TOP-11-029
First measurement of $R=B(t \rightarrow Wb)/B(t \rightarrow Wq)$ in the dilepton channel in pp collisions at $\sqrt(s)$=7 TeV

Abstract

The flavor content of $t \bar{t} \rightarrow (l^{+}\nu q)(l^{-}\bar{\nu} \bar{q})$ events is studied using a sample corresponding to an integrated luminosity of $2.2 fb^{-1}$ of proton-proton collisions produced at $\sqrt{s}$=7 TeV and acquired by the CMS detector. Data-driven strategies are used to constrain the background contributions. A measurement of the ratio of branching fractions $R=B(t\rightarrow Wb)/B(t\rightarrow Wq)$ is performed by counting the jets identified as $b$-jets. We measure $R=~0.98~\pm~0.04$ which is consistent with the SM prediction. We also set a lower limit $R>$0.85 at $95\%$ C.L. which is obtained after requiring $R\leq$1.

Public document

The document CMS-PAS-TOP-11-029 published on the CERN document server can be found here.

The Tables and Figures from the document are reproduced below. Click on the figures to retrieve the PDF version.

Tables

Figures

Figure Caption
Number of $b$-tagged jets per event in different dilepton channels. For each channel two subsets are shown corresponding to events with two or three jets. The MC corresponds to a scenario of $R=$1. The bottom plot shows the ratio between data and MC expectations.
Invariant mass of the lepton-jet pairs in the inclusive dilepton channel. The ``correct assignment'' contribution is computed using MC truth from the pairs with jets matched to the $b$~quarks (i.e. from $t\rightarrow Wb$), while the ``wrong assignment'' distribution is generated from all the other jets found the event and includes background contributions. The sum of the correct and wrong assignments is compared to data. All possible lepton-jet combinations are considered when obtaining the spectrum. The distribution for the model of wrong assignments in data is superimposed, as well as the average model obtained from MC based pseudo-experiments.
Distribution after subtraction of the misassignment contribution in data (and in MC simulation) is compared to the expected distribution of correct assignments.
Inclusive model for the observation of different $b$-tag multiplicities in dilepton events with two or three jets as function of $R$.
Variation of the profile likelihood used to extract $R$ from data. The variation observed in the exclusive dilepton channels is depicted by the dashed lines. The inset shows the inclusive $b$-tag multiplicity distribution and the result of the fit.
Limit bands at different CL on $R$ with the measured value overlaid as a dashed line. The favored values of $R_{obs}$ obtained for different CL (horizontal axis) are shown for each true value of $R$ (vertical axis).
Summary of different measurements on R. The shaded band shows the lower endpoint for the confidence interval established at a 95% CL. The references used for each measurement are quoted in the plot.

-- PedroSilva - 01-Mar-2012

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf HFCProfLikelihood.pdf r1 manage 18.3 K 2012-03-01 - 16:13 PedroSilva  
PNGpng HFCProfLikelihood.png r1 manage 18.8 K 2012-03-01 - 16:13 PedroSilva  
PDFpdf HeavyFlavorModelInclusive.pdf r1 manage 16.5 K 2012-03-01 - 16:12 PedroSilva  
PNGpng HeavyFlavorModelInclusive.png r1 manage 15.6 K 2012-03-01 - 16:12 PedroSilva  
PDFpdf MljSubtracted.pdf r1 manage 17.9 K 2012-03-01 - 16:13 PedroSilva  
PNGpng MljSubtracted.png r1 manage 22.5 K 2012-03-01 - 16:13 PedroSilva  
PDFpdf MljWithModel.pdf r1 manage 18.6 K 2012-03-01 - 16:13 PedroSilva  
PNGpng MljWithModel.png r1 manage 22.7 K 2012-03-01 - 16:14 PedroSilva  
PNGpng Table1.png r2 r1 manage 43.3 K 2012-03-07 - 18:27 PietroVischia  
PNGpng Table2.png r2 r1 manage 82.4 K 2012-03-07 - 18:27 PietroVischia  
PNGpng Table3.png r2 r1 manage 34.3 K 2012-03-07 - 18:28 PietroVischia  
PDFpdf fc_smooth_Rlimits.pdf r2 r1 manage 19.9 K 2012-03-07 - 18:29 PietroVischia  
PNGpng fc_smooth_Rlimits.png r2 r1 manage 16.4 K 2012-03-07 - 18:29 PietroVischia  
PNGpng nbtagstcheextended.png r1 manage 29.0 K 2012-03-01 - 16:10 PedroSilva  
PDFpdf r_dileptons2011_final.pdf r1 manage 14.3 K 2012-03-01 - 16:44 PedroSilva  
PNGpng r_dileptons2011_final.png r1 manage 25.4 K 2012-03-01 - 16:44 PedroSilva  
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Topic revision: r2 - 2012-03-07 - PietroVischia
 
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