Search for new physics in events with two soft oppositely charged leptons and missing transverse momentum in proton-proton collisions at $\sqrt{s}=$ 13 TeV

摘要

A search is presented for new physics in events with two low-momentum,oppositely charged leptons (electrons or muons) and missing transverse momentumin proton-proton collisions at a centre-of-mass energy of 13 TeV. The datacollected using the CMS detector at the LHC correspond to an integratedluminosity of 35.9 fb$^{-1}$. The observed event yields are consistent with theexpectations from the standard model. The results are interpreted in terms ofpair production of charginos and neutralinos ($\widetilde{\chi}^\pm_1$ and$\widetilde{\chi}^0_2$) with nearly degenerate masses, as expected in naturalsupersymmetry models with light higgsinos, as well as in terms of the pairproduction of top squarks ($\widetilde{\mathrm{t}}$), when the lightestneutralino and the top squark have similar masses. At 95% confidence level,wino-like $\widetilde{\chi}^\pm_1$/$\widetilde{\chi}^0_2$ masses are excludedup to 230 GeV for a mass difference of 20 GeV relative to the lightestneutralino, a region constrained thus far only by the LEP experiments. For$\widetilde{\mathrm{t}}$ pair production, top squark masses up to 450 GeV areexcluded for a mass difference of 40 GeV relative to the lightest neutralino.