A search for tt̄ resonances in the lepton plus jets final state using 4.66/fb of pp collisions at √s = 7 TeV

A search for tt̄ resonances in the lepton plus jets final state using 4.66/fb of pp collisions at √s = 7 TeV

ATLAS-CONF-2012-136

20 September 2012

These preliminary results are superseded by the following paper:

TOPQ-2012-14
ATLAS recommends to use the results from the paper.

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Abstract

A search for new particles that decay into ttbar pairs is performed with the ATLAS experiment at the LHC using 4.66 fb^-1 of data collected at 7 TeV. The ttbar system is reconstructed using the lepton plus jets decay channel, both with standard jets and by exploiting jet substructure. No evidence for a ttbar resonance is observed. For a narrow Z' boson, the 95% credibility level cross section times branching ratio upper limits range from 3.2 pb at a resonance mass of 0.7 TeV to 0.05 for a mass of 2 TeV. Leptophobic topcolor Z' resonances are excluded for masses below 1.7 TeV and Randall-Sundrum Kaluza-Klein gluon excitations are excluded for masses below 1.9 TeV at a 95% credibility level.

Figures

Figure 01a:
Figure 1a. Reconstructed tt̄ invariant mass distribution using the resolved selection for several Z' masses. The broad Kaluza-Klein gluon resonance at mass 1.3 TeV is also shown for comparison.

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Figure 01b:
Figure 1a. Reconstructed tt̄ invariant mass distribution using the boosted selection for several Z' masses. The broad Kaluza-Klein gluon resonance at mass 1.3 TeV is also shown for comparison.

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Figure 02a:
Figure 2a. Reconstructed tt̄ invariant mass distribution in the multi-jets control region using the resolved selection in the e+jets channel. The 60% uncertainty on the multi-jets contribution is indicated.

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Figure 02b:
Figure 2b. Reconstructed tt̄ invariant mass distribution in the multi-jets control region using the resolved selection in the μ +jets channel. The 60% uncertainty on the multi-jets contribution is indicated.

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Figure 02c:
Figure 2c. Reconstructed tt̄ invariant mass distribution in the multi-jets control region using the boosted selection in the e+jets channel. The 60% uncertainty on the multi-jets contribution is indicated.

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Figure 02d:
Figure 2b. Reconstructed tt̄ invariant mass distribution in the multi-jets control region using the boosted selection in the μ +jets channel. The 60% uncertainty on the multi-jets contribution is indicated.

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Figure 03a:
Figure 3a. Comparison of the data and the Standard Model prediction for the transverse momentum of the leading jet using the resolved selection in the e+jets channel. The shaded areas indicate the total systematic uncertainties.

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Figure 03b:
Figure 3a. Comparison of the data and the Standard Model prediction for the transverse momentum of the leading jet using the resolved selection in the μ+jets channel. The shaded areas indicate the total systematic uncertainties.

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Figure 04a:
Figure 4a. Comparison of the data and the Standard Model prediction for the transverse momentum of the hadronically decaying top using the boosted selection in the e+jets channel. The shaded areas indicate the total systematic uncertainties.

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Figure 04b:
Figure 4b. Comparison of the data and the Standard Model prediction for the transverse momentum of the hadronically decaying top using the boosted selection in the μ+jets channel. The shaded areas indicate the total systematic uncertainties.

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Figure 05a:
Figure 5a. Comparison of the data and the Standard Model prediction for the invariant mass of the semi-leptonically decaying top quark using the boosted selection in the e+jets channel. The shaded areas indicate the total systematic uncertainties.

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Figure 05b:
Figure 5b. Comparison of the data and the Standard Model prediction for the invariant mass of the semi-leptonically decaying top using the boosted selection in the μ+jets channel. The shaded areas indicate the total systematic uncertainties.

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Figure 06a:
Figure 6a. Comparison of the data and the Standard Model prediction for the invariant mass of the hadronic top jet using the boosted selection in the e+jets channel. The requirement of jet mass greater than 100 GeV is not applied. The shaded areas indicate the total systematic uncertainties.

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Figure 06b:
Figure 6b. Comparison of the data and the Standard Model prediction for the invariant mass of the hadronic top jet using the boosted selection in the μ+jets channel. The requirement of jet mass greater than 100 GeV is not applied. The shaded areas indicate the total systematic uncertainties.

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Figure 07a:
Figure 7a. Comparison of the data and the Standard Model prediction for the first k_t splitting scale √d₁₂ of the hadronic top jet using the boosted selection in the e+jets channel. The requirement of √d₁₂ greater than 40 GeV is not applied. The shaded areas indicate the total systematic uncertainties.

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Figure 07b:
Figure 7b. Comparison of the data and the Standard Model prediction for the first k_t splitting scale √d₁₂ of the hadronic top jet using the boosted selection in the μ+jets channel. The requirement of √d₁₂ greater than 40 GeV is not applied. The shaded areas indicate the total systematic uncertainties.

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Figure 08a:
Figure 8a. Comparison of the data and the Standard Model prediction for the tt̄ invariant mass using the resolved selection in the e+jets channel. The shaded areas indicate the total systematic uncertainties.

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Figure 08b:
Figure 8b. Comparison of the data and the Standard Model prediction for the tt̄ invariant mass using the resolved selection in the μ+jets channel. The shaded areas indicate the total systematic uncertainties.

