Search for new physics in events with two low momentum opposite-sign leptons and missing transverse energy at $\sqrt{s}=13~\mathrm{TeV}$

A search for new physics in events with low-momentum opposite-sign leptons and missing transverse momentum, using $35.9~\mathrm{fb}^{-1}$ of integrated luminosity collected by CMS experiment at $\sqrt{s}=13~\mathrm{TeV}$, is presented. The data observed are consistent with expectations from the standard model. The results are interpreted in terms of pair production of charginos and neutralinos ($\tilde{\chi}_1^{\pm}$, $\tilde{\chi}_2^{0}$) with nearly degenerate masses, as expected in natural compressed higgsino models, and in terms of the pair production of top squarks for the case that the neutralino and the top squark have similar masses. At $95\%$ confidence level, $\tilde{\chi}_1^{\pm}$/$\tilde{\chi}_2^{0}$ are excluded for masses up to $230~\mathrm{GeV}$ for a mass difference of $20~\mathrm{GeV}$ with respect to the lightest neutralino, which is a region constrained so far by the LEP experiments only. An interpretation is also provided in terms of top squark ($\tilde{t}$) pair production processes with degenerate mass spectra and chargino-mediated decays. Masses of the $\tilde{t}$ up to $450~\mathrm{GeV}$ are excluded for a mass difference of $40~\mathrm{GeV}$ with respect to the lightest neutralino.