Richard Nickerson

Abstract:

A measurement of the cross section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy √s=7TeV is presented. The measurement covers the pseudorapidity ranges |ηγ|<1. 37 and 1.52≤|ηγ|<1.81 in the transverse energy range 15≤ETγ<100GeV. The results are based on an integrated luminosity of 880nb-1, collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner tracker. Residual background in the selected sample is estimated from data based on the observed distribution of the transverse isolation energy in a narrow cone around the photon candidate. The results are compared to predictions from next-to-leading-order perturbative QCD calculations. © 2011 CERN, for the ATLAS Collaboration.

Abstract:

The ATLAS detector at the LHC is used to search for high-mass states, such as heavy charged gauge bosons (W'), decaying to a charged lepton (electron or muon) and a neutrino. Results are presented based on the analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 1.04 fb-1. No excess above Standard Model expectations is observed. A W' with Sequential Standard Model couplings is excluded at the 95% confidence level for masses up to 2.15 TeV.

Abstract:

Dijet angular distributions from the first LHC pp collisions at center-of-mass energy s=7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet Χ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the λ distributions excludes quark contact interactions with a compositeness scale Χ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits. © 2010 CERN.

Abstract:

A search for new interactions and resonances produced in LHC proton-proton (pp) collisions at a centre-of-mass energy √s = 7 TeV was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb -1, dijet mass and angular distributions were measured up to dijet masses of ∼3.5TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space-time dimensions for quantum gravity scales between 0.75 and 3.67 TeV. Production cross section limits as a function of dijet mass are set using a simplified Gaussian signal model to facilitate comparisons with other hypotheses. Analysis of the dijet angular distribution using a novel technique simultaneously employing the dijet mass excludes quark contact interactions with a compositeness scale A below 9.5 TeV. © 2011 CERN for the benefit of the ATLAS Collaboration.

Abstract:

We have used the energy-energy angular pattern of hadrons in inelastic muon-deuteron scattering to study perturbative QCD effects and to extract the gluon distribution function ηG(η) of the nucleon, where η is the fractional momentum carried by the gluon. The data were taken with the E665 spectrometer using the Fermilab Tevatron muon beam with a mean beam energy of 490 GeV. We present ηG(η) for 0.005 < η < 0.05 and at an average age Q2 of 8 GeV2 using this new technique. We find that ηG(η) in this region can be described by ηG(η) ∝ηλ with λ = -0.87±0.09(stat.)±0.3.2±(sys.). We compare our results to expectations from various parametrizations of the parton distribution function and also to results from HERA. © Springer-Verlag 1996.