TOP-12-024

First Measurement of Cross Section Ratio $\sigma(t\bar{t}b\bar{b})$ / $\sigma(t\bar{t}jj)$ in pp Collisions at 7 TeV

Abstract

We present the first measurement of the cross section ratio $\sigma(ttbb)$ / $\sigma(ttjj)$ in the dilepton decay mode, using a data sample corresponding to an integrated luminosity of 5.0 $fb^{-1}$ collected in pp collisions at $\sqrt{s}$ = 7 TeV with the CMS detector at LHC. The cross section ratio is measured in the visible phase space corresponding to the detector acceptance, and corrected to the particle level. The measurement was performed by means of a fit to the measured multiplicity distribution of b-tagged jets in a sample of dileptonic top quark pair candidate events with at least four reconstructed jets. The result of the measurement, 3.6 $\pm$ 1.1 (stat.) $\pm$ 0.9 (sys.) %, is compared with various theory predictions.

Result

$\sigma ( t \bar{t}b \bar{b}) / \sigma(t \bar{t}jj) = 3.6 \pm 1.1 (stat.) \pm 0.9 (sys.)~\%$

Figures

Figure Caption
cLL_jet1pt30.png Distribution of the transverse momentum of the leading jet after the requirement of at least four reconstructed jets. The distributions correspond to the sum of the $ee$, $\mu\mu$ and $e\mu$ final states. Data are compared with Monte Carlo simulations where the $t\bar{t}b\bar{b}$ process is required to have two additional b-jets, $t\bar{t}c\bar{c}$ to have at least two c-jets and $t\bar{t}LF$ events are from Light Flavor (LF) jets such as gluon, u, d or s quark. The contribution labelled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. The last bin includes overflow. pdf
cLL_jet2pt30.png Distribution of the transverse momentum of the 2nd leading jet after the requirement of at least four reconstructed jets. The distributions correspond to the sum of the $ee$, $\mu\mu$ and $e\mu$ final states. Data are compared with Monte Carlo simulations where the $t\bar{t}b\bar{b}$ process is required to have two additional b-jets, $t\bar{t}c\bar{c}$ to have at least two c-jets and $t\bar{t}LF$ events are from Light Flavor (LF) jets such as gluon, u, d or s quark. The contribution labelled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. pdf
cLL_jet3pt30.png Distribution of the transverse momentum of the 3rd leading jet after the requirement of at least four reconstructed jets. The distributions correspond to the sum of the $ee$, $\mu\mu$ and $e\mu$ final states. Data are compared with Monte Carlo simulations where the $t\bar{t}b\bar{b}$ process is required to have two additional b-jets, $t\bar{t}c\bar{c}$ to have at least two c-jets and $t\bar{t}LF$ events are from Light Flavor (LF) jets such as gluon, u, d or s quark. The contribution labelled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. pdf
cLL_jet4pt30.png Distribution of the transverse momentum of the 4th leading jet after the requirement of at least four reconstructed jets. The distributions correspond to the sum of the $ee$, $\mu\mu$ and $e\mu$ final states. Data are compared with Monte Carlo simulations where the $t\bar{t}b\bar{b}$ process is required to have two additional b-jets, $t\bar{t}c\bar{c}$ to have at least two c-jets and $t\bar{t}LF$ events are from Light Flavor (LF) jets such as gluon, u, d or s quark. The contribution labelled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. pdf
cLL_nbJet30_CSVM.png Distribution of the b-jet multiplicity for the "medium" working point of the b-tagging algorithm (CSVM), corresponding to a light flavor mistagging efficiency of 1 % after the requirement of at least four reconstructed jets. The distributions correspond to the sum of the $ee$, $\mu\mu$ and $e\mu$ final states. Data are compared with Monte Carlo simulations where the $t\bar{t}b\bar{b}$ process is required to have two additional b-jets, $t\bar{t}c\bar{c}$ to have at least two c-jets and $t\bar{t}LF$ events are from Light Flavor (LF) jets such as gluon, u, d or s quark. The contribution labelled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. pdf
cLL_nbJet30_CSVT.png Distribution of the b-jet multiplicity for the "tight" working point of the b-tagging algorithm (CSVT), corresponding to a light flavor mistagging efficiency of 0.1 % after the requirement of at least four reconstructed jets. The distributions correspond to the sum of the $ee$, $\mu\mu$ and $e\mu$ final states. Data are compared with Monte Carlo simulations where the $t\bar{t}b\bar{b}$ process is required to have two additional b-jets, $t\bar{t}c\bar{c}$ to have at least two c-jets and $t\bar{t}LF$ events are from Light Flavor (LF) jets such as gluon, u, d or s quark. The contribution labelled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. pdf
c_reco_jet_ttbb_ttcc_ttll_CSVM.png Normalized distribution of the b-tagged jet multiplicity using the "medium" working point of the b-tagging algorithm (CSVM), after the requirement of at least four reconstructed jets, shown for simulated $t\bar{t}b\bar{b}$, $t\bar{t}c\bar{c}$ and $t\bar{t}LF$ events. pdf
c_reco_jet_ttbb_ttcc_ttll_CSVT.png Normalized distribution of the b-tagged jet multiplicity using the "tight" working point of the b-tagging algorithm (CSVT), after the requirement of at least four reconstructed jets, shown for simulated $t\bar{t}b\bar{b}$, $t\bar{t}c\bar{c}$ and $t\bar{t}LF$ events. pdf
c_ttbb_fraction_Combined_CSVM.png Distribution of the b-tagged jet multiplicity using the "medium" working point of the b-tagging algorithm (CSVM) for data and simulated samples of $t\bar{t}b\bar{b}$ and $t\bar{t}c\bar{c}$+$t\bar{t}LF$ events, where the normalizations of the latter were obtained from the fit to the data, as discribed in the text. pdf
c_ttbb_fraction_Combined_CSVT.png Distribution of the b-tagged jet multiplicity using the "tight" working point of the b-tagging algorithm (CSVT) for data and simulated samples of $t\bar{t}b\bar{b}$ and $t\bar{t}c\bar{c}$+$t\bar{t}LF$ events, where the normalizations of the latter were obtained from the fit to the data, as discribed in the text. pdf

