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The development of X-ray and electron diffraction methods with ultrahigh time resolution has made it possible to map directly, at the atomic level, structural changes in solids induced by laser excitation. This has resulted in unprecedented insights into the lattice dynamics of solids undergoing phase transitions. In aluminium, for example, femtosecond optical excitation hardly affects the potential energy surface of the lattice; instead, melting of the material is governed by the transfer of thermal energy between the excited electrons and the initially cold lattice. In semiconductors, in contrast, exciting approximately 10 per cent of the valence electrons results in non-thermal lattice collapse owing to the antibonding character of the conduction band. These different material responses raise the intriguing question of how Peierls-distorted systems such as bismuth will respond to strong excitations. The evolution of the atomic configuration of bismuth upon excitation of its A(1g) lattice mode, which involves damped oscillations of atoms along the direction of the Peierls distortion of the crystal, has been probed, but the actual melting of the material has not yet been investigated. Here we present a femtosecond electron diffraction study of the structural changes in crystalline bismuth as it undergoes laser-induced melting. We find that the dynamics of the phase transition depend strongly on the excitation intensity, with melting occurring within 190 fs (that is, within half a period of the unperturbed A(1g) lattice mode) at the highest excitation. We attribute the surprising speed of the melting process to laser-induced changes in the potential energy surface of the lattice, which result in strong acceleration of the atoms along the longitudinal direction of the lattice and efficient coupling of this motion to an unstable transverse vibrational mode. That is, the atomic motions in crystalline bismuth can be electronically accelerated so that the solid-to-liquid phase transition occurs on a sub-vibrational timescale.

A search for charged and neutral excited leptons is performed in 217 pb−1 of e+e− collision data collected with the L3 detector at LEP at centre-of-mass energies from 202 up to 209 GeV. The pair- and single-production mechanisms of excited electrons, muons and taus, as well as of excited electron-, muon- and tau-neutrinos, are investigated and no signals are detected. Combining with L3 results from searches at lower centre-of-mass energies, gives improved limits on the masses and couplings of excited leptons. Facultad de Ciencias Exactas

