TOP-12-021
Search for Flavor Changing Neutral Currents in tZ events in proton-proton collisions at sqrt(s)=7 TeV

Abstract

A study of top-quark anomalous couplings is performed through the search for a single top-quark produced in association with a Z boson. The event selection requires the presence of three isolated leptons, electrons or muons, and of at least one jet. The signal extraction is done using kinematic variables and information related to b-tagging, combined using a Boosted Decision Tree. The search is performed in a data sample corresponding to about of proton-proton collisions at with the CMS detector. No evidence of flavor changing neutral currents is observed and upper limits at 95% confidence level are determined. The corresponding upper limits on the couplings strengths of an effective model are found to be , , and , with the expected scale at which new physics could appear. The equivalent top-quark-decay branching fractions are found to be , , and .

Figures

Figures Caption
bdt_gut.png BDT output distribution for the coupling, summed for the four tri-lepton channels. Total uncertainty are shown as hatched regions. The signal is scaled to a cross section of 0.1 pb.
bdt_gct.png BDT output distribution for the coupling, summed for the four tri-lepton channels. Total uncertainty are shown as hatched regions. The signal is scaled to a cross section of 0.1 pb.
bdt_Zut.png BDT output distribution for the coupling, summed for the four tri-lepton channels. Total uncertainty are shown as hatched regions. The signal is scaled to a cross section of 0.1 pb.
bdt_Zct.png BDT output distribution for the coupling, summed for the four tri-lepton channels. Total uncertainty are shown as hatched regions. The signal is scaled to a cross section of 0.1 pb.

res_gut.png 95% exclusion limit for the coupling as a function of the parameter. The blue line show the theoretical cross-section, as calculated by MadGraph.
res_gct.png 95% exclusion limit for the coupling as a function of the parameter. The blue line show the theoretical cross-section, as calculated by MadGraph.
res_Zut.png 95% exclusion limit for the coupling as a function of the parameter. The blue line show the theoretical cross-section, as calculated by MadGraph.
res_Zct.png 95% exclusion limit for the coupling as a function of the parameter. The blue line show the theoretical cross-section, as calculated by MadGraph.

Tables

Tables Caption
cutflow_tab.png Events yield after the different steps of the event selection. Uncertainty is statistical only. The signal corresponds to an anomalous coupling and is rescaled to a cross section of 0.1 pb
result_tab.png Expected and observed exclusion limits at 95% CL, and the corresponding limits on the top-quark-decay branching ratios.

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf Limits_param_kct.pdf r1 manage 1047.2 K 2013-07-18 - 17:13 EricConte  
PDFpdf Limits_param_kut.pdf r1 manage 1045.0 K 2013-07-18 - 17:13 EricConte  
PDFpdf Limits_param_zct.pdf r1 manage 1078.4 K 2013-07-18 - 17:13 EricConte  
PDFpdf Limits_param_zut.pdf r1 manage 1090.9 K 2013-07-18 - 17:13 EricConte  
PDFpdf MVA_BDT_kct.pdf r1 manage 17.2 K 2013-07-18 - 11:56 JeremyAndrea  
PNGpng MVA_BDT_kct.png r1 manage 24.1 K 2013-07-18 - 11:53 JeremyAndrea  
PDFpdf MVA_BDT_kut.pdf r1 manage 17.3 K 2013-07-18 - 11:50 JeremyAndrea  
PNGpng MVA_BDT_kut.png r1 manage 24.1 K 2013-07-18 - 11:50 JeremyAndrea  
PDFpdf MVA_BDT_zct.pdf r1 manage 17.4 K 2013-07-18 - 11:50 JeremyAndrea  
PNGpng MVA_BDT_zct.png r1 manage 24.2 K 2013-07-18 - 11:50 JeremyAndrea  
PDFpdf MVA_BDT_zut.pdf r1 manage 17.4 K 2013-07-18 - 11:50 JeremyAndrea  
PNGpng MVA_BDT_zut.png r1 manage 24.4 K 2013-07-18 - 11:50 JeremyAndrea  
PNGpng cutflow_tab.png r1 manage 77.8 K 2013-07-17 - 11:56 JeremyAndrea  
PNGpng res_Zct.png r2 r1 manage 21.9 K 2013-07-18 - 17:10 EricConte  
PNGpng res_Zut.png r2 r1 manage 22.4 K 2013-07-18 - 17:10 EricConte  
PNGpng res_gct.png r2 r1 manage 22.3 K 2013-07-18 - 17:11 EricConte  
PNGpng res_gut.png r2 r1 manage 23.9 K 2013-07-18 - 17:10 EricConte  
PNGpng result_tab.png r1 manage 5.2 K 2013-07-17 - 11:56 JeremyAndrea  
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Topic revision: r6 - 2013-07-18 - EricConte
 
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