Search for Resonant Production of High-Mass Photon Pairs in Proton-Proton Collisions at $\sqrt{s}=8$ and 13 TeV

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Search for Resonant Production of High-Mass Photon Pairs in Proton-Proton Collisions at $\sqrt{s} = 8$ and 13 TeV

V. Khachatryan et al. (CMS Collaboration)

Phys. Rev. Lett. 117, 051802 – Published 28 July 2016

Abstract

A search for the resonant production of high-mass photon pairs is presented. The analysis is based on samples of proton-proton collision data collected by the CMS experiment at center-of-mass energies of 8 and 13 TeV, corresponding to integrated luminosities of 19.7 and $3.3 {fb}^{- 1}$ , respectively. The interpretation of the search results focuses on spin-0 and spin-2 resonances with masses between 0.5 and 4 TeV and with widths, relative to the mass, between $1.4 \times 10^{- 4}$ and $5.6 \times 10^{- 2}$ . Limits are set on scalar resonances produced through gluon-gluon fusion, and on Randall-Sundrum gravitons. A modest excess of events compatible with a narrow resonance with a mass of about 750 GeV is observed. The local significance of the excess is approximately 3.4 standard deviations. The significance is reduced to 1.6 standard deviations once the effect of searching under multiple signal hypotheses is considered. More data are required to determine the origin of this excess.

Received 13 June 2016

DOI:https://doi.org/10.1103/PhysRevLett.117.051802

This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

Physics Subject Headings (PhySH)

Extensions of Higgs sector Particle production

Hypothetical scalars Photons

Hadron colliders

Particles & Fields

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Vol. 117, Iss. 5 — 29 July 2016

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Figure 1
Observed diphoton invariant mass $m_{γ γ}$ spectra for the event categories used in the analysis of the 13 TeV data: (upper row) magnetic field strength $B = 3.8 T$ ; (lower row) $B = 0 T$ ; (left column) both photons in the ECAL barrel detector, (right column) one photon in the ECAL barrel detector and the other in an ECAL endcap detector. No event with $m_{γ γ} > 1600 GeV$ is selected in the analysis. The results of a likelihood fit to the background-only hypothesis are also shown. The shaded regions show the 1 and 2 standard deviation uncertainty bands associated with the fit, and reflect the statistical uncertainty of the data. The lower panels show the difference between the data and fit, divided by the statistical uncertainty in the data points.
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Figure 2
Observed diphoton invariant mass $m_{γ γ}$ spectra for the event categories used in the analysis of the 8 TeV data for resonance mass $m_{X} \leq 850 GeV$ : (upper row) $\min (R_{9}) > 0.94$ , (lower row) $\min (R_{9}) \leq 0.94$ ; (left column) both photons in the ECAL barrel detector; (right column) one photon in the ECAL barrel detector and the other in the ECAL endcap detector. The results of background-only parametric fits to the data corresponding to the fit range used for the $m_{X} = 750 GeV$ hypothesis test are also shown [8]. The shaded regions show the 1 and 2 standard deviation uncertainty bands associated with the fit, and reflect the statistical uncertainty of the data. The lower panels show the difference between the data and fit, divided by the statistical uncertainty in the data points.
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Figure 3
The 95% C.L. upper limits on the production of diphoton resonances as a function of the resonance mass $m_{X}$ , from the combined analysis of the 8 and 13 TeV data. The 8 TeV results are scaled by the ratio of the 8 to 13 TeV cross sections. The blue-grey (darker) curves and the green (lighter) ones correspond to the scalar and RS graviton signals, respectively. Solid (dashed) curves represent the observed (median expected) exclusion limit. The expected results are shown with their 1 standard deviation dispersion bands. The leading-order RS graviton production cross section is shown by the red dot-dashed curves. The results are shown for (upper) a narrow, (middle) an intermediate width, and (lower) a broad resonance, with the value of the width $Γ_{X} / m_{X}$ , relative to the mass, indicated in the legend of each plot.
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Figure 4
Observed background-only $p$ values for narrow-width scalar resonances as a function of the resonance mass $m_{X}$ , from the combined analysis of the 8 and 13 TeV data. The results for the separate 8 and 13 TeV data sets are also shown. The inset shows an expanded region around $m_{X} = 750 GeV$ .
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Physical Review Letters

Search for Resonant Production of High-Mass Photon Pairs in Proton-Proton Collisions at s=8 and 13 TeV

V. Khachatryan et al. (CMS Collaboration)

Phys. Rev. Lett. 117, 051802 – Published 28 July 2016

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Search for Resonant Production of High-Mass Photon Pairs in Proton-Proton Collisions at $\sqrt{s} = 8$ and 13 TeV