Additional results on b-quark fragmentation in top-quark pair events

The study presented here is an extension to the analysis [ CMS-PAS-TOP-13-007 ]. Top-quark pair events are selected in the dilepton and lepton+jets final states using the same approach as for the study of the underlying event.

Charmed mesons, D0, D±, and J/ψ are reconstructed in b-jets originating from top quark pair events. In each event the two jets with highest rank in the b-tagged combined secondary vertex (CSV) discriminator are selected [ JINST 8 (2013) ]. In each jet, reconstructed tracks associated to the jets by the jet algorithm, are used to reconstruct an invariant mass according to the meson final state. The tracks are selected according to the result of the particle-flow algorithm [ CMS-PAS-PFT-10-002 ] which classifies charged candidates as electrons, muons or charged hadrons. For charged hadrons, the mass hypothesis (π± or K±) is assigned depending on the decay hypothesis. Three charmed mesons are considered:

  • D0 mesons are reconstructed in the K+π- decay channel from all opposite-charged pairs among the three leading-pT charged hadrons. In order to identify the D0 flavour, an additional soft lepton is required in the same jet, as originating from semi-leptonic decays of B± and B0;
  • D± mesons are reconstructed in the K± decay channel;
  • J/ψ mesons are reconstructed using identified muons of opposite charge.

The resulting invariant distributions are fitted in a range around the mass peak using probability-distribution functions for the signal and for the combinatorial background. For the pT-distributions of the charmed mesons the fits are performed separately in different bins of pT. Other kinematic properties are extracted from the inclusive sample using the sPlot technique [ NIM A555 (2005) ] given the variables explored are uncorrelated with the invariant mass distribution. The sPlot technique allows to examine the invariant mass distribution in data, as originating from different sources: the result of the likelihood fit to the invariant mass distribution is used to determine the contribution from the signal and background sources and to unfold the distributions of uncorrelated variables separately for each signal and background source present in data. The differential distributions observed in the data are then compared to the expectations from different Monte-Carlo (MC) simulations, obtained using the same procedure. All MC simulations include a full simulation of the CMS detector.

Distributions of reconstructed charmed meson candidates in top-quark pair events: D0 (left), D± (center), and J/ψ (right).

-- PedroSilva - 04 Sep 2014

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PDFpdf D0_deltar.pdf r1 manage 15.0 K 2014-09-26 - 10:58 BenjaminStieger  
PNGpng D0_deltar.png r1 manage 15.8 K 2014-09-26 - 10:58 BenjaminStieger  
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PNGpng D0_diffpt.png r1 manage 18.5 K 2014-09-26 - 10:58 BenjaminStieger  
PDFpdf D0_ptchfrac.pdf r1 manage 14.9 K 2014-09-26 - 10:59 BenjaminStieger  
PNGpng D0_ptchfrac.png r1 manage 17.9 K 2014-09-26 - 10:59 BenjaminStieger  
PDFpdf D0_ptfrac.pdf r1 manage 14.9 K 2014-09-26 - 10:59 BenjaminStieger  
PNGpng D0_ptfrac.png r1 manage 17.5 K 2014-09-26 - 10:59 BenjaminStieger  
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PDFpdf D0_pzchfrac.pdf r1 manage 15.1 K 2014-09-26 - 10:59 BenjaminStieger  
PNGpng D0_pzchfrac.png r1 manage 18.0 K 2014-09-26 - 10:59 BenjaminStieger  
PDFpdf Dpm_deltar.pdf r1 manage 14.9 K 2014-09-26 - 11:00 BenjaminStieger  
PNGpng Dpm_deltar.png r1 manage 17.5 K 2014-09-26 - 11:00 BenjaminStieger  
PDFpdf Dpm_diffpt.pdf r1 manage 14.5 K 2014-09-26 - 11:00 BenjaminStieger  
PNGpng Dpm_diffpt.png r1 manage 18.9 K 2014-09-26 - 11:00 BenjaminStieger  
PDFpdf Dpm_ptchfrac.pdf r1 manage 14.9 K 2014-09-26 - 11:00 BenjaminStieger  
PNGpng Dpm_ptchfrac.png r1 manage 18.9 K 2014-09-26 - 11:00 BenjaminStieger  
PDFpdf Dpm_ptfrac.pdf r1 manage 14.8 K 2014-09-26 - 11:00 BenjaminStieger  
PNGpng Dpm_ptfrac.png r1 manage 18.5 K 2014-09-26 - 11:00 BenjaminStieger  
PDFpdf Dpm_ptrel.pdf r1 manage 15.2 K 2014-09-26 - 11:00 BenjaminStieger  
PNGpng Dpm_ptrel.png r1 manage 18.8 K 2014-09-26 - 11:00 BenjaminStieger  
PDFpdf Dpm_pzchfrac.pdf r1 manage 14.9 K 2014-09-26 - 11:00 BenjaminStieger  
PNGpng Dpm_pzchfrac.png r1 manage 19.1 K 2014-09-26 - 11:00 BenjaminStieger  
PDFpdf JPsi_deltar.pdf r1 manage 15.0 K 2014-09-26 - 11:00 BenjaminStieger  
PNGpng JPsi_deltar.png r1 manage 17.1 K 2014-09-26 - 11:00 BenjaminStieger  
PDFpdf JPsi_diffpt.pdf r1 manage 14.5 K 2014-09-26 - 11:01 BenjaminStieger  
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PDFpdf JPsi_ptchfrac.pdf r1 manage 15.0 K 2014-09-26 - 11:01 BenjaminStieger  
PNGpng JPsi_ptchfrac.png r1 manage 18.3 K 2014-09-26 - 11:01 BenjaminStieger  
PDFpdf JPsi_ptfrac.pdf r1 manage 14.9 K 2014-09-26 - 11:01 BenjaminStieger  
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PNGpng JPsi_pzchfrac.png r1 manage 18.2 K 2014-09-26 - 11:01 BenjaminStieger  
PDFpdf cfit_411.pdf r1 manage 23.6 K 2014-09-26 - 10:58 BenjaminStieger  
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