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Measurement of t t̄ production in the all-hadronic channel in 1.02 fb-1 ofpp collisions at √s = 7 TeV with the ATLAS detector. ATLAS-CONF-2011-140 24 September 2011
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| Abstract | ||
| We present a measurement of the $t\bar{t}$ production cross-section in the all-hadronic channel with the ATLAS detector. The analysis is performed using 1.02 $\mathrm{fb}^{-1}$ of $pp$ collisions produced at the LHC with a centre-of-mass energy of $\sqrt{s}=$ 7 TeV and recorded with the ATLAS detector. After selecting events passing a multi-jet trigger and kinematic requirements, we require events to have two reconstructed jets identified as $b$-jets. After preselection, an {\it Event Mixing} method is used to model the kinematics of a higher jet-multiplicity \mj sample from a lower jet-multiplicity one, depleted in signal events. The total $t\bar{t}$ cross-section is then extracted using a binned likelihood fit of the $\chi^2$ from a kinematic fit assuming the $t\bar{t}$ event hypothesis and measured to be $\sigma_{t\bar{t}}$ = 167 $\pm$ 18 (stat.) $\pm$ 78 (syst.) $\pm$ 6 (lum.) pb, consistent with the Standard Model prediction. As a cross-check of this analysis, an alternative one using a method exploiting $b$-tagging information and the centrality of the events, the {\it ABCD} method, is also discussed. | ||
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Figure 01a: Comparison between inclusive six-jets data (dots) and the prediction modelled from five jet data for events without b-tagging for the number of jets. All histograms are normalized to have integral equal to one. Also shown the ratio between data and prediction. png (39kB) eps (15kB) pdf (7kB) |
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Figure 01b: Comparison between inclusive six-jets data (dots) and the prediction modelled from five jet data for events without b-tagging for the aplanarity. All histograms are normalized to have integral equal to one. Also shown the ratio between data and prediction. png (39kB) eps (15kB) pdf (8kB) |
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Figure 01c: Comparison between inclusive six-jets data (dots) and the prediction modelled from five jet data for events without b-tagging for the centrality. All histograms are normalized to have integral equal to one. Also shown the ratio between data and prediction. png (41kB) eps (15kB) pdf (8kB) |
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Figure 01d: Comparison between inclusive six-jets data (dots) and the prediction modelled from five jet data for events without b-tagging for HT. All histograms are normalized to have integral equal to one. Also shown the ratio between data and prediction. png (42kB) eps (15kB) pdf (8kB) |
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Figure 02: Fit of the minimal mass χ2 distribution with the binned likelihood (blue line) to the selected data (dots). The t t̄ signal fitted fraction is shown in red and the QCD inclusive six-jet background in green. The errors bars associated to the data are statistical only. png (37kB) eps (11kB) pdf (6kB) |
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Figure 03: Top mass reconstructed from minimal mass χ2 distribution without top-quark mass constraint, signal and background are normalized according to the result of the fit shown in Figure 2. The errors bars represent the statistical uncertainties while the hatching represent the systematic ones. png (45kB) eps (37kB) pdf (14kB) |
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Figure 04a: Distribution of simulated t t̄ signal events in the plane defined by the centrality and a logical variable describing the presence of at least two b-tagged jets separated by Δ R > 1.2. png (29kB) eps (9kB) pdf (4kB) |
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Figure 04b: Distribution of data events in the plane defined by the centrality and a logical variable describing the presence of at least two b-tagged jets separated by Δ R > 1.2. png (30kB) eps (9kB) pdf (4kB) |
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Figure 05a: χ2 comparison between inclusive six-jets data (dots) and the background modelled from five-jet data (green) for events without b-tagging. All histograms are normalized to have integral equal to one. png (42kB) eps (15kB) pdf (8kB) |
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Figure 05b: comparison of the two χ2 distributions for the inclusive six-jet modelled with four-jet data (red) and the inclusive six-jet modelled with five-jet data for the four-jet trigger selected events, all events have at least two b-tagged jets. All histograms are normalized to have integral equal to one. png (48kB) eps (17kB) pdf (9kB) |
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