A search for a chargino-neutralino pair decaying via the 125 GeV Higgs boson into photons is presented. The study is based on the data collected between 2015 and 2018 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 139 fb(-1) of pp collisions at a centre-of-mass energy of 13 TeV. No significant excess over the expected background is observed. Upper limits at 95% confidence level for a massless (chi) over tilde (0)(1) are set on several electroweakino production cross-sections and the visible cross-section for beyond the Standard Model processes. In the context of simplified supersymmetric models, 95% confidence-level limits of up to 310 GeV in m((chi) over tilde (+/-)(1)/(chi) over tilde (0)(2)), where m((chi) over tilde (0)(1)) = 0.5 GeV, are set. Limits at 95% confidence level are also set on the (chi) over tilde (+/-)(1)(chi) over tilde (0)(2) cross-section in the mass plane of m((chi) over tilde (+/-)(1)/(chi) over tilde (0)(2)) and m((chi) over tilde (0)(1)), and on scenarios with gravitino as the lightest supersymmetric particle. Upper limits at the 95% confidence-level are set on the higgsino production cross-section. Higgsino masses below 380 GeV are excluded for the case of the higgsino fully decaying into a Higgs boson and a gravitino. Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science Ministry of Education, Youth & Sports - Czech Republic Czech Republic Government Netherlands Organization for Scientific Research (NWO) Netherlands Government Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Departamento Administrativo de Ciencia, Tecnología e Innovación Colciencias Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) National Council for Scientific and Technological Development (CNPq) German-Israeli Foundation for Scientific Research and Development Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) Natural Sciences and Engineering Research Council of Canada European Union (EU) European Research Council (ERC) National Natural Science Foundation of China (NSFC) Centre National de la Recherche Scientifique (CNRS) Ministry of Science and Higher Education, Poland Portuguese Foundation for Science and Technology PROMETEO Programme Generalitat Valenciana, Spain Ministry of Energy & Natural Resources - Turkey CERCA Programme Generalitat de Catalunya, Spain Federal Ministry of Education & Research (BMBF) Science & Technology Facilities Council (STFC) Azerbaijan National Academy of Sciences (ANAS) Istituto Nazionale di Fisica Nucleare (INFN) Ministry of Science and Technology, Taiwan Ministry of Science and Technology, China United States Department of Energy (DOE) Swiss National Science Foundation (SNSF) Danish Natural Science Research Council French National Research Agency (ANR) Herakleitos program - EU-ESF, Greece Slovenian Research Agency - Slovenia Goran Gustafssons Stiftelse, Sweden Greek Ministry of Development-GSRT National Science Foundation (NSF) Aristeia program - EU-ESF, Greece German Research Foundation (DFG) Canada Foundation for Innovation MES of Russia, Russia Federation Thales program - EU-ESF, Greece Wallenberg Foundation, Sweden Canton of Geneva, Switzerland Horizon 2020, European Union Canton of Bern, Switzerland Australian Research Council Austrian Science Fund (FWF) Chinese Academy of Sciences Israel Science Foundation NRC KI, Russia Federation Czech Republic Government Royal Society of London Benoziyo Center, Israel Compute Canada, Canada DST/NRF, South Africa Hong Kong SAR, China COST, European Union CEA-DRF/IRFU, France Greek NSRF, Greece Max Planck Society SERI, Switzerland Leverhulme Trust MNE/IFA, Romania SRNSFG, Georgia BSF-NSF, Israel CANARIE, Canada YerPhI, Armenia MSSR, Slovakia BMWFW, Austria CNRST, Morocco MIZS, Slovenia BCKDF, Canada DNRF, Denmark MESTD, Serbia SSTC, Belarus MINECO, Spain HGF, Germany RCN, Norway NCN, Poland NRC, Canada CRC, Canada SRC, Sweden RGC, China ANPCyT CERN JINR

Although liquid water is ubiquitous in chemical reactions at roots of life and climate on the earth, the prediction of its properties by high-level ab initio molecular dynamics simulations still represents a formidable task for quantum chemistry. In this article, we present a room temperature simulation of liquid water based on the potential energy surface obtained by a many-body wave function through quantum Monte Carlo (QMC) methods. The simulated properties are in good agreement with recent neutron scattering and X-ray experiments, particularly concerning the position of the oxygen-oxygen peak in the radial distribution function, at variance of previous density functional theory attempts. Given the excellent performances of QMC on large scale supercomputers, this work opens new perspectives for predictive and reliable ab initio simulations of complex chemical systems.

The cross section for the production of W bosons with subsequent decay W to tau nu is measured with the ATLAS detector at the LHC. The analysis is based on a data sample that was recorded in 2010 at a proton-proton center-of-mass energy of sqrt(s) = 7 TeV and corresponds to an integrated luminosity of 34 pb^-1. The cross section is measured in a region of high detector acceptance and then extrapolated to the full phase space. The product of the total W production cross section and the W to tau nu branching ratio is measured to be 11.1 +/- 0.3 (stat) +/- 1.7 (syst) +/- 0.4 (lumi) nb.

We measure the $D^0 - {\bar{D}}^0$ mixing parameters using a time-dependent amplitude analysis of the decay $D^0\to\pi^+\pi^-\pi^0$. The data were recorded with the BABAR detector at center-of-mass energies at and near the $\Upsilon(4S)$ resonance, and correspond to an integrated luminosity of approximately 468.1 ${\rm fb}^{-1}$. The neutral $D$ meson candidates are selected from $D^{*}(2010)^+\to D^0 \pi_s^+$ decays where the flavor at the production is identified by the charge of the low momentum pion, $\pi_s^+$. The measured mixing parameters are $x = (1.5\pm1.2\pm0.6) \%$ and $y = (0.2\pm0.9\pm0.5) \%$, where the quoted uncertainties are statistical and systematic, respectively.