Projections of Top FCNC Searches in 3000/fb at LHC


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.

ttczbw2-.png Feynman diagram of a top-quark pair with one top quark FCNC decay.

Projection with Cross Section and Luminosity

pas_table1.png 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

pas_table2.png 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

pas_table3.png 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.


Reconstructed top quark Mass Distributions in b-tagging selection

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

Projections of Systematic Uncertainties

pas_table4.png 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

pas_table5.png Projections made for 14 TeV with an integrated luminosity up to 3000 fb^−1 using DELPHES simulated samples.


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

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf hist_mass_tbw.pdf r1 manage 16.9 K 2013-10-02 - 15:06 YuanChao  
PNGpng hist_mass_tbw.png r2 r1 manage 20.4 K 2013-10-02 - 14:58 YuanChao Reconstructed mass of a top candidate from a b-jet and W
PDFpdf hist_mass_tcz.pdf r1 manage 16.9 K 2013-10-02 - 15:06 YuanChao  
PNGpng hist_mass_tcz.png r2 r1 manage 20.3 K 2013-10-02 - 14:58 YuanChao Reconstructed mass of a top candidate from a non-b-jet and Z
PNGpng pas_table1.png r1 manage 22.9 K 2013-10-02 - 15:08 YuanChao  
PNGpng pas_table2.png r1 manage 62.2 K 2013-10-02 - 15:09 YuanChao  
PNGpng pas_table3.png r1 manage 59.7 K 2013-10-06 - 17:30 YuanChao  
PNGpng pas_table4.png r1 manage 40.3 K 2013-10-06 - 17:31 YuanChao  
PNGpng pas_table5.png r1 manage 36.4 K 2013-10-02 - 15:09 YuanChao  
PNGpng ttczbw2-.png r1 manage 36.7 K 2013-10-06 - 17:25 YuanChao  
PDFpdf ttczbw2.pdf r1 manage 9.6 K 2013-10-06 - 17:25 YuanChao  
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Topic revision: r6 - 2014-03-26 - AndreasMeyer
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