1 / 29

The Measurement of A FB in Electron-Positron Pairs

The Measurement of A FB in Electron-Positron Pairs. Gregory Veramendi (Illinois) for the CDF Collaboration. Outline  A Brief History of A FB  Signal and Background  Acceptance  Results. f ’. f ’. f. f. f. f. f ’. f ’. f ’. q. f. f. f ’. A FB.

bsomerville
Download Presentation

The Measurement of A FB in Electron-Positron Pairs

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. The Measurement of AFB in Electron-Positron Pairs Gregory Veramendi (Illinois) for the CDF Collaboration Outline A Brief History of AFB Signal and Background Acceptance Results

  2. f ’ f ’ f f f f f ’ f ’ f ’ q f f f ’ AFB • Interference between Z and g* exchanges • q-dependent cross sections ds / dcosq = A(1+cos2q) + Bcosq • AFB = 3B / 8A • Directly probing the couplings • Reduces systematics • Luminosity, efficiencies and acceptance g* Z + f = e, quarks

  3. AFB at e+e- Colliders • CESR • PEP • PETRA • TRISTAN • SLC • measure s L,R using polarized e beams • LEP • Tevatron needs >10 fb-1 to compete

  4. CDF Run I (~110 pb-1) e- q q e+ AFB 2.2s dev. from SM q AFB at Hadron Colliders

  5. AFB beyond LEPII: Z´,etc... 500 GeV/c2 Z’: • Looking for symmetries beyond the SM • Various models predict new neutral, heavy bosons: Z´s • New resonance could interfere with g and Z. • Complementary to cross-section search (see Muge’s talk) Rosner, J.L.: Phys. Rev. D 54, 1078 (1996) AFB Zx Z Mee(GeV/c2)

  6. Z/g* Candidates and CDF • Selection (5211 candidates) • 2 high PT isolated electrons • ET > 20 GeV CDF II Preliminary CDF detector CDF II Preliminary

  7. Backgrounds for Z/g* • Dijet dominant Background Summary CDF II Preliminary CDF II Preliminary

  8. Data-MC Comparisons CDF II Preliminary

  9. Data-MC: Cos(*) CDF II Preliminary

  10. Calculating AFB • Calculating AFB: • cos* in Collin-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*

  11. Acceptance:Event Loss • Generator Level: • Acceptance is symmetric, but distribution is not • Grey: • |1 | <1,|1 | <3, • ET > 20 GeV • Tends to shift AFB in a bin Raw Distr. Acceptance Low Mass Pole Region High Mass

  12. Acceptance:Event Migration • Event Migration Matrix • Large correlations between bins near Z pole • Unfolding Problem • Invert Matrix by fitting for AFB • Large variances • Correction factors • Biases result • High Mass O.K. Sum AFB in Rows: 600 GeV/c2 CDF II Preliminary 40GeV/c2 600GeV/c2

  13. Fit with smoothing • Result fitting AFB • Large uncertainties • Tikhonov regularization • Only in bins with correlations CDF II Preliminary CDF II Preliminary

  14. Fitting for Z Couplings • Fit at Raw AFB Level • Test AFB is smeared • c2 show good agreement with SM c2=10.66/11

  15. Couplings Results Quark Couplings Electron Couplings:

  16. 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

  17. SM w/ measured Z couplings • Result with correction factors • Not useful for non-SM physics near Z-pole CDF II Preliminary CDF II Preliminary

  18. Conclusions • Unfolding Problem near Z pole • Fit for couplings using uncorrected AFB • Good agreement with current world ave. • Contribute to Z-quark couplings in future? • High mass not affected by smearing • Nothing new above pole, yet… • PRD on its way…

  19. Backup Slides

  20. Understanding the detector • Radiation Effects: Charge ID • Get Mee dependence from MC • two effects: “tridents”, (pT) • Trident: • Energy Scale and Resolution CDF II Preliminary CDF II Preliminary MisID rate (trident):0.7%

  21. Cross-Check: SS vs OS • SS vs. OS • CC : Find 36 SS events in our sample • Have to worry about Material  Tridents • Subtracting peak from MC • 13 ± 6(stat) ± 4(sys) events • Checks both radiation in Simulation and background estimation CDF II Preliminary CDF II Preliminary

  22. Dijet background • From Data • Mee from jet sample • AFB from background sample • AFB ~ 0 CDF II Preliminary CDF II Preliminary

  23. Acceptance Line: backward | Dashed: forward • Generator Level Studies: • Event Loss: • A: Fiducial Cuts • B: Kinematic Cuts • Event Migration: • C: ET Smearing • D: FSR Corrections scal(E) |1 | <1 |2 | <3 FSR ET > 20 GeV

  24. Correlations in Couplings

  25. Theory Band • Number of MC’s • VPB • g resummation • ZGRad • O() EW corr. • Pythia • Parton shower (QED+QCD) • Nothing w/ NLO QCD & O() EW

  26. Systematics • Energy Scale • Central: 0.5% • Plug: 1% • Energy Resolution • Central: +0.5 GeV • Plug: +1.5 GeV • Material • Central: ±0.015 Xo Copper • Plug: ±1/6 Xo Iron • Background • QCD: ±fake rate • Montecarlo: • Checked(negligible): • AFB(dijet) • AFB(W+X) • Fiducial acceptance • Charge mis-ID • Trigger efficiency • For SM plot: • AFB input from couplings measurement

  27. Fitting for AFB • Parameterization takes f(AFBphysics) AFBraw • Construct -log(likelihood): binomial function • Some bins poorly constrained… • Add smoothing function  • Choose l such that a’=a+0.5

  28. Add Smoothing • Using Tikhonov regularization • We assume parabolic form for • Solve for three adjacent bins • New likelihood: • Choose l such that a’=a+0.5

  29. Parameterizing Acceptance • Define 4 15x15 matrices: • Efficiency for bin i to end up in bin j • Mean # of events in bin i: • Number of raw/detector level events:

More Related