Probing the littlest Higgs model with $T$ parity using di-Higgs events   through $Z_H$-pair production at the LHC in NLO QCD
  We investigate the di-Higgs events through $Z_H$-pair production at the CERN Large Hadron Collider including the pure next-to-leading order (NLO) QCD correction and the $gg$-fusion contribution in the framework of the littlest Higgs model with $T$ parity. We employ the diagram subtraction scheme in the QCD NLO calculations to avoid double counting and keep the convergence of the perturbative QCD description for the $Z_H$-pair production. We investigate the dependence of the leading order and QCD corrected integrated cross sections on the renormalization/factorization scale, and find that the total QCD corrections slightly reduce the scale uncertainty in the plotted range. By considering the subsequent decays of the intermediately produced $Z_H$ bosons and adopting the exclusive four-$b$-jet event selection criterion, the QCD correction provides considerable enhancement of the kinematic distributions for final decay products. We find that it is possible to select the signature of the $Z_H$-pair production from possible standard model background by taking proper kinematic cuts. 
Chen Liang-Wen, Zhang Ren-You, Ma Wen-Gan, Li Wei-Hua, Duan Peng-Fei   and Guo Lei
hep-ph hep-ex