TOP-13-012 - Search for standard model production of four top quarks in the lepton + jets channel in pp collisions at √s=8 TeV

arXiv:1409.7339 - JHEP 11 (2014) 154
Inspire - HepData - RIVET

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Abstract

A search is presented for standard model (SM) production of four top quarks (tttt) in pp collisions in the lepton + jets channel. The data correspond to an integrated luminosity of 19.6 fb-1 recorded at a centre-of-mass energy of 8 TeV with the CMS detector at the CERN LHC. The expected cross section for SM tttt production is about 1 fb. A combination of kinematic reconstruction and multivariate techniques is used to distinguish between the small signal and large background. The data are consistent with expectations of the SM, and an upper limit of 32 fb is set at a 95% confidence level on the cross section for producing four top quarks in the SM, where a limit of 32 17 fb is expected.

Results

A search for events containing four top quarks was performed using data collected with the CMS detector in lepton + jets final states at √s= 8 TeV, corresponding to an integrated luminosity of 19.6 fb-1. The analysis had three stages. First, a baseline selection was used to select signal events while suppressing backgrounds. Second, to further discriminate between signal and background, an event classification scheme based on a BDT algorithm was defined to exploit differences in the multiplicity of top quarks, jet activity, and the multiplicity of bottom quarks. Third, a simultaneous maximum likelihood fit of the BDT event discriminant distributions was performed, from which an upper limit on σ tttt of 32 fb was calculated at a 95% CL, where a limit of 32 17 fb was expected. These limits are approximately 25 σ SMtttt. This result raises the prospect of the direct observation of SM tttt in future CMS data at the higher centre-of-mass energies of 13 and 14 TeV, where the cross section is predicted to be 9 fb and 15 fb, respectively. Furthermore, this result has the potential to constrain BSM theories producing tttt final states with kinematics similar to the SM process, and enhance the discovery reach of BSM searches where SM production of tttt constitutes a possible background.

Figures

Figure 1a: Leading-order Feynman diagram for tttt production in the SM from gluon-gluon fusion.

PDF - PNG - EPS
Figure 1b: Leading-order Feynman diagram for tttt production in the SM from quark-antiquark annihilation.

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Figure 2a: The distribution in the BDTtrijet2 discriminant for the mu + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas show the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 2b: The distribution in the BDTtrijet2 discriminant for the e + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas show the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 2c: The distribution in Njets for the mu + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas show the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 2d: The distribution in Njets for the e + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas show the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 2e: The distribution in Nbtags for the mu + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas show the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 2f: The distribution in Nbtags for the e + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas show the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 3a: The distribution in the BDTevent discriminant for data and simulation in events with Njets = 6 for the mu + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas reflect the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 3b: The distribution in the BDTevent discriminant for data and simulation in events with Njets = 6 for the e + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas reflect the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 3c: The distribution in the BDTevent discriminant for data and simulation in events with Njets = 7 for the mu + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas reflect the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 3d: The distribution in the BDTevent discriminant for data and simulation in events with Njets = 7 for the e + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas reflect the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 3e: The distribution in the BDTevent discriminant for data and simulation in events with Njets > 7 for the mu + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas reflect the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS
Figure 3f: The distribution in the BDTevent discriminant for data and simulation in events with Njets > 7 for the e + jets channel. The ratios plotted at the bottom of each panel reflect the percent differences between data and MC events. The hatched areas reflect the changes in the calculated predictions produced by factors of two and one half changes in the factorisation and renormalisation scales in the tt simulation.

PDF - PNG - EPS

-- AndreasMeyer - 2015-03-20

Topic attachments
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