CMS-PAS-SMP-14-019

CMS-PAS-SMP-14-019
Measurement of the production cross section for $\mathrm{Z} \gamma \to \nu \bar{\nu} \gamma$ in pp collisions at $\sqrt{s} =$ 8 TeV and limits on $\mathrm{Z Z} \gamma$ and $\mathrm{Z} \gamma \gamma$ triple gauge boson couplings
CMS Collaboration
July 2015

Abstract: A measurement of the $\mathrm{ Z } \gamma \rightarrow \nu \bar{\nu} \gamma$ 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 missing transverse momentum above 140 GeV and a single photon with transverse momentum above 145 GeV and absolute pseudorapidity range $\|\eta\| < 1.44$ . The measured $\mathrm{ Z } \gamma \rightarrow \nu \bar{\nu} \gamma$ 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. The results yield the most stringent limits to date on the anomalous $\mathrm{ZZ} \gamma$ and $\mathrm{Z}\gamma\gamma$ trilinear gauge boson couplings.
Links: CDS record (PDF) ; Public twiki page ; CADI line (restricted) ; Figures are also available from the CDS record. These preliminary results are superseded in this paper, PLB 760 (2016) 448.

Figures
png ; pdf	Figure 1-a: Feynman diagrams of ${\mathrm {Z}}\gamma$ production via initial state radiation in the SM at tree level (a) and via anomalous ${\mathrm {Z}} {\mathrm {Z}}\gamma$ and ${\mathrm {Z}}\gamma \gamma$ trilinear gauge couplings (b).
png ; pdf	Figure 1-b: Feynman diagrams of ${\mathrm {Z}}\gamma$ production via initial state radiation in the SM at tree level (a) and via anomalous ${\mathrm {Z}} {\mathrm {Z}}\gamma$ and ${\mathrm {Z}}\gamma \gamma$ trilinear gauge couplings (b).
png ; pdf	Figure 2-a: The $E_\mathrm {T}^{\gamma }$ and ${E_{\mathrm {T}}}$ distributions in data (points with error bars) compared with the SM $Z {\gamma }\rightarrow {\nu } {\overline {\nu }} {\gamma }$ signal and estimated contributions from backgrounds. A typical anomalous TGC signal 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 $E_\mathrm {T}^{\gamma }$ and ${E_{\mathrm {T}}}$ distributions in data (points with error bars) compared with the SM $Z {\gamma }\rightarrow {\nu } {\overline {\nu }} {\gamma }$ signal and estimated contributions from backgrounds. A typical anomalous TGC signal 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.

Compact Muon Solenoid
LHC, CERN