Pearce, James D.2011-12-122011-12-1220112011-12-12http://hdl.handle.net/1828/3713One of the dominant backgrounds in new physics searches at the Large Hadron Collider comes from the leptonic decays of Standard Model W and Z bosons recoiling off jets associated with the underlying event. The ratio of the W+jets and Z+jets cross sections, Rn, is predicted with high precision due to the similar masses and production mechanisms of the W and Z bosons. Any significant departures of Rn from predicted values would be an indication of new physics. This thesis studies a strategy to enhance the sensitivity of Rn to a specific type of signal. A measurement of the ratio Rn is presented, and its sensitivity to pair production of top quarks and leptoquarks is studied. Using a set of topology-discriminating variables, based upon calorimeter topoclusters, the sensitivity of Rn to top quark and leptoquark signals is enhanced using multivariate analysis techniques.enW bosonZ bosonleptoquarkjetneural networknew physics searchW/Z + jets cross sectionevent shape variablesATLASLHCThesisAvailable to the World Wide Web