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CMS-PAS-SUS-18-005
Combined search for gauge-mediated supersymmetry with photons in 13 TeV collisions at the CMS experiment
Abstract: A combination of searches for signatures with at least one photon motivated by generalized models of gauge-mediated supersymmetry breaking is presented. All searches make use of proton-proton collision data at $\sqrt{s}= $ 13 TeV recorded by the CMS detector at the LHC. The results of four analyses targeting separate experimental signatures incorporating an isolated photon and significant missing transverse energy are combined. These signatures include events with two isolated photons, events with single leptons that accompany the photon, and events with additional jets. Based on the 35.9 fb$^{-1}$ of integrated luminosity collected in 2016, this combination probes the allowed parameter space of General Gauge Mediation and exceeds the sensitivity of the individual searches to supersymmetric particles by up to 100 GeV in mass.
Figures & Tables Summary References CMS Publications
Figures

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Figure 1:
In the GGM scenarios several production and decay channels are possible. The diagram of one possible process based on $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{2}} $ production is shown (upper left), where the gaugino decays depend on the corresponding composition of the gauge eigenstates. In the Neutralino BF scenario $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ (upper right) and $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{1}} $ production are probed. The Chargino BF scenario (lower left) probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production. In the lower right diagram gluino pair production is shown including the charged and uncharged gluino decay.

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Figure 1-a:
In the GGM scenarios several production and decay channels are possible. The diagram of one possible process based on $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{2}} $ production is shown (upper left), where the gaugino decays depend on the corresponding composition of the gauge eigenstates. In the Neutralino BF scenario $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ (upper right) and $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{1}} $ production are probed. The Chargino BF scenario (lower left) probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production. In the lower right diagram gluino pair production is shown including the charged and uncharged gluino decay.

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Figure 1-b:
In the GGM scenarios several production and decay channels are possible. The diagram of one possible process based on $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{2}} $ production is shown (upper left), where the gaugino decays depend on the corresponding composition of the gauge eigenstates. In the Neutralino BF scenario $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ (upper right) and $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{1}} $ production are probed. The Chargino BF scenario (lower left) probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production. In the lower right diagram gluino pair production is shown including the charged and uncharged gluino decay.

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Figure 1-c:
In the GGM scenarios several production and decay channels are possible. The diagram of one possible process based on $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{2}} $ production is shown (upper left), where the gaugino decays depend on the corresponding composition of the gauge eigenstates. In the Neutralino BF scenario $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ (upper right) and $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{1}} $ production are probed. The Chargino BF scenario (lower left) probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production. In the lower right diagram gluino pair production is shown including the charged and uncharged gluino decay.

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Figure 1-d:
In the GGM scenarios several production and decay channels are possible. The diagram of one possible process based on $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{2}} $ production is shown (upper left), where the gaugino decays depend on the corresponding composition of the gauge eigenstates. In the Neutralino BF scenario $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ (upper right) and $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{1}} $ production are probed. The Chargino BF scenario (lower left) probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production. In the lower right diagram gluino pair production is shown including the charged and uncharged gluino decay.

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Figure 2:
Branching fractions for the NLSP decay to a photon and a gravitino for the M1M2 scenario (left). The phase space is spanned by the bino and wino mass parameters and a change of the NLSP composition is visible. The change of the NLSP composition also influences the dependence of the physical mass of the neutralino on the gauge mass parameters (right).

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Figure 2-a:
Branching fractions for the NLSP decay to a photon and a gravitino for the M1M2 scenario (left). The phase space is spanned by the bino and wino mass parameters and a change of the NLSP composition is visible. The change of the NLSP composition also influences the dependence of the physical mass of the neutralino on the gauge mass parameters (right).

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Figure 2-b:
Branching fractions for the NLSP decay to a photon and a gravitino for the M1M2 scenario (left). The phase space is spanned by the bino and wino mass parameters and a change of the NLSP composition is visible. The change of the NLSP composition also influences the dependence of the physical mass of the neutralino on the gauge mass parameters (right).

