Measurement of Wgamma and Zgamma Production in ppbar Collisions at sqrt(s)=1.96 TeV


The analysis was performed by
Al Goshaw, Michael Kirby (Duke University)
Helen Hayward,, Beate Heinemann (Liverpool University)
and Naho Tanimoto (Okayama University)
Please refer to the publication for details.
The Standard Model predictions for Wgamma and Zgamma production are tested using an integrated luminosity of 200 pb^-1 of ppbar 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 E_T>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
Electron
 Et (transverse energy) > 25GeV, |eta(electron)|<2.8
Muon
 Pt (transverse momentum) > 20GeV, |eta(muon)|<1.1
Neutrino MEt (missing transverse energy) > 25 GeV (electron analysis), 20 GeV (muon analysis)
Transverse mass(electron, neutrino)
 30 < Mt < 120 GeV
Photon
 Et(transverse energy) > 7 GeV,  |eta(photon)|<1.1


Wgamma events yields

 Electrons Muons
signal MC 126.8 ± 5.8 95.2 ± 4.9
W+jet Backgound
 59.5 ± 18.1 27.6 ± 7.5
Zgamma Background
 6.3 ± 0.3 17.4 ± 1.0
Wgamma-> tau nu gamma
 1.5 ± 0.2 2.3 ± 0.2
total SM+BG
 194.1± 19.1 142.4± 9.5
Data
 195 128


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

sigma(Wgamma) x BR(W->lepton +nu) [pb]
 18.1±3.1
Theory : sigma(Wgamma) x BR(W-> lepton + nu)  [pb] 19.3±1.4

Event criteria for Z+gamma
Electron
 Et (transverse energy) > 25GeV, |eta(electron)|<2.8
central EM calorimeter (CEM) covers |eta|< 1.1 and plug calorimeter covers 1.2 < |eta|<2.8
Muon
 Pt (transverse energy) > 20GeV, |eta(muon)|<1.1
Invariant mass(lepton,lepton)
M > 40 GeV
Photon
 Et(transverse energy) > 7 GeV,  |eta(photon)|<1.1


Zgamma events yields

 Electrons Muons
signal MC 31.3 ± 1.6 33.6 ± 1.5
Z+jet Backgound
 2.8 ± 0.9 2.1 ± 0.6
total SM+BG
 34.1± 1.8 35.7± 1.7
Data
 36 35


Cross section for Et(gamma)>7 GeV, DeltaR(lepton,gamma)>0.7 and M(ll)>40 GeV

sigma(Zgamma) x BR(Z->lepton + lepton) [pb]
 4.6±0.6
Theory : sigma(Zgamma) x BR(Z-> lepton + lepton)  [pb] 4.5±0.3

Kinematic Distributions Wgamma
 Zgamma
Et(gamma) photonEt
gif | eps
 photonEt
gif | eps
Wgamma: Cluster Transverse mass (lepton, photon, neutrino)
Zgamma: 3-body-mass(lepton, lepton, neutrino)		 Mt(lgamma, nu)
gif | eps
 M(llgamma, nu)
gif | eps
Wgamma: (l,v,g) cluster transverse mass versus (l,v) transverse mass
Zgamma: (l+,l-,g) 3-body mass versus (l+,l-) 2-body mass		 cluster mass vs mt
gif | eps
 M(l+,l-,g) vs M(l+,l-)
gif | eps


Last Updated February 01, 2005
Beate Heinemann(beate@fnal.gov) (Liverpool University)