Abstract
The observation of the electroweak production of a Z boson with two jets in pp collisions at s=8 TeV with the CMS experiment at the CERN LHC is presented, based on a data sample with an integrated luminosity of 19.7 fb-1. The cross section measurement, combining the muon and electron channels, is in agreement with the theoretical expectations. Radiation patterns of selected Z plus two jets events, and the hadronic activity in the rapidity interval between the jets are also measured. These results are of substantial importance in the more general study of vector boson fusion processes, of relevance for Higgs boson searches and for measurements of electroweak gauge couplings and vector boson scattering.
Highlights
In proton collisions at the LHC Vector Boson Fusion (VBF) happens when a valence quark of each one of the colliding protons radiates a W or Z boson that subsequently interact or “fuse”
Radiation patterns of selected Z plus two jets events, and the hadronic activity in the rapidity interval between the jets are measured. These results are of substantial importance in the more general study of vector boson fusion processes, of relevance for Higgs boson searches and for measurements of electroweak gauge couplings and vector boson scattering
DY events are generated with MADGRAPH using a leading order (LO) matrix element (ME) calculation that includes up to four partons generated from quantum chromodynamics (QCD) interactions, and interfaced to PYTHIA for parton showering (PS)
Summary
In proton collisions at the LHC Vector Boson Fusion (VBF) happens when a valence quark of each one of the colliding protons radiates a W or Z boson that subsequently interact or “fuse” For both valence quark radiating the weak bosons a t-channel four-momentum with Q2 ∼ m2Z, m2W is exchanged. Considering only the classes of diagrams with purely electroweak (EW) interactions, (like the VBF one), shown, and no QCD interactions, the additional diagrams have strong negative interferences with the VBF productions These large negative interference effects are related to well-known non-abelian gauge cancellations that preserve the scattering unitarity and the electroweak model theory renormalizability [8]. Different methods have been used to confirm the presence of the signal: two multivariate analyses methods (A) and (B) as developed for the 7 TeV analysis [12], and new method (C) with a data-driven model of the main Drell-Yan (DY) background
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