Evidence of Z0Z0 Production in the ppbar Collisions at √s=1.96 TeV

• Authors:
• Blessed: March 15, 2007
• Data: Run II, 1.1/fb (llνν) and 1.5/fb(4 charged leptons)
• Note: Description with more details

Contents

• Introduction
• Summary of Results
  • ZZ decaying to 4 charged leptons
  • ZZ decaying to llνν
  • Combination
• Control Regions
  • Summary Control Regions
  • Drell-Yan Control Region
  • Same-Sign Control Region
  • Low Met Significance Control Region
  • Low Met Special Control Region
• Event Displays
  • ZZ to 4 Charged Leptons Candidate
  • Highest likilhood ratio ZZ to llνν Candidates

Introduction

We report a search for Z⁰Z⁰ production in the ppbar collisions at √s=1.96 TeV using the combination of the four charged (e,μ) leptons and the two charge lepton two neutrino final state. At tree level, the Z⁰Z⁰ final state is dominated the t-channel process shown in the left diagram below. If an anomalous (not in the Standard Model) triple gauge coupling (ZZ&gamma and ZZZ) exists, then an additional contribution would be made by the s-channel right diagram below.

t-channel

s-channel

Summary of Results

ZZ decaying to 4 charged leptons

TEX or GIF of Signal and background expectations and observed events in the signal region for the Z0Z0 to four charge lepton search analysis.

ZZ decaying to two charged leptons and two neutrinos

TEX or GIF of Signal and background expectations and observed events in the ZZ to llνν fit region.

TEX or GIF of Systematic uncertainties on the expected llνν fit region.yield in percent.

Likelihood Ratio plots for llνν fit

JPG or EPS Likelihood Ratio Distribution	JPG or EPS log (1-Likelihood Ratio Distribution) (distribution actually fit)

Kinematic and Lepton Type plots for llνν

Combined Results

TEX or GIF of Probability of the observing a Z0Z0 with 2, 3, and 5 σ significance, the observed significance, and the observed 95% CL limit on the cross-section.

The observed signal has a P-value of 0.00293 ± 0.00008 which corresponds to a 3.0 σ one-side Gaussian significance. We find the cross-section to be:

This is to be compared the on-shell Z0Z0 cross-section 1.4 ± 0.1 pb at NLO.

Control Regions Overview

• The Drell-Yan Control Region is the same lepton selection, but with a MET < 25 GeV requirement instead of the MET special and MET signficance cuts and tests the lepton identification, trigger efficiency, and luminosity/cross-section calculations.
• The Same-Sign Control Region is the same event selection, but with an same sign instead of opposite sign requirement on the lepton charges. This region tests the modeling of jets and photons misidentified as leptons.
• The Low Met Significance Control Region is the same event selection, but with the MET significance required to be less instead of greater than 2.5 GeV^1/2. This tests the modeling of false MET due the uncluster energy resolution.
• The Low Met Special Control Region is the same event selection, but with the Met Special required to be between 15 and 25 GeV instead of above 25 GeV. This tests the effects of lost lepton or jet energy.

The two met control regions are shown graphically here:

EPS or GIF

Drell-Yan Control Region

TEX or GIF of Expected and observed events in the Drell-Yan Control Region

Same-Sign Control Region

TEX or GIF of Expected and observed events in the Same-Sign Control Region

Kinematic and Lepton Type plots for llνν Same-Sign Control Region

Low Met Significance Control Region

TEX or GIF of Expected and observed events in the Low Met Significance Control Region

Kinematic and Lepton Type plots for llνν Low Met Significance Control Region

Low Met Special Control Region

TEX or GIF of Expected and observed events in the Low Met Special Control Region

Kinematic and Lepton Type plots for llνν Low Met Special Control Region

Event Displays

Z⁰Z⁰ to Four Lepton Candidates

• Run=211311, Event=233113

Z⁰Z⁰ to llνν Candidates

• Run=197288 Event=11891

• Run=203265 Event=3792931

• Run=209021 Event=4038281

Mark Neubauer and Elliot Lipeles

Last modified: Thu Mar 22 16:17:16 CET 2007