Browsing by Issue Date, starting with "2013-07-24"
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- Top quark physics: A tool for discoveriesPublication . Gallinaro, MicheleThe top quark, the heaviest known elementary particle discovered at the Fermilab Tevatron almost twenty years ago, has taken a central role in the study of fundamental interactions. The top quark behaves differently from all other quarks due to its large mass and its correspondingly short lifetime. Its large mass suggests that it may play a special role in nature. The top quark decays before it hadronizes, passing its spin information on to its decay products. Therefore, it is possible to measure observables that depend on the top quark spin, providing a unique environment for tests of the standard model and for new physics searches. With approximately 10 fb−1 of luminosity delivered to each experiment at the Tevatron, and about 20 fb−1 collected by the ATLAS and CMS experiments at the Large Hadron Collider in the first three years of operation, top quark physics is at a turning point from first studies to precision measurements with sensitivity to new physics processes. This report summarizes the latest experimental measurements and studies of top quark properties and rare decays.
- The SNO$+$ experiment: status and overviewPublication . Maneira, JoséSNO+ is a multi-purpose Neutrino Physics experiment, succeeding to the Sudbury Neutrino Observatory by replacing heavy water with liquid scintillator. Its scientific goals are the search for neutrinoless double-beta decay, the study of solar neutrinos and antineutrinos from reactors and the Earth's natural radioactivity, as well as supernovae neutrinos. The experimental advantages of SNO+ are the possibility of loading large quantities of double-beta decaying isotope in the liquid scintillator volume, and the very low backgrounds allowed by the deep underground location and radiopurity of the employed materials. The installation of the detector at SNOLAB is being completed, and commissioning has already started, with a dry run. Filling with water and later, with scintillator, will start next year. This talk will summarize the Physics goals of SNO+, as well as the main detector developments.
- MEtop – a top FCNC event generatorPublication . Coimbra, Rita; Onofre, António; Santos, Rui; Won, MiguelWe present a new Monte Carlo generator for Direct top and Single top production via flavour-changing neutral currents (FCNC). This new tool calculates the cross section and generates events with Next-to-Leading order precision for the Direct top process and Leading-Order precision for all other FCNC single top processes. A set of independent dimension six FCNC operators has been implemented - including four-fermion operators - where at least one top-quark is present in the interaction.
- Overview of Recent ATLAS Physics ResultsPublication . Conde Muíño, PatriciaThe ATLAS experiment is situated at the Large Hadron Collider at CERN (Geneva). It was designed to cover a wide range of physics topics, such as precision measurements of Standard Model physics, the determination of the Electroweak Symmetry Breaking mechanism through the search for the Higgs boson, and searches for new physics beyond the Standard Model, like super-symmetric particles. ATLAS started operation at the LHC at the end of 2009, collecting poton-proton collisions at 7 and 8 TeV centre of mass energies. In this paper a summary of some of the most interesting recent physics ATLAS results will be presented.
- Measurement of the properties of the 125 GeV Higgs boson with the CMS detectorPublication . Varela, JoãoThe measurement of the properties of the recently discovered boson is central to the LHC physics program. In this contribution we review preliminary measurements of the properties of the new 125 GeV boson performed by the CMS experiment using the full proton-proton dataset collected in 2011–12 (~25 fb−1). In the H → ZZ (4l) channel, a signal significance of 6.7σ is now observed. In the other high-resolution mode, H → γγ, updated results were obtained on the signal strength, μ = σ/σSM, which is now measured to be ~0.8 ± 0.3. The two high-resolution modes allowed independent determinations of the Higgs mass: 125.8±0.6 GeV, in H → ZZ (4l); and 125.4±0.8 GeV, in H → γγ. The four-lepton channel permitted tests of the spin-parity of the new boson. From these studies, the pure pseudoscalar hypothesis is excluded at 99.8% C.L. and, for the first time, simple spin 2 models are excluded with greater than 98.5% C.L. Significantly, strong evidence is seen in a fermionic decay mode of the Higgs for the first time, namely in the H → ττ channel, which is reported with a significance of nearly 3σ. The new measurements of the spin-parity (JP) assignments for this particle, coupled with the measured strength of the interaction of this particle with other particles, strongly indicates that the new particle is a Higgs boson, responsible for the Electroweak Symmetry Breaking. While all of these measurements are consistent with values predicted for a SM Higgs boson, they still fall far short of the requisite precision to rule out all BSM scenarios. Additional data from Run 2 of the LHC and HL-LHC will be needed to firmly establish this conclusion.