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Figure 08c:
Figure 8c. Comparison of the data and the Standard Model prediction for the tt̄ invariant mass using the boosted selection in the e+jets channel. The shaded areas indicate the total systematic uncertainties.
Updated on Sept. 28 with a corrected version of the ratio error band.

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Figure 08d:
Figure 8d. Comparison of the data and the Standard Model prediction for the tt̄ invariant mass using the boosted selection in the μ+jets channel. The shaded areas indicate the total systematic uncertainties.

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Figure 09:
Figure 9. Comparison of the data and the Standard Model prediction for the tt̄ invariant mass for both resolved and boosted selections in both the e+jets and μ+jets channels. That is, all four spectra are summed. The shaded areas indicate the total systematic uncertainties.

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Figure 10a:
Figure 10a. Expected (dashed line) and observed (solid line) upper limits on the cross section times the tt̄ branching fraction of Z' using the resolved selection. The dark (green) and light (yellow) bands show the range in which the limit is expected to lie in 68% and 95% of pseudo-experiments, respectively, and the smooth solid (red) lines correspond to the predicted cross section times branching fraction. Both statistic and systematic uncertainties have been included.

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Figure 10b:
Figure 10b. Expected (dashed line) and observed (solid line) upper limits on the cross section times the tt̄ branching fraction of Kaluza-Klein gluons using the resolved selection. The dark (green) and light (yellow) bands show the range in which the limit is expected to lie in 68% and 95% of pseudo-experiments, respectively, and the smooth solid (red) lines correspond to the predicted cross section times branching fraction. Both statistic and systematic uncertainties have been included.

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Figure 10c:
Figure 10c. Expected (dashed line) and observed (solid line) upper limits on the cross section times the tt̄ branching fraction of Z' using the boosted selection. The dark (green) and light (yellow) bands show the range in which the limit is expected to lie in 68% and 95% of pseudo-experiments, respectively, and the smooth solid (red) lines correspond to the predicted cross section times branching fraction. Both statistic and systematic uncertainties have been included.

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Figure 10d:
Figure 10d. Expected (dashed line) and observed (solid line) upper limits on the cross section times the tt̄ branching fraction of Kaluza-Klein gluons using the boosted selection. The dark (green) and light (yellow) bands show the range in which the limit is expected to lie in 68% and 95% of pseudo-experiments, respectively, and the smooth solid (red) lines correspond to the predicted cross section times branching fraction. Both statistic and systematic uncertainties have been included.

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Figure 10e:
Figure 10e. Expected (dashed line) and observed (solid line) upper limits on the cross section times the tt̄ branching fraction of Z' using the combined resolved and boosted selections. The dark (green) and light (yellow) bands show the range in which the limit is expected to lie in 68% and 95% of pseudo-experiments, respectively, and the smooth solid (red) lines correspond to the predicted cross section times branching fraction. Both statistic and systematic uncertainties have been included.

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Figure 10f:
Figure 10f. Expected (dashed line) and observed (solid line) upper limits on the cross section times the tt̄ branching fraction of Kaluza-Klein gluons using the combined resolved and boosted selections. The dark (green) and light (yellow) bands show the range in which the limit is expected to lie in 68% and 95% of pseudo-experiments, respectively, and the smooth solid (red) lines correspond to the predicted cross section times branching fraction. Both statistic and systematic uncertainties have been included.

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Auxiliary figures and tables

Figure 11a:
Figure 11a. Various selection efficiencies as a function of the tt̄ invariant mass for the Z' resonance. The efficiencies for the e+jets (red) and μ+jets (blue) channels are shown for pre-tagged (solid) and b-tagged (dashed) selections. These efficiencies are for the resolved selection, including events which overlap with the boosted selection.

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Figure 11b:
Figure 11b. Various selection efficiencies as a function of the tt̄ invariant mass for the Z' resonance. The efficiencies for the e+jets (red) and μ+jets (blue) channels are shown for pre-tagged (solid) and b-tagged (dashed) selections. These efficiencies are for the resolved selection plus a requirement of at least one jet mass greater than 60 GeV, including events which overlap with the boosted selection.

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Figure 11c:
Figure 11c. Various selection efficiencies as a function of the tt̄ invariant mass for the Z' resonance. The efficiencies for the e+jets (red) and μ+jets (blue) channels are shown for pre-tagged (solid) and b-tagged (dashed) selections. These efficiencies are for the resolved selection, excluding events which overlap with the boosted selection.

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Figure 11d:
Figure 11d. Various selection efficiencies as a function of the tt̄ invariant mass for the Z' resonance. The efficiencies for the e+jets (red) and μ+jets (blue) channels are shown for pre-tagged (solid) and b-tagged (dashed) selections. These efficiencies are for the resolved selection plus a requirement of at least one jet mass greater than 60 GeV, excluding events which overlap with the boosted selection.

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Figure 11e:
Figure 11e. Various selection efficiencies as a function of the tt̄ invariant mass for the Z' resonance. The efficiencies for the e+jets (red) and μ+jets (blue) channels are shown for pre-tagged (solid) and b-tagged (dashed) selections. These efficiencies are for the boosted selection.

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2024-05-19 01:17:13