Next-to-next-to-leading order event generation for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>Z</mml:mi> </mml:math> -boson production in association with a bottom-quark pair
Javier Mazzitelli, V. Sotnikov, Marius Wiesemann
Abstract
We consider the production of a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>Z</a:mi> </a:math> boson decaying to leptons in association with a bottom-quark pair in hadronic collisions. For the first time, we compute predictions at next-to-next-to-leading order (NNLO) in QCD, and we combine them with the all-order radiative corrections from a parton-shower simulation ( <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mrow> <c:mi>NNLO</c:mi> <c:mo>+</c:mo> <c:mi>PS</c:mi> </c:mrow> </c:math> ). Our method represents the first approach to <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mrow> <e:mi>NNLO</e:mi> <e:mo>+</e:mo> <e:mi>PS</e:mi> </e:mrow> </e:math> event generation applicable to processes featuring a color singlet and a heavy-quark pair in the final state. The novel two-loop corrections are computed for massless bottom quarks, and the leading mass corrections are restored through a small-mass expansion. The calculation is carried out in the four-flavor scheme, and we find that the sizable NNLO QCD corrections lift the long-standing tension between lower-order predictions in four- and five-flavor schemes. Our predictions are compared to a CMS measurement for <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:mi>Z</g:mi> </g:math> boson plus <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mi>b</i:mi> </i:math> -jet production, achieving an excellent description of the data.