The heavy quark search at the LHC

We explore further the discovery potential for heavy quarks at the LHC, with emphasis on the $t'$ and $b'$ of a sequential fourth family associated with electroweak symmetry breaking. We consider QCD multijets, $t\bar{t}+\rm{jets}$, $W+\rm{jets}$ and single $t$ backgrounds using event generation based on improved matrix elements and low sensitivity to the modeling of initial state radiation. We exploit a jet mass technique for the identification of hadronically decaying $W$'s and $t$'s, to be used in the reconstruction of the $t'$ or $b'$ mass. This along with other aspects of event selection can reduce backgrounds to very manageable levels. It even allows a search for both $t'$ and $b'$ in the absence of $b$-tagging, of interest for the early running of the LHC. A heavy quark mass of order 600 GeV is motivated by the connection to electroweak symmetry breaking, but our analysis is relevant for any new heavy quarks with weak decay modes.Comment: 12 pages, 7 figure

Accurate QCD predictions for heavy-quark jets at the Tevatron and LHC

Heavy-quark jets are important in many of today's collider studies and searches, yet predictions for them are subject to much larger uncertainties than for light jets. This is because of strong enhancements in higher orders from large logarithms, ln(p_t/m_Q). We propose a new definition of heavy-quark jets, which is free of final-state logarithms to all orders and such that all initial-state collinear logarithms can be resummed into the heavy-quark parton distributions. Heavy-jet spectra can then be calculated in the massless approximation, which is simpler than a massive calculation and reduces the theoretical uncertainties by a factor of three. This provides the first ever accurate predictions for inclusive b- and c-jets, and the latter have significant discriminatory power for the intrinsic charm content of the proton. The techniques introduced here could be used to obtain heavy-flavour jet results from existing massless next-to-leading order calculations for a wide range of processes. We also discuss the experimental applicability of our flavoured jet definition.Comment: 22 pages, 7 figure