CMS-PAS-EXO-16-019

CMS-PAS-EXO-16-019
Search for high-mass resonances in $\mathrm{Z} \gamma \rightarrow \mathrm{ e^+e^- } \gamma/\mu^+\mu^-\gamma$ final states in proton-proton collisions at $\sqrt{s}=$ 13 TeV
CMS Collaboration
March 2016

Abstract: A search for a heavy resonance decaying to $\mathrm{ Z } \gamma$ , with the Z boson further decaying to pairs of electrons or muons is presented. The search makes use of 13 TeV proton-proton collision data collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 2.7 fb $^{-1}$ . The analysis extracts the background directly from data, through an unbinned likelihood fit. No significant excess over the background-only hypothesis is observed, therefore limits at 95% confidence level are set on the production cross section of particles with a mass between 350 GeV and 2 TeV, with two different assumptions on the resonance width.
Links: CDS record (PDF) ; inSPIRE record ; CADI line (restricted) ;

Figures	Summary	Additional Figures	CMS Publications

Figures
png pdf	Figure 1: Expected signal efficiency after full selections, as a function of the generated resonance mass, for the $\mathrm{e^+e^-\gamma }$ (red) and ${\mu ^+\mu ^-\gamma }$ (blue) channels in narrow-width signals.
png pdf	Figure 2-a: Fits of the ${m_{\mathrm{ Z\gamma } } }$ distribution in the data, for the $\mathrm{e^+e^-\gamma }$ channel (a) and the ${\mu ^+\mu ^-\gamma }$ channel (b). Data are shown as black markers, in bins of 20 GeV, and the fitted function is represented by a red line, with the 68% uncertainty band as gray shade.
png pdf	Figure 2-b: Fits of the ${m_{\mathrm{ Z\gamma } } }$ distribution in the data, for the $\mathrm{e^+e^-\gamma }$ channel (a) and the ${\mu ^+\mu ^-\gamma }$ channel (b). Data are shown as black markers, in bins of 20 GeV, and the fitted function is represented by a red line, with the 68% uncertainty band as gray shade.
png pdf	Figure 3-a: Observed (solid) and expected (dashed) 95% C.L. exclusion limits on $\sigma ( \mathrm{ A \rightarrow Z \gamma \rightarrow \ell ^{+}\ell ^{-}\gamma })$ , as a function of signal mass, together with the 68% and 95% ranges of expectation in the background-only hypothesis, separately for the $\mathrm{e^+e^-\gamma }$ (a) and ${\mu ^+\mu ^-\gamma }$ (b) channels. The top row shows limits on a narrow width signal, the bottom row on a wide width signal.
png pdf	Figure 3-b: Observed (solid) and expected (dashed) 95% C.L. exclusion limits on $\sigma ( \mathrm{ A \rightarrow Z \gamma \rightarrow \ell ^{+}\ell ^{-}\gamma })$ , as a function of signal mass, together with the 68% and 95% ranges of expectation in the background-only hypothesis, separately for the $\mathrm{e^+e^-\gamma }$ (a) and ${\mu ^+\mu ^-\gamma }$ (b) channels. The top row shows limits on a narrow width signal, the bottom row on a wide width signal.
png pdf	Figure 3-c: Observed (solid) and expected (dashed) 95% C.L. exclusion limits on $\sigma ( \mathrm{ A \rightarrow Z \gamma \rightarrow \ell ^{+}\ell ^{-}\gamma })$ , as a function of signal mass, together with the 68% and 95% ranges of expectation in the background-only hypothesis, separately for the $\mathrm{e^+e^-\gamma }$ (a) and ${\mu ^+\mu ^-\gamma }$ (b) channels. The top row shows limits on a narrow width signal, the bottom row on a wide width signal.
png pdf	Figure 3-d: Observed (solid) and expected (dashed) 95% C.L. exclusion limits on $\sigma ( \mathrm{ A \rightarrow Z \gamma \rightarrow \ell ^{+}\ell ^{-}\gamma })$ , as a function of signal mass, together with the 68% and 95% ranges of expectation in the background-only hypothesis, separately for the $\mathrm{e^+e^-\gamma }$ (a) and ${\mu ^+\mu ^-\gamma }$ (b) channels. The top row shows limits on a narrow width signal, the bottom row on a wide width signal.
png pdf	Figure 4-a: Observed (solid) and expected(dashed) 95% C.L. exclusion limits on $\sigma ( \mathrm{ A \rightarrow Z \gamma } )$ as a function of signal mass, together with the 68% (green) and 95% (yellow) ranges of expectation in the background-only hypothesis. The range 350 $< {m_{\mathrm{Z}\gamma }} <$ 2000 GeV is shown, for narrow width (a) and wide width signals (b).
png pdf	Figure 4-b: Observed (solid) and expected(dashed) 95% C.L. exclusion limits on $\sigma ( \mathrm{ A \rightarrow Z \gamma } )$ as a function of signal mass, together with the 68% (green) and 95% (yellow) ranges of expectation in the background-only hypothesis. The range 350 $< {m_{\mathrm{Z}\gamma }} <$ 2000 GeV is shown, for narrow width (a) and wide width signals (b).

Summary

A search for heavy resonances with mass between 350 GeV and 2 TeV decaying to

$\mathrm{Z} \gamma$ , with further decay

$\mathrm{Z} \rightarrow \ell^+\ell^-$ , with

$\ell = \mathrm{e}$ ,

$\mu$ , has been presented. The search makes use of 13 TeV proton-proton collision data collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 2.7 fb

$^{-1}$ . The search strategy measures the non-resonant background directly on data, and looks for localized excesses. No significant excess over the Standard Model expectation is found, and limits at 95% confidence level are set on the production cross section of resonances for masses between 350 GeV and 2 TeV for two different hypothetical signal widths.

Additional Figures
png pdf	Additional Figure 1-a: The invariant mass spectra of $\mathrm{ Z(e^+e^-)\gamma }$ events. The points with error bars represent the data. The stacked histograms represent the expectations from $\mathrm{ Z\gamma }$ and Z+jets SM processes. The gray bands indicate the background uncertainty. The ratio of the data to the background prediction is shown at the bottom.
png pdf	Additional Figure 1-b: The invariant mass spectra of $\mathrm{ Z(\mu ^+\mu ^-)\gamma }$ events. The points with error bars represent the data. The stacked histograms represent the expectations from $\mathrm{ Z\gamma }$ and Z+jets SM processes. The gray bands indicate the background uncertainty. The ratio of the data to the background prediction is shown at the bottom.