Z + gamma at CDF

Z γ Production and Limits on Neutral Anomalous Coupling in ppbar Collisions at √s=1.96 TeV and Limits on Neutral Anomalous Coupling

Authors:
Blessed: January 31, 2008
Data: Run II, 1.1/fb (ee) and 2.0/fb(μμ)

Introduction
Summary of Results

Abstract

We have measured (Z -> l⁺l^-)+γ production with central photons using both electronic and muonic Z decays. The measured cross section for Z+γ where (M_ll > 40 GeV/c²) and the photon is central, has E_Tγ > 7 GeV, and is separated from both leptons by ΔR > 0.7 is σ_obs = 4.6 ± 0.2 (stat) ± 0.3 (syst) ± 0.3 (lum) picobarns. This compares to the next-to-leading-order calculation of σ_NLO = 4.5 ± 0.3 pb, so the measured value is consistent with the expected value. The measured cross section for the subset of these events with M_μμγ > 100 GeV/c² (predominently Initial-State-Radiation (ISR) events) is σ_obs = 1.2 ± 0.1 (stat) ± 0.2 (syst) ± 0.1 (lum) picobarns. The kinematic distributions also agree with the expected shapes.

These data have been used to set limits on neutral anomalous couplings.

Summary of Results

Combined electron + muon Results

Summary of $Z\gamma$ ( Z to electrons + Z to muons) data including the measured cross section for both the final-state radiation (FSR) and initial-state radiation (ISR):

Summary of $Z\gamma$ ( Z to electrons + Z to muons) data including the measured cross section for the final-state radiation (FSR) dominated region (three-body mass less than 100 GeV/c^2):

Summary of $Z\gamma$ ( Z to electrons + Z to muons) data including the measured cross section for the initial-state radiation (ISR) dominated region (three-body mass greater than 100 GeV/c^2):

	Et_7GeV_ZeeZmm
	Photon Et in the $Z\to ee$ and the $Z\to \mu\mu$ datasets.
	eps pdf gif
	Delta_Ra_ZeeZmm
	Separation (Delta Ra) between leading lepton and photon (Et > 7 GeV) in the $Z\to ee$ and the $Z\to \mu\mu$ datasets.
	eps pdf gif
	Delta_Rb_ZeeZmm
	Separation (Delta Rb) between non-leading lepton and photon (Et > 7 GeV) in the $Z\to ee$ and the $Z\to \mu\mu$ datasets.
	eps pdf gif
	llgMass10GeV_Zll_log
	$M_{ll\gamma}$ distribution in the $Z\to \mu\mu$ + $Z\to ee $ datasets for events with photon Et > 7 GeV.
	eps pdf gif
	llgMass10GeV_Zll
	$M_{ll\gamma}$ distribution in the $Z\to \mu\mu$ + $Z\to ee $ datasets for events with photon Et > 7 GeV.
	eps pdf gif
	MllVsMllg1GeV_Zll
	$M_{ll} - M_{ll\gamma}$ distribution in the $Z\to \mu\mu$ + $Z\to ee $ datasets for photons with Et > 7 GeV.
	eps pdf gif
	MllVsMllg1GeVMC_Zll
	$M_{ll} - M_{ll\gamma}$ distribution in the $Z\to \mu\mu$ + $Z\to ee$ Monte Carlo (Baur) dataset for photons with Et > 7 GeV.
	eps pdf gif
	MllVsMllg1GeVBkg
	$Z$ + jet and #gamma + fake $Z$ background to the $M_{ll} - M_{ll\gamma}$ distribution in the $Z\to \mu\mu$ + $Z\to ee $ dataset for photons with Et > 7 GeV.
	eps pdf gif
	MllVsMllg1GeVAll
	$Zgamma$ overlaid on Monte Carlo + jet background to the $M_{\mu\mu} - M_{\mu\mu\gamma}$ distribution in the $Z\to \mu\mu$ + $Z\to ee $ dataset for photons with Et > 7 GeV.
	eps pdf gif
	Mll_10GeV_Zmm
	$M_{ll}$ distribution in the $Z\to \mu\mu$ + $Z\to ee $ datasets for events with photon Et > 7 GeV.
	eps pdf gif
	EleMuon-Lambda_1200_ZZg_h4_ALLC_gammaEt_LogX
	Photon Et in the $Z\to \mu^+\mu^-$ plus $Z\to e^+e^-$ datasets. The solid blue line is the Standard Model prediction, while the dashed red line is the anomalous coupling prediction for $h_4^Z = 0.0047$.
	eps pdf gif
	EleMuon-Lambda_1200_ZZg_h4_ALLC_gammaEt_LogX1
	Same plot as above, but with an expanded range on the y-axis to show the Standard Model prediction in the two highest bins.
	pdf gif

