HighpTtop quarks at the CERN Large Hadron Collider

Abstract

Many new physics models predict resonances with masses in the TeV range which decay into a pair of top quarks. With its large cross section, $t\overline{t}$ production at the Large Hadron Collider (LHC) offers an excellent opportunity to search for such particles. The identification of very energetic top quarks is crucial in such an analysis. We consider in detail the $t\overline{t}\ensuremath{\rightarrow}{\ensuremath{\ell}}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\nu}b\overline{b}q{\overline{q}}^{\ensuremath{'}}$ ($\ensuremath{\ell}=e,\ensuremath{\mu}$) final state for high ${p}_{T}$ top quarks. In this phase space region, two or more of the final state quarks can merge into a single jet due to the large Lorentz boost of the parent top quark. As a result, a large fraction of $t\overline{t}\ensuremath{\rightarrow}{\ensuremath{\ell}}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\nu}b\overline{b}q{\overline{q}}^{\ensuremath{'}}$ events with an invariant mass in the TeV region contains less than four observable jets. Requiring one or two tagged $b$-quarks, we calculate the $W+\mathrm{\text{jets}}$, $Wb+\mathrm{\text{jets}}$, $Wb\overline{b}+\mathrm{\text{jets}}$, $Wbt$, and single top plus jets backgrounds for these final states, and identify cuts which help to suppress them. In particular, we discuss whether a cut on the jet invariant mass may be useful in reducing the background in the $\ensuremath{\ell}\ensuremath{\nu}+2\text{ }\text{ }\mathrm{\text{jets}}$ channel. We also investigate how next-to-leading-order QCD corrections affect high ${p}_{T}$ top quark production at the LHC. We find that the $\ensuremath{\ell}\ensuremath{\nu}+2\text{ }\text{ }\mathrm{\text{jets}}$ and $\ensuremath{\ell}\ensuremath{\nu}+3\text{ }\text{ }\mathrm{\text{jets}}$ final states with one or two $b$-tags will significantly improve the chances for discovering new heavy particles in the $t\overline{t}$ channel at the LHC.