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.
Highlights
The standard model (SM) description of electroweak and strong interactions can be tested through measurements of the WþW− boson pair production cross section at a hadron collider
For the analysis presented in this paper, the gg → WþW− contribution is corrected by a factor of 1.4, which comes from the ratio of the gg → WþW− cross section at next-to-leading order (NLO) to the same cross section at LO [9]
XI, this paper reports a measurement of the normalized jet multiplicity distribution based on the random forest analysis
Summary
The standard model (SM) description of electroweak and strong interactions can be tested through measurements of the WþW− boson pair production cross section at a hadron collider. WþW− production cross section in pp collisions at 1⁄4 13 TeV gives the value 118.7þ−23..60 pb [8] This calculation includes the qqannihilation process calculated. The random forest technique allows for flexible control over the top quark background contamination, which is exploited to study the jet multiplicity in WþW− signal events. The sensitivity of the random forest to QCD uncertainties is significantly larger than that of the sequential cut analysis, as discussed in Sec. IX A.
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