Opening Up the Compressed Region of Top Squark Searches at 13 TeV LHC

Light top superpartners play a key role in stabilizing the electroweak scale in supersymmetric theories. For R-parity conserved supersymmetric models, traditional searches are not sensitive to the compressed regions. In this Letter, we propose a new method targeting this region, with top squark and neutralino mass splitting ranging from m((t) over tildet) - m(chi) greater than or similar to m(t) to about 20 GeV. In particular, we focus on the signal process in which a pair of top squarks are produced in association with a hard jet, and we define a new observable R-M whose distribution has a peak in this compressed region. The position of the peak is closely correlated with m((t) over tildet). We show that for the 13 TeV LHC with a luminosity of 3000 fb(-1), this analysis can extend the reach of the top squark in the compressed region to m((t) over tildet) around 800 GeV.