Ref Arxiv: 1407.1796
DOI: 10.1103/PhysRevD.90.052007
WoS: 000342147500002
Ref. & Cit.: NASA ADS
17 Citations
Résumé:

A measurement of the $B_s \rightarrow J/\psi \phi$ decay parameters, updated to include flavour tagging is reported using $4.9 fb^{-1}$ of integrated luminosity collected by the ATLAS detector from $\sqrt{s}= 7$TeV $pp$ collisions recorded in 2011 at the LHC. The values measured for the physical parameters are: \begin{eqnarray*} \phi_s & = & 0.12 \pm 0.25(stat.)\pm 0.05(syst.)rad \\ \Delta\Gamma & = & 0.053 \pm 0.021(stat.) 0.010(syst.)ps^{-1} \\ \Gamma_s & = & 0.677 \pm 0.007 (stat.)\pm 0.004 (syst.)ps^{-1}\\ |A_{\parallel}(0)|^2 & = & 0.220 \pm 0.008 (stat.)\pm 0.009(syst.)\\ |A_{0}(0)|^2 & = & 0.529 \pm 0.006 (stat.)\pm 0.012(syst.)\\ \delta_\perp & = & 3.89 \pm 0.47(stat.) \pm 0.11(syst.)rad \end{eqnarray*} where the parameter $\Delta\Gamma$ is constrained to be positive. The $S$-wave contribution was measured and found to be compatible with zero. Results for $\phi_s$ and $\Delta\Gamma$ are also presented as $68\%$ and $95\%$ likelihood contours, which show agreement with the Standard Model expectations.

Commentaires: 26 pages plus author list + cover pages (54 pages total), 9 figures, 7 tables, submitted to PRD, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2013-01/ - See paper for full list of authors

Ref Arxiv: 1406.7690
DOI: 10.1088/1748-0221/9/09/P09009
WoS: 000343281300046
Ref. & Cit.: NASA ADS
15 Citations
Résumé:

A novel technique to identify and split clusters created by multiple charged particles in the ATLAS pixel detector using a set of artificial neural networks is presented. Such merged clusters are a common feature of tracks originating from highly energetic objects, such as jets. Neural networks are trained using Monte Carlo samples produced with a detailed detector simulation. This technique replaces the former clustering approach based on a connected component analysis and charge interpolation. The performance of the neural network splitting technique is quantified using data from proton--proton collisions at the LHC collected by the ATLAS detector in 2011 and from Monte Carlo simulations. This technique reduces the number of clusters shared between tracks in highly energetic jets by up to a factor of three. It also provides more precise position and error estimates of the clusters in both the transverse and longitudinal impact parameter resolution.

Commentaires: See paper for full list of authors - 6 pages plus author list + cover pages (38 pages total), 10 figures, 0 tables, submitted to JINST, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/PERF-2012-05

Ref Arxiv: 1407.0583
DOI: 10.1007/JHEP11(2014)118
WoS: 000347908700001
Ref. & Cit.: NASA ADS
149 Citations
Résumé:

The results of a search for top squark (stop) pair production in final states with one isolated lepton, jets, and missing transverse momentum are reported. The analysis is performed with proton-proton collision data at $\sqrt{s}=$ 8 TeV collected with the ATLAS detector at the LHC in 2012 corresponding to an integrated luminosity of 20 fb$^{-1}$. The lightest supersymmetric particle (LSP) is taken to be the lightest neutralino which only interacts weakly and is assumed to be stable. The stop decay scenarios considered are those to a top quark and the LSP as well as to a bottom quark and the lightest chargino, where the chargino decays to the LSP by emitting a W boson. A wide range of scenarios with different mass splittings between the stop, the lightest neutralino and the lightest chargino are considered, including cases where the W bosons or the top quarks are off-shell. Decay scenarios involving the heavier charginos and neutralinos are addressed using a set of phenomenological models of supersymmetry. No significant excess over the Standard Model prediction is observed. A stop with a mass between 210 and 640 GeV decaying directly to a top quark and a massless LSP is excluded at 95% confidence level, and in models where the mass of the lightest chargino is twice that of the LSP, stops are excluded at 95% confidence level up to a mass of 500 GeV for an LSP mass in the range of 100 to 150 GeV. Stringent exclusion limits are also derived for all other considered stop decay scenarios, and generic upper limits are set on the visible cross-section for processes beyond the Standard Model.

