TOP-13-010

Measurement of Cross Section Ratio $\sigma(t\bar{t}b\bar{b})$ / $\sigma(t\bar{t}jj)$ in pp Collisions at 8 TeV

Abstract

We present a 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 19.6 $fb^{-1}$ collected in pp collisions at $\sqrt{s}$ = 8 TeV with the CMS detector at the LHC. The cross section ratio $\sigma(ttbb)$ / $\sigma(ttjj)$ is measured in the visible phase space corresponding to the detector acceptance, and corrected to particle level. For events with at least four reconstructed jets, the measurement is performed by means of a fit to the measured b-tagging algorithm output. The result of the measurement is 0.023 $\pm$ 0.003 (stat.) $\pm$ 0.005 (sys.) ( 0.022 $\pm$ 0.004 (stat.) $\pm$ 0.005 (sys.) ) for a minimum pt of 20 (40) GeVc. Measurements of the absolute cross sections $\sigma(ttjj)$ and $\sigma(ttbb)$ are also presented.

Result

$\sigma ( t \bar{t}b \bar{b}) / \sigma(t \bar{t}jj) = 0.023 \pm 0.003 (stat.) \pm 0.005 (syst.) ~{\rm at}~20~{\rm GeV} ~$

$\sigma ( t \bar{t}b \bar{b}) / \sigma(t \bar{t}jj) = 0.022 \pm 0.004 (stat.) \pm 0.005 (syst.) ~{\rm at}~40~{\rm GeV} ~$

Figures

Figure Caption
c_ttbb_fraction_Combined_CSVM.png Figure 1 (left): Distributions of the b-jet multiplicity in events with particle level jets with a minimum pt of 20 GeV after the requirement of at least four reconstructed jets. The distributions corresponds 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, $t\bar{t}bj$ to have exactly one additional b-jet and $t\bar{t}LF$ events are from light flavor partons such as gluon, u, d or s quark. The contribution labeled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. The normalizations of the simulation were obtained from the fit to the data, as described in the text. The sum of the statistical and the systematic uncertainties are shown as hatched regions while only statistical uncertainty is shown in the ratio. pdf
c_ttbb_fraction_Combined_CSVT.png Figure 1 (right): Distributions of the b-jet multiplicity in events with particle level jets with a minimum pt of 40 GeV after the requirement of at least four reconstructed jets. The distributions corresponds 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, $t\bar{t}bj$ to have exactly one additional b-jet and $t\bar{t}LF$ events are from light flavor partons such as gluon, u, d or s quark. The contribution labeled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. The normalizations of the simulation were obtained from the fit to the data, as described in the text. The sum of the statistical and the systematic uncertainties are shown as hatched regions while only statistical uncertainty is shown in the ratio. pdf
csvshape_x.png Figure 2 (left): The distributions of the b-Jet discriminator for $t\bar{t}bb$, $t\bar{t}bj$, $t\bar{t}cc$ and $t\bar{t}LF$ processes. The process $t\bar{t}bb$ is required to have two additional b-jets, $t\bar{t}cc$ to have at least two c-jets, $t\bar{t}bj$ to have exactly one additional b-jet and $t\bar{t}LF$ events are from light flavor partons such as gluon, u, d or s quark. The distributions are after the final selection in the defined visible phase space for the first additional jet. pdf
csvshape_y.png.png Figure 2 (right): The distributions of the b-Jet discriminator for $t\bar{t}bb$, $t\bar{t}bj$, $t\bar{t}cc$ and $t\bar{t}LF$ processes. The process $t\bar{t}bb$ is required to have two additional b-jets, $t\bar{t}cc$ to have at least two c-jets, $t\bar{t}bj$ to have exactly one additional b-jet and $t\bar{t}LF$ events are from light flavor partons such as gluon, u, d or s quark. The distributions are after the final selection in the defined visible phase space for the second additional jet.pdf
cLL_Step_5_addjet1_bDisCSV_20GeV.png Figure 3 (upper left): Distribution of the b-Jet discriminator for the first additional jet in events with particle-level jets with a minimum pt of 20 GeV after the final selection. The distributions corresponds 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, $t\bar{t}bj$ to have exactly one additional b-jet and $t\bar{t}LF$ events are from light flavor partons such as gluon, u, d or s quark. The contribution labeled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. The normalizations of the simulation were obtained from the fit to the data, as described in the text. The sum of the statistical and the systematic uncertainties are shown as hatched regions while only statistical uncertainty is shown in the ratio.pdf
cLL_Step_5_addjet2_bDisCSV_20GeV.png Figure 3 (upper right): Distribution of the b-Jet discriminator for the second additional jet in events with particle-level jets with a minimum pt of 20 GeV after the final selection. The distributions corresponds 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, $t\bar{t}bj$ to have exactly one additional b-jet and $t\bar{t}LF$ events are from light flavor partons such as gluon, u, d or s quark. The contribution labeled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. The normalizations of the simulation were obtained from the fit to the data, as described in the text. The sum of the statistical and the systematic uncertainties are shown as hatched regions while only statistical uncertainty is shown in the ratio. pdf
cLL_Step_5_addjet1_bDisCSV_40GeV.png Figure 3 (lower left): Distribution of the b-Jet discriminator for the first additional jet in events with particle-level jets with a minimum pt of of 40 GeV after the final selection. The distributions corresponds 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, $t\bar{t}bj$ to have exactly one additional b-jet and $t\bar{t}LF$ events are from light flavor partons such as gluon, u, d or s quark. The contribution labeled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. The normalizations of the simulation were obtained from the fit to the data, as described in the text. The sum of the statistical and the systematic uncertainties are shown as hatched regions while only statistical uncertainty is shown in the ratio.pdf
cLL_Step_5_addjet2_bDisCSV_40GeV.png Figure 3 (lower right): Distribution of the b-Jet discriminator for the second additional jet in events with particle-level jets with a minimum pt of 40 GeV after the final selection. The distributions corresponds 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, $t\bar{t}bj$ to have exactly one additional b-jet and $t\bar{t}LF$ events are from light flavor partons such as gluon, u, d or s quark. The contribution labeled "$t\bar{t}$ others" is from top quark pair events that do not pass the visible phase space definition. The normalizations of the simulation were obtained from the fit to the data, as described in the text. The sum of the statistical and the systematic uncertainties are shown as hatched regions while only statistical uncertainty is shown in the ratio. pdf

