1 / 26

Asymmetries in W± and Z0/g* Production at the TeVatron

This paper discusses various asymmetries in the production of W± and Z0 bosons at the TeVatron, including the W charge asymmetry, lepton charge asymmetry, and the AFB asymmetry in Z0/g* decays. It also explores the impact on quark PDF constraints and tests QCD predictions.

sriley
Download Presentation

Asymmetries in W± and Z0/g* Production at the TeVatron

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Asymmetries in W ± and Z0/ g* Production at the TeVatron ICHEP ‘04 August 17, 2004 Eva Halkiadakis University of Rochester For the CDF and D0 Collaborations

  2. W Charge Asymmetry EWK “Spectroscopy” • Lots of interesting physics in production of W ± and Z0 bosons at the Tevatron! • Rapidity Spectrum: ds/dy • quark PDF constraints • Direct impact on MW • Polar Angle Spectrum: ds/dcosq • In Z’s vs. Mee • AFB, sin2qW • quark, lepton couplings • In W’s vs. pT • Tests QCD predictions • Boson pT Spectrum: ds/dpT • Tests QCD predictions • Direct impact on MW Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  3. u d – d – u W ± Charge Asymmetry xf(x,Q2) log(x) u quark carries higher fraction of p momentum! [http://durpdg.dur.ac.uk/hepdata/pdf3.html] Measurement of the W charge asymmetry constrains PDF’s of the proton. yW ←anti-proton direction proton direction→ Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  4. Lepton Charge Asymmetry CDF Run I: PRL 81, 5754, (1998) • Leptonic W decay involves n → pzn is unmeasured. • Use experimentally more direct l ± direction to measure A(hl). • This convolves W production asymmetry with V-A decay distribution. • Sensitivity to the ratio of PDFs for u and d quarks, u(x)/d(x). Least constrained at high h! Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  5. Event Selection hl Out to ~2.8! • W ± →e ±n Candidates [ET, MET > 25GeV, 50 GeV < MT < 100 GeV] • Central: 49214 events • Forward: 28806 events • Charge ID in forward region is key! • Use new silicon tracker and forward calorimeters. • Align forward calorimeters with tracks from central tracker. • Global offsets, rotations. • Internal misalignments. Residuals after alignment look very good. Global Df (mRad) Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  6. Raw Asymmetry Shape is convolution ofA(yW) and V-A Sign switch @ |h| > 2 • Corrections to extract true asymmetry: • Charge misidentification rate. • Background subtraction. • Both bias the asymmetry low → dilution. • Measured in each h bin. • Uncertainties in corrections go directly in A. |h|< 1 ~ linear Curve is just to guide the eye. Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  7. Corrected W Charge Asymmetry Data lower than existing CTEQ prediction. • Gain sensitivity to W production asymmetry A(yW) with ET dependence. • Higher ET: electron direction closer to W direction. Production asymmetry enhanced. • Lower ET: decay asymmetry enhanced Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  8. f ’ q f f ’ f f f ’ AFB f f ’ AFB in Z0 / g* → e+e- Decays Z0 / g* f = e, quarks • Vector (V) and Axial-vector (A) couplings give rise to AFB. • Interference between Z0 and g* exchanges. • Different combinations of V and A couplings contribute to ds/dcosq dMee. • AFB direct probe of relative strengths of coupling between Z0 and quarks. • Mass dependence is sensitive to u and d quarks separately. Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  9. AFB Beyond LEPII • Interesting for Mee above LEP II energies. • New interactions → deviations of AFB and ds/dM from SM predictions. • Various models predict new neutral, heavy bosons: Z´s • New resonance could interfere with g and Z. • Complementary to direct searches → excess in total cross section. CDF Run I (~110 pb-1) 2.2 s deviation from SM Rosner, J.L.: Phys. Rev. D 54, 1078 (1996) AFB 500 GeV/c2 Z’ Zx Z Mee(GeV/c2) Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  10. Calculating AFB • 5211 Candidate Z0→ e+e- events • 2 isolated electrons ET>20 GeV • 1892 Central-Central • 3319 Central-Forward • Backgrounds: • Central-Central: 1% • Central-Forward: 5% • Dijet background dominant Low mass CDF II Preliminary Pole Backward Forward High mass AFB is largest Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  11. Acceptance Corrections Low mass High mass ok! Pole Large correlations at pole 600 GeV/c2 • Unconstrained unfolding analysis • Acceptance and event migration parameterized to transform AFBphys to AFBraw. • Use maximum log likelihood method to compare to data at the detector level. High mass 40GeV/c2 600GeV/c2 Kin. and geom. cuts sculpt the cosq* distrib., esp. in forward region. Detector resolution and radiative effects → event migration. Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  12. Unconstrained Fit with Smoothing • Result fitting AFB • Large statistical uncertainties • No SM assumptions about AFB! • Systematic uncertainties small compared to statistical: • Energy Scale, Resolution • Detector Material • Backgrounds CDF II Preliminary CDF II Preliminary • All results consistent with SM. • Not useful for non-SM physics near Z pole. • Nothing new above the pole yet. Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  13. Couplings Results Quark Couplings: Electron Couplings: Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  14. Summary Future • ds/dy measurements in Z’s will further constrain PDF uncertainties. • ds/dpT in both W’s and Z’s will further test QCD predictions. • CDF has a new measurement of the lepton charge asymmetry in W→en decays. • Look at data at large ET and large h. • Uncertainty on PDFs could be reduced by inclusion of this data in global fits. • First Run II measurement of W charge asymmetry! • We also measure AFB vs. Mee in Z→ee events. • Unfolded AFB with out SM assumptions. • Fit for Z couplings. • Nothing new above the Z pole yet. Important for MW! Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  15. Backup Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  16. Phoenix (Calorimeter-Seeded) Tracking Two points and a curvature define a helix: • Primary collision vertex position. • Fitted position of calorimeter shower maximum. Use both central and forward electrons! |h| < 2.8 Zoom into Silicon: Phoenix SiTrack Cal. Seed Tracks Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  17. Charge Misidentification Rate • Charge mis-ID rate, fQ: • Residual misalignments in silicon and plug shower maximum detectors. • Measured in data using Z0→ e+e- events, with one leg in the central tracker (COT). • Measured in each h bin. • Uncertainties in fQ directly go in A. • Monte Carlo predicts fQ<1% even at h=2 → naïve. Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  18. Background Corrections • We correct A for backgrounds: • W →t n → e nn , Z → e e • Measured from Monte Carlo • Asymmetric • QCD Jets • Measured from data • Use Calorimeter Isolation (e) and MET distributions (n) projected into signal region. • Isolation correlated with other selection criteria. • Estimate is upper limit. • Biases A toward 0. QCD background is upper limit → use 0.5% ± 0.25% → gives full coverage. Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  19. Past Results from e+e- • Previous experiments have done very precise measurements (LEP, SLC, etc.) • Need > 10 fb-1 to compete on sin2(W) • Difficult to compete with LEPII • 120<s<207 GeV Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  20. Calculating AFB • cos* in Collins-Soper frame (minimize ambiguity in the incoming quark pT) • cos*>0 Forward • cos*<0 Backward lab frame Z0/g* PZ =0 Z-Axis Z0/g* Correct AFBraw to obtain AFBphys →compare to theory: Sculpt cosq* dist. Mee bin migration Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  21. Mee and h for Z→ee Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  22. Backgrounds for Z/g* • Dijet dominant Background Summary CDF II Preliminary CDF II Preliminary Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  23. Fitting for Z Couplings • Fit at Raw AFB Level • Test AFB is smeared • c2 show good agreement with SM c2=10.66/11 Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  24. Acceptance*Efficiency • Correction Factors: • Energy Resolution • Kinematic and Fiducial cuts • Radiation from FSR and Brems • Electron ID efficiency • Assumes SM • Allow Z couplings to float CDF II Preliminary Couplings fit used as input AFB Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  25. Theory Band • Different MC’s: • VPB • g resummation • ZGRad • O() EW corr. • Pythia • Parton shower (QED+QCD) • Nothing w/ NLO QCD & O() EW • Indicates size of effects • PDF’s, ISR… Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

  26. SM with Measured Z0 couplings Using couplings fit as input AFB gives: • All results consistent with SM. • Not useful for non-SM physics near Z pole • Nothing new above the pole yet. Asymmetries in W and Z/Drell-Yan Production at the Tevatron E. Halkiadakis

More Related