Searches for Electroweak Production of Compressed Supersymmetry with Soft Leptons and Missing Transverse Momentum in $pp$ Collisions at $\sqrt{s}=$ 13 TeV with the ATLAS Detector

Supersymmetry (SUSY) is an extension of the Standard Model that predicts a boson (fermion) partner for each fermion (boson) in the Standard Model. Weak scale SUSY is attractive for reasons like improving gauge coupling unification, reducing fine-tuning in the Higgs sector and providing a dark matter candidate. In this talk, I present a dedicated search for direct production of new colorless weak scale states in a compressed mass spectra with final states characterized by soft visible decay products. This analysis uses $pp$ collisions at $\sqrt s$ = 13 TeV at the Large Hadron Collider and collected by the ATLAS experiment during 2015 and 2016 corresponding to 36.1 $fb^{-1}$ of integrated luminosity. This analysis selects events with two soft electrons or muons and missing transverse momentum ($E_T^{miss}$) recoiling against hadronic initial state radiation. Backgrounds from $t\bar{t}$, diboson, and other production mechanisms with prompt leptons are estimated with Monte Carlo simulation while reducible backgrounds with instrumental $E_T^{miss}$ and fake/non-prompt leptons is estimated with a mix of Monte Carlo and data-driven methods. Results are consistent with Standard Model expectation and limits on compressed supersymmetric states are extended for the first time since LEP.