Single production of $X_{\pm 5/3}$ and $Y_{\mp 4/3}$ vectorlike quarks at the LHC

Abstract

Two triplet vector-like quarks (VLQs) with hypercharges of $Y=2/3,-1/3$ and one singlet scalar boson are embedded in the standard model (SM) 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 $BR(t\to c(h,Z))<(6.8,0.48)\times 10^{-5}$. We find that the production cross section of a single VLQ by electroweak processes is larger than that of VLQ-pair by QCD processes. To explore the signals of the heavy VLQs at the LHC, we throughly analyze the production of single $X_{\pm 5/3}$ and $Y_{\mp 4/3}$ via $q_i{q}_j^{\prime }$ annihilations in $pp$ collisions at $\sqrt{s}=13$ TeV. It is found that the electroweak production cross sections for $d{X}_{5/3}$, $u{Y}_{-4/3}$, and $d{Y}_{4/3}$ channels with $m_X=m_Y=1$ TeV can be $84.3$, $72.3$, and $157.8$ fb, respectively; and the dominant decay modes are $X_{5/3}\to (c,t)W^{+}$ and $Y_{-4/3}\to (s,b)W^{-}$. With adopting kinematic cuts, the significance for $pp\to d{W}^{+}t$ channel can be over $5\sigma$.

Comments: 32 pages, 8 figures, 4 tables, version published in PRD