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 centreofmass 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.
Figure 1a: Leadingorder Feynman diagram for tttt production in the SM from gluongluon fusion. PDF  PNG  EPS 

Figure 1b: Leadingorder Feynman diagram for tttt production in the SM from quarkantiquark annihilation. PDF  PNG  EPS 

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  20150320