CMS-SUS-14-016

CMS-SUS-14-016 ; CERN-EP-2016-012
Search for supersymmetry in electroweak production with photons and large missing transverse energy in pp collisions at $\sqrt{s}= $ 8 TeV
CMS Collaboration
28 February 2016
Phys. Lett. B 759 (2016) 479
Abstract: Results are reported from a search for supersymmetry with gauge-mediated supersymmetry breaking in electroweak production. Final states with photons and large missing transverse energy ($E_{\mathrm{T}}^{\text{miss}}$) were examined. The data sample was collected in pp collisions at $ \sqrt{s} = $ 8 TeV with the CMS detector at the LHC and corresponds to 7.4 fb$^{-1}$. The analysis focuses on scenarios in which the lightest neutralino has bino- or wino-like components, resulting in decays to photons and gravitinos, where the gravitinos escape undetected. The data were obtained using a specially designed trigger with dedicated low thresholds, providing good sensitivity to signatures with photons, $E_{\mathrm{T}}^{\text{miss}}$, and low hadronic energy. No excess of events over the standard model expectation is observed. The results are interpreted using the model of general gauge mediation. With the wino mass fixed at 10 GeV above that of the bino, wino masses below 710 GeV are excluded at 95% confidence level. Constraints are also set in the context of two simplified models, for which the analysis sets the lowest cross section limits on the electroweak production of supersymmetric particles.
Links: e-print arXiv:1602.08772 [hep-ex] (PDF) ; CDS record ; inSPIRE record ; CADI line (restricted) ;

Figures & Tables	Summary	References	CMS Publications

Figures
png pdf	Figure 1-a: Scenarios for the production and decay of charginos and neutralinos considered in this analysis. In the TChiNg scenario (a,b), the charginos are only slightly heavier than the neutralinos, leading to chargino to neutralino decays accompanied by soft radiation. One neutralino decays to a photon and a gravitino, while the other decays into a Z or an H boson and a gravitino with equal probability. In the TChiWg scenario (c), the gauginos are mass-degenerate and the $\tilde{\chi}^0 _1$ decays are as shown. Within GGM models, the $\tilde{\chi}^0 _1\to \gamma \tilde{\mathrm{G}} $ to $\tilde{\chi}^0 _1\to {\mathrm{ Z } } \tilde{\mathrm{G}} $ branching fraction depends on the neutralino mass. The dominant process for electroweak GGM production is shown in (d). A smaller amount of hadronic energy compared to strong production and at least one photon and ${E_{\mathrm {T}}^{\text {miss}}}$ are common features of all scenarios.
png pdf	Figure 1-b: Scenarios for the production and decay of charginos and neutralinos considered in this analysis. In the TChiNg scenario (a,b), the charginos are only slightly heavier than the neutralinos, leading to chargino to neutralino decays accompanied by soft radiation. One neutralino decays to a photon and a gravitino, while the other decays into a Z or an H boson and a gravitino with equal probability. In the TChiWg scenario (c), the gauginos are mass-degenerate and the $\tilde{\chi}^0 _1$ decays are as shown. Within GGM models, the $\tilde{\chi}^0 _1\to \gamma \tilde{\mathrm{G}} $ to $\tilde{\chi}^0 _1\to {\mathrm{ Z } } \tilde{\mathrm{G}} $ branching fraction depends on the neutralino mass. The dominant process for electroweak GGM production is shown in (d). A smaller amount of hadronic energy compared to strong production and at least one photon and ${E_{\mathrm {T}}^{\text {miss}}}$ are common features of all scenarios.
png pdf	Figure 1-c: Scenarios for the production and decay of charginos and neutralinos considered in this analysis. In the TChiNg scenario (a,b), the charginos are only slightly heavier than the neutralinos, leading to chargino to neutralino decays accompanied by soft radiation. One neutralino decays to a photon and a gravitino, while the other decays into a Z or an H boson and a gravitino with equal probability. In the TChiWg scenario (c), the gauginos are mass-degenerate and the $\tilde{\chi}^0 _1$ decays are as shown. Within GGM models, the $\tilde{\chi}^0 _1\to \gamma \tilde{\mathrm{G}} $ to $\tilde{\chi}^0 _1\to {\mathrm{ Z } } \tilde{\mathrm{G}} $ branching fraction depends on the neutralino mass. The dominant process for electroweak GGM production is shown in (d). A smaller amount of hadronic energy compared to strong production and at least one photon and ${E_{\mathrm {T}}^{\text {miss}}}$ are common features of all scenarios.
png pdf	Figure 1-d: Scenarios for the production and decay of charginos and neutralinos considered in this analysis. In the TChiNg scenario (a,b), the charginos are only slightly heavier than the neutralinos, leading to chargino to neutralino decays accompanied by soft radiation. One neutralino decays to a photon and a gravitino, while the other decays into a Z or an H boson and a gravitino with equal probability. In the TChiWg scenario (c), the gauginos are mass-degenerate and the $\tilde{\chi}^0 _1$ decays are as shown. Within GGM models, the $\tilde{\chi}^0 _1\to \gamma \tilde{\mathrm{G}} $ to $\tilde{\chi}^0 _1\to {\mathrm{ Z } } \tilde{\mathrm{G}} $ branching fraction depends on the neutralino mass. The dominant process for electroweak GGM production is shown in (d). A smaller amount of hadronic energy compared to strong production and at least one photon and ${E_{\mathrm {T}}^{\text {miss}}}$ are common features of all scenarios.
png pdf	Figure 2-a: The ${E_{\mathrm {T}}^{\text {miss,signif}} }$ (a) and $ {S_{\mathrm {T}}^{\gamma } } $ (b) variables are shown in the signal selection and used to define four search regions with ${E_{\mathrm {T}}^{\text {miss,signif}} } =$ 200 and $ {S_{\mathrm {T}}^{\gamma } } =$ 600 GeV partitions. A benchmark TChiNg signal point with an NLSP mass of 500 GeV is shown for comparison.
png pdf	Figure 2-b: The ${E_{\mathrm {T}}^{\text {miss,signif}} }$ (a) and $ {S_{\mathrm {T}}^{\gamma } } $ (b) variables are shown in the signal selection and used to define four search regions with ${E_{\mathrm {T}}^{\text {miss,signif}} } =$ 200 and $ {S_{\mathrm {T}}^{\gamma } } =$ 600 GeV partitions. A benchmark TChiNg signal point with an NLSP mass of 500 GeV is shown for comparison.
png pdf	Figure 3-a: Exclusion limits at 95%CL for the TChiNg (a) and TChiWg (b) scenario. In the TChiNg scenario NLSP masses below 570 GeV are excluded, in the TChiWg scenario NLSP masses below 680 GeV are excluded.
png pdf	Figure 3-b: Exclusion limits at 95%CL for the TChiNg (a) and TChiWg (b) scenario. In the TChiNg scenario NLSP masses below 570 GeV are excluded, in the TChiWg scenario NLSP masses below 680 GeV are excluded.
png pdf	Figure 4-a: Observed upper cross section CL$_\mathrm {s}$ limit at the 95%CL for the GGM signal points in the $M_{\text {wino}}$-$M_{\text {bino}}$ plane (a). Also shown are the 95%CL expected and observed exclusion contours. The GGM signal points near the diagonal, e.g. for $M_{\text {wino}} = M_{\text {bino}} =$ 10 GeV up to a wino mass of $M_{\text {wino}} =$ 710 GeV are excluded (b).
png pdf	Figure 4-b: Observed upper cross section CL$_\mathrm {s}$ limit at the 95%CL for the GGM signal points in the $M_{\text {wino}}$-$M_{\text {bino}}$ plane (a). Also shown are the 95%CL expected and observed exclusion contours. The GGM signal points near the diagonal, e.g. for $M_{\text {wino}} = M_{\text {bino}} =$ 10 GeV up to a wino mass of $M_{\text {wino}} =$ 710 GeV are excluded (b).

