Measurement of Z Forward-backward Asymmetry with 4.1/fb data

Authors: Yeonsei Chung, Jiyeon Han, Geumbong Yu, Arie Bodek, Willis Sakumoto, Kevin McFarland
Last Updated: Nov 02th, 2009


We present a measurement of the Z boson forward-backward asymmetry of the process ppbar -> &gamma*/Z + X -> e+e- + X, in the region where the dielectron invariant mass is larger than 50 GeV/c^2. The measurement uses 4.1/fb of CDF Run II data. The method of matrix inversion is used to correct for the distortion in the measurement caused by the detector resolution and photon radiation in the final state. The measurement is compared with PYTHIA v6.216 and it agrees well with PYTHIA prediction.

Data Sample

The integrated luminosity of the data sample is 4.1/fb.
The inclusive signle high pt central electron trigger is used.
The Monte Carlo sample is tuned to match to data for the efficiencies.
The dielectrons from Z->tautau process are also considered as a signal.

Event Selection

In the analysis, we use two different topologies based on the electron selection.
The CC topology is selected to have two central electron and the CP topology has a central and a plug electron.

Variable Central Plug
Fiducial Track Fiduciality 1.2 < |eta| < 2.8
ET > 25 GeV for CC (> 20 GeV for CP) > 20 GeV
|Track Z0| <= 60 cm <= 60 cm
PT > 10 GeV N/A
Ehad/Eem <= 0.055 + 0.00045 * E <= 0.05
Isolation(GeV) <= 3 + 0.02 ET <= 1.6 + 0.02 ET
E/p <= 2.0 or PT(Track) > 50 GeV N/A
Q*(delta X) -3.0 cm < Q*(delta X) < 1.5 cm N/A
|delta Z| < 3 cm N/A
Lshr < 0.2 N/A
PEM chi2 3x3 N/A 10
Charge Opposite charge for CC events.
For the CP events, plug electron charge is assumed to be the opposite
to the central electron.
Mee > 50 GeV

Response Matrix

The response matrix is used to unfold the forward-backward charge asymmetry.
The response matrix includes all efficiencies as well as the acceptance.

Tables and Plots

Dielectron invariant mass distribution
Response matrix .gif
Pseudo experiments result.
The blue points are AFB in the reconstructed level and the red points are the unfolded AFB.
The band corresponds to the statistical uncertainty of 4.1/fb data.
AFB in the reconstructed level.
Only statistical errors are considered.
The measurement is compared with PYTHIA v6.216
Unfolded AFB.
The blue line corresponds to the statistical error.
The red line corresponds to the statistical+systematic error.
The measurement is compared with PYTHIA v6.216.


Suggestions or contributions ? Contact Us (Yeonsei Chung or Jiyeon Han)