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| CMS-PAS-TOP-16-016 | ||
| Search for standard model production of four top quarks in proton-proton collisions at 13 TeV | ||
| CMS Collaboration | ||
| August 2016 | ||
| Abstract: A search for standard model four top quark production, combining the single lepton and dilepton channels, is presented. The analysis utilises the data recorded by the CMS experiment at √s= 13 TeV in 2015, which corresponds to an integrated luminosity of 2.6 fb−1. A boosted decision tree algorithm is used to select signal and suppress background events. Upper limits on four top quark production of 10.2×σSMt¯tt¯t observed and 10.8+6.7−3.8×σSMt¯tt¯t expected are calculated at the 95% confidence level. | ||
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Links:
CDS record (PDF) ;
inSPIRE record ;
CADI line (restricted) ;
These preliminary results are superseded in this paper, PLB 772 (2017) 336. The superseded preliminary plots can be found here. |
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| Figures | |
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Figure 1:
The dominant diagram for t¯tt¯t production in the SM at leading order. |
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Figure 2-a:
The BDTtrijet1 discriminant for data and simulation in the dilepton channel for the μμ (a), μe (b) and ee (c) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t, t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 2-b:
The BDTtrijet1 discriminant for data and simulation in the dilepton channel for the μμ (a), μe (b) and ee (c) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t, t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 2-c:
The BDTtrijet1 discriminant for data and simulation in the dilepton channel for the μμ (a), μe (b) and ee (c) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t, t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 3-a:
The BDTtrijet2 discriminant for data and simulation in the single lepton channel for the μ+jets (a) and e+jets (b) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 3-b:
The BDTtrijet2 discriminant for data and simulation in the single lepton channel for the μ+jets (a) and e+jets (b) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 4-a:
The Nj distributions for data and simulation in the single lepton channel for the μ+jets (a), e+jets (b), the dilepton channel for the μμ (c), μe (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 4-b:
The Nj distributions for data and simulation in the single lepton channel for the μ+jets (a), e+jets (b), the dilepton channel for the μμ (c), μe (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 4-c:
The Nj distributions for data and simulation in the single lepton channel for the μ+jets (a), e+jets (b), the dilepton channel for the μμ (c), μe (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 4-d:
The Nj distributions for data and simulation in the single lepton channel for the μ+jets (a), e+jets (b), the dilepton channel for the μμ (c), μe (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 4-e:
The Nj distributions for data and simulation in the single lepton channel for the μ+jets (a), e+jets (b), the dilepton channel for the μμ (c), μe (d) and ee (e) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 5-a:
The S distributions for data and simulation in the dilepton channel for the μμ (a), μe (b) and ee (bottom) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 5-b:
The S distributions for data and simulation in the dilepton channel for the μμ (a), μe (b) and ee (bottom) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 5-c:
The S distributions for data and simulation in the dilepton channel for the μμ (a), μe (b) and ee (bottom) final states with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 6-a:
The T distributions for data and simulation in the single lepton channel for the μ+jets (a) and e+jets (b) final states are shown with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 6-b:
The T distributions for data and simulation in the single lepton channel for the μ+jets (a) and e+jets (b) final states are shown with the dominant systematic uncertainty shown in hatched bands and the t¯t+X sample representing the sum of t¯t , t¯t+Z, t¯t+W, and t¯t+H production. |
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Figure 7-a:
Dilepton BDT output discriminator summed across lepton species channels for 4-5 jets (upper left), 6-7 jets (upper right), and ≥8 jets (bottom). |
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Figure 7-b:
Dilepton BDT output discriminator summed across lepton species channels for 4-5 jets (upper left), 6-7 jets (upper right), and ≥8 jets (bottom). |
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Figure 7-c:
Dilepton BDT output discriminator summed across lepton species channels for 4-5 jets (upper left), 6-7 jets (upper right), and ≥8 jets (bottom). |
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Figure 8-a:
BDT output distributions in the μ+jets channel (a) and e+jets channel (b) for the ≥9Nj and 3NMtagscategory. |
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Figure 8-b:
BDT output distributions in the μ+jets channel (a) and e+jets channel (b) for the ≥9Nj and 3NMtagscategory. |
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Figure 9-a:
BDT output distributions in the μ jets channel (a) and e+jets channel (b) for the ≥9Nj and ≥4NMtags category. |
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Figure 9-b:
BDT output distributions in the μ jets channel (a) and e+jets channel (b) for the ≥9Nj and ≥4NMtags category. |
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Figure 10:
Expected and observed upper limits on σSMt¯tt¯t for the single lepton, dilepton, and combined analysis in multiples of σSMt¯tt¯t. |
| Tables | |
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Table 1:
Expected and observed 95% CL upper limits on the standard model four top quark production as a multiple of σSMt¯tt¯t. The values quoted on the expected limits are the 1σ uncertainties. |
| Summary |
| A search for events containing four top quarks has been performed using 2.6 fb−1 of data recorded by the CMS experiment at √s= 13 TeV. The analysis focuses on a combination of the single lepton channel in the μ+jets and e+jets final states and dilepton channel in the μμ, μe, and ee final states. The analysis is comprised of three stages. Firstly, a baseline selection is defined for each final state that is used to broadly select signal events while suppressing backgrounds. Secondly, an event classification scheme based on a BDT algorithm is defined, further enhancing sensitivity to four top quark production. The BDT algorithm exploits the differences in event activity, event topology, b content and t content to discriminate between signal and background. Thirdly, upper limits on four top quark production of 10.2×σt¯tt¯tSM observed and 10.8+6.7−3.8×σSMt¯tt¯t expected are calculated at the 95% CL. |
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