Color sextet scalars at the CERN Large Hadron Collider

Taking a phenomenological approach, we study a color sextet scalar at the LHC. We focus on the QCD production of a color sextet pair ${\Phi }_6{\overline{\Phi }}_6$ through $gg$ fusion and $q\overline{q}$ annihilation. Its unique coupling to ${\overline{\psi }}^c\psi$ allows the color sextet scalar to decay into same-sign diquark states, such as ${\Phi }_6\to tt/t{t}^{*}$. We propose a new reconstruction in the multijet plus same-sign dilepton with missing transverse energy samples ($bb+{\ell }^{\pm }{\ell }^{\pm }+{\mathrm{E̸}}_T+Nj$, $N\ge 6$) to search for on-shell $tt\overline{t}\overline{t}$ final states from sextet scalar pair production. Thanks to the large QCD production, the search covers the sextet mass range up to 1 TeV for $100{\mathrm{fb}}^{-1}$ integrated luminosity.

Figure 1

Decay width contour for ${\Phi }_6$ in the mass and coupling plane.

Figure 2

Production of ${\overline{\Phi }}_6{\Phi }_6$ at the LHC and Tevatron with ${\mu }_F=M_{{\Phi }_6}$, fixed scale ${\alpha }_S({\mu }_R)$ with ${\mu }_R=m_Z$. The PDF set CTEQ6L has been used in all calculations.

Figure 3

$\max \{p_T^J\}$ and next-to-$\max \{p_T^J\}$.

Figure 4

Reconstructed Hadronic top pair. The black (red) line represents the first (second) reconstructed hadronically decaying antitop quark.

Figure 5

Reconstructed sextet from $m_{6j}$ and $M_T$.

Figure 6

Distribution of $\cos \theta$ between reconstructed top momentum and reconstructed sextet momentum. Dashed (solid) line shows the distribution without (with) smearing effects and kinematic cuts.

Figure 7

Production rate normalized by $\mathrm{BR}({\Phi }_6\to tt{)}^2$ and significance contour. Dashed (solid) curves in left plot represent production before (after) selection cuts.