Z + gamma at CDF

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

Authors:
Blessed: September 3, 2009 (added neutrino results)
Data: Run II, 1.1/fb (ee) and 2.0/fb(μμ and νν)

Introduction
Summary of Results

Abstract

We have measured (Z -> l⁺l^-)+γ production with central photons using electronic, muonic, and invisible (neutrino) 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:

Observed Expected

|h₃^Z| < 0.050 < 0.062 ±0.014

|h₄^Z| < 0.0034 < 0.0043 ±0.0009

|h₃^γ| < 0.051 < 0.064 ±0.014

|h₄^γ| < 0.0034 < 0.0043 ±0.0009

Summary of Results

Electron + Muon + Neutrino Combined Results

Limits:

	Lambda_1200_Zgg_h3_ALLC_Likelihood_Rebin
	Likelihood function for h₃^γ Z-γ-γ vertex.
	eps pdf
	Lambda_1200_ZZg_h3_ALLC_Likelihood_Rebin
	Likelihood function for h₃^Z; Z-Z-γ vertex.
	eps pdf
	Lambda_1200_Zgg_h4_ALLC_Likelihood_Rebin
	Likelihood function for h₄^γ Z-γ-γ vertex.
	eps pdf
	Lambda_1200_ZZg_h4_ALLC_Likelihood_Rebin
	Likelihood function for h₄^Z; Z-Z-γ vertex.
	eps pdf

Combined electron + muon Results

Limits from electron and muon data only:

Summary of Zγ ( 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 Zγ ( 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 Zγ ( 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 → ee and the Z → μμ datasets.
	eps pdf gif
	Delta_Ra_ZeeZmm
	Separation (Delta Ra) between leading lepton and photon (Et > 7 GeV) in the Z → ee and the Z → μμ datasets.
	eps pdf gif
	Delta_Rb_ZeeZmm
	Separation (Delta Rb) between non-leading lepton and photon (Et > 7 GeV) in the Z → ee and the Z → μμ datasets.
	eps pdf gif
	llgMass10GeV_Zll_log
	M_llγ distribution in the Z → μμ + Z → ee datasets for events with photon Et > 7 GeV.
	eps pdf gif
	llgMass10GeV_Zll
	M_llγ distribution in the Z → μμ + Z → ee datasets for events with photon Et > 7 GeV.
	eps pdf gif
	MllVsMllg1GeV_Zll
	M_ll - M_llγ distribution in the Z → μμ + Z → ee datasets for photons with Et > 7 GeV.
	eps pdf gif
	MllVsMllg1GeVMC_Zll
	M_ll - M_llγ distribution in the Z → μμ + Z → ee Monte Carlo (Baur) dataset for photons with Et > 7 GeV.
	eps pdf gif
	MllVsMllg1GeVBkg
	Z + jet and γ + fake Z background to the M_ll - M_llγ distribution in the Z → μμ + Z → ee dataset for photons with Et > 7 GeV.
	eps pdf gif
	MllVsMllg1GeVAll
	Zγ overlaid on Monte Carlo + jet background to the M_μμ - M_μμγ distribution in the Z → μμ + Z → ee dataset for photons with Et > 7 GeV.
	eps pdf gif
	Mll_10GeV_Zmm
	M_ll distribution in the Z → μμ + Z → 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→ μ⁺μ^- plus Z→ 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 h₃^γ with the Z→ μ⁺μ^- plus Z→ e⁺e^- datasets.
	eps pdf gif
	EleMuon-Lambda_1200_Zgg_h4_ALLC_2DeltaLogLikelihood_Fit
	Fit for h₄^γ with the Z→ μ⁺μ^- plus Z→ e⁺e^- datasets.
	eps pdf gif
	EleMuon-Lambda_1200_ZZg_h3_ALLC_2DeltaLogLikelihood_Fit
	Fit for h₃^Z with the Z→ μ⁺μ^- plus Z→ e⁺e^- datasets.
	eps pdf gif
	EleMuon-Lambda_1200_ZZg_h4_ALLC_2DeltaLogLikelihood_Fit
	Fit for h₄^Z with the Z→ μ⁺μ^- plus Z→ 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→ 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 → μμ dataset.
	eps pdf gif
	Delta_Ra_Zmm
	Separation (Delta Ra) between leading muon and photon (Et > 7 GeV) in the Z → μμ dataset.
	eps pdf gif
	Delta_Rb_Zmm
	Separation (Delta Rb) between non-leading muon and photon (Et > 7 GeV) in the Z → μμ dataset.
	eps pdf gif
	mmgMass10GeV_Zmm
	M_μμγ$ distribution in the Z → μμ dataset for events with photon Et > 7 GeV.
	eps pdf gif
	MmumuVsMmumug1GeV_Zmm
	M_μμ - M_μμγ$ distribution in the Z → μμ dataset for photons with Et > 7 GeV.
	eps pdf gif
	MmumuVsMmumug1GeVMC_Zmm
	M_μμ - M_μμγ$ distribution in the Z → μμ Monte Carlo (Baur) dataset for photons with Et > 7 GeV.
	eps pdf gif
	MmumuVsMmumug1GeVBkg
	Z + jet background to the M_μμ - M_μμγ$ distribution in the Z → μμ dataset for photons with Et > 7 GeV.
	eps pdf gif
	MmumuVsMmumug1GeVAll
	Zγ overlaid on Monte Carlo + jet background to the M_μμ - M_μμγ$ distribution in the Z → μμ dataset for photons with Et > 7 GeV.
	eps pdf gif
	Mmm_10GeV_Zmm
	M_μμ$ distribution in the Z → μμ dataset for events with photon Et > 7 GeV.
	eps pdf gif

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

Zγ, Z decaying to νν

	phoEt_data_log
	Photon Et in the photon + missing Et dataset.
	eps pdf

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	Observed	Expected
\|h₃^Z\|	< 0.050	< 0.062 ±0.014
\|h₄^Z\|	< 0.0034	< 0.0043 ±0.0009
\|h₃^γ\|	< 0.051	< 0.064 ±0.014
\|h₄^γ\|	< 0.0034	< 0.0043 ±0.0009

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