Combined analysis of Z′→tt¯ and Z′→tt¯j production for vector resonance searches at LHC

We have implemented a code for Z′+n jets production in ALPGEN, with Z′ decays into several final states, including ℓ+ℓ− and tt¯. The MLM prescription is used for matching the matrix element with the parton shower, including in this way the leading soft and collinear corrections. In order to demonstrate its capabilities, we perform a combined analysis of Z′→tt¯ and Z′→tt¯j production for a heavy leptophobic gauge boson. It is found that the effect of the extra jet cannot only be accounted for by a K factor multiplying the leading-order cross section. In fact, the combined analysis for Z′→tt¯ and Z′→tt¯j presented improves the statistical significance of the signal by 25% (8.55σ versus 6.77σ for a Z′ mass of 1 TeV), compared with the results of an inclusive analysis carried out on the same sample of tt¯+tt¯j events.