TOP-13-012 Search for standard model four top quark production at 8 TeV in the lepton + jets channel

Abstract

A search for four top quark production in the single lepton plus jets channel is presented. The dataset used corresponds to an integrated luminosity of 19.6 fb−1 at √s= 8 TeV recorded by the CMS experiment in 2012. A combination of kinematic reconstruction and multivariate techniques is used to distinguish between signal and backgrounds. No excess of events over the standard model expectation is observed. Upper limits on the cross section of standard model four top quark production of 42 +18 -13 fb (expected) and 63 fb (observed) at 95 % CL are calculated.

Document

The document can be found here: link

PAS figures

In the data-simulation comparison plots the error bands represent the systematic uncertainty arising from the missing higher order terms in the ttbar simulation and is derived by varying the factorisation and renormalisation scale by a factor of 2.

Figure 1: A Feyman diagram of four top production in the Standard Model via gluon fusion is shown. pdf

Figure 2 (a): The Multitopness distributions for data and simulation in the mu + jets is shown. pdf

Figure 2 (b): The Multitopness distributions for data and simulation in the e + jets channel is shown. pdf

Figure 3 (a) The Njets distributions for data and simulation in the mu + jets channel is shown. pdf

Figure 3 (b) The Njets distributions for data and simulation in the e + jets channel is shown. pdf

Figure 4 (a) : The Ntags distributions for data and simulation in the mu + jets channel is shown. pdf

Figure 4 (b) : The Ntags distributions for data and simulation in the e + jets channel is shown. pdf

BDT discriminant:

Figure 5 (a): The BDT discriminator distributions for data and simulation in the μ + jets channel is shown. pdf

Figure 5 (b): The BDT discriminator distributions for data and simulation in the e + jets channel is shown pdf

Supplementary material (not in PAS)

Schematic of removal of hadronic top quark. pdf

Post-fit BDT distributions of the null hypothesis in the mu +jets channel. pdf

Post-fit BDT distributions of the null hypothesis in the electron plus jets channel. pdf

The performance curve of the kinematic reconstruction procedure to identify hadronically decaying top quarks (BDT) is compared to other methods. The efficiencies of selecting bad tri-jets are plotted against the the efficiencies of selecting good tri-jets for all possible choices of a cut on the discriminator value. To emphasise the gain in performance provided by the MVA methods and for illustrative purposes, curves showing the efficiencies of selecting the tri-jet using a traditional chi-squared method and using a random choice are included. The kinks in the random choice and chi-squared curves are arise from the finite number of bins in the histrograms from which the curves are derived. The BDT method shows better performance than the alternative methods. pdf

Result

No excess of data events over the tt background is observed, therefore upper limits on the standard model four top cross section of 42 +18 -13 fb (expected) and 63 fb (observed) using the frequentist CLs approach with the asymptotic approximation are calculated.

-- JamesKeaveney - 19 Dec 2013

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf KinReco_perfCurve_rev0.pdf r2 r1 manage 16.3 K 2014-01-05 - 19:08 JamesKeaveney  
PNGpng KinReco_perfCurve_rev0.png r2 r1 manage 16.4 K 2014-01-05 - 19:08 JamesKeaveney  
PDFpdf MVA_e.pdf r1 manage 17.1 K 2014-01-05 - 22:39 JamesKeaveney  
PNGpng MVA_e.png r1 manage 15.4 K 2014-01-05 - 22:39 JamesKeaveney  
PDFpdf MVA_mu.pdf r1 manage 17.2 K 2014-01-05 - 23:17 JamesKeaveney  
PNGpng MVA_mu.png r1 manage 16.0 K 2014-01-05 - 22:39 JamesKeaveney  
PDFpdf MultiTopness_e.pdf r2 r1 manage 20.3 K 2014-01-05 - 22:41 JamesKeaveney  
PNGpng MultiTopness_e.png r2 r1 manage 18.2 K 2014-01-05 - 22:44 JamesKeaveney  
PDFpdf MultiTopness_mu.pdf r2 r1 manage 19.7 K 2014-01-05 - 22:44 JamesKeaveney  
PNGpng MultiTopness_mu.png r2 r1 manage 17.6 K 2014-01-05 - 22:44 JamesKeaveney  
PDFpdf NbOfSelectedBJets_e.pdf r2 r1 manage 15.7 K 2014-01-05 - 22:50 JamesKeaveney  
PNGpng NbOfSelectedBJets_e.png r2 r1 manage 13.5 K 2014-01-05 - 22:50 JamesKeaveney  
PDFpdf NbOfSelectedBJets_mu.pdf r2 r1 manage 15.7 K 2014-01-05 - 22:50 JamesKeaveney  
PNGpng NbOfSelectedBJets_mu.png r2 r1 manage 13.4 K 2014-01-05 - 22:50 JamesKeaveney  
PDFpdf NbOfSelectedJets_e.pdf r2 r1 manage 16.5 K 2014-01-05 - 22:50 JamesKeaveney  
PNGpng NbOfSelectedJets_e.png r2 r1 manage 14.8 K 2014-01-05 - 22:50 JamesKeaveney  
PDFpdf NbOfSelectedJets_mu.pdf r2 r1 manage 16.5 K 2014-01-05 - 22:50 JamesKeaveney  
PNGpng NbOfSelectedJets_mu.png r2 r1 manage 14.8 K 2014-01-05 - 22:50 JamesKeaveney  
PDFpdf TTRemoval.pdf r1 manage 14.3 K 2013-12-20 - 15:06 JamesKeaveney  
PNGpng TTRemoval.png r1 manage 325.7 K 2013-12-20 - 15:31 JamesKeaveney  
PDFpdf fitanalysis_nullhyp_public_el.pdf r1 manage 17.0 K 2014-01-21 - 18:37 JamesKeaveney  
PNGpng fitanalysis_nullhyp_public_el.png r1 manage 12.4 K 2014-01-21 - 18:36 JamesKeaveney  
PDFpdf fitanalysis_nullhyp_public_mu.pdf r1 manage 17.1 K 2014-01-21 - 18:37 JamesKeaveney  
PNGpng fitanalysis_nullhyp_public_mu.png r1 manage 13.2 K 2014-01-21 - 18:37 JamesKeaveney  
PDFpdf tttt_t_LO.pdf r1 manage 19.4 K 2014-01-08 - 18:06 JamesKeaveney  
PNGpng tttt_t_LO.png r1 manage 2.8 K 2014-01-08 - 18:16 JamesKeaveney  
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Topic revision: r12 - 2014-03-26 - AndreasMeyer
 
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