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Measurement of tt̄ production in the all-hadronic channel in 4.7 fb-1 ofpp collisions at √s = 7 TeV with the ATLAS detector ATLAS-CONF-2012-031 14 March 2012 |
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| Abstract | |
| A measurement of the $t\bar{t}$ production cross section in the all-hadronic channel is presented. The analysis is performed using 4.70/fb 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, events are required to have two reconstructed jets tagged as $b$-jets to identify $t\bar{t}$-event candidates. A kinematical fit which exploits the event topology of the all-hadronic $t\bar{t}$ final state is used to compute the top mass in the selected events. This variable is finally used to measure the total $t\bar{t}$ cross section using an unbinned likelihood fit, giving as a result $\sigma_{t\bar{t}}$ = 168 +/- 12 (stat.) +60 -57 (syst.) +/- 7 (lumi.) pb, consistent with the Standard Model prediction. | |
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Figure 01a: Mass distributions obtained from the kinematic fit for simulated signal events with a top quark mass hypothesis of 172.5 GeV and passing the event selection. The distributions are normalized to unity. The distribution is obtained from permutations that are fully matched to the tt̄ system. Filled circles (filled triangles) indicate that the fitted (reconstructed) jet energies are used to compute the mass of the top quark candidates. png (54kB) eps (19kB) pdf (8kB) |
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Figure 01b: Mass distributions obtained from the kinematic fit for simulated signal events with a top quark mass hypothesis of 172.5 GeV and passing the event selection. The distributions are normalized to unity. The distribution is obtained from permutations with at least one jet not correctly matched to the tt̄ system. Filled circles (filled triangles) indicate that the fitted (reconstructed) jet energies are used to compute the mass of the top quark candidates. png (83kB) eps (24kB) pdf (11kB) |
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Figure 02a: Fit of the top-quark mass mt distribution with an unbinned likelihood to the selected data sample (dots). The error bars associated to the data are statistical only. The two signal and background mt templates are indicated as well. png (57kB) eps (18kB) pdf (8kB) |
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Figure 02b: The top-quark mass mt distribution obtained after the kinematic fit to the untagged data sample (full line). The distributions after applying different corrections derived from Monte Carlo are overlaid (dashed and dotted lines). png (88kB) eps (11kB) pdf (6kB) |
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