Latest results on differential cross sections as a function of kinematic variables at the LHC and Tevatron

An overview of recent measurements of differential top quark pair ($t\bar{t}$) production cross sections is presented, including results in boosted topologies and results both at parton and particle level. The first measurements of differential single top quark t-channel production cross sections in proton-proton collisions are as well presented. The results are obtained using data collected with the ATLAS and CMS experiments in proton-proton collisions at centre-of-mass energies of 7 TeV and 8 TeV. References to the latest results by the Tevatron experiments are also given. The data are compared with several predictions from perturbative QCD calculations up to approximate next-to-next-to-leading-order precision (approx. NNLO).Comment: 5 pages, 4 figures, TOP2014 Conferenc

ttˉ{\rm t\bar{t}} cross section measurements in CMS

An overview of the most recent measurements of inclusive top quark pair production cross section is presented. The results are obtained using data collected with the CMS experiment in proton-proton collisions at centre-of-mass energies of 5.02, 7, 8 and 13 TeV. The data are compared with the predictions from perturbative QCD calculations at full NNLO+NNLL accuracy.Comment: 6 pages, 5 figures, TOP2016 conferenc

Influence of low-density polyethylene addition on coking pressure

Different amounts of low-density polyethylene (LDPE) were added to a bituminous coal used to produce metallurgical coke. The effect of the plastic waste on the carbonization process and more exactly, on the coking pressure were investigated. A movable wall oven at semi-pilot scale was used for measuring coking pressure generated. It was found that coking pressure increases for low LDPE addition levels (1-3 wt.%); however higher amounts of LDPE reduce coking pressure. To explain this behavior different blends of the coal and the residue were pyrolysed at three different temperatures (450, 500 and 600 C) in a Gray-King apparatus. The results show that LDPE causes a modification in the pyrolysis process and also influences the swelling process of the plastic stage. The increase of the coking pressure at low LDPE addition rates is associated with a less permeable coal plastic layer, which prevents the removal of the decomposition products and causes their retention in the semicoke matrix, evolving them in the post-plastic stage. Coking pressure decrease at high LDPE addition rates can be due to the charge shrinkage and the better permeability to the migration of oil components, which suggest a lower interaction between the coal and the LDPE. A delay in the degradation of LDPE is confirmed by the data provided by DRIFT and SEM

Relevance of the composition of municipal plastic wastes for metallurgical coke production

This study is concerned with the effects of the composition of mixed plastic wastes on the thermoplastic properties of coal, the generation of coking pressure and the quality of the resulting cokes in a movable wall oven at semipilot scale. The mixed plastic wastes were selected to cover a wide spectrum in the relative proportions of high- and low-density polyethylenes (HDPE and LDPE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET). From the results it was deduced that the reduction in Gieseler fluidity in the coal blend is linked to the total amount of polyolefins in the waste. It was also found that these thermoplastics increase the pressure exerted against the wall in the course of the coking process and that coke quality is maintained or even improved. However, when the level of aromatic polymers such PS and PET are increased at the expense of polyolefins, the coking pressure decreases. Thus, the amount of aromatic polymers such as PS and PET in the waste is critical, not only for controlling Gieseler fluidity and coking pressure, but also for avoiding deterioration in coke quality (reactivity towards CO CRI and mechanical strength of the partially-gasified coke CSR). An amount of polyolefins in the waste lower than 65 wt.% for a secure coking pressure is established

Extended topological group structure due to average reflection symmetry

We extend the single-particle topological classification of insulators and superconductors to include systems in which disorder preserves average reflection symmetry. We show that the topological group structure of bulk Hamiltonians and topological defects is exponentially extended when this additional condition is met, and examine some of its physical consequences. Those include localization-delocalization transitions between topological phases with the same boundary conductance, as well as gapless topological defects stabilized by average reflection symmetry.Comment: 8 pages, 5 figures, 1 table; improved section 4 "Extended topological classification" incl. example of stacked QSH layer

Emergence of massless Dirac fermions in graphene's Hofstadter butterfly at switches of the quantum Hall phase connectivity

The fractal spectrum of magnetic minibands (Hofstadter butterfly), induced by the moir\'e super- lattice of graphene on an hexagonal crystal substrate, is known to exhibit gapped Dirac cones. We show that the gap can be closed by slightly misaligning the substrate, producing a hierarchy of conical singularities (Dirac points) in the band structure at rational values Phi = (p/q)(h/e) of the magnetic flux per supercell. Each Dirac point signals a switch of the topological quantum number in the connected component of the quantum Hall phase diagram. Model calculations reveal the scale invariant conductivity sigma = 2qe^2 / pi h and Klein tunneling associated with massless Dirac fermions at these connectivity switches.Comment: 4 pages, 6 figures + appendix (3 pages, 1 figure

Critical point for the CAF-F phase transition at charge neutrality in bilayer graphene

We report on magneto-transport measurements up to 30 T performed on a bilayer graphene Hall bar, enclosed by two thin hexagonal boron nitride flakes. Our high mobility sample exhibits an insulating state at neutrality point which evolves into a metallic phase when a strong in-plane field is applied, as expected for a transition from a canted antiferromagnetic to a ferromagnetic spin ordered phase. For the first time we individuate a temperature-independent crossing in the four-terminal resistance as a function of the total magnetic field, corresponding to the critical point of the transition. We show that the critical field scales linearly with the perpendicular component of the field, as expected from the underlying competition between the Zeeman energy and interaction-induced anisotropies. A clear scaling of the resistance is also found and an universal behavior is proposed in the vicinity of the transition

Bimodal conductance distribution of Kitaev edge modes in topological superconductors

A two-dimensional superconductor with spin-triplet p-wave pairing supports chiral or helical Majorana edge modes with a quantized (length $L$-independent) thermal conductance. Sufficiently strong anisotropy removes both chirality and helicity, doubling the conductance in the clean system and imposing a super-Ohmic $1/\sqrt{L}$ decay in the presence of disorder. We explain the absence of localization in the framework of the Kitaev Hamiltonian, contrasting the edge modes of the two-dimensional system with the one-dimensional Kitaev chain. While the disordered Kitaev chain has a log-normal conductance distribution peaked at an exponentially small value, the Kitaev edge has a bimodal distribution with a second peak near the conductance quantum. Shot noise provides an alternative, purely electrical method of detection of these charge-neutral edge modes.Comment: 11 pages, 13 figure