These electron + muon data have been used to set limits on neutral anomalous couplings:

	EleMuon-Lambda_1200_Zgg_h3_ALLC_2DeltaLogLikelihood_Fit
	Fit for ]$h_3^\gamma$ with the $Z\to \mu^+\mu^-$ plus $Z\to e^+e^-$ datasets.
	eps pdf gif
	EleMuon-Lambda_1200_Zgg_h4_ALLC_2DeltaLogLikelihood_Fit
	Fit for ]$h_4^\gamma$ with the $Z\to \mu^+\mu^-$ plus $Z\to e^+e^-$ datasets.
	eps pdf gif
	EleMuon-Lambda_1200_ZZg_h3_ALLC_2DeltaLogLikelihood_Fit
	Fit for ]$h_3^Z$ with the $Z\to \mu^+\mu^-$ plus $Z\to e^+e^-$ datasets.
	eps pdf gif
	EleMuon-Lambda_1200_ZZg_h4_ALLC_2DeltaLogLikelihood_Fit
	Fit for ]$h_4^Z$ with the $Z\to \mu^+\mu^-$ plus $Z\to e^+e^-$ datasets.
	eps pdf gif

Zγ, Z decaying to e⁺e^- (1 fb^-1)

	Ele-Lambda_1200_ZZg_h4_ALLC_gammaEt_LogX
	Photon Et in the $Z\to e^+e^-$ dataset. The solid blue line is the Standard Model prediction, while the dashed red line is the anomalous coupling prediction for $h_4^Z = 0.0074$.
	eps pdf gif
	Ele-Lambda_1200_ZZg_h4_ALLC_gammaEt_LogX1
	Same plot as above, but with an expanded range on the y-axis to show the Standard Model prediction in the two highest bins.
	pdf gif

These electron data have been used to set limits on neutral anomalous couplings:

Zγ, Z decaying to μ⁺μ^-(2 fb^-1)

	Et_7GeV_Zmm
	Photon Et in the $Z\to \mu\mu$ dataset.
	eps pdf gif
	Delta_Ra_Zmm
	Separation (Delta Ra) between leading muon and photon (Et > 7 GeV) in the $Z\to \mu\mu$ dataset.
	eps pdf gif
	Delta_Rb_Zmm
	Separation (Delta Rb) between non-leading muon and photon (Et > 7 GeV) in the $Z\to \mu\mu$ dataset.
	eps pdf gif
	mmgMass10GeV_Zmm
	$M_{\mu\mu\gamma}$ distribution in the $Z\to \mu\mu$ dataset for events with photon Et > 7 GeV.
	eps pdf gif
	MmumuVsMmumug1GeV_Zmm
	$M_{\mu\mu} - M_{\mu\mu\gamma}$ distribution in the $Z\to \mu\mu$ dataset for photons with Et > 7 GeV.
	eps pdf gif
	MmumuVsMmumug1GeVMC_Zmm
	$M_{\mu\mu} - M_{\mu\mu\gamma}$ distribution in the $Z\to \mu\mu$ Monte Carlo (Baur) dataset for photons with Et > 7 GeV.
	eps pdf gif
	MmumuVsMmumug1GeVBkg
	$Z$ + jet background to the $M_{\mu\mu} - M_{\mu\mu\gamma}$ distribution in the $Z\to \mu\mu$ dataset for photons with Et > 7 GeV.
	eps pdf gif
	MmumuVsMmumug1GeVAll
	$Zgamma$ overlaid on Monte Carlo + jet background to the $M_{\mu\mu} - M_{\mu\mu\gamma}$ distribution in the $Z\to \mu\mu$ dataset for photons with Et > 7 GeV.
	eps pdf gif
	Mmm_10GeV_Zmm
	$M_{\mu\mu}$ distribution in the $Z\to \mu\mu$ dataset for events with photon Et > 7 GeV.
	eps pdf gif