Combination of searches for WW, WZ, and ZZ resonances in pp collisions at √s = 8 TeV with the ATLAS detector

December 2015

The ATLAS experiment at the CERN Large Hadron Collider has performed searches for new, heavy bosons decaying to WW, WZ and ZZ final states in multiple decay channels using 20.3 fb⁻¹ of pp collision data at √s = 8 TeV. In the current study, the results of these searches are combined to provide a more stringent test of models predicting heavy resonances with couplings to vector bosons. Direct searches for a charged diboson resonance decaying to WZ in the lνl'l' (l = μ, e), llqq, lνqq and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WZ bosons are compared with predictions of an extended gauge model with a heavy W' boson. In addition, direct searches for a neutral diboson resonance decaying to WW and ZZ in the llqq, lνqq, and fully hadronic final states are combined and upper limits on the rate of production times branching ratio to the WW and ZZ bosons are compared with predictions for a heavy, spin-2 graviton in an extended Randall–Sundrum model where the Standard Model fields are allowed to propagate in the bulk of the extra dimension.

Paper

PhD Thesis: Search for diboson resonance production at √s = 8 TeV with the ATLAS detector

October 2015

A search for heavy exotic diboson resonances decaying to llqq final states is presented using pp collision data collected with the ATLAS detector at the Large Hadron Collider. The analysis uses a data sample corresponding to an integrated luminosity of 20.3 fb⁻¹ at √s = 8 TeV collected between April and December 2012. No significant excess of data events over the predicted Standard Model background is observed and 95% confidence level upper limits are set on the product of the production cross-section and the branching ratio for spin-2 KaluzaKlein gravitons predicted by the bulk Randall-Sundrum model and for Extended Gauge Model W' bosons. These results are subsequently combined with limits obtained from searches using the lνll, lνqq and qqqq final states, and new mass limits are set on both signal models.

Thesis

Search for resonant diboson production in the llqq final state in pp collisions at √s = 8 TeV with the ATLAS detector

September 2014

This paper reports on a search for narrow resonances in diboson production in the llqq final state using pp collision data corresponding to an integrated luminosity of 20 fb^-1 collected at √s = 8 TeV with the ATLAS detector at the Large Hadron Collider. No significant excess of data events over the Standard Model expectation is observed. Upper limits at the 95% confidence level are set on the production cross section times branching ratio for Kaluza–Klein gravitons predicted by the Randall–Sundrum model and for Extended Gauge Model W' bosons. These results lead to the exclusion of mass values below 740 and 1590 GeV for the graviton and W' boson respectively.

Paper

Search for resonant diboson production in the llqq final state in pp collisions at √s = 8 TeV with the ATLAS detector

July 2014

A search for resonances in diboson production in the llqq final state using 20.3 fb⁻¹ of pp collision data collected at √s = 8 TeV with the ATLAS detector is reported. No significant excess over the Standard Model expectation is observed. Consequently 95% confidence level upper limits are set on the cross section times branching ratio for the production of Kaluza-Klein gravitons in the Randall-Sundrum model and extended gauge model W' bosons, leading to the exclusion of mass values below 740 and 1590 GeV for the graviton and W′ boson, respectively.

Conference Note

Search for resonant ZZ production in the ZZ→llqq channel with the ATLAS detector using 7.2 fb^-1 of √s = 8 TeV pp collision data

November 2012

A search for a heavy particle that decays to a pair of Z bosons is presented, using events recorded by the ATLAS detector in proton-proton collisions at √s = 8 TeV corresponding to an integrated luminosity of 7.2 fb^-1. The analysis considers the llqq final state (l = e, μ) and uses the diboson mass reconstructed from the leptons and jets as the discriminating variable. No significant deviation in the mass distribution from a smoothly falling background distribution is observed. Upper limits on the production cross section times branching fraction into a ZZ boson pair are set for the bulk Randall-Sundrum graviton with coupling parameter κ/m̅_Pl = 1.0, and the corresponding 95% credibility level observed (expected) lower limit on the mass for the graviton is 850 (870) GeV.

Conference Note

Masters Thesis: Development of machine learning methods to search for the Standard Model Higgs boson produced in association with top quarks and decaying into bb in DØ data

May 2011

The feasibility of using machine learning techniques to search for a 125 GeV Standard Model Higgs boson produced in association with top quarks and decaying into bb is investigated. Boosted decision trees are trained to analyse data collected at DØ in Run II (2001-2011) at √s = 1.96 TeV of the Tevatron pp collider, corresponding to an integrated luminosity of 9.7 fb⁻¹. Novel methods are developed to prevent overtraining, but it is concluded that a larger dataset is required for meaningful results.

Talks and Posters