Search for diphoton events with large missing transverse momentum in 7 TeV proton-proton collision data with the ATLAS detector

TL;DR

An ATLAS search for gamma gamma plus large MET in 4.8 fb^-1 of 7 TeV pp collisions tests gauge-mediated SUSY breaking scenarios (GGM and SPS8) and a single extra-dimension UED model. The analysis uses three signal regions defined by MET, HT, and photon–MET separation, with data-driven estimates of QCD and EW backgrounds; no excess is found and 95% CL limits are placed on gaugino/gluino/squark masses, the SPS8 Lambda parameter, and the UED compactification scale 1/R. These results provide the most stringent constraints to date on these models and demonstrate ATLAS's sensitivity to gamma gamma + MET signatures.

Abstract

A search for diphoton events with large missing transverse momentum has been performed using proton-proton collision data at sqrt(s) = 7 TeV recorded with the ATLAS detector, corresponding to an integrated luminosity of 4.8 fb^-1. No excess of events was observed above the Standard Model prediction and model-dependent 95% confidence level exclusion limits are set. In the context of a generalised model of gauge-mediated supersymmetry breaking with a bino-like lightest neutralino of mass above 50 GeV, gluinos (squarks) below 1.07 TeV (0.87 TeV) are excluded, while a breaking scale Lambda below 196 TeV is excluded for a minimal model of gauge-mediated supersymmetry breaking. For a specific model with one universal extra dimension, compactification scales 1/R < 1.40 TeV are excluded. These limits provide the most stringent tests of these models to date.

Figures (9)

• Figure 1: The $E_{\mathrm{T}}$ spectrum of the leading photon in the $\gamma\gamma$ candidate events in the data (points, statistical uncertainty only) together with the spectra from simulated GGM ($m_{\tilde{g}\xspace} = \unit[1000]{GeV},m_{\tilde{\chi}^{0}_{1}\xspace} = \unit[450]{GeV}$), SPS8 ($\Lambda = \unit[190]{TeV}$), and UED ($1/R = \unit[1.3]{TeV}$) samples after the diphoton requirement. The signal samples are scaled by a factor of 100 for clarity.
• Figure 2: The $E_{\mathrm{T}}$ spectrum of the sub-leading photon in the $\gamma\gamma$ candidate events in the data (points, statistical uncertainty only) together with the spectra from simulated GGM ($m_{\tilde{g}\xspace} = \unit[1000]{GeV},m_{\tilde{\chi}^{0}_{1}\xspace} = \unit[450]{GeV}$), SPS8 ($\Lambda = \unit[190]{TeV}$), and UED ($1/R = \unit[1.3]{TeV}$) samples after the diphoton requirement. The signal samples are scaled by a factor of 100 for clarity.
• Figure 3: The $H_{\mathrm{T}}$ spectrum of $\gamma\gamma$ candidate events in the data (points, statistical uncertainty only) together with the spectra from simulated GGM ($m_{\tilde{g}\xspace} = \unit[1000]{GeV},m_{\tilde{\chi}^{0}_{1}\xspace} = \unit[450]{GeV}$), SPS8 ($\Lambda = \unit[190]{TeV}$), and UED ($1/R = \unit[1.3]{TeV}$) samples after the diphoton requirement. The signal samples are scaled by a factor of 100 for clarity.
• Figure 4: The minimum $\Delta \phi(\gamma,E_{\mathrm{T}}^{\mathrm{miss}}\xspace)$ spectrum of $\gamma\gamma$ candidate events in the data (points, statistical uncertainty only) together with the spectra from simulated GGM ($m_{\tilde{g}\xspace} = \unit[1000]{GeV},m_{\tilde{\chi}^{0}_{1}\xspace} = \unit[450]{GeV}$), SPS8 ($\Lambda = \unit[190]{TeV}$), and UED ($1/R = \unit[1.3]{TeV}$) samples after the diphoton requirement. The signal samples are scaled by a factor of 100 for clarity.
• Figure 5: $E_{\mathrm{T}}^{\mathrm{miss}}$ spectra in SR C for the $\gamma\gamma$ candidate events in data (points, statistical uncertainty only) and the estimated QCD background (normalised to the number of $\gamma\gamma$ candidates with $E_{\mathrm{T}}^{\mathrm{miss}}\xspace < \unit[20]{GeV}$), the $W(\to e\nu)+\mathrm{jets}/\gamma\xspace$ and $t\bar{t}\xspace(\to e\nu)+\mathrm{jets}\xspace$ backgrounds as estimated from the electron--photon control sample, and the irreducible background of $Z(\to \nu\bar{\nu})+\gamma\gamma$ and $W(\to \ell\nu)+\gamma\gamma$. The hatched region represents the extent of the uncertainty on the total background prediction. Also shown is the expected signal from the SPS8 ($\Lambda = \unit[190]{TeV}$) sample.