CMS-SUS-18-005 ; CERN-EP-2019-114 | ||
Combined search for supersymmetry with photons in proton-proton collisions at $\sqrt{s} = $ 13 TeV | ||
CMS Collaboration | ||
1 July 2019 | ||
Phys. Lett. B 801 (2020) 135183 | ||
Abstract: A combination of four searches for new physics involving signatures with at least one photon and large missing transverse momentum, motivated by generalized models of gauge-mediated supersymmetry (SUSY) breaking, is presented. All searches make use of proton-proton collision data at $\sqrt{s} = $ 13 TeV, which were recorded with the CMS detector at the LHC in 2016, and correspond to an integrated luminosity of 35.9 fb$^{-1}$ . Signatures with at least one photon and large missing transverse momentum are categorized into events with two isolated photons, events with a lepton and a photon, events with additional jets, and events with at least one high-energy photon. No excess of events is observed beyond expectations from standard model processes, and limits are set in the context of gauge-mediated SUSY. Compared to the individual searches, the combination extends the sensitivity to gauge-mediated SUSY in both electroweak and strong production scenarios by up to 100 GeV in neutralino and chargino masses, and yields the first CMS result combining various SUSY searches in events with photons at $\sqrt{s} = $ 13 TeV. | ||
Links: e-print arXiv:1907.00857 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; HepData record ; CADI line (restricted) ; |
Figures & Tables | Summary | Additional Figures | References | CMS Publications |
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Figures | |
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Figure 1:
Diagrams of the SUSY processes considered in this Letter: one process within the GGM scenario (upper left), two EW SMS processes, with possible neutralino and chargino decays (upper right and lower left), and a strong SMS process based on gluino pair production (lower right). |
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Figure 1-a:
Diagram of SUSY process within the GGM scenario. |
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Figure 1-b:
Diagram of a EW SMS process, with possible chargino and neutralino decays. |
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Figure 1-c:
Diagram of a EW SMS process, with possible chargino and neutralino decays. |
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Figure 1-d:
Diagram of a strong SMS process based on gluino pair production. |
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Figure 2:
Branching fractions ($B$) for the NLSP decay to a photon and a gravitino for the GGM scenario (left). The phase space is spanned by the bino ($ {{M_\mathrm {1}}} $) and wino ($ {{M_\mathrm {2}}} $) mass parameters showing the change of the NLSP composition. This change also influences the dependence of the physical mass of the neutralino ($m_{\tilde{\chi}^0_1}$) on the gauge mass parameters (right). |
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Figure 2-a:
Branching fractions ($B$) for the NLSP decay to a photon and a gravitino for the GGM scenario. The phase space is spanned by the bino ($ {{M_\mathrm {1}}} $) and wino ($ {{M_\mathrm {2}}} $) mass parameters showing the change of the NLSP composition. This change also influences the dependence of the physical mass of the neutralino ($m_{\tilde{\chi}^0_1}$) on the gauge mass parameters (right). |
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Figure 2-b:
Physical mass of the neutralino ($m_{\tilde{\chi}^0_1}$). The phase space is spanned by the bino ($ {{M_\mathrm {1}}} $) and wino ($ {{M_\mathrm {2}}} $) mass parameters. |
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Figure 3:
Predicted pre-fit background yields, where the values are not constrained by the likelihood fit, and observed number of events in data for all search bins used in the combination. The search bins are defined in Table 2. The hatched red bands in both parts of the plot represent the total uncertainty of the background prediction. The red line in the upper panel shows the signal prediction for one specific signal point of the GGM scenario with $M_{1} = $ 1000 GeV and $M_{2} = $ 750 GeV. The lower panel shows the ratio between the observed data and the predicted backgrounds. |
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Figure 4:
The 95% CL exclusion limits for the GGM scenario in terms of the GGM model parameters (upper) and the physical neutralino and chargino masses (lower). The upper left panel shows the expected exclusion limits, where the area denoted as "all'' is excluded by all four individual categories. The upper right panel shows both the corresponding observed (full lines) and expected (dotted lines) exclusion limits for the combination in terms of the GGM model parameters. The lower panel shows the observed and the expected exclusion limits for the physical mass plane, where the phase space between the colored lines and the black line is excluded. In the physical mass plane only signal points with a mass difference above 120 GeV are shown to enable a precise projection of the physical masses from the GGM model parameters. The band around the expected limit of the combination indicates the region containing 68% of the distribution of limits expected under the background-only hypothesis. The band around the observed limit of the combination shows the spread in the observed limit from variation of the signal cross sections within their theoretical uncertainties. |
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Figure 4-a:
The 95% CL exclusion limits for the GGM scenario in terms of the GGM model parameters. The panel shows the expected exclusion limits, where the area denoted as "all'' is excluded by all four individual categories. |
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Figure 4-b:
