CDF Logo A Z' Search in High Pt Dielectron Events using the Dielectron Invariant Mass and Angular Distribution Exotics Logo

We report results from a search for massive Z' bosons in the dielectron channel using a 448 pb-1 dataset accumulated with the CDF II detector in ppbar collisions at sqrt(s) = 1.96 TeV at the Fermilab Tevatron. To identify the Z' signal, we use both the dielectron invariant mass Mee distribution, and the angular distribution cos(θ*) of the electron pair in the Collins-Soper frame. The CDF data is found to be consistent with the null (no Z') hypothesis, with a probability greater than the values obtained in 87% of pseudo-experiments. So we set 95% confidence level upper limits on the Z' mass for many Z' models: the sequential Z'SM, the canonical superstring-inspired E6 models (Zχ, Zψ, Zη, ZI,ZN), the four general U(1) model-lines advocated in Phys.Rev.D70:093009,2004 , the "littlest" Higgs ZH model, and contact-interaction searches.


Plots and Tables:

Highest Mass Event
Mee=470 GeV/c2 GIF.
Background Distributions
Dijet Invariant Mass (Mjj) Distribution EPS or GIF.
Dijet cos(θ*) Distribution for three mass ranges. EPS or GIF.
Data-Monte Carlo comparisons
Mee Distribution EPS or GIF.
cos(θ*) Distribution for three mass ranges. EPS or GIF.
AFB Distribution EPS or GIF.
Mee Distribution for the search region Mee>200 GeV/c2. EPS or GIF.
cos(θ*) Distribution for the search region Mee>200 GeV/c2. Note that the yellow band includes only the statistical uncertainty. There is also a 50% uncertainty on the background, which makes the left-most bin less significant. EPS or GIF.
Model Exclusions:
Z' Exclusion plot for general U(1) model lines. We derive exclusion contours in the (x, MZ') plane for different gZ values of the strength of the coupling between the Z' boson and the Standard Model fermions. Current limits are compared with LEP. EPS, JPG or GIF.


95% C.L. lower limits on sequential and canonical E6 models.
Z' Model Z'SM Zχ Zψ Zη ZI ZN Zsec
Expected Limit (GeV/c2) 860 735 725 745 650 710 675
Observed Limit (GeV/c2) 850 740 725 745 650 710 680
JPG or GIF.

95% C.L. lower limits on the littlest Higgs Z' models.
Z' Model ZH0.3 ZH0.5 ZH0.7 ZH1.0
Expected Limit (GeV/c2) 625 765 835 910
Observed Limit (GeV/c2) 625 760 830 900
JPG or GIF.

95% C.L. lower limits on contact interaction mass scales.
Z' Model LL LR RL RR VV AA
Λqe+(TeV/c2) 3.7 4.7 4.5 3.9 5.6 7.8
Λqe-(TeV/c2) 5.9 5.5 5.8 5.6 8.7 7.8
JPG or GIF.


Page was last updated Feb. 2nd, 2006 by Catalin Ciobanu.
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