Angular Coefficients of Drell-Yan Dielectron Pairs with 2.1 fb -1

Authors: Jiyeon Han, Arie Bodek, Willis Sakumoto, Y.S.Chung
Last Updated: Feb, 24th, 2011

Public Note : CDFNote 10312

Abstract

We report on the measurement of the angular distributions of final state electrons in ppbar &rarr &gamma*/Z &rarr e+e- events produced in the Z boson region mass range of 66 to 116 GeV/c2 from 2.1 fb-1 of proton anti-proton collisions at (s)^½ = 1.96 TeV taken by the CDF detector at Fermilab. The transverse momentum (PT) dependent angular coefficients A0, A2, A3, and A4 are compared with several predictions based on Quantum Chromodymnamics (QCD). The PT dependence of A0 and A2 is in agreement with the predictions of perturbative QCD and shows that the production of Z bosons at large PT proceeds via a combination of the quark-antiquark annihilation and the quark-gluon Compton processes. We find a good agreement with the Lam-Tung relation (A0 = A2), which implies that the spin of the gluon is 1.

Data set and Trigger Efficiency

The dataset is based on 2.1 fb-1 of integrated luuminosity taken with two triggers: an inclusive single central electron trigger and a two electron trigger (central or forward). The trigger efficiency is determined as a function of electron ET and is close to 100%

Event Selection

Two high pt electrons selected with ET > 25GeV(higher ET leg) and 15GeV (lower ET leg) for Z(CC), ET > 20 GeV for Z(CP), and ET > 25 GeV for Z(PP). For CC events, one electron is required to pass tight electron ID cuts and the other loose. The CC topology is required to have oppositely charged electron pairs. For CP events, the central electron is required to pass the tight cuts and the plug electron the standard plug ID cuts. For the PP topology, both electrons are required to pass the standard plug ID cuts and have the same pseudo-rapidity direction (positive or negative direction). All events are required to have a track on both electrons to reduce the background contamination.
138,172 ± 372 of Z boson events are selected.

This measurement is extension of d&sigma/dy analysis with 2.1 fb-1 data.
The more details is described in the webpage or public note of d&sigma/dy analysis.
Webpage : d&sigma/dy Public webpage
Public Note : d&sigma/dy Public note

Background

The QCD background is estimated from the electron isolation energy distribution and mass spectrunm using the data. The background from Electronweak processe is also measured using the MC simulations. The total background rate is 0.49 % in total (0.30 % for QCD and 0.19 % from Electroweak process)

Plots

Z PT spectrum.
The total QCD background is 0.30 % level and the Electroweak background is 0.19 % level.
.eps
Z PT distribution.
y-axis corresponds to the total number of events in the bin.
.eps
Z PT spectrum.
The number of events in the bin is normalized by the bin width.
.eps
A0 in PT measurement.
The uncertainty is total error.
(stat. and syst. error are summed in quadrature.)
The dominant uncertainty is the statistical error. .eps
A2 in PT measurement.
The uncertainty is total error. (stat. and syst. error is summed in quadrature.)
The dominant uncertainty is the statistical error. .eps
A3 in PT measurement.
The uncertainty is total error.
(stat. and syst. error is summed in quadrature.)
The dominant uncertainty is the statistical error. .eps
A4 in PT measurement.
The uncertainty is total error.
(stat. and syst. error is summed in quadrature.) The dominant uncertainty is the statistical error. .eps
Table : Angular coefficients measurement in PT
The uncertainty is total error.
(stat. and syst. error is summed in quadrature.)
The dominant uncertainty is the statistical error. .pdf
Lam-Tung Relation ( A0 - A2 = 0 ) in PT measurement.
The uncertainty is total error.
(stat. and syst. error is summed in quadrature.)
The dominant uncertainty is the statistical error. .eps
Table : Lam-Tung relation in PT
The average A0 - A2 = 0.017 ± 0.023.
.pdf
sin2(thetaW) vs. A4 in FEWZ(NNLO) and Powheg(NLO) prediction
The extracted sin2(thetaW) in FEWZ = 0.2331 ± 0.0008
The extracted sin2(thetaW) in Powheg = 0.2328 ± 0.0008
The uncertainty corresponds to the total error of A4 measurement.
.eps
sin2(thetaW) vs. A4 in ResBos, VBP, and Pythia prediction
.eps
The measured A4 = 0.1098 ± 0.0079.
sin2(thetaW) vs. A4
The extracted sin2(thetaW) = 0.2329 ± 0.0008 (A4 total error)+0.0010-0.0009 (QCD theory)

FEWZ, Powheg, ResBos, VBP, and Pythia predictions are used.
.eps

 

Contact the Authors : Jiyeon Han on behalf of Authors.