Search for signatures of electroweakinos with photons, jets, and large missing transverse momentum in $\sqrt{s}=13$ TeV pp collisions with the ATLAS detector

TL;DR

This ATLAS analysis searches for signatures of electroweakinos in gauge-mediated SUSY with photons, jets and large MET using the full Run-2 dataset of 140 fb$^{-1}$ at $ oot s = 13$ TeV. It targets bino–higgsino NLSP scenarios with decays to $ ilde{G}+ ext{(} ext{photon}, Z, h)$, implementing a broad, BR-scanning approach across multiple signal regions to maximize sensitivity. No excess over the SM is observed; the study yields 95% CL exclusions with $m_{ ilde{ ablachi_1^0}}$ up to about 1.2 TeV for favorable BRs, and provides model-independent limits on the visible cross section. The work demonstrates the power of inclusive, multi-region searches and BR-parameterization for constraining GGM electroweakino scenarios at the LHC, informing future high-luminosity explorations.

Abstract

A search for final states characterised by at least one isolated high transverse-momentum photon, jets and large missing transverse momentum is presented. Such a final state might occur in gauge-mediated supersymmetric models where a pair of binos and higgsinos mix to form neutralinos, one of which decays into a photon plus a gravitino while the other decays into a Higgs boson, a Z boson or a photon, plus a gravitino. The search is performed using the full Run-2 data sample of 140 fb$^{-1}$ of $\sqrt{s}=13$ TeV proton-proton collisions collected by the ATLAS detector at the Large Hadron Collider. No significant excess of events is observed above the Standard Model prediction and model-dependent exclusion limits at the 95% confidence level are set. These limits are interpreted in terms of the masses of gauginos, which are excluded up to 1.2 TeV depending on their branching ratios, and on their branching ratios as a function of their mass.

Figures (8)

• Figure 1: Example production diagrams of neutralinos and their subsequent decay into a final state with a photon, jets and missing transverse momentum.
• Figure 2: Schematic view of the three signal regions, defined in the and significance plane, used in the simultaneous fit for exclusion limits (SRLe, SRMe and SRH). The other inclusive SRs can be defined from these as $\text{SRL} = \text{SRLe}\, \cup\, \text{SRMe}\, \cup\, \text{SRH}$ and $\text{SRM} = \text{SRMe}\, \cup\, \text{SRH}$. The dotted lines represent the requirements on the corresponding variables.
• Figure 3: The observed and expected yields after the background-only fit in the control and validation regions. The lower panel shows the background normalisation factors (NF) estimated in each control region, and the significance, in standard deviations, between the observed and expected yields in the validation regions, considering both the systematic and statistical uncertainties in the background expectation. The significance shown is calculated with the profile likelihood method from Cowan:2010js, adding a minus sign if the yield is below the prediction. Minor background processes, such as $\gamma+\mathrm{jets}$, $\gamma\gamma$ and $W\gamma\gamma/Z\gamma\gamma$, are included under 'Others'.
• Figure 4: The observed and expected yields in all the signal regions. The lower panel shows the difference, in standard deviations, between the observed and expected yields considering both the systematic and statistical uncertainties in the background expectation.
• Figure 5: Observed distributions in the signal region SRL after the background-only fit for (a) and (b) significance variables. The and significance requirements (that simultaneously define the other signal regions, SRM and SRH), are indicated in the distributions. The uncertainties in the SM background are statistical only. The last bin includes overflow. The figure shows predictions for different models and masses of neutralinos.