Reconstruction of boosted $W^{\pm}$ and $Z^{0}$ bosons from fat jets

We present the reconstruction of heavily boosted $W^{\pm}$ and $Z^{0}$ bosons from large R-parameter jets (fat jets) in all-hadronic proton-proton collisions at $\sqrt{s} = 8$ TeV at the LHC. The electroweak gauge bosons are boosted to a degree at which their hadronic decay products are collimated enough to be reconstructed as a single fat jet. A mass-drop filtering procedure which is validated in studies on Monte Carlo (MC) samples is then applied to the fat jets with $p_{T} > 420$ GeV to suppress pileup and soft radiation. $W^{\pm}$ and $Z^{0}$ bosons are identified based on their filtered jet mass. The efficiency of common substructure observables and event shape variables, in distinguishing between signal and QCD background is evaluated on MC and the optimized observable selection used for the training of two boosted decision trees (BDT), in order to reduce the dijet background not originating from the decay of an electroweak gauge boson. For the first BDT, signal MC has been trained against background MC, while for the second one the background is taken from sidebands in data. A peak corresponding to the mass of the electroweak gauge bosons can be observed in the filtered fat jet mass spectrum. The production cross section for hadronically decaying electroweak gauge bosons for $p_{T} > 420$ GeV and $|\eta| < 1.9$ is measured to be $\sigma_{1} = 0.557 \pm 0.032 (\text{stat.}) \pm 0.054 (\text{sys.})$ pb and $\sigma_{2} = 0.599 \pm 0.031 (\text{stat.})\pm 0.058 (\text{sys.})$ pb for the two BDTs respectively. The data sample corresponds to 20.3 fb$^{−1}$ collected with the ATLAS detector in 2012.