CMS-SMP-14-019

CMS-SMP-14-019 ; CERN-EP-2016-007
Measurement of the $\mathrm{Z}\gamma\to\nu\bar{\nu}\gamma$ production cross section in pp collisions at $ \sqrt{s} = $ 8 TeV and limits on anomalous $\mathrm{Z}\mathrm{Z}\gamma$ and $\mathrm{Z}\gamma\gamma$ trilinear gauge boson couplings
CMS Collaboration
23 February 2016
Phys. Lett. B 760 (2016) 448
Abstract: An inclusive measurement of the $\mathrm{Z}\gamma\to\nu\bar{\nu}\gamma$ production cross section in pp collisions at $ \sqrt{s} = $ 8 TeV is presented, using data corresponding to an integrated luminosity of 19.6 fb$^{-1}$ collected with the CMS detector at the LHC. This measurement is based on the observation of events with large missing energy and with a single photon with transverse momentum above 145 GeV and absolute pseudorapidity in the range $\|\eta\| < $ 1.44 . The measured $\mathrm{Z}\gamma\to\nu\bar{\nu}\gamma$ production cross section, 52.7 $\pm$ 2.1 (stat) $\pm$ 6.4 (syst) $\pm$ 1.4 (lumi) fb, agrees well with the standard model prediction of 50.0$^{+ 2.4}_{- 2.2}$ fb. A study of the photon transverse momentum spectrum yields the most stringent limits to date on the anomalous $\mathrm{ Z }\mathrm{ Z }\gamma$ and $\mathrm{ Z } \gamma\gamma$ trilinear gauge boson couplings.
Links: e-print arXiv:1602.07152 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Feynman diagrams of $\mathrm{ Z } \gamma $ production via initial-state radiation in the SM at tree level (left), and via anomalous $\mathrm{ Z } \mathrm{ Z } \gamma $ or $\mathrm{ Z } \gamma \gamma $ trilinear gauge couplings (right).
png pdf	Figure 1-a: Feynman diagram of $\mathrm{ Z } \gamma $ production via initial-state radiation in the SM at tree level.
png pdf	Figure 1-b: Feynman diagrams of $\mathrm{ Z } \gamma $ production via anomalous $\mathrm{ Z } \mathrm{ Z } \gamma $ or $\mathrm{ Z } \gamma \gamma $ trilinear gauge couplings.
png pdf	Figure 2: The $E_\mathrm {T}^{\gamma }$ and $E_{\mathrm{T}}^{\text{miss}}$ distributions in data (points with error bars) compared with the SM $\mathrm{ Z } \gamma \to \nu \bar{\nu} \gamma $ signal and estimated contributions from backgrounds. A typical aTGC signal from $\mathrm{ Z } \gamma \gamma $ with $h_{3}^\gamma = -0.001$, $h_{4}^\gamma $ = 0.0 would provide an excess, as shown in the dot-dashed histogram. The background uncertainty includes statistical and systematic components.
png pdf	Figure 2-a: The $E_\mathrm {T}^{\gamma }$ distribution in data (points with error bars) compared with the SM $\mathrm{ Z } \gamma \to \nu \bar{\nu} \gamma $ signal and estimated contributions from backgrounds. A typical aTGC signal from $\mathrm{ Z } \gamma \gamma $ with $h_{3}^\gamma = -0.001$, $h_{4}^\gamma $ = 0.0 would provide an excess, as shown in the dot-dashed histogram. The background uncertainty includes statistical and systematic components.
png pdf	Figure 2-b: The $E_{\mathrm{T}}^{\text{miss}}$ distribution in data (points with error bars) compared with the SM $\mathrm{ Z } \gamma \to \nu \bar{\nu} \gamma $ signal and estimated contributions from backgrounds. A typical aTGC signal from $\mathrm{ Z } \gamma \gamma $ with $h_{3}^\gamma = -0.001$, $h_{4}^\gamma $ = 0.0 would provide an excess, as shown in the dot-dashed histogram. The background uncertainty includes statistical and systematic components.
png pdf	Figure 3: Two-dimensional 95% CL limits on $\mathrm{ Z } \mathrm{ Z } \gamma $ couplings.
png pdf	Figure 4: Two-dimensional 95% CL limits on $\mathrm{ Z } \gamma \gamma $ couplings.

Tables
png pdf	Table 1: Summary of estimated $\mathrm{ Z } (\to \nu \bar{\nu} )+\gamma $ signal, backgrounds, and observed total number of candidates. Backgrounds listed as ``Others'' include the small contributions from $\mathrm{ W } \to \mu \nu $, $\mathrm{ Z } \gamma \to \ell \ell \gamma $, $\gamma \gamma $, and $\gamma $+jet. Uncertainties include both statistical and systematic contributions.
png pdf	Table 2: Systematic uncertainties considered in $A \epsilon $ for the $\mathrm{ Z } (\nu \bar{\nu} )\gamma $ signal sample from various sources.
png pdf	Table 3: One-dimensional 95% CL limits on $\mathrm{ Z } \mathrm {V}\gamma $ anomalous trilinear gauge couplings from the $\mathrm{ Z } \gamma \to \nu \bar{\nu} \gamma $ channel. The limits obtained from data with $\sqrt {s} = $ 7 TeV are also shown.

Summary

We have presented an inclusive measurement of the $\mathrm{ Z }\gamma\to\nu\bar{\nu}\gamma$ production cross section in pp collisions at $ \sqrt{s} = $ 8 TeV using data collected with the CMS experiment in 2012, corresponding to an integrated luminosity of 19.6 fb$^{-1}$. The measured cross section $\sigma(\mathrm{ p }\mathrm{ p }\to \mathrm{ Z }\gamma) \, \mathcal{B} (\mathrm{ Z } \to\nu\bar{\nu})$ for photons with $E_\mathrm{T}^{\gamma} > $ 145 GeV and $|\eta^{\gamma}| < $ 1.44 is 52.7 $\pm$ 2.1 (stat) $\pm$ 6.4 (syst) $\pm$ 1.4 (lumi) fb, in agreement with the NNLO prediction [31,32] of 50.0$^{+ 2.4}_{- 2.2}$ fb. No evidence was found for anomalous neutral trilinear gauge couplings in $\mathrm{ Z }\gamma$ production. Limits at 95% CL were placed on the $h_3^\mathrm{V}$ and $h_4^\mathrm{V}$ parameters of $\mathrm{Z}\mathrm{Z}\gamma$ and $\mathrm{Z}\gamma\gamma$ couplings:

$ -1.5 \times 10^{-3} < h_3^{\mathrm{Z}} < 1.6 \times 10^{-3}$
$ -3.9 \times 10^{-6} < h_4^{\mathrm{Z}} < 4.5 \times 10^{-6}$
$ -1.1 \times 10^{-3} < h_3^{\gamma} < 0.9 \times 10^{-3}$
$ -3.8 \times 10^{-6} < h_4^{\gamma} < 4.3 \times 10^{-6}$

These results yield the most stringent limits to date on anomalous neutral trilinear gauge couplings.

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