# Search for standard model production of four top quarks in proton-proton collisions at sqrt(s) = 13 TeV

## TL;DR

This study searches for four top quark production in proton-proton collisions at 13 TeV using CMS data, setting the most stringent limits to date on the production rate, consistent with the Standard Model.

## Contribution

First combined analysis of multiple channels to set the strongest limits on four top quark production at 13 TeV.

## Key findings

- Observed event counts agree with background and SM predictions.
- Upper limit on cross section is 69 fb at 95% CL, 7.4 times the SM prediction.
- No significant excess indicating new physics was found.

## Abstract

A search for events containing four top quarks (ttbar-ttbar) is reported from proton-proton collisions recorded by the CMS experiment at sqrt(s) = 13 TeV and corresponding to an integrated luminosity of 2.6 inverse femtobarns. The analysis considers the single-lepton (e or mu)+jets and the opposite-sign dilepton (mu+mu-, mu+/- e-/+, or e+e-)+jets channels. It uses boosted decision trees to combine information on the global event and jet properties to distinguish between ttbar-ttbar and ttbar production. The number of events observed after all selection requirements is consistent with expectations from background and standard model signal predictions, and an upper limit is set on the cross section for ttbar-ttbar production in the standard model of 94 fb at 95% confidence level (10.2 times the prediction), with an expected limit of 118 fb. This is combined with the results from the published CMS search in the same-sign dilepton channel, resulting in an improved limit of 69 fb at 95% confidence level (7.4 times the prediction), with an expected limit of 71 fb. These are the strongest constraints on the rate of ttbar-ttbar production to date.