A search for ttbar resonances in the lepton plus jets final state with ATLAS using 4.7 fb^{-1} of pp collisions at sqrt{s} = 7 TeV
Abstract:
A search for new particles that decay into top quark pairs (ttbar) is performed with the ATLAS experiment at the LHC using an integrated luminosity of 4.7 fb^-1 of proton-proton (pp) collision data collected at a center-of-mass energy sqrt(s)=7 TeV. In the ttbar --> WbWb decay, the lepton plus jets final state is used, where one W boson decays leptonically and the other hadronically. The ttbar system is reconstructed using both small-radius and large-radius jets, the latter being supplemented by a jet substructure analysis. A search for local excesses in the number of data events compared to the Standard Model expectation in the ttbar invariant mass spectrum is performed. No evidence for a ttbar resonance is found and 95% credibility-level limits on the production rate are determined for massive states predicted in two benchmark models. The upper limits on the cross section times branching ratio of a narrow Z' resonance range from 5.1 pb for a boson mass of 0.5 TeV to 0.03 pb for a mass of 3 TeV. A narrow leptophobic topcolor Z' resonance with a mass below 1.74 TeV is excluded. Limits are also derived for a broad color-octet resonance with Gamma/m = 15.3%. A Kaluza-Klein excitation of the gluon in a Randall-Sundrum model is excluded for masses below 2.07 TeV.AION: An Atom Interferometer Observatory and Network
Abstract:
We outline the experimental concept and key scientific capabilities of AION (Atom Interferometer Observatory and Network), a proposed UK-based experimental programme using cold strontium atoms to search for ultra-light dark matter, to explore gravitational waves in the mid-frequency range between the peak sensitivities of the LISA and LIGO/Virgo/ KAGRA/INDIGO/Einstein Telescope/Cosmic Explorer experiments, and to probe other frontiers in fundamental physics. AION would complement other planned searches for dark matter, as well as probe mergers involving intermediate mass black holes and explore early universe cosmology. AION would share many technical features with the MAGIS experimental programme in the US, and synergies would flow from operating AION in a network with this experiment, as well as with other atom interferometer experiments such as MIGA, ZAIGA and ELGAR. Operating AION in a network with other gravitational wave detectors such as LIGO, Virgo and LISA would also offer many synergies.Combined CDF and D0 Upper Limits on Standard Model Higgs Boson Production with up to 8.2 fb$^-1$ of Data
Development, characterisation, and deployment of the SNO+ liquid scintillator
Abstract:
A liquid scintillator consisting of linear alkylbenzene as the solvent and 2,5-diphenyloxazole as the fluor was developed for the SNO+ experiment. This mixture was chosen as it is compatible with acrylic and has a competitive light yield to pre-existing liquid scintillators while conferring other advantages including longer attenuation lengths, superior safety characteristics, chemical simplicity, ease of handling, and logistical availability. Its properties have been extensively characterized and are presented here. This liquid scintillator is now used in several neutrino physics experiments in addition to SNO+.Investigating nonlinear integrable optics with a Paul trap
Abstract:
Designing high-intensity accelerators has traditionally relied on using computer simulations to study the beam dynamics. As intense beams are comprised of large numbers of particles, all interacting via Coulomb forces, such simulations require significant computational power in order to numerically predict these interactions. The Intense Beams Experiment (IBEX) is a linear Paul trap that can replicate the transverse beam dynamics in accelerators by trapping low-energy ions using RF electric fields that emulate the magnetic focusing elements of particle accelerators. IBEX’s flexibility allows different lattice designs and beam intensities to be tested with ease, which means that it can be used to test novel lattice configurations for high-intensity accelerators. Examples of such lattices arise from the theory of Nonlinear Integrable Optics, and, as discussed in this thesis, the related theory of Quasi-Integrable Optics (QIO). These theories suggest techniques for introducing nonlinear elements such as octupoles into an accelerator lattice, while keeping the system integrable and hence maintaining stable particle motion.
In this work, an upgrade to the original IBEX trap was designed, manufactured, and commissioned with the aim of experimentally testing the principles of QIO. Simulations were used to test the ability of a quasi-integrable lattice to damp a space-charge-driven coherent resonance without exciting the 4th order incoherent resonance in the vicinity. This lattice was then compared to a lattice which broke the integrability conditions, which was shown to excite the 4th order resonance. Using the newly-commissioned IBEX-2 trap, we were then able to test the quasi-integrable lattice experimentally and verify the results from simulations. This thesis demonstrates the first ions successfully trapped in a quasi-integrable lattice in a Paul trap, and discusses the benefits of introducing octupole elements according to the method prescribed by the theory of QIO. The experimental results presented here show the potential value of QIO to research on high-intensity beams in accelerators.