Search for electroweak production of gauge mediated supersymmetry with photons at CMS (SUS-14-016)


In this letter a search for electroweak production of gauge mediated supersymmetry at CMS is reported. The lightest neutralino is assumed to have bino- or wino-like components, resulting in decays to photons and gravitinos, where the gravitino escapes undetected. The analysis focuses on electroweak production of low mass sparticles resulting in final states with photons and missing transverse energy. A special dataset with relaxed photon transverse momentum and missing transverse energy trigger thresholds is used to search for the signal characterized by low hadronic energy in the final state. This dataset collected in pp collisions in 2012 corresponds to 7.4 fb$^{-1}$ at$\sqrt{s}$= 8 TeV. No significant excess over the standard model background expectation is observed. Cross section limits and exclusion contours for various scenarios of direct electroweak gaugino production are presented.

Figures in the paper

Figures Caption
Figure 1: In the TChiNg scenario (left), 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, where the other decays into a Z or an h boson and a gravitino with equal probability. In the TChiWg scenario (top right), the gauginos are mass-degenerate and the $\widetilde{\chi}^0_1$ and $\widetilde{\chi}^{\pm}_1$ decays are as shown. Within the GGM, the branching ratio $\widetilde{\chi}^0_1\rightarrow$ $\gamma\tilde{G}$ to $\widetilde{\chi}^0_1\rightarrow$ $Z\tilde{G}$ depends on the neutralino-mass. The dominant process for electroweak GGM production is shown in (bottom right). A small amount of hadronic energy and at least one photon and $E_{\mathrm{T}}^{\text{miss}}$ are common features of the scenarios.
Figure 2: The $E_{\mathrm{T}}^{\text{miss,signif}}$ (left) and $S_{\text{T}}^{\gamma}$ (right) variables are seen to span the signal region. Four search regions are formed with $E_{\mathrm{T}}^{\text{miss,signif}}$ = 200 and $S_{\text{T}}^{\gamma}$ = 600 GeV partitions. A benchmark TChiNg signal point with M$_{\text{wino}}$ = 500 GeV is shown for comparison.
Figure 3: Exlcusion limits for the TChiNg (left) and TChiWg (right) scenario. In the TChiNg scenario NLSP masses below 570 GeV are excluded, in the TChiWg scenario NLSP masses below 680 GeV are excluded. Electronic versions of limits: TChiNg_Obs.root, TChiNg_Exp.root, TChiWg_Obs.root, TChiWg_Exp.root
Figure 4: Observed upper cross-section CLs limit at 95% C.L. for the GGM signal points for data corresponding to an integrated luminosity of 7.4 fb$^{-1}$ in theM$_{\text{wino}} -$ M$_{\text{bino}}$ plane (left). Also shown are the expected and observed exclusion contours. 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 (right). Electronic versions of limits: WinoBino_Exclusion.root, WinoBino_10_Obs.root, WinoBino_10_Exp.root

Tables in the paper

Tables Caption
Table 1: 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 Mwino = 500 GeV shown in Fig. 2.

Additional material

Figures and tables Caption
Table 2: 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 t$\bar{\text{t}}\gamma$, diboson and multijet, and for the signal. The overall uncertainty of the background yields in the final selection are dominated by the uncertainty on the $V\gamma$ background.
Figure 5: Validation of the prediction of background events arising from electrons misidentified as photons depending on the $E_{\mathrm{T}}^{\text{miss,signif}}$. The prediction (red area) is obtained by replacing the $\gamma_{\text{tight}}$ definition by the $\gamma_{\text{pixel}}$ definition and scaling the distribution with the fake factor. This prediction is compared to the distribution of electrons fulfilling $\Delta$R(sim. $e$, $\gamma_{\text{tight}}$) $<$ 0.1 using generator information (black points). Good agreement is observed.
Figure 6: Measurement of the trigger efficiency of the $E_{\mathrm{T}}^{\text{miss}}$-req. as a function of the missing transverse energy. The trigger efficiency shows a broad turn-on due to the difference in the $E_{\mathrm{T}}^{\text{miss}}$ calculation used by the trigger and the offline selection. The trigger efficiency is flat for $E_{\mathrm{T}}^{\text{miss}}$ $>$ 100 GeV and given by $\varepsilon_{\text{$E_{\mathrm{T}}^{\text{miss}}$-req}} = \text{(98.3 }^{+0.8}_{-1.3}\text{(stat.))} \%$.
Figure 7: Measurement of the trigger efficiency of the photon part in dependency of the spherical distance of the photon and the nearest jet $\Delta$R(1st $\gamma$, nearest jet). The trigger efficiency is strongly reduced for small spherical distances. Therefore, $\Delta$R(1st $\gamma$, nearest jet) $>$ 0.5 is required in the analysis.
Figure 8: Measurement of the trigger efficiency of the photon part as a function of the transverse momentum of the photon with the highest transverse momentum. The plateau region is reached for $p_{\text{T}}$ = 40 GeV and the efficiency for $p_{\text{T}}$ $>$ 40 GeV is given by $\varepsilon_{\text{$\gamma$-req}}$ = (88.0 $\pm$ 0.7({stat.)}) $\%$.
Figure 9: Control region where the $V\gamma$ and $\gamma$jets background simulations are fitted to the data using the template variable $E_{\mathrm{T}}^{\text{miss}}$/$\sqrt{\text{ $H_{\text{T}}$}}$.
Table 3: Number of signal events and the selection efficiency after each selection step for three signal points, each corresponding to a different signal scenario. The TChiNg_500 point corresponds to a NLSP mass of 500 GeV, The TChiWg_650 point corresponds to a NLSP mass of 650 GeV and the GGM_640_630 point corresponds to a wino mass of 640 GeV and a bino mass of 630 GeV.
Figure 10: Efficiencies for the GGM signal points in the plane spanned by of the wino and bino mass. Electronic version: WinoBino_Acceptance.root
Figure 11: Effciencies for the TChiNg signal scenario depending on the mass of the NLSP after the full selection. Eelectronic version: TChiNg_acc.root
Figure 12: Effciencies for the TChiWg signal scenario depending on the mass of the NLSP after the full selection. The TChiWg simulation has a higher granularity compared to the TChiNg simulation. Electronic version: TChiwg_acc.root

-- JohannesSchulz - 2015-07-22

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PDFpdf TChiNg_ex.pdf r1 manage 234.4 K 2015-07-23 - 14:35 JohannesSchulz  
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