Tables

cutflow20GeV.png Table 1: Expected and observed counts of events after the final event selection and with particle level jet pt of at least 20 GeV, summed over $ee/\mu\mu/e\mu$ final states. Only statistical uncertainties are given in the Table.
cutflow40GeV.png Table 2: Expected and observed counts of events after the final event selection and with particle level jet pt of at least 40 GeV, summed over $ee/\mu\mu/e\mu$ final states. Only statistical uncertainties are given in the Table.
systematic.png Table 3: Break-down of the systematic uncertainties on various sources contributing to the fraction of $ \sigma(t\bar{t}b\bar{b})/\sigma(t\bar{t}jj)  $. "b-tag" indicates the scale factor for b-tagging discriminator.
absoluteX.png Table 4: The measured absolute cross section $t\bar{t}b\bar{b}$ and $t\bar{t}jj$ at the visible phase space (VS) are shown in the Table. Additionally the absolute cross sections unfolding to the full phase space (FS) for the b-jets from the top decays are also shown. Correction factors for full phase space is derived using MADGRAPH as described in the text. The 2.6 % uncertainty on the luminosity for the absolute cross section is not included in the Table.

-- TaeJeongKim - 15-Sep-2012

Topic attachments
I Attachment History Action Size Date Who Comment
PNGpng absoluteX.png r1 manage 159.2 K 2013-09-17 - 14:37 TaeJeongKim  
PDFpdf cLL_Step_4_nbJet30_CSVT_20GeV.pdf r1 manage 7.4 K 2013-09-17 - 10:55 TaeJeongKim  
PNGpng cLL_Step_4_nbJet30_CSVT_20GeV.png r1 manage 76.4 K 2013-09-17 - 10:48 TaeJeongKim  
PDFpdf cLL_Step_4_nbJet30_CSVT_40GeV.pdf r1 manage 7.4 K 2013-09-17 - 10:55 TaeJeongKim  
PNGpng cLL_Step_4_nbJet30_CSVT_40GeV.png r1 manage 76.5 K 2013-09-17 - 10:48 TaeJeongKim  
PDFpdf cLL_Step_5_addjet1_bDisCSV_20GeV.pdf r1 manage 9.7 K 2013-09-17 - 10:55 TaeJeongKim  
PNGpng cLL_Step_5_addjet1_bDisCSV_20GeV.png r1 manage 89.0 K 2013-09-17 - 10:49 TaeJeongKim  
PDFpdf cLL_Step_5_addjet1_bDisCSV_40GeV.pdf r1 manage 9.9 K 2013-09-17 - 10:55 TaeJeongKim  
PNGpng cLL_Step_5_addjet1_bDisCSV_40GeV.png r1 manage 90.9 K 2013-09-17 - 10:49 TaeJeongKim  
PDFpdf cLL_Step_5_addjet2_bDisCSV_20GeV.pdf r1 manage 9.9 K 2013-09-17 - 10:55 TaeJeongKim  
PNGpng cLL_Step_5_addjet2_bDisCSV_20GeV.png r1 manage 94.0 K 2013-09-17 - 10:49 TaeJeongKim  
PDFpdf cLL_Step_5_addjet2_bDisCSV_40GeV.pdf r1 manage 9.9 K 2013-09-17 - 10:55 TaeJeongKim  
PNGpng cLL_Step_5_addjet2_bDisCSV_40GeV.png r1 manage 97.0 K 2013-09-17 - 10:49 TaeJeongKim  
PDFpdf csvshape_x.pdf r1 manage 4.6 K 2013-09-17 - 10:55 TaeJeongKim  
PNGpng csvshape_x.png r1 manage 78.0 K 2013-09-17 - 10:49 TaeJeongKim  
PDFpdf csvshape_y.pdf r1 manage 4.6 K 2013-09-17 - 10:55 TaeJeongKim  
PNGpng csvshape_y.png r1 manage 78.8 K 2013-09-17 - 10:49 TaeJeongKim  
PNGpng cutflow20GeV.png r1 manage 401.5 K 2013-09-17 - 16:47 TaeJeongKim  
PNGpng cutflow40GeV.png r2 r1 manage 394.5 K 2013-09-17 - 16:53 TaeJeongKim  
PDFpdf result.pdf r2 r1 manage 58.7 K 2013-09-18 - 09:27 TaeJeongKim  
PNGpng result.png r1 manage 53.6 K 2013-09-17 - 10:07 TaeJeongKim  
PNGpng systematictable.png r1 manage 302.6 K 2013-09-17 - 13:46 TaeJeongKim  
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