# Search for the production of four top quarks in the single-lepton and opposite-sign dilepton final states in proton-proton collisions at $\sqrt{s} =$ 13 TeV

## TL;DR

This paper reports a search for four top quark production in proton-proton collisions at 13 TeV using CMS data, setting upper limits on the production cross section and combining results with previous analyses.

## Contribution

It introduces a multivariate analysis method to discriminate four top quark events from background and provides the first combined measurement with previous CMS results.

## Key findings

- No significant excess observed over background.
- Upper limit on four top quark production cross section is 48 fb.
- Combined analysis yields a cross section of 13^{+11}_{-9} fb.

## Abstract

A search for the standard model production of four top quarks (pp $\to$ $\mathrm{t\bar{t}t\bar{t}}$) is reported using single-lepton plus jets and opposite-sign dilepton plus jets signatures. Proton-proton collisions are recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV in a sample corresponding to an integrated luminosity of 35.8 fb$^{-1}$. A multivariate analysis exploiting global event and jet properties is used to discriminate $\mathrm{t\bar{t}t\bar{t}}$ from $\mathrm{t\bar{t}}$ production. No significant deviation is observed from the predicted background. An upper limit is set on the cross section for $\mathrm{t\bar{t}t\bar{t}}$ production in the standard model of 48 fb at 95% confidence level. When combined with a previous measurement by the CMS experiment from an analysis of other final states, the observed signal significance is 1.4 standard deviations, and the combined cross section measurement is 13 $^{+11}_{-9}$ fb. The result is also interpreted in the framework of effective field theory.