Search for compressed supersymmetry at the LHC in final states with one hadronic tau and one energetic jet

We present an experimental search of supersymmetry (SUSY) in compressed mass spectra scenarios with scalar taus ($\widetilde{\tau}$'s), using data from proton-proton (pp) collisions in the Large Hadron Collider, LHC, at CERN laboratory, at $\sqrt{}$ = 13 TeV, collected by the CMS experiment in 2016 and 2017. Compressed mass spectra scenarios, where the mass difference between the lightest neutralino ($\widetilde{X}$$_{1}^{0}$ and the $\widetilde{\tau}$ is small, have been proposed in several models in order to incorporate coannihilation as a mechanism to obtain a relic dark matter density consistent with that predicted by astronomy. The compressed mass region in SUSY is challenging to probe experimentally. We focus on a final state containing exactly one tau lepton, with low transverse momentum ($pT$), that has decayed hadronically ($\tau$$_{h}$), at least one initial state radiation jet (ISR) with high $pT$, and a large imbalance of missing transverse momentum ($p$$_{T}^{miss}$). An integrated luminosity of 77.2 fb$^{−1}$ of pp data was used for this analysis. The data was found to be in agreement with respect to the expected background. Therefore, upper limits on the production cross-section as function of $\widetilde{X}$$_{1}^{\pm}$ ($\widetilde{X}$$_{2}^{0}$) mass were set, excluding masses up to 290 GeV for a mass splitting of ∆$m$($\widetilde{X}$$_{1}^{0}$, $\widetilde{\tau}$) = 50 GeV. The limits set on this search, constitute the most stringent limits today for all $\widetilde{\tau}$ related searches.