Single production of X±5 /3 and y 4 /3 vectorlike quarks at the LHC SINGLE PRODUCTION of X±5 /3 and y 4 /3 ... CHUAN-HUNG CHEN and TAKAAKI NOMURA

Two triplet vectorlike quarks (VLQs) with hypercharges of Y=2/3, -1/3 and one singlet scalar boson are embedded in the standard model to resolve the 750 GeV diphoton excess. The constraints on the tree-level Higgs- and Z-mediated flavor-changing neutral currents are discussed in detail. Besides the resolution of excess, it is found that the signal strength of diphoton Higgs decay can have a 10% deviation from the SM prediction and that the upper limits of the branching ratios for rare top-quark decays are BR(t→c(h,Z))<(6.8,0.48)×10-5. We find that the production cross section of a single VLQ by electroweak processes is larger than that of a VLQ pair by QCD processes. To explore the signals of the heavy VLQs at the LHC, we thoroughly analyze the production of single X±5/3 and Y 4/3 via qiqj′ annihilations in pp collisions at s=13 TeV. It is found that the electroweak production cross sections for dX5/3, uY-4/3, and dY4/3 channels with mX=mY=1 TeV can be 84.3, 72.3, and 157.8 fb, respectively, and the dominant decay modes are X5/3→(c,t)W+ and Y-4/3→(s,b)W-. With adopting kinematic cuts, the significance for the pp→dW+t channel can be over 5σ.