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Geneva, Switzerland

The European Organization for Nuclear Research , known as CERN is a European research organization that operates the largest particle physics laboratory in the world. Established in 1954, the organization is based in the northwest suburbs of Geneva on the Franco–Swiss border, and has 21 European member states. Israel is the first non-European country granted full membership.The term CERN is also used to refer to the laboratory, which in 2013 counted 2,513 staff members, and hosted some 12,313 fellows, associates, apprentices as well as visiting scientists and engineers representing 608 universities and research facilities and 113 nationalities.CERN's main function is to provide the particle accelerators and other infrastructure needed for high-energy physics research – as a result, numerous experiments have been constructed at CERN following international collaborations.CERN is also the birthplace of the World Wide Web. The main site at Meyrin has a large computer centre containing powerful data processing facilities, primarily for experimental-data analysis; because of the need to make these facilities available to researchers elsewhere, it has historically been a major wide area networking hub. Wikipedia.

Bird I.,CERN
Annual Review of Nuclear and Particle Science | Year: 2011

Following the first full year of Large Hadron Collider (LHC) data taking, the Worldwide LHC Computing Grid (WLCG) computing environment built to support LHC data processing and analysis has been validated. In this review, I discuss the rationale for the design of a distributed system and describe how this environment was constructed and deployed through the use of grid computing technologies. I discuss the experience with large-scale testing and operation with real accelerator data, which shows that expectations have been met and sometimes exceeded. The computing system's key achievements are that (a) the WLCG infrastructure is distributed and makes use of all the dispersed resources, (b) the experiments' computing models are also distributed and can make excellent use of the infrastructure, and (c) the computing system has enabled physics output in a very short time. Finally, I present prospects for the future evolution of the WLCG infrastructure. © 2011 by Annual Reviews. All rights reserved. Source

We present the complete next-to-leading-order (NLO) contributions to the pp→e+νeμ-ν̄μbb̄+X process in the four-flavor scheme, i.e., with massive b quarks, and its contribution to the H→WW(*) →llνν measurement in the 1-jet bin at the LHC. This background process includes top pair, single top, and non-top-quark resonant contributions. The uncertainty at NLO from the renormalization and factorization scale dependence is about +30%-20%. We show that the NLO corrections are relatively small, and that separating this background in top pair, Wt- and b-quark-associated llνν production is a fair approximation. © 2014 American Physical Society. Source

Schwaller P.,CERN
Physical Review Letters | Year: 2015

In this work, we show that a large class of models with a composite dark sector undergo a strong first order phase transition in the early Universe, which could lead to a detectable gravitational wave signal. We summarize the basic conditions for a strong first order phase transition for SU(N) dark sectors with nf flavors, calculate the gravitational wave spectrum and show that, depending on the dark confinement scale, it can be detected at eLISA or in pulsar timing array experiments. The gravitational wave signal provides a unique test of the gravitational interactions of a dark sector, and we discuss the complementarity with conventional searches for new dark sectors. The discussion includes the twin Higgs and strongly interacting massive particle models as well as symmetric and asymmetric composite dark matter scenarios. © 2015 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "http://creativecommons.org/licenses/by/3.0/" Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. © American Physical Society 2015. Source

Skands P.Z.,CERN
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2010

We present 9 new tunes of the p-ordered shower and underlying-event model in Pythia 6.4. These "Perugia" tunes update and supersede the older "S0" family. The data sets used to constrain the models include hadronic Z0 decays at LEP, Tevatron min-bias data at 630, 1800, and 1960 GeV, Tevatron Drell-Yan data at 1800 and 1960 GeV, and SPS min-bias data at 200, 546, and 900 GeV. In addition to the central parameter set, called "Perugia 0," we introduce a set of 8 related "Perugia variations" that attempt to systematically explore soft, hard, parton density, and color structure variations in the theoretical parameters. Based on these variations, a best-guess prediction of the charged track multiplicity in inelastic, nondiffractive minimum-bias events at the LHC is made. Note that these tunes can only be used with Pythia 6, not with Pythia 8. © 2010 The American Physical Society. Source

Zapp K.C.,CERN
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

In this publication the performance of the Monte Carlo event generator Jewel in non-central heavy-ion collisions is investigated. Jewel is a consistent perturbative framework for jet evolution in the presence of a dense medium. It yields a satisfactory description of a variety of jet observables in central collisions at the LHC, although so far with a simplistic model of the medium. Here, it is demonstrated that also jet measurements in non-central collisions, and in particular the dependence of the jet suppression on the angle relative to the reaction plane, are reproduced by the same model. © 2014 Elsevier B.V. Source

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