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Figure 3:
Comparison between the observed yield and the background prediction for all search bins used in the combination. The yields for the Photon+Lepton{} and Diphoton{} categories correspond to the published results, while the yields of the Photon+${S^{\gamma}_{T}}$ and Photon+$ {H^{\gamma}_{T}}$ categories are based on the modified event selections ensuring exclusive signal regions.

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Figure 4:
Combined exclusion limits for the M1M2 scenario in terms of the GGM model parameters (left) and the physical neutralino and chargino masses (right). The left panel shows the expected exclusion, while the right panel shows both the observed and the expected exclusion limits. In the physical mass plane only signal points with a mass splitting above $120 GeV $ are shown to enable a precise assignment of the physical masses and the GGM model parameters. The uncertainty bands around the expected and observed limit of the combination in the right panel correspond to the experimental ($\sigma _{\text {exp.}}$) and theory uncertainty ($\sigma _{\text {theo.}}$), respectively.

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Figure 4-a:
Combined exclusion limits for the M1M2 scenario in terms of the GGM model parameters (left) and the physical neutralino and chargino masses (right). The left panel shows the expected exclusion, while the right panel shows both the observed and the expected exclusion limits. In the physical mass plane only signal points with a mass splitting above $120 GeV $ are shown to enable a precise assignment of the physical masses and the GGM model parameters. The uncertainty bands around the expected and observed limit of the combination in the right panel correspond to the experimental ($\sigma _{\text {exp.}}$) and theory uncertainty ($\sigma _{\text {theo.}}$), respectively.

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Figure 4-b:
Combined exclusion limits for the M1M2 scenario in terms of the GGM model parameters (left) and the physical neutralino and chargino masses (right). The left panel shows the expected exclusion, while the right panel shows both the observed and the expected exclusion limits. In the physical mass plane only signal points with a mass splitting above $120 GeV $ are shown to enable a precise assignment of the physical masses and the GGM model parameters. The uncertainty bands around the expected and observed limit of the combination in the right panel correspond to the experimental ($\sigma _{\text {exp.}}$) and theory uncertainty ($\sigma _{\text {theo.}}$), respectively.

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Figure 5:
Combined exclusion for the Neutralino BF scenario (left), which probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{1}} $ and $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production combined with the NLSP BF scanned between decays to $Z\tilde{G}$ and $\gamma \tilde{G}$. Combined exclusion for the Chargino BF scenario (right), which probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production combined with the Chargino BF scanned between decays to $W\tilde{G}$ and $\tilde{\chi}^0_1+\mathrm {soft}$, where the $\tilde{\chi}^0_1$ decays into a photon and a gravitino. The uncertainty bands around the expected and observed limit of the combination correspond to the experimental ($\sigma _{\text {exp.}}$) and theory uncertainty ($\sigma _{\text {theo.}}$), respectively.

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Figure 5-a:
Combined exclusion for the Neutralino BF scenario (left), which probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{1}} $ and $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production combined with the NLSP BF scanned between decays to $Z\tilde{G}$ and $\gamma \tilde{G}$. Combined exclusion for the Chargino BF scenario (right), which probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production combined with the Chargino BF scanned between decays to $W\tilde{G}$ and $\tilde{\chi}^0_1+\mathrm {soft}$, where the $\tilde{\chi}^0_1$ decays into a photon and a gravitino. The uncertainty bands around the expected and observed limit of the combination correspond to the experimental ($\sigma _{\text {exp.}}$) and theory uncertainty ($\sigma _{\text {theo.}}$), respectively.

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Figure 5-b:
Combined exclusion for the Neutralino BF scenario (left), which probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}^{0}_{1}} $ and $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production combined with the NLSP BF scanned between decays to $Z\tilde{G}$ and $\gamma \tilde{G}$. Combined exclusion for the Chargino BF scenario (right), which probes $ {\tilde{\chi}^\pm _{1}} {\tilde{\chi}_{1}^{\mp}}$ production combined with the Chargino BF scanned between decays to $W\tilde{G}$ and $\tilde{\chi}^0_1+\mathrm {soft}$, where the $\tilde{\chi}^0_1$ decays into a photon and a gravitino. The uncertainty bands around the expected and observed limit of the combination correspond to the experimental ($\sigma _{\text {exp.}}$) and theory uncertainty ($\sigma _{\text {theo.}}$), respectively.