The 95% CL exclusion limits for the GGM scenario in terms of the GGM model parameters. The panel shows both the corresponding observed (full lines) and expected (dotted lines) exclusion limits for the combination in terms of the GGM model parameters.The band around the expected limit of the combination indicates the region containing 68% of the distribution of limits expected under the background-only hypothesis. The band around the observed limit of the combination shows the spread in the observed limit from variation of the signal cross sections within their theoretical uncertainties. |
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Figure 4-c:
The 95% CL exclusion limits for the GGM scenario in terms of the physical neutralino and chargino masses. The panel shows the observed and the expected exclusion limits for the physical mass plane, where the phase space between the colored lines and the black line is excluded. Only signal points with a mass difference above 120 GeV are shown to enable a precise projection of the physical masses from the GGM model parameters. The band around the expected limit of the combination indicates the region containing 68% of the distribution of limits expected under the background-only hypothesis. The band around the observed limit of the combination shows the spread in the observed limit from variation of the signal cross sections within their theoretical uncertainties. |
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Figure 5:
The combined 95% CL NLSP mass exclusion limits for EW SMS production above 300 GeV. For the neutralino branching fraction scenario (left), the limit is shown as a function of the branching fraction $\tilde{\chi}^0_1 \to \gamma + \tilde{\mathrm{G}} $, the other decay channel being $\tilde{\chi}^0_1 \to \mathrm{Z} + \tilde{\mathrm{G}} $. For the chargino branching fraction scenario (right), the limit is shown as a function of the branching fraction $ {\tilde{\chi} _1^{\pm}}\to \tilde{\chi}^0_1 (\gamma \tilde{\mathrm{G}}) + \text {soft}$, the other decay channel being $ {\tilde{\chi} _1^{\pm}}\to \mathrm{W} + \tilde{\mathrm{G}} $. The full lines represent the observed and the dashed lines the expected exclusion limits, where the phase space below the lines is excluded. The band around the expected limit of the combination indicates the region containing 68% of the distribution of limits expected under the background-only hypothesis. The band around the observed limit of the combination shows the spread in the observed limit from variation of the signal cross sections within their theoretical uncertainties. |
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Figure 5-a:
The combined 95% CL NLSP mass exclusion limits for EW SMS production above 300 GeV in the neutralino branching fraction scenario. The limit is shown as a function of the branching fraction $\tilde{\chi}^0_1 \to \gamma + \tilde{\mathrm{G}} $, the other decay channel being $\tilde{\chi}^0_1 \to \mathrm{Z} + \tilde{\mathrm{G}} $. The full lines represent the observed and the dashed lines the expected exclusion limits, where the phase space below the lines is excluded. The band around the expected limit of the combination indicates the region containing 68% of the distribution of limits expected under the background-only hypothesis. The band around the observed limit of the combination shows the spread in the observed limit from variation of the signal cross sections within their theoretical uncertainties. |
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Figure 5-b:
The combined 95% CL NLSP mass exclusion limits for EW SMS production above 300 GeV in the chargino branching fraction scenario. The limit is shown as a function of the branching fraction $ {\tilde{\chi} _1^{\pm}}\to \tilde{\chi}^0_1 (\gamma \tilde{\mathrm{G}}) + \text {soft}$, the other decay channel being $ {\tilde{\chi} _1^{\pm}}\to \mathrm{W} + \tilde{\mathrm{G}} $. The full lines represent the observed and the dashed lines the expected exclusion limits, where the phase space below the lines is excluded. The band around the expected limit of the combination indicates the region containing 68% of the distribution of limits expected under the background-only hypothesis. The band around the observed limit of the combination shows the spread in the observed limit from variation of the signal cross sections within their theoretical uncertainties. |
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Figure 6:
The 95% CL exclusion limits for the nominal gluino scenario (left) assuming equal probabilities of 50% for the gluino decay to $\mathrm{q} \mathrm{\bar{q}} {\tilde{\chi} _1^{\pm}}$ and $\mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^0_1 $. For the gluino branching fraction scenario (right) the ratio of the probabilities for both decays are scanned and the gluino mass is fixed to 1950 GeV. The Photon+Lepton category shows no exclusion power for the latter scenario. The full lines represent the observed and the dashed lines the expected exclusion limits, where the phase space below the lines is excluded. The band around the expected limit of the combination indicates the region containing 68% of the distribution of limits expected under the background-only hypothesis. The band around the observed limit of the combination shows the spread in the observed limit from variation of the signal cross sections within their theoretical uncertainties. |
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Figure 6-a:
The 95% CL exclusion limits for the nominal gluino scenario assuming equal probabilities of 50% for the gluino decay to $\mathrm{q} \mathrm{\bar{q}} {\tilde{\chi} _1^{\pm}}$ and $\mathrm{q} \mathrm{\bar{q}} \tilde{\chi}^0_1 $. The full lines represent the observed and the dashed lines the expected exclusion limits, where the phase space below the lines is excluded. The band around the expected limit of the combination indicates the region containing 68% of the distribution of limits expected under the background-only hypothesis. The band around the observed limit of the combination shows the spread in the observed limit from variation of the signal cross sections within their theoretical uncertainties. |
