Search for high-mass diphoton resonances in $pp$ collisions at $\sqrt{s}=8\text{ }\text{ }\mathrm{TeV}$ with the ATLAS detector

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Search for high-mass diphoton resonances in $p p$ collisions at $\sqrt{s} = 8 TeV$ with the ATLAS detector

G. Aad et al. (ATLAS Collaboration)

Phys. Rev. D 92, 032004 – Published 14 August 2015

Abstract

This article describes a search for high-mass resonances decaying to a pair of photons using a sample of $20.3 {fb}^{- 1}$ of $p p$ collisions at $\sqrt{s} = 8 TeV$ recorded with the ATLAS detector at the Large Hadron Collider. The data are found to be in agreement with the Standard Model prediction, and limits are reported in the framework of the Randall-Sundrum model. This theory leads to the prediction of graviton states, the lightest of which could be observed at the Large Hadron Collider. A lower limit of 2.66 (1.41) TeV at 95% confidence level is set on the mass of the lightest graviton for couplings of $k / {\bar{M}}_{Pl} = 0.1$ (0.01).

Received 22 April 2015

DOI:https://doi.org/10.1103/PhysRevD.92.032004

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.

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Vol. 92, Iss. 3 — 1 August 2015

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Figure 1
Top: distribution of the isolation energy $E_{T}^{iso}$ for the leading photon candidate in events in the low-mass control region. Middle: corresponding distribution for the subleading photon. The black points represent the data. The blue line shows the result of the template fit to the data. The red and green lines show the templates for photon and jet background respectively, normalized according to the fit result. The red and green bands represent the uncertainties in the photon and jet contributions due to the uncertainties in the template shapes. Bottom: distribution of $E_{T}^{iso}$ for photon candidates with $E_{T}^{γ} > 400 GeV$ at any diphoton mass. The $E_{T}^{iso}$ values always include the $E_{T}^{γ}$ -dependent offset discussed in the text.
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Figure 2
Uncertainty on the total background estimate as a function of $m_{γ γ}$ . The individual contributions due to the uncertainties in the irreducible and reducible components, as well as the contribution from the uncertainties in the normalization of the different background components (labeled “background composition”), are also shown.
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Figure 3
Observed invariant mass distribution of the selected diphoton events (black dots; the vertical and horizontal axes on logarithmic scales). To compensate for the rapid decrease of the spectrum, the bins are chosen to have constant logarithmic width. Specifically, the ratio of the upper to lower bin boundary is equal to 1.038 for all bins, and the first bin starts at 179 GeV. Superimposed are the SM background prediction including irreducible and reducible components and two examples of signal predictions. The low-mass control region is indicated by an arrow. Bottom: bin-by-bin significance of the difference between data and background expectation.
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Figure 4
Expected and observed upper limits on $σ \times B R (G^{*} \to γ γ)$ expressed at 95% CL, as a function of the graviton mass. At large $m_{G^{*}}$ , the $- 1 σ$ and $- 2 σ$ variations of the expected limit tend to be particularly close to the expected limit. This is expected, since signals with high $m_{G^{*}}$ would appear in regions of $m_{γ γ}$ where the background expectation is small and the Poissonian fluctuations around the mean expected background are highly asymmetric. The curves show the RS model prediction for given values of $k / {\bar{M}}_{Pl}$ as a function of $m_{G^{*}}$ . They are obtained using the pythia generator plus a $K$ -factor to account for NLO corrections (see text). The thickness of the theory curve for $k / {\bar{M}}_{Pl} = 0.1$ illustrates the PDF uncertainties expressed at 90% CL.
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Figure 5
Expected and observed upper limits on $k / {\bar{M}}_{Pl}$ expressed at 95% CL, as a function of the graviton mass.
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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for high-mass diphoton resonances in $p p$ collisions at $\sqrt{s} = 8 TeV$ with the ATLAS detector

G. Aad et al. (ATLAS Collaboration)

Phys. Rev. D 92, 032004 – Published 14 August 2015

Abstract

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Article Text

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Physical Review D

covering particles, fields, gravitation, and cosmology

Search for high-mass diphoton resonances in pp collisions at s=8 TeV with the ATLAS detector

G. Aad et al. (ATLAS Collaboration)

Phys. Rev. D 92, 032004 – Published 14 August 2015

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Search for high-mass diphoton resonances in $p p$ collisions at $\sqrt{s} = 8 TeV$ with the ATLAS detector