEQ6.1M uncertainty band Combined uncertainties Pseudorapidity Statistical uncertainties comparable to or much larger than systematic for |h| > 0.4 ~ Asymmetry vs pseudorapidity PRD 71, 051104(R) (2005) W production and decay are CP invariant; fold the asymmetry to increase statistics. Susan Blessing

8. Asymmetry in ET bins (CDF) Improve correspondence between he and yW Statistical and total uncertainties For a given he, ET regions probe different ranges of yW (x); higher ET bin covers a narrower yW range pZ ambiguity is a smaller effect for high-ET electrons 25 < ET < 35 GeV 35 < ET < 45 GeV PRD 71, 051104(R) (2005) Susan Blessing

9. n1(y1) W+ events n2(y2) valence-valence u _ sea-sea e+ d cosq* W- events valence-valence depends on cosq*, y1,2, pT, s(y1,2), yW sea-sea W Direct W asymmetry method – CDF Reconstruct yW distribution W mass constraint Weight the two solutions weight takes production and decay into account Iterate since weight depends on yW cosq* q* = angle of charged lepton in W frame Susan Blessing

10. 400 pb-1 Pythia events ET > 25 GeV ET > 25 GeV e / Projected uncertainties of direct method Compare expected statistical uncertainties in W asymmetry and lepton asymmetry with CTEQ6M error sets Direct method for W asymmetry measurement shows improved statistical uncertainty Estimated systematics are small Susan Blessing

11. e- e- q q Z g(*) + e+ e+ - - q q e- _ q q ) = A(1+cos2q) + Bcosq q ds s(cosq>0) - s(cosq<0) e+ AFB = dcosq s(cosq>0) + s(cosq<0) A and B depend on gV, gA, Qq and Ql and are related through the forward-backward asymmetry, AFB = q,l q,l NF- NB 3B = NF+ NB 8A Z  ee forward-backward asymmetry (CDF) Interference between g(*) and Z exchanges Interference depends on Mee Primarily g* exchange below Z Z exchange at Z Z/g exchange above Z Susan Blessing

12. AFB AFB ZX Mee (GeV) AFB - uu  e+e- Zy Mee (GeV) - uu  e+e- - dd  e+e- AFB distributions Probe relative strengths of Z-q couplings; sensitive to u and d quarks separately 500 GeV Z´ Exchange of new particle(s) would alter AFB J.L. Rosner, PRD 54, 1078 (1996) Susan Blessing

13. bkg bkg bkg bkg NF- NF NF- NF NB- NB NB- NB + - aF aB aF aB AFB = Determining AFB Since it’s a ratio, reduced systematics of luminosity, acceptances/efficiencies Correct for background, acceptance/efficiency Acceptance is symmetric; distribution is not shifts AFB within a mass bin Use a matrix based on MC events to “unfold” raw AFB distribution (correct for acceptance/efficiency and smearing) Event migration between bins large correlations between bins near Z pole ISR and FSR Susan Blessing

14. 72 pb-1 Unfolded AFB distribution Agreement with LO SM calculation is c2/dof = 10.9/12 No evidence for additional gauge bosons Can fit for quark and electron couplings Example using 72 pb-1 result Updating to 1 fb-1 CDF: PRD 71, 052002 (2005) Wichmann, HCP 2006 Susan Blessing

15. useful for constraining PDF fits for gaining information on quark and electron EW couplings for searching for additional gauge bosons and, of course, for testing the Standard Model Summary Both DØ and CDF are measuring W and Z/g asymmetries Both experiments have significantly more data available, over 1fb-1, and are making progress on extending these analyses to include this data. Susan Blessing

16. Backup Slides Susan Blessing

17. Lepton asymmetry and pT cut Susan Blessing

18. e+ e- = 0.99 ± 0.01 DØ overall efficiency ratio Overall efficiency ratio = product of individual ratios L2 muon trigger efficiency L3 track trigger efficiency Offline muon reconstruction efficiency Offline tracking efficiency c2/dof = 0.71 Susan Blessing

19. Cross checks no Z invariant mass cut reduced muon pT cut use other triggers study misid in GEANT MC No difference charge misid rate charge misid rate charge misid rate charge misid rate DØ charge misidentification 1. Only isolated muons 3. Plus additional c2/dof Sample of 10,000 ee events. After all selection cuts, only one same-sign event remains. 2. Plus hits in the tracker 4. dca but no c2 Charge misid rate = (0.01±0.01)% for |h| ≤ 1.0 (0.01±0.05)% for |h| > 1.0 inflate uncertainty at high |h| due to low statistics Susan Blessing

20. Data differences in efficiencies for m+ and m- take = 1.0 and use uncertainty as a systematic charge misidentification Background PMCS modeling of EW backgrounds muon energy in calorimeter hadronic energy scale (ET) uncertainty in signal isolation efficiency uncertainty in background isolation efficiency e+ e- DØ systematic uncertainties / Vary everything by ±1s, use change in asymmetry as uncertainty. Susan Blessing

21. DØ magnet polarities Solenoid polarities Toroid polarities Data is 50.7% : 49.4% Susan Blessing

22. ≈230 pb-1 m MRST02 pT > 20 GeV Statistical - black Systematic - red Envelope of CTEQ6.1M error sets Pseudorapidity W mn (DØ) and W  en (CDF) W mn W  en Z  mm Z  tt, t  mnn W  tn, t  mnn QCD multijet Z  ee W  tn, t  enn QCD multijet Analyses done bin-by-bin PRD D 71, 051104(R) (2005) Susan Blessing

23. DØ folded asymmetry plot Red curve: CTEQ6.1M central value Blue curve: MRST02 Combined uncertainties. Susan Blessing

24. W+ events valence-valence valence-valence ratio of two distributions sea-sea W ± sea-sea * * W W + P±(cosq1, y1, pT) s(y1) P±(cosq2, y2, pT) s(y2) cosq* W- events valence-valence * * W W P±(cosq1,2, y1,2, pT) s(y1,2) P±(cosq1,2, y1,2, pT ) = (1 cosq*)2 + Q(yW, pT )(1 ± cosq*)2 sea-sea ± F = 1,2 cosq* CDF W asymmetry weighting Susan Blessing

25. CDF Z → ee mass distributions Low mass region High mass region Susan Blessing

26. CDF AFB background Susan Blessing