Measurement of Wgamma and Zgamma Production in pp Collisions at √s=1.96 TeV


The analysis was performed by
Jianrong Deng, Al Goshaw, Thomas Phillips (Duke University)
Beate Heinemann (Liverpool University)
and Ai Nagano (University of Tsukuba)
The Standard Model predictions for Wgamma and Zgamma production are tested using an integrated luminosity of 1 fb-1 of pp collision data collected at the Collider Detector at Fermilab. The cross sections are measured by selecting leptonic decays of the W and Z bosons, and photons with transverse energy ET > 7 GeV that are well separated from leptons. The production cross sections and kinematic distributions for the Wgamma and Zgamma data are compared to SM predictions.
Event criteria for W+gamma
Muon
 pT (transverse momentum) > 20GeV, |eta(muon)|<1.1
Neutrino MET (missing transverse energy) > 20 GeV
Transverse mass(muon,neutrino)
 30 < Mt < 120 GeV
Photon
 ET(transverse energy) > 7 GeV, |eta(photon)|<1.1





Cross section for Et(gamma)>7 GeV and DeltaR(lepton,gamma)>0.7:

sigma(Wgamma) x BR(W->muon +nu) [pb]
 19.11±1.04(stat.)±2.40(sys.)±1.11(lumi.)
Theory : sigma(Wgamma) x BR(W-> lepton + nu) [pb] 19.3±1.4

Event criteria for Z+gamma
Electron
 Et (transverse energy) > 20GeV, |eta(electron)|<2.8
central EM calorimeter (CEM) covers |eta|< 1.1
plug EM calorimeter(PEM) covers 1.2 < |eta|<2.8
Invariant mass(lepton,lepton)
Mee > 40 GeV
Invariant three-body mass(lepton,lepton, photon)
Meeγ > 40 GeV
Photon
 Et(transverse energy) > 7 GeV,  |eta(photon)|<1.1

Zgamma events yields
Luminosity 1 fb-1
 Meeγ> 40 GeV
 Meeγ> 100 GeV (ISR dominate)
signal MC 323.8 ± 17.3
 117.2 ± 6.3
Background
 51.0 ± 15.7
 39.2 ± 12.4
total SM+BG
 374.8 ± 23.4
156.4 ± 13.9
Data
 390
 154


Cross section for Et(γ)>7 GeV
and ΔR(l,γ)<0.7
Meeγ> 40 GeV
 Meeγ> 100 GeV
sigma(Z(ee)γ)
4.9 ± 0.3 (stat.) ± 0.3(sys.) ± 0.3 (lum.) 1.4 ± 0.1 (stat.) ± 0.2(sys.) ± 0.1 (lum.)
Theory : sigma(Z(ee)γ)   4.7 ± 0.4 [pb]
1.4 ± 0.1 [pb]

Kinematic Distributions W+gamma in Muon Channel
Z+gamma in Electron Channel
pT(gamma) photon pT
gif | eps
 photon pT
gif | eps
Wgamma: DeltaR(muon,gamma)
Zgamma: DeltaR(electron,gamma)
 DeltaR(muon,gamma)
gif | eps
 DeltaR(electron,gamma)
gif | eps
Wgamma: transverse mass(muon,neutrino)
Zgamma: invariant mass(electron,electron)
MT(muon,nu)
gif | eps
 M(e,e)
gif | eps
Wgamma: cluster transverse mass (lepton, photon, neutrino)
Zgamma: three-body mass (electron, electron, photon)
MT(lgamma, nu)
gif | eps
 M(e,e,gamma)
gif | eps
Wgamma: cluster transverse mass versus transverse mass
Zgamma: (l+,l-) two-body mass versus (l+,l-,γ) three-body mass
cluster mass vs mt
gif | eps
 Mee vs Meeg
gif | eps


Last Updated November 21, 2006
Ai Nagano(naganoai@fnal.gov) (University of Tsukuba)
Jianrong Deng(jdeng@fnal.gov) (Duke University)