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Figure 6-b:
The 95% CL exclusion limits for the gluino branching fraction scenario where the ratio of the probabilities for both decays are scanned and the gluino mass is fixed to 1950 GeV. The Photon+Lepton category shows no exclusion power for the latter scenario. The full lines represent the observed and the dashed lines the expected exclusion limits, where the phase space below the lines is excluded. The band around the expected limit of the combination indicates the region containing 68% of the distribution of limits expected under the background-only hypothesis. The band around the observed limit of the combination shows the spread in the observed limit from variation of the signal cross sections within their theoretical uncertainties. |
Tables | |
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Table 1:
Definitions of the four exclusive categories. The kinematic selections and the search bins are based on the four individual searches, while the additional vetoes shown in the third columns ensure exclusive event categories. The transverse mass of a photon/lepton and ${{p_{\mathrm {T}}} ^\text {miss}}$ is denoted as $ {m_{\mathrm {T}}} \left (\gamma /\ell, {{p_{\mathrm {T}}} ^\text {miss}} \right)$. The search bins always include the lower bounds. The Diphoton and Lepton veto match the kinematic selections of the Diphoton and Photon+Lepton category, respectively. The Diphoton veto is only used in the interpretation of the EW produced scenarios, but dropped for the strong produced scenarios, where the Diphoton category is not part of the combination. |
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Table 2:
Predicted pre-fit background yields, where the values are not constrained by the likelihood fit, the observed number of events in data, and the post-fit background yields after the constraint from the likelihood fit for all search bins used in the combination. In addition the range covered by each individual bin is shown. |
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Table 3:
Predicted pre-fit background yields, where the values are not constrained by the likelihood fit, the observed number of events in data, and the post-fit background yields after the constraint from the likelihood fit for all search bins used in the combination. In addition the range covered by each individual bin is shown. For these yields, the Diphoton category is not included and the Diphoton veto is removed to increase the sensitivity of the Photon+$ {{H_{\mathrm {T}}} ^{\gamma}} $ category to strong production of gluinos. |
Summary |
A combination of four different searches for general gauge-mediated (GGM) supersymmetry (SUSY) in final states with photons and a large transverse momentum imbalance was 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 data recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV, and corresponding to an integrated luminosity of 35.9 fb$^{-1}$ , the combination improves the expected sensitivity of the searches described in Ref. [20,21,19,18]. The results are interpreted in the context of GGM SUSY and in simplified models. 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 results of the GGM scenario are expressed as limits on the physical mass parameters. Here, chargino masses up to 890 (1080) GeV are excluded by the observed (expected) limit across the tested neutralino mass spectrum, which ranges from 120 to 720 GeV. In electroweak production models, limits for neutralino masses are set up to 1050 (1200) GeV for combined $\tilde{\chi}_{1}^{\pm}\tilde{\chi}_{1}^{0}$ and $\tilde{\chi}_{1}^{\pm}\tilde{\chi}_{1}^{\mp}$ production, while for pure $\tilde{\chi}_{1}^{\pm}\tilde{\chi}_{1}^{\mp}$ production these limits are reduced to 825 (1000) GeV. For a strong production scenario based on gluino pair production, the highest excluded gluino mass is at 1975 (2050) GeV. The combination improves on the expected limits on neutralino and chargino masses by up to 100 GeV, while the expected limit on the gluino mass is increased by 50 GeV compared to the individual searches. |
Additional Figures | |
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Additional Figure 1:
Combined observed exclusion for the GGM scenario in terms of the GGM model parameters. |
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Additional Figure 1-a:
Pre-fit background covariance matrix for the combination. The matrix shows the correlations between search regions of the combination and provides the necessary information for merging search regions for re-interpretation of the results. The first four bins are the Photon+$ {S^{\gamma}_{T}}$ bins and the next three ${{p_{\mathrm {T}}} ^\text {miss}}$ bins are at high Photon+$ {H^{\gamma}_{T}}$. This is followed by the thirty-six analysis search bins for muon-photon and electron-photon final states, and the last six bins are the ${{p_{\mathrm {T}}} ^\text {miss}}$ search bins of diphoton events. |
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Additional Figure 1-b:
Correlation matrix computed from the pre-fit covariance matrix. The matrix shows the correlations between search regions of the combination and provides the necessary information for merging search regions for re-interpretation of the results. The first four bins are the Photon+$ {S^{\gamma}_{T}}$ bins and the next three ${{p_{\mathrm {T}}} ^\text {miss}}$ bins are at high Photon+$ {H^{\gamma}_{T}}$. This is followed by the thirty-six analysis search bins for muon-photon and electron-photon final states, and the last six bins are the ${{p_{\mathrm {T}}} ^\text {miss}}$ search bins of diphoton events. |
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Compact Muon Solenoid LHC, CERN |