Search for photonic signatures of gauge-mediated supersymmetry in 8 TeV $pp$ collisions with the ATLAS detector

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Search for photonic signatures of gauge-mediated supersymmetry in 8 TeV $p p$ collisions with the ATLAS detector

G. Aad et al. (ATLAS Collaboration)

Phys. Rev. D 92, 072001 – Published 6 October 2015

Abstract

A search is presented for photonic signatures motivated by generalized models of gauge-mediated supersymmetry breaking. This search makes use of $20.3 {fb}^{- 1}$ of proton-proton collision data at $\sqrt{s} = 8 TeV$ recorded by the ATLAS detector at the LHC, and explores models dominated by both strong and electroweak production of supersymmetric partner states. Four experimental signatures incorporating an isolated photon and significant missing transverse momentum are explored. These signatures include events with an additional photon, lepton, $b$ -quark jet, or jet activity not associated with any specific underlying quark flavor. No significant excess of events is observed above the Standard Model prediction and model-dependent 95% confidence-level exclusion limits are set.

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Received 21 July 2015

DOI:https://doi.org/10.1103/PhysRevD.92.072001

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. 7 — 1 October 2015

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Images

Figure 1
Typical production and decay-chain processes for the gluino-production (left) and electroweak-production (right) instances of the GGM model for which the NLSP is a binolike neutralino, referred to in the text as the gluino-bino and wino-bino models, respectively.
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Figure 2
Typical production and decay-chain processes for the gluino-production instance of the GGM model for which the NLSP is a higgsino-bino neutralino admixture, referred to in the text as the higgsino-bino model. For the model with $μ < 0$ (left), the final step of the cascade (the ${\tilde{χ}}_{1}^{0}$ decay) would have a probability of order 50% of producing a Higgs boson rather than a photon or $Z$ boson; for the model with $μ > 0$ (right), the ${\tilde{χ}}_{1}^{0}$ decay would have a probability of order 50% of producing a $Z$ boson rather than a photon. For both of these models, production can also proceed through gaugino and neutralino states, which can dominate the production cross section for high values of gluino mass.
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Figure 3
Typical production and decay-chain processes for the wino-NLSP model. In this model, the ${\tilde{χ}}_{1}^{0}$ is a pure ${\tilde{W}}^{0}$ state, while the ${\tilde{χ}}_{1}^{\pm}$ are the two charged wino states.
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Figure 4
(Left) Distribution of $m_{eff}$ , the sum of the total visible transverse energy and $E_{T}^{miss}$ , for selected diphoton events, after requiring $Δ ϕ_{\min} (jet, E_{T}^{miss}) > 0.5$ but before application of a requirement on $E_{T}^{miss}$ and $Δ ϕ_{\min} (γ, E_{T}^{miss})$ . Also shown are the expected contributions of SM processes, estimated as described in Sec. 7, as well as the expected $m_{eff}$ distributions for the $(m_{\tilde{g}}, m_{{\tilde{χ}}_{1}^{0}}) = (1300, 150) GeV$ and $(m_{\tilde{g}}, m_{{\tilde{χ}}_{1}^{0}}) = (1300, 1050) GeV$ gluino-bino GGM models. (Right) Distribution of $R_{T}^{4}$ , the scalar sum of the transverse momentum of the four highest- $p_{T}$ jets in the event divided by the sum of the transverse momentum of all jets in the event, for the sample surviving all ${SR}_{L}^{γ j}$ selection criteria except the $R_{T}^{4}$ requirement itself. Also shown are the expected contributions of SM processes, estimated as described in Sec. 7, as well as the signal expectation for the two points in the $M_{3} - μ$ parameter space characteristic of the $μ > 0$ GGM model relevant to the $photon + j$ analysis. For both figures, the lower plot shows the ratio of observed data to the combined SM expectation, with the inner band representing the range of statistical uncertainty and the outer band (visible only in the highest $R_{T}^{4}$ bin in the right-hand figure) the combined statistical and systematic uncertainty. Events outside the range of the displayed region are included in the highest-valued bin.
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Figure 5
Distribution of the missing transverse momentum $E_{T}^{miss}$ for the sample surviving all requirements of the ${SR}_{W - H}^{γ γ}$ (left) and ${SR}_{W - L}^{γ γ}$ (right) selection except the $E_{T}^{miss}$ requirement itself. Overlain are the expected SM backgrounds as a function of $E_{T}^{miss}$ , separated into the various contributing sources. Also shown are the signal expectations for the $(m_{\tilde{W}}, m_{{\tilde{χ}}_{1}^{0}}) = (600, 100) GeV$ and $(m_{\tilde{W}}, m_{{\tilde{χ}}_{1}^{0}}) = (600, 500) GeV$ models. The lower plots show the ratio of observed data to the combined SM expectation. For these plots, the inner band represents the range of statistical uncertainty while the outer band represents the combined statistical and systematic uncertainty. Events outside the range of the displayed region are included in the highest-valued bin.
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Figure 6
