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A Search for tt̄ Resonances in the Lepton Plus Jets Channel using 2.05 fb-1 pp Collisions at √s = 7 TeV ATLAS-CONF-2012-029 9 March 2012
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| Abstract | ||
| A search for top quark pair ($t\bar{t}$) resonances in the lepton plus jets final states has been performed with the ATLAS experiment at the LHC. The search uses a data sample corresponding to an integrated luminosity of 2.05 fb$^{-1}$, and was recorded in 2011 at a proton-proton centre-of-mass energy of 7 TeV. Limits are set on the production cross-section times branching ratio to top quark pairs of such resonances, ranging from approximately 9.3 pb at $m=$ 500 GeV to 0.95 pb at $m=$ 1300 GeV, excluding a leptophobic topcolour $Z'$ boson with 500 GeV $< m_{\rm Z'} <$ 860 GeV at 95\% probability. In Randall-Sundrum models, Kaluza-Klein gluons with masses between 500 and 1025 GeV are excluded at 95\% probability. | ||
| Figures | ||
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Figure 01a: Reconstructed t pair invariant mass (left) and its resolution (right) for four Z′
boson masses: mZ′ = 500, 700, 1000 and 1300 GeV.
png (57kB) pdf (14kB) |
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Figure 01b: Reconstructed t pair invariant mass (left) and its resolution (right) for four Z′
boson masses: mZ′ = 500, 700, 1000 and 1300 GeV.
png (61kB) pdf (14kB) |
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Figure 02a: Leading jet pT (a), leading jet mass (b) and charged lepton pT (c)
distributions after all cuts. The electron and muon channels have been added
together and the grey hashed area shows the background normalization
uncertainties. Overflows have been added to the last bin.
png (84kB) pdf (24kB) |
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Figure 02b: Leading jet pT (a), leading jet mass (b) and charged lepton pT (c)
distributions after all cuts. The electron and muon channels have been added
together and the grey hashed area shows the background normalization
uncertainties. Overflows have been added to the last bin.
png (62kB) pdf (19kB) |
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Figure 02c: Leading jet pT (a), leading jet mass (b) and charged lepton pT (c)
distributions after all cuts. The electron and muon channels have been added
together and the grey hashed area shows the background normalization
uncertainties. Overflows have been added to the last bin.
png (71kB) pdf (21kB) |
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Figure 03a: Reconstructed t mass for all events (left) and for events with a jet with mass
mj > 60 GeV (right), on linear (top) and logarithmic (bottom) scales. The
electron and muon channels have been added together and all events beyond the
range of the histogram have been added to the last bin. The grey hashed area
shows the background normalization uncertainties.
png (63kB) pdf (19kB) |
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Figure 03b: Reconstructed t mass for all events (left) and for events with a jet with mass
mj > 60 GeV (right), on linear (top) and logarithmic (bottom) scales. The
electron and muon channels have been added together and all events beyond the
range of the histogram have been added to the last bin. The grey hashed area
shows the background normalization uncertainties.
png (68kB) pdf (18kB) |
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Figure 03c: Reconstructed t mass for all events (left) and for events with a jet with mass
mj > 60 GeV (right), on linear (top) and logarithmic (bottom) scales. The
electron and muon channels have been added together and all events beyond the
range of the histogram have been added to the last bin. The grey hashed area
shows the background normalization uncertainties.
png (70kB) pdf (20kB) |
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Figure 03d: Reconstructed t mass for all events (left) and for events with a jet with mass
mj > 60 GeV (right), on linear (top) and logarithmic (bottom) scales. The
electron and muon channels have been added together and all events beyond the
range of the histogram have been added to the last bin. The grey hashed area
shows the background normalization uncertainties.
png (67kB) pdf (17kB) |
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Figure 04a: Expected (dashed line) and observed (solid line) upper limits on
σ× BR(Z′→ t) (a) and σ× BR(gKK → t) (b) The green and yellow bands
show the range in which the limit is expected to lie in 68% and 95% of
experiments, respectively, and the red lines correspond to the predicted
cross-section times branching ratio in the leptophobic topcolour and RS models.
The bands around the signal cross-section curves represent the effect of the PDF
uncertainty on the prediction.
png (81kB) pdf (17kB) |
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Figure 04b: Expected (dashed line) and observed (solid line) upper limits on
σ× BR(Z′→ t) (a) and σ× BR(gKK → t) (b) The green and yellow bands
show the range in which the limit is expected to lie in 68% and 95% of
experiments, respectively, and the red lines correspond to the predicted
cross-section times branching ratio in the leptophobic topcolour and RS models.
The bands around the signal cross-section curves represent the effect of the PDF
uncertainty on the prediction.
png (81kB) pdf (15kB) |
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