Tables
png pdf	Table 1: Summary table of systematic uncertainties relevant for the analysis. Uncertainties due to the luminosity and trigger efficiency measurement apply only to the backgrounds estimated using MC simulation without data normalization, namely ${\mathrm{ t } {}\mathrm{ \bar{t} } } \gamma $, diboson, and multijet, and for the signal. The total uncertainty is dominated by the uncertainty in the $ {\mathrm {V}} \gamma $ background.
png pdf	Table 2: Event yields for data corresponding to 7.4 fb$^{-1}$ and the estimated backgrounds. The signal yields correspond to the benchmark TChiNg signal point with $M_{\text {wino}}= $ 500 GeV shown in Fig. 2, also stating the acceptance times efficiency $A\varepsilon $ for each search region. The contribution from QCD multijet background is negligible in all regions.

Summary

We have searched for electroweak production of gauginos in the framework of gauge mediated supersymmetry breaking in final states with photons and $E_{\mathrm{T}}^{\text{miss}}$. A dataset, corresponding to an integrated luminosity of 7.4 fb$^{-1}$, recorded with a special trigger with low thresholds is used. The data are found to agree with the SM expectation. The analysis is sensitive to electroweak production and compressed mass spectra which are characterized by minimal hadronic activity in the final state, complementing previously published searches. Limits in the TChiNg scenario are set for the first time, excluding NLSP masses below 570 GeV at 95% CL. In the TChiWg scenario, NLSP masses below 680 GeV are excluded at 95% CL, increasing the previous mass limit in this scenario [31] by 140 GeV. In the general gauge mediation model for compressed mass spectrum scenarios with e.g. $M_{\text{wino}}-M_{\text{bino}} = $ 10 GeV, wino masses below 710 GeV can be excluded, increasing the previous CMS limit [19] by about 220 GeV.

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