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The possible usage of HPC resources by ATLAS is now becoming viable due to the changing nature of these systems and it is also very attractive due to the need for increasing amounts of simulated data. In recent years the architecture of HPC systems has evolved, moving away from specialized monolithic systems, to a more generic linux type platform. This change means that the deployment of non HPC specific codes has become much easier. The timing of this evolution perfectly suits the needs of ATLAS and opens a new window of opportunity. The ATLAS experiment at CERN will begin a period of high luminosity data taking in 2015. This high luminosity phase will be accompanied by a need for increasing amounts of simulated data which is expected to exceed the capabilities of the current Grid infrastructure. ATLAS aims to address this need by opportunistically accessing resources such as cloud and HPC systems. This paper presents the results of a pilot project undertaken by ATLAS and the MPP RZG to provide access to the HYDRA supercomputer facility. Hydra is the supercomputer of the Max Planck Society, it is a linux based supercomputer with over 80000 cores and 4000 physical nodes located at the RZG near Munich. This paper describes the work undertaken to integrate Hydra into the ATLAS production system by using the Nordugrid ARC-CE and other standard Grid components. The customization of these components and the strategies for HPC usage are discussed as well as possibilities for future directions.

In a grid computing infrastructure tasks such as continuous upgrades, services installations and software deployments are part of an admins daily work. In such an environment tools to help with the management, provisioning and monitoring of the deployed systems and services have become crucial. As experiments such as the LHC increase in scale, the computing infrastructure also becomes larger and more complex. Moreover, today's admins increasingly work within teams that share responsibilities and tasks. Such a scaled up situation requires tools that not only simplify the workload on administrators but also enable them to work seamlessly in teams. In this paper will be presented our experience from managing the Max Planck Institute Tier2 using Puppet and Gitolite in a cooperative way to help the system administrator in their daily work. In addition to describing the Puppet-Gitolite system, best practices and customizations will also be shown.

The production rates of prompt and non-prompt J/psi and psi(2S) mesons in their dimuon decay modes are measured using 2.1 and 11.4 fb(-1) of data collected with the ATLAS experiment at the Large Hadron Collider, in proton-proton collisions at root s = 7 and 8 respectively. Production cross-sections for prompt as well as non-prompt sources, ratios of psi(2S) to J/psi production, and the fractions of non-prompt production for J/psi and psi(2S) are measured as a function of meson transverse momentum and rapidity. The measurements are compared to theoretical predictions.

The Young Researcher Meeting (www.yrmr.it) has been a rapidly growing event for the last few years. Together with other initiatives which have emerged in several research areas, the young researcher meeting marks the awareness and the desire of PhD students, postdoctoral fellows and young researchers to play a major role in scientific progress. Devoted to the discussion and the interchange of new developments and ideas in physics, the meeting is primarily aimed at graduate students and postdoctoral researchers, who are encouraged to present their work in an informal atmosphere. One of the main purposes of the conference is to create an international network of young researchers, both experimentalists and theorists, and fruitful collaborations across the different branches of physics. Born in Rome in 2009, after three editions that strengthened it, the Young Researcher Meeting 2013 was held in Trieste. Propelled by the past success, the fourth meeting was a two-day conference on 3–4June. It was sponsored by the International School for Advanced Studies – SISSA – and the University of Padova, thus acquiring an even further international drive. In this volume, we collect some of the contributions that were presented at the conference. They cover topics in astrophysics and cosmology, particle and theoretical physics, soft and condensed matter, biophysics and medical physics. YRM Organising and Editorial Committee Fabio Agostini (fabio.agostini@roma2.infn.it) Dipartimento di Fisica, Università di Roma 'Tor Vergata' Via della Ricerca Scientifica 1, 00133 Roma, Italy Claudia Antolini (claudia.antolini@sissa.it) SISSA - Scuola Internazionale Superiore di Studi Avanzati Via Bonomea 265, 34136 Trieste, Italy Rossella Aversa (raversa@sissa.it) SISSA - Scuola Internazionale Superiore di Studi Avanzati Via Bonomea 265, 34136 Trieste, Italy Giordano Cattani (giordano.cattani@gmail.com) Matteo Martinelli (mmartin@sissa.it) SISSA - Scuola Internazionale Superiore di Studi Avanzati Via Bonomea 265, 34136 Trieste, Italy Luca Mazzaferro (luca.mazzaferro@roma2.infn.it) Dipartimento di Fisica, Università di Roma 'Tor Vergata' Via della Ricerca Scientifica 1, 00133 Roma, Italy Marina Migliaccio (mm858@ast.cam.ac.uk) Institute of Astronomy and Kavli Institute for Cosmology Madingley Road, CB3 0HA Cambridge, United Kingdom Francesco Paci (fpaci@sissa.it) SISSA - Scuola Internazionale Superiore di Studi Avanzati Via Bonomea 265, 34136 Trieste, Italy Davide Pietrobon (davide.pietrobon@jpl.nasa.gov) California Institute of Technology - Jet Propulsion Laboratory 4800 Oak Grove Drive 169-237 91109 Pasadena, CA, USA Daniel Ricci Pacifici (Daniel.Ricci.Pacifici@pd.infn.it) Dipartimento di Fisica e Astronomia, Università degli Studi di Padova INFN, Sezione di Padova Via Marzolo 8, 35131, Padova, Italy Francesco Stellato (francesco.stellato@cfel.de) Center for Free-Electron Laser Science, DESY Notkestrase 85, 22607 Hamburg, Germany Marcella Veneziani (marcella@ipac.caltech.edu) Infrared Processing and Analysis Center California Institute of Technology 1200 E California Blvd, Pasadena, CA 91125, USA Acknowledgments The organizers of the 4th Young Researcher Meeting, held in Trieste, would like to thank all the scientists who participated in the meeting. We thank the International School for Advanced Studies (SISSA) for hosting the conference, covering the organization costs and allowing some travel grants for the speakers. We are greateful to Professor Guido Martinelli, director of SISSA, for his valuable support and advice. The publication of the proceedings of the conference is sponsored by the Padova university project CPDA119349 (P I Professor Marco Matone). The event was broadcast live by OggiScienza (http://oggiscienza.wordpress.com).

The differential cross section for the process $Z/\\gamma^*\\rightarrow ll$ ($l=e,\\mu$) as a function of dilepton invariant mass is measured in pp collisions at $\\sqrt{s}=$7 TeV at the LHC using the ATLAS detector. The measurement is performed in the $e$ and $\\mu$ channels for invariant masses between 26 GeV and 66 GeV using an integrated luminosity of 1.6 fb$^{-1}$ collected in 2011 and these measurements are combined. The analysis is extended to invariant masses as low as 12 GeV in the muon channel using 35 pb$^{-1}$ of data collected in 2010. The cross sections are determined within fiducial acceptance regions and corrections to extrapolate the measurements to the full kinematic range are provided. Next-to-next-to-leading-order QCD predictions provide a significantly better description of the results than next-to-leading-order QCD calculations, unless the latter are matched to a parton shower calculation.