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

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, 24^th, 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 (P_T) dependent angular coefficients A₀, A₂, A₃, and A₄ are compared with several predictions based on Quantum Chromodymnamics (QCD). The P_T dependence of A₀ and A₂ is in agreement with the predictions of perturbative QCD and shows that the production of Z bosons at large P_T 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 E_T and is close to 100%

Event Selection

Two high pt electrons selected with E_T > 25GeV(higher E_T leg) and 15GeV (lower E_T leg) for Z(CC), E_T > 20 GeV for Z(CP), and E_T > 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 P_T spectrum.
The total QCD background is 0.30 % level and the Electroweak background is 0.19 % level.
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Z P_T distribution.
y-axis corresponds to the total number of events in the bin.
.eps

	Z P_T spectrum. The number of events in the bin is normalized by the bin width. .eps
	A₀ in P_T measurement. The uncertainty is total error. (stat. and syst. error are summed in quadrature.) The dominant uncertainty is the statistical error. .eps
	A₂ in P_T measurement. The uncertainty is total error. (stat. and syst. error is summed in quadrature.) The dominant uncertainty is the statistical error. .eps
	A₃ in P_T measurement. The uncertainty is total error. (stat. and syst. error is summed in quadrature.) The dominant uncertainty is the statistical error. .eps
	A₄ in P_T 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 P_T 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 P_T 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 P_T The average A₀ - A₂ = 0.017 ± 0.023. .pdf
	sin²(theta_W) vs. A₄ in FEWZ(NNLO) and Powheg(NLO) prediction The extracted sin²(theta_W) in FEWZ = 0.2331 ± 0.0008 The extracted sin²(theta_W) in Powheg = 0.2328 ± 0.0008 The uncertainty corresponds to the total error of A₄ measurement. .eps
	sin²(theta_W) vs. A₄ in ResBos, VBP, and Pythia prediction .eps
	The measured A₄ = 0.1098 ± 0.0079. sin²(theta_W) vs. A₄ The extracted sin²(theta_W) = 0.2329 ± 0.0008 (A₄ total error)^+0.0010_-0.0009 (QCD theory) FEWZ, Powheg, ResBos, VBP, and Pythia predictions are used. .eps