Tables

cutflow_CSVM.png Expected and observed event counts after applying the final event selection, using the "medium" working point of the b-tagging algorithm (CSVM) and summing over $ee/\mu\mu/e\mu$ final states. Only statistical uncertainties are quoted.
cutflow_CSVT.png Expected and observed event counts after applying the final event selection, using the "tight" working point of the b-tagging algorithm (CSVT) and summing over $ee/\mu\mu/e\mu$ final states. Only statistical uncertainties are quoted.
efficiency.png Selection efficiencies for $t\bar{t}jj = t\bar{t}b\bar{b} + t\bar{t}c\bar{c} + t\bar{t}LF$ and $t\bar{t}b\bar{b}$ events at various steps of the event selection (see text), as well as their ratios, shown for both working points of the b-tagging algorithm.
systematic.png Break-down of the contributions of the various sources of systematic uncertainty considered to the measurement of the $\sigma(t\bar{t}b\bar{b})$ / $\sigma(t\bar{t}jj)$ cross section ratio, shown for both working points of the b-tagging algorithm.

-- TaeYeonKim - 14-Sep-2012

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf cLL_Step_4_jet1pt30.pdf r1 manage 22.4 K 2012-09-14 - 17:23 TaeJeongKim  
PDFpdf cLL_Step_4_jet2pt30.pdf r1 manage 20.7 K 2012-09-14 - 17:23 TaeJeongKim  
PDFpdf cLL_Step_4_jet3pt30.pdf r1 manage 18.9 K 2012-09-14 - 17:23 TaeJeongKim  
PDFpdf cLL_Step_4_jet4pt30.pdf r1 manage 18.1 K 2012-09-14 - 17:23 TaeJeongKim  
PDFpdf cLL_Step_4_nbJet30_CSVM.pdf r1 manage 14.6 K 2012-09-14 - 17:23 TaeJeongKim  
PDFpdf cLL_Step_4_nbJet30_CSVT.pdf r1 manage 14.6 K 2012-09-14 - 17:23 TaeJeongKim  
PNGpng cLL_jet1pt30.png r1 manage 10.9 K 2012-09-14 - 14:49 TaeYeonKim  
PNGpng cLL_jet2pt30.png r1 manage 10.6 K 2012-09-14 - 14:50 TaeYeonKim  
PNGpng cLL_jet3pt30.png r1 manage 10.0 K 2012-09-14 - 14:51 TaeYeonKim  
PNGpng cLL_jet4pt30.png r1 manage 9.8 K 2012-09-14 - 14:51 TaeYeonKim  
PNGpng cLL_nbJet30_CSVM.png r1 manage 8.3 K 2012-09-14 - 14:51 TaeYeonKim  
PNGpng cLL_nbJet30_CSVT.png r1 manage 8.2 K 2012-09-14 - 14:52 TaeYeonKim  
PDFpdf c_reco_jet_ttbb_ttcc_ttll_CSVM.pdf r1 manage 4.6 K 2012-09-14 - 17:18 TaeJeongKim  
PNGpng c_reco_jet_ttbb_ttcc_ttll_CSVM.png r1 manage 8.6 K 2012-09-14 - 15:55 TaeJeongKim  
PDFpdf c_reco_jet_ttbb_ttcc_ttll_CSVT.pdf r1 manage 4.6 K 2012-09-14 - 17:18 TaeJeongKim  
PNGpng c_reco_jet_ttbb_ttcc_ttll_CSVT.png r1 manage 8.6 K 2012-09-14 - 15:55 TaeJeongKim  
PDFpdf c_ttbb_fraction_Combined_CSVM.pdf r1 manage 5.8 K 2012-09-14 - 17:18 TaeJeongKim  
PNGpng c_ttbb_fraction_Combined_CSVM.png r1 manage 8.2 K 2012-09-14 - 15:55 TaeJeongKim  
PDFpdf c_ttbb_fraction_Combined_CSVT.pdf r1 manage 5.4 K 2012-09-14 - 17:18 TaeJeongKim  
PNGpng c_ttbb_fraction_Combined_CSVT.png r1 manage 8.0 K 2012-09-14 - 15:55 TaeJeongKim  
PNGpng cutflow_CSVM.png r5 r4 r3 r2 r1 manage 86.5 K 2012-09-17 - 20:44 TaeJeongKim  
PNGpng cutflow_CSVT.png r3 r2 r1 manage 84.5 K 2012-09-17 - 20:44 TaeJeongKim  
PNGpng efficiency.png r1 manage 51.4 K 2012-09-14 - 16:35 TaeJeongKim  
PNGpng final.png r1 manage 13.4 K 2012-09-14 - 16:35 TaeJeongKim  
PNGpng systematic.png r1 manage 94.2 K 2012-09-14 - 16:35 TaeJeongKim  
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