Commentaires: See paper for full list of authors - 71 pages plus author list + cover page (94 pages total), 25 figures, 20 tables, submitted to JHEP, All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2013-15/

Ref Arxiv: 1407.0608
DOI: 10.1103/PhysRevD.90.052008
WoS: 000342148000001
Ref. & Cit.: NASA ADS
127 Citations
Résumé:

Results of a search for supersymmetry via direct production of third-generation squarks are reported, using $20.3$ fb$^{-1}$ of proton-proton collision data at $\sqrt{s} = 8$ TeV recorded by the ATLAS experiment at the LHC in 2012. Two different analysis strategies based on monojet-like and $c$-tagged event selections are carried out to optimize the sensitivity for direct top squark pair production in the decay channel to a charm quark and the lightest neutralino ($\tilde{t}_1 \to c + \tilde{\chi}_{1}^{0}$) across the top squark--neutralino mass parameter space. No excess above the Standard Model background expectation is observed. The results are interpreted in the context of direct pair production of top squarks and presented in terms of exclusion limits in the ($m_{\tilde{t}_1}$, $m_{\tilde{\chi}_{1}^{0}}$) parameter space. A top squark of mass up to about 240 GeV is excluded at 95$\%$ confidence level for arbitrary neutralino masses, within the kinematic boundaries. Top squark masses up to 270 GeV are excluded for a neutralino mass of 200 GeV. In a scenario where the top squark and the lightest neutralino are nearly degenerate in mass, top squark masses up to 260 GeV are excluded. The results from the monojet-like analysis are also interpreted in terms of compressed scenarios for top squark pair production in the decay channel $\tilde{t}_1 \to b + ff^{'} + \tilde{\chi}^{0}_{1}$ and sbottom pair production with $\tilde{b}_1 \to b + \tilde{\chi}^{0}_{1}$, leading to a similar exclusion for nearly mass-degenerate third-generation squarks and the lightest neutralino. The results in this paper significantly extend previous results at colliders.

Commentaires: See paper for full list of authors - 24 pages + author list + 1 cover page (35 pages in total), 11 figures, 9 tables, submitted to Physical Review D, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/SUSY-2013-21/

Ref HAL: hal-01025923_v1
PMID 25019770
Ref Arxiv: 1403.3410
DOI: 10.1103/PhysRevE.89.062301
WoS: 000336979500008
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
85 Citations
Résumé:

We introduce a kinetic Monte-Carlo model for self-propelled hard disks to capture with minimal ingredients the interplay between thermal fluctuations, excluded volume and self-propulsion in large assemblies of active particles. We analyze in detail the resulting (density, self-propulsion) nonequilibrium phase diagram over a broad range of parameters. We find that purely repulsive hard disks spontaneously aggregate into fractal clusters as self-propulsion is increased, and rationalize the evolution of the average cluster size by developing a kinetic model of reversible aggregation. As density is increased, the nonequilibrium clusters percolate to form a ramified structure reminiscent of a physical gel. We show that the addition of a finite amount of noise is needed to trigger a nonequilibrium phase separation, showing that demixing in active Brownian particles results from a delicate balance between noise, interparticle interactions and self-propulsion. We show that self-propulsion has a profound influence on the dynamics of the active fluid. We find that the diffusion constant has a nonmonotonic behaviour as self-propulsion is increased at finite density and that activity produces strong deviations from Fickian diffusion that persist over large time scales and length scales, suggesting that systems of active particles generically behave as dynamically heterogeneous systems.

Commentaires: 17 pages, 13 figures Journal: Phys. Rev. E 89, 062301 (2014)

Ref HAL: hal-01023271_v1
Ref Arxiv: 1407.3222
DOI: 10.1016/j.actamat.2014.04.057
WoS: 000340854200019
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
9 Citations
Résumé:

In this work, we report on the addition of GeH4 gas during homoepitaxial growth of 4H-SiC by chemical vapour deposition. Ge introduction does not affect dramatically the surface morphology and defect density though it is accompanied with Ge droplets accumulation at the surface. The Ge incorporation level inside the 4H-SiC matrix, ranging from few 1017 to few 1018 at.cm-3, was found to be mainly affected by the growth temperature and GeH4 flux. Other growth parameters like C/Si ratio, polarity, or off-orientation did not show any significant influence. On the other hand, adding GeH4 led to the increase of the intentional n type doping level by a factor of 2 to 5 depending on the C/Si ratio in the gas phase.

Commentaires: 8 pages

Ref HAL: hal-01022581_v1
DOI: 10.1021/bm500345u
WoS: 000337497100026
Exporter : BibTex | endNote
153 Citations
Résumé:

Monolithic pectin aerogels, aeropectins, were prepared via dissolution gelation coagulation and subsequent drying with supercritical CO2. Aeropectin had pore sizes that varied from mesopores to small macropores and compression moduli in the range from 4 to 18 MPa. Aeropectins show plastic deformation up to 60% strain before the pore walls collapse. Pectin aerogels have a thermal conductivity below that of air in ambient conditions, making them new thermal superinsulating fully biomass-based materials. The contribution of gas and solid conduction plus radiative heat transfer were determined and discussed.