Search for new particles in events with energetic jets and large missing transverse momentum in proton-proton collisions at $\sqrt{s} = $ 13 TeV

TL;DR

This paper reports a search for new particles at the LHC using events with energetic jets and missing transverse momentum, setting new limits on dark matter models, leptoquarks, and extra dimensions.

Contribution

It introduces machine learning techniques for event categorization and combines data from multiple years to improve sensitivity in new particle searches.

Findings

No significant excess observed over the standard model background.

Set the most restrictive limits to date on several dark matter mediator models.

Constrained models of leptoquarks and large extra dimensions.

Abstract

A search is presented for new particles produced at the LHC in proton-proton collisions at $\sqrt{s} =$ 13 TeV, using events with energetic jets and large missing transverse momentum. The analysis is based on a data sample corresponding to an integrated luminosity of 101 fb$^{-1}$, collected in 2017-2018 with the CMS detector. Machine learning techniques are used to define separate categories for events with narrow jets from initial-state radiation and events with large-radius jets consistent with a hadronic decay of a W or Z boson. A statistical combination is made with an earlier search based on a data sample of 36 fb$^{-1}$, collected in 2016. No significant excess of events is observed with respect to the standard model background expectation determined from control samples in data. The results are interpreted in terms of limits on the branching fraction of an invisible decay of the Higgs boson, as well as constraints on simplified models of dark matter, on first-generation scalar leptoquarks decaying to quarks and neutrinos, and on models with large extra dimensions. Several of the new limits, specifically for spin-1 dark matter mediators, pseudoscalar mediators, colored mediators, and leptoquarks, are the most restrictive to date.