arXiv subjects

C. Arnault

Publications and source records attributed to C. Arnault.

5 recordsLinked to original sources

arXiv2022

Scaling pair count to next galaxy surveys

Counting pairs of galaxies or stars according to their distance is at the core of real-space correlation analyzes performed in astrophysics and cosmology. Upcoming galaxy surveys (LSST, Euclid) will measure properties of billions of galaxies challenging our ability to perform such counting in a minute-scale time relevant for the usage of simulations. The problem is only limited by efficient access to the data, hence belongs to the big data category. We use the popular Apache Spark framework to address it and design an efficient high-throughput algorithm to deal with hundreds of millions to billions of input data. To optimize it, we revisit the question of nonhierarchical sphere pixelization based on cube symmetries and develop a new one dubbed the "Similar Radius Sphere Pixelization" (SARSPix) with very close to square pixels. It provides the most adapted indexing over the sphere for all distance-related computations. Using LSST-like fast simulations, we compute autocorrelation functions on tomographic bins containing between a hundred million to one billion data points. In each case we achieve the construction of a standard pair-distance histogram in about 2 minutes, using a simple algorithm that is shown to scale, over a moderate number of nodes (16 to 64). This illustrates the potential of this new techniques in the field of astronomy where data access is becoming the main bottleneck. They can be easily adapted to other use-cases as nearest-neighbors search, catalog cross-match or cluster finding. The software is publicly available from https://github.com/astrolabsoftware/SparkCorr.

astro-ph.IM↗

arXiv2019

Analyzing billion-objects catalog interactively: Apache Spark for physicists

Apache Spark is a Big Data framework for working on large distributed datasets. Although widely used in the industry, it remains rather limited in the academic community or often restricted to software engineers. The goal of this paper is to show with practical uses-cases that the technology is mature enough to be used without excessive programming skills by astronomers or cosmologists in order to perform standard analyses over large datasets, as those originating from future galaxy surveys. To demonstrate it, we start from a realistic simulation corresponding to 10 years of LSST data taking (6 billions of galaxies). Then, we design, optimize and benchmark a set of Spark python algorithms in order to perform standard operations as adding photometric redshift errors, measuring the selection function or computing power spectra over tomographic bins. Most of the commands execute on the full 110 GB dataset within tens of seconds and can therefore be performed interactively in order to design full-scale cosmological analyses. A jupyter notebook summarizing the analysis is available at https://github.com/astrolabsoftware/1807.03078.

astro-ph.IM↗

arXiv2012

PHIL photoinjector test line

LAL is now equiped with its own platform for photoinjectors tests and Research and Developement, named PHIL (PHotoInjectors at LAL). This facility has two main purposes: push the limits of the photoinjectors performances working on both the design and the associated technology and provide a low energy (MeV) short pulses (ps) electron beam for the interested users. Another very important goal of this machine will be to provide an opportunity to form accelerator physics students, working in a high technology environment. To achieve this goal a test line was realised equipped with an RF source, magnets and beam diagnostics. In this article we will desrcibe the PHIL beamline and its characteristics together with the description of the first two photoinjector realised in LAL and tested: the ALPHAX and the PHIN RF Guns.

physics.acc-ph↗

arXiv2009

Expected Performance of the ATLAS Experiment - Detector, Trigger and Physics

A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN.

hep-ex↗

arXiv2003

Use of a Generic Identification Scheme Connecting Events and Detector Description in the ATLAS Experiment

High energy physics detectors can be described hierarchically from the different subsystems to their divisions in r, phi, theta and to the individual readout channels. An identification schema that follows the logical decomposition of the ATLAS detector has been introduced allowing identification of individual readout channels as well as other parts of the detector, in particular detector elements. These identifiers provide a sort of ?glue? allowing, for example, the connection of raw event data to their detector description for position calculation or alignment corrections, as well as fast access to subsets of the event data for event trigger selection. There are two important requirements on the software to support such an identification scheme. First is the possibility to formally specify these identifiers in terms of their structure and allowed values. And second is to generate different forms of the identifiers optimised in terms of access efficiency to information content, compactness or search key efficiency. We present here the generic toolkit developed in the context of the ATLAS experiment to primarily provide the identification of the readout channels and detector elements. The architecture of the toolkit is decomposed into three parts: an XML-based dictionary containing the formal specification of a particular range of identifiers, a set of various identifier classes (offering various level of compaction), and finally a set of ?helper? classes, specific for each detector system, which serve as intermediaries between the dictionary and the identifier classes to create, manipulate and interpret the identifiers. This architecture will be described as well as the various applications of this identification scheme.

physics.comp-ph↗