Mono-top signature from stop decay at the HE-LHC

Searching for the top squark(stop)is a key task to test the naturalness of SUSY.Different from stop pair production,single stop production relies on its electroweak properties and can provide some unique signatures.Following the single production process pp→t^(~)1X(~)1→tX^(~)1^(0)X^(~)1^(-),the top quark has two decay channels:leptonic channel and hadronic channel.In this paper,we probe the observability of these two channels in a simplified minimal supersymmetric standard model scenario.We find that,at the 27 TeV LHC with the integrated luminosity of L=15 ab^(-1),mt^(-)1<1900 GeV andμ<750 GeV can be excluded at 2σthrough the leptonic mono-top channel,while m_(t^(-)1)<1200 GeV andμ<350 GeV can be excluded at 2σthrough the hadronic channel.

Probing tq Z anomalous couplings in the trilepton signal at the HL-LHC,HE-LHC,and FCC-hh

We investigate the prospect of discovering the Flavour Changing Neutral Current(FCNC)tqZ couplings via two production processes yielding trilepton signals:top quark pair production pp→tt with one top quark decaying to the Z boson and one light jet and the anomalous single top quark plus Z boson production process pp→tZ.We study these channels at various successors of the Large Hadron Collider(LHC),i.e,the approved High-Luminosity LHC(HL-LHC)as well as the proposed High-Energy LHC(HE-LHC)and Future Circular Collider in hadron-hadron mode(FCC-hh).We perform a full simulation for the signals and the relevant Standard Model(SM)backgrounds and obtain limits on the Branching Ratios(BRs)of t→qZ(q=u,c),eventually yielding a trilepton final state through the decay modes t→bW+→bl^(+)V_(l)and Z→l^(+)l^(-).The upper limits on these FCNC BRs at 95%Confidence Level(CL)are obtained at the HL-LHC with√s=14 TeV and 3 ab^(-1),at the HE-LHC with√s=27TeV and 15 ab^(-1),and at the FCC-hh with√s=100 TeV and 30ab^(-1).