TOP-11-028
Search for Flavor Changing Neutral Currents in Top Quark Decays in pp Collisions at √s= 7 TeV

Abstract

The results of a search for flavor changing neutral current in top decays, t → Zq, with a sample of tt → Wb + Zq → νb + q events are presented. The search is performed in a data sample corresponding to a total integrated luminosity of 4.6 fb−1 of proton-proton collisions at a center-of-mass energy of 7 TeV, collected with the CMS detector at the LHC. The observed number of events agrees with the standard model prediction, and no evidence of flavor changing neutral currents in top decays is found. A branching fraction of t → Zq larger than 0.34% is excluded at the 95% confidence level.

Public Document

The document CMS-PAS-TOP-11-028 published on the CERN document server will be linked here. Until it is made public, collaboration members can find the private version can be found on CADI here.

Signal Efficiencies

Channel HTs selection b-tag selection
eee 12.4 ± 1.1 3.8 ± 0.62
eeμ 13.8 ± 1.2 5.0 ± 0.69
μμe 14.8 ± 1.2 5.1 ± 0.73
μμμ 14.7 ± 1.2 5.3 ± 0.73

Numbers are given in percent. The simulated events used to calculate these acceptances are weighted such that the trigger efficiencies, reconstruction efficiencies and the distribution of reconstructed vertexes observed in data are reproduced.

Results

Signal Selection HT_S-cut Based b-tag Based
Total background prediction (data-driven) 16.16+-3.86+-2.63 0.65+-0.14+-0.11
Data 11 0
Expected limit at the 95% CL Br( t → Zq) < 0.42% Br( t → Zq) < 0.34%
Observed limit at the 95% CL Br( t → Zq) < 0.39% Br( t → Zq) < 0.34%

Figures

Some basic kinematic distributions

Figure Caption
tMass.png Transverse mass of the third lepton in the event and the missing transverse energy, in events which pass the basic selection + 2 jets requirement.
METWithLepton2_log.png Missing transverse energy, in events which pass the basic selection + 2 jets requirement.
hist_hts_sc.png HTs in events which pass the basic selection + 2 jets requirement. HTs is defined as the scalar sum of the missing transverse energy, the transverse energy of the three leptons in the event, and the two jets which are used to reconstruct the top quarks.

Reconstructed top quark Mass Distributions in b-tagging selection

Figure Caption
topMassW.png Reconstructed mass of a b-jet, the third lepton in the event, and the neutrino.
topMassZ.png Reconstructed mass of a non-b-tagged-jet with the two leptons in the event which reconstruct a Z.

Reconstructed top quark Mass Distributions in HTs selection

Figure Caption
hist_tcz_sc.png Reconstructed mass of a jet, the third lepton in the event, and the neutrino.
hist_tbw_sc.png Reconstructed mass of a jet with the two leptons in the event which reconstruct a Z.

Results

Figure Caption

-- StevenWon - 05-Mar-2012

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng METWithLepton2_log.png r1 manage 16.8 K 2012-03-05 - 23:28 StevenWon  
PNGpng TMass.png r1 manage 17.3 K 2012-03-05 - 23:19 StevenWon  
Unknown file formateps feynman_ttbar_ZllWlnu_FCNC.eps r1 manage 151.8 K 2012-03-05 - 23:33 StevenWon  
PNGpng feynman_ttbar_ZllWlnu_FCNC.png r2 r1 manage 8.4 K 2012-03-05 - 23:54 StevenWon  
PNGpng feynman_ttbar_ljets_longt.png r1 manage 70.1 K 2012-03-05 - 23:36 StevenWon  
PNGpng hist_hts_sc.png r1 manage 15.8 K 2012-03-05 - 23:17 StevenWon  
PNGpng hist_tbw_sc.png r1 manage 16.6 K 2012-03-05 - 23:18 StevenWon  
PNGpng hist_tcz_sc.png r1 manage 16.6 K 2012-03-05 - 23:18 StevenWon  
PNGpng topMassW.png r1 manage 15.1 K 2012-03-05 - 23:19 StevenWon  
PNGpng topMassZ.png r1 manage 15.6 K 2012-03-05 - 23:19 StevenWon  
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Topic revision: r6 - 2013-05-15 - RobertoTenchini
 
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