Observation of WZγ production and constraints on new physics scenarios in proton-proton collisions at s=13 TeV

Abstract

A measurement of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:mrow><a:mi>W</a:mi></a:mrow><a:mi>Z</a:mi><a:mi>γ</a:mi></a:mrow></a:math> triboson production cross section is presented. The analysis is based on a data sample of proton-proton collisions at a center-of-mass energy of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:msqrt><c:mi>s</c:mi></c:msqrt><c:mo>=</c:mo><c:mn>13</c:mn><c:mtext> </c:mtext><c:mtext> </c:mtext><c:mi>TeV</c:mi></c:math> recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mn>138</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:msup><e:mi>fb</e:mi><e:mrow><e:mo>−</e:mo><e:mn>1</e:mn></e:mrow></e:msup></e:math>. The analysis focuses on the final state with three charged leptons, <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mrow><g:mrow><g:msup><g:mrow><g:mo>ℓ</g:mo></g:mrow><g:mrow><g:mo>±</g:mo></g:mrow></g:msup></g:mrow><g:mi>ν</g:mi><g:mrow><g:msup><g:mrow><g:mo>ℓ</g:mo></g:mrow><g:mrow><g:mo>+</g:mo></g:mrow></g:msup></g:mrow><g:mrow><g:msup><g:mrow><g:mo>ℓ</g:mo></g:mrow><g:mrow><g:mo>−</g:mo></g:mrow></g:msup></g:mrow></g:mrow></g:math>, where <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mo>ℓ</i:mo><i:mo>=</i:mo><i:mi>e</i:mi></i:math> or <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mrow><k:mi>μ</k:mi></k:mrow></k:math>, accompanied by an additional photon. The observed (expected) significance of the <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mrow><m:mi>W</m:mi></m:mrow><m:mi>Z</m:mi><m:mrow><m:mi>γ</m:mi></m:mrow></m:math> signal is 5.4 (3.8) standard deviations. The cross section is measured in a fiducial region, where events with an ℓ originating from a tau lepton decay are excluded, to be <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mn>5.48</o:mn><o:mo>±</o:mo><o:mn>1.11</o:mn><o:mtext> </o:mtext><o:mtext> </o:mtext><o:mi>fb</o:mi></o:math>, which is compatible with the prediction of <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mn>3.69</q:mn><q:mo>±</q:mo><q:mn>0.24</q:mn><q:mtext> </q:mtext><q:mtext> </q:mtext><q:mi>fb</q:mi></q:math> at next-to-leading order in quantum chromodynamics. Exclusion limits are set on anomalous quartic gauge couplings and on the production cross sections of massive axionlike particles.