W$^+$W$^-$ boson pair production in proton-proton collisions at $\sqrt{s} =$ 13 TeV

TL;DR

This paper reports a precise measurement of W$^+$W$^-$ boson pair production at 13 TeV using CMS data, employing advanced background suppression techniques and probing for new physics beyond the Standard Model.

Contribution

It introduces two novel background reduction methods and provides detailed differential and fiducial cross section measurements, including constraints on effective field theory operators.

Findings

Measured total cross section: 117.6 ± 6.8 pb, consistent with theory.

Reported fiducial cross sections for zero and one jet events.

Set limits on dimension-6 operators indicating no significant deviation from the Standard Model.

Abstract

A measurement of the W$^+$W$^-$ boson pair production cross section in proton-proton collisions at $\sqrt{s} =$ 13 TeV is presented. The data used in this study are collected with the CMS detector at the CERN LHC and correspond to an integrated luminosity of 35.9 fb$^{-1}$. The W$^+$W$^-$ candidate events are selected by requiring two oppositely charged leptons (electrons or muons). Two methods for reducing background contributions are employed. In the first one, a sequence of requirements on kinematic quantities is applied allowing a measurement of the total production cross section: 117.6 $\pm$ 6.8 pb, which agrees well with the theoretical prediction. Fiducial cross sections are also reported for events with zero or one jet, and the change in the zero-jet fiducial cross section with the jet transverse momentum threshold is measured. Normalized differential cross sections are reported within the fiducial region. A second method for suppressing background contributions employs two random forest classifiers. The analysis based on this method includes a measurement of the total production cross section and also a measurement of the normalized jet multiplicity distribution in W$^+$W$^-$ events. Finally, a dilepton invariant mass distribution is used to probe for physics beyond the standard model in the context of an effective field theory, and constraints on the presence of dimension-6 operators are derived.