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Figure 6:
Combined exclusion for the nominal Gluino scenario (left) assuming equal probabilities for the charged and uncharged gluino decay. For the Gluino BF scenario (right) the ratio of the probabilities for both decays are scanned and the gluino mass is fixed to $1950 GeV $. For both interpretations the Diphoton{} category is not used. The uncertainty bands around the expected and observed limit of the combination correspond to the experimental ($\sigma _{\text {exp.}}$) and theory uncertainty ($\sigma _{\text {theo.}}$), respectively.

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Figure 6-a:
Combined exclusion for the nominal Gluino scenario (left) assuming equal probabilities for the charged and uncharged gluino decay. For the Gluino BF scenario (right) the ratio of the probabilities for both decays are scanned and the gluino mass is fixed to $1950 GeV $. For both interpretations the Diphoton{} category is not used. The uncertainty bands around the expected and observed limit of the combination correspond to the experimental ($\sigma _{\text {exp.}}$) and theory uncertainty ($\sigma _{\text {theo.}}$), respectively.

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Figure 6-b:
Combined exclusion for the nominal Gluino scenario (left) assuming equal probabilities for the charged and uncharged gluino decay. For the Gluino BF scenario (right) the ratio of the probabilities for both decays are scanned and the gluino mass is fixed to $1950 GeV $. For both interpretations the Diphoton{} category is not used. The uncertainty bands around the expected and observed limit of the combination correspond to the experimental ($\sigma _{\text {exp.}}$) and theory uncertainty ($\sigma _{\text {theo.}}$), respectively.
Tables

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Table 1:
Exclusive definitions of the four categories. The kinematic cuts and the search bins are based on the four initial searches. The additional vetoes ensure exclusive event categories. Diphoton and Lepton veto match the event selection described in [19] and [18].

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Table 2:
Predicted background yields and observed data for the Photon+${S^{\gamma}_{T}}$ category (left) and the Photon+$ {H^{\gamma}_{T}}$ category (right). The excess in the second bin of the Photon+$ {H^{\gamma}_{T}}$ category was also found in the initial search [16].
Summary
A combination of four different searches for gauge-mediated supersymmetry in final states with photons and a large transverse momentum imbalance has been performed. Based on the event selection of the individual searches four event categories were defined. Overlaps between the categories were removed by additional vetoes designed to maximize the sensitivity of the combination. Using 36 fb$^{-1}$ of data recorded by the CMS detector at the LHC at a center-of-mass energy of 13 TeV the combination maximizes the exclusion power of the searches described in [17,16,18,19].

The results are interpreted in the context of General Gauge Mediation (GGM) and in model-independent mass scans using simplified topologies. The sensitivity of the combination is also interpreted across a range of branching fractions allowing for generalization to a wide range of SUSY scenarios. The GGM scan is performed in an ${{M_\mathrm{1}}} $ and ${{M_\mathrm{2}}} $ parameter space where most of the signal points below $M2 < $ 1100 (1300) GeV are excluded based on the observed (expected) limit. The results of the GGM scenario is also shown in physical mass parameters, which show competitive constraints on the chargino and neutralino masses. Here, chargino masses up to 890 (1080) GeV are excluded by the the observed (expected) limit across the tested neutralino mass spectrum. For a strong production scenario based on gluino pair production the highest observed (expected) excluded gluino masses are at 1975 (2050) GeV. In electroweak production models observed (expected) limits for neutralino masses are set up to 1050 (1200) GeV for combined ${\tilde{\chi}_{1}^{\mp}}{\tilde{\chi}_{1}^{0}}$ and ${\tilde{\chi}_{1}^{\mp}} {\tilde{\chi}_{1}^{\mp}}$ production, while for pure ${\tilde{\chi}_{1}^{\mp}} {\tilde{\chi}_{1}^{\mp}}$ production these limits are reduced to 850 (1000) GeV. The combination improves on the expected limits on neutralino and chargino masses by 100 GeV while the expected limit on the gluino mass is increased by 50 GeV compared to the individual searches.
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Compact Muon Solenoid
LHC, CERN