Professor Claire Gwenlan

Abstract:

We describe how one may employ a very simple event selection, using only the kinematic variable mT2, to search for new particles at the LHC. The method is useful when searching for evidence of models (such as R-parity conserving supersymmetry), which have a Z2 parity and a weakly interacting lightest parity-odd particle. We discuss the kinematic properties which make this variable an excellent discriminant against the great majority of standard model backgrounds. Monte Carlo simulations suggest that this approach could be used to discover supersymmetry with somewhat smaller integrated luminosities (or perhaps lower center-of-mass energies) than would be required for other comparable analyses. © 2009 The American Physical Society.

Abstract:

Previously published data on inclusive neutral and charged current e+ p and e- p deep inelastic scattering from HERA have been combined. The new, model-independent method of combining the measured cross sections takes full account of correlated systematics in a coherent way, leading to significantly reduced uncertainties in the combined measurement across the (x, Q2) plane. The combined cross section data have been used as the sole input for a new next-to-leading order QCD fit to extract the parton distribution functions (PDFs) of the proton. The PDFs extracted have greatly reduced experimental uncertainties, compared to separate QCD analyses on data from H1 and ZEUS. Model uncertainties, including those arising from the parameterisation dependence, have also been carefully considered. The resulting HERA PDFs have impressive precision. © 2009 Elsevier B.V. All rights reserved.