FTR-13-016
Projections of Top FCNC Searches in 3000/fb at LHC

Abstract

Studies of searching for t → Zq in top pair events with a topology compatible with the decay chain tt → Wb + Zq → l νb + l l q are presented. Projections on limits with luminosities of up to 3000 fb^−1 of proton-proton collisions at a center-of-mass energy of 14 TeV are considered.

Feynman diagram of a top-quark pair with one top quark FCNC decay.

Projection with Cross Section and Luminosity

These projections are done assuming the same event selection efficiencies for both signal and background processes as those of the 8 TeV study.

Expected Event Yields with DELPHES Simulation

The expected signal and SM background expected contributions at 14 TeV with 3000 fb^−1 data. The cross sections of each processes shown are based on LO calculation times the corresponding k-factors, which are obtained from the NNLL+NNLO or NLO cross sections calculations. The errors shown contain only the simulation statistical uncertainty.

Signal Selection Efficiencies with DELPHES Simulation

Summary of cut efficiencies and estimated signal events from simulation. The numbers are after each cut sequentially. Leptonic decays of W and Z bosons are required in the simulated events.

Figures

Reconstructed top quark Mass Distributions in b-tagging selection

Figure	Caption
	Reconstructed mass of a top candidate from a non-b-jet and Z for an integrated luminosity of 3000 fb^−1.
	Reconstructed mass of a top candidate from a b-jet and W for an integrated luminosity of 3000 fb^−1.

Projections of Systematic Uncertainties

Summary of the systematic uncertainties for the background estimation in percent. A conservative projection on systematic uncertainty of signal efficiency estimation is set to be 20%, the same as that of the 8 TeV study.

Projections with DELPHES Simulation

Projections made for 14 TeV with an integrated luminosity up to 3000 fb^−1 using DELPHES simulated samples.

Summary

Based on the DELPHES simulated samples, the expected 95% CL upper limit on the branching fraction B(t → Zq) can reach 0.010% with 3000 fb^−1 integrated luminosity data. The one-sigma range of the expected limit is 0.007 - 0.014% while the two-sigma range of the expected limit is 0.005 - 0.020%. In the case of B(t → Zq) greater than 0.03%, an evidence of 3σ significance can be seen with a data of 300 fb^−1 integrated luminosity. For a B(t → Zq) greater than 0.02%, one can expect an observation of 5σ significance with 3000 fb^−1 data.

-- YuanChao - 29-Sep-2013