$E_{T}^{miss}$ distribution for the sample surviving all requirements of the ${SR}_{L}^{γ b}$ (left) and ${SR}_{H}^{γ b}$ (right) selection except the $E_{T}^{miss}$ requirement itself. Overlain are the expected SM backgrounds as a function of $E_{T}^{miss}$ , separated into the various contributing sources. Also shown are the signal expectations for the $(m_{\tilde{g}}, m_{{\tilde{χ}}_{1}^{0}}) = (1200, 150)$ , (1200, 450), and (1200, 850) GeV models. The lower plots show the ratio of observed data to the combined SM expectation. For these plots, the inner band represents the range of statistical uncertainty while the outer band represents the combined statistical and systematic uncertainty. Events outside the range of the displayed region are included in the highest-valued bin.
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Figure 7
(Left) $E_{T}^{miss}$ distribution for the sample surviving all ${SR}_{L}^{γ j}$ requirements except the $E_{T}^{miss}$ requirement itself. Overlain are the expected SM backgrounds as a function of $E_{T}^{miss}$ , separated into the various contributing sources. Also shown are the signal expectations for the two points in the $M_{3} - μ$ parameter space of the GGM model relevant to the $photon + j$ analysis. (Right) $E_{T}^{miss}$ distribution for the combined sample of events surviving all ${SR}_{e}^{γ ℓ}$ and ${SR}_{μ}^{γ ℓ}$ requirements except the $E_{T}^{miss}$ requirement itself. Overlain are the expected SM backgrounds as a function of $E_{T}^{miss}$ , separated into the various contributing sources. Also shown is the signal expectation for the $m_{\tilde{W}} = 300 GeV$ GGM model relevant to the $photon + ℓ$ analysis. For both figures, the lower plot shows the ratio of observed data to the combined SM expectation, with the inner band representing the range of statistical uncertainty and the outer band the combined statistical and systematic uncertainty. Events outside the range of the displayed region are included in the highest-valued bin.
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Figure 8
Exclusion limits in the gluino-bino mass plane, using the ${SR}_{S - H}^{γ γ}$ analysis for $m_{{\tilde{χ}}_{1}^{0}} \geq 800 GeV$ and the ${SR}_{S - L}^{γ γ}$ analysis for $m_{{\tilde{χ}}_{1}^{0}} < 800 GeV$ . Combinations of gluino and bino mass are excluded at 95% CL in the area below the unbroken curve. The observed limits are exhibited for the nominal SUSY model cross-section expectation, as well as for a SUSY cross section increased and decreased by 1 standard deviation of the cross-section systematic uncertainty. Also shown is the expected limit, as well as the $\pm 1$ and $\pm 2$ standard-deviation ranges of the expected limit.
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Figure 9
Exclusion limits in the wino-bino mass plane, using the ${SR}_{W - H}^{γ γ}$ analysis for $m_{{\tilde{χ}}_{1}^{0}} \geq 350 GeV$ and the ${SR}_{W - L}^{γ γ}$ analysis for $m_{{\tilde{χ}}_{1}^{0}} < 350 GeV$ . The vertical axis represents wino mass while the horizontal axis represents bino mass. The observed limits are exhibited for the nominal SUSY model cross-section expectation, as well as for a SUSY cross section increased and decreased by 1 standard deviation of the cross-section systematic uncertainty. Also shown is the expected limit, along with its $\pm 1$ standard-deviation range. The discontinuity at $m_{{\tilde{χ}}_{1}^{0}} = 350 GeV$ is due to the switch between the use of the ${SR}_{W - L}^{γ γ}$ and ${SR}_{W - H}^{γ γ}$ analyses, the former of which exhibits a small excess of observed events relative to the expected SM background.
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Figure 10
Exclusion limits in the gluino-neutralino mass plane, for the higgsino-bino GGM model with $μ < 0$ , using the merged (see text) ${SR}_{L}^{γ b}$ and ${SR}_{H}^{γ b}$ analyses. The observed limits are shown for the nominal SUSY model cross-section expectation, as well as for a SUSY cross section increased and decreased by 1 standard deviation of the cross-section systematic uncertainty. The expected limit is also shown, along with its $\pm 1 σ$ range. For NLSP masses below approximately 450 GeV, the onset of the direct production of gaugino states makes the analysis insensitive to the value of the gluino mass.
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Figure 11
Exclusion limits imposed by the $photon + j$ analysis in the two-dimensional plane of the GGM parameters $M_{3}$ and $μ$ , for the higgsino-bino GGM model with $μ > 0$ , using the merged (see text) ${SR}_{L}^{γ j}$ and ${SR}_{H}^{γ j}$ analyses. The observed limits are shown for the nominal SUSY model cross-section expectation, as well as for a SUSY cross section increased and decreased by 1 standard deviation of the cross-section systematic uncertainty. The expected limit is also shown, along with its $\pm 1$ standard-deviation range. Values of $M_{3}$ below 1100 GeV are excluded for most values of the $μ$ parameter, although a significant region corresponding to the case for which the gluino mass is close to that of the lightest neutralino masses remains unexcluded due to the requirements of one or more jets arising from the gluino decay. The top and right axes represent the corresponding values of the lightest neutralino and gluino masses, respectively.
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Figure 12
Contour of exclusion in wino production cross section from the $photon + ℓ$ analysis, as a function of the wino mass parameter $M_{\tilde{W}}$ . The expected limit is shown along with its $\pm 1$ and $\pm 2$ standard-deviation ranges. Also shown is the total cross section for the production of $\tilde{W}$ pairs, again as a function of $M_{\tilde{W}}$ .
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