The ATLAS Trigger and data acquisition system has been designed to use more than 2000 CPUs. During the current development stage it is crucial to test the system on a number of CPUs of similar scale. ...A dedicated farm of this size is difficult to find, and can only be made available for short periods. On the other hand many large farms have become available recently as part of computing grids, leading to the idea of using them to test the TDAQ system of ATLAS. However the task of adapting the TDAQ system to run on the Grid is not trivial, as it requires full access to the computing resources it runs on and real-time interaction. Moreover the Grid virtualises the resources to present a common interface to the user. We will describe the implementation and first tests of a scheme that resolves these issues using a pilot job mechanism. The Tier2 cluster in Manchester was successfully used to run a full TDAQ system on 400 nodes using this implementation. Apart from the tests described above, this scheme also has great potential for other applications, like running Grid remote farms to perform detector calibration and monitoring in real-time, and automatic nightly testing of the TDAQ system.
ATLAS offline data quality monitoring Adelman, J; Baak, M; Boelaert, N ...
Journal of physics. Conference series,
04/2010, Letnik:
219, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The ATLAS experiment at the Large Hadron Collider reads out 100 Million electronic channels at a rate of 200 Hz. Before the data are shipped to storage and analysis centres across the world, they ...have to be checked to be free from irregularities which render them scientifically useless. Data quality offline monitoring provides prompt feedback from full first-pass event reconstruction at the Tier-0 computing centre and can unveil problems in the detector hardware and in the data processing chain. Detector information and reconstructed proton-proton collision event characteristics are distilled into a few key histograms and numbers which are automatically compared with a reference. The results of the comparisons are saved as status flags in a database and are published together with the histograms on a web server. They are inspected by a 24/7 shift crew who can notify on-call experts in case of problems and in extreme cases signal data taking abort.
The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of efficiently selecting interesting candidate events in pp collisions at 14 TeV centre-of-mass energy, whilst ...rejecting the enormous number of background events. The High-Level-Trigger (HLT second level trigger and Event Filter), which is a software based trigger will need to reduce the first level trigger output rate of kHz to Hz written out to mass storage. In this paper an overview of the steering mechanism of the HLT is given. The HLT Steering is responsible for the scheduling of algorithms and for the global event trigger decision evaluation. The concept of step-wise and seeded selection strategy implemented by the steering will be presented. Integration of large number of trigger menus and sophisticated physics selection strategies will also be discussed. The electron and photon menus will be described to demonstrate that the trigger is well adapted for the physics program at the LHC.
The ATLAS high level trigger steering Berger, N; Bold, T; Eifert, T ...
Journal of physics. Conference series,
07/2008, Letnik:
119, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The High Level Trigger (HLT) of the ATLAS experiment at the Large Hadron Collider receives events which pass the LVL1 trigger at ∼75 kHz and has to reduce the rate to ∼200 Hz while retaining the most ...interesting physics. It is a software trigger and performs the reduction in two stages: the LVL2 trigger and the Event Filter (EF). At the heart of the HLT is the Steering software. To minimise processing time and data transfers it implements the novel event selection strategies of seeded, step-wise reconstruction and early rejection. The HLT is seeded by regions of interest identified at LVL1. These and the static configuration determine which algorithms are run to reconstruct event data and test the validity of trigger signatures. The decision to reject the event or continue is based on the valid signatures, taking into account pre-scale and pass-through. After the EF, event classification tags are assigned for streaming purposes. Several new features for commissioning and operation have been added: comprehensive monitoring is now built in to the framework; for validation and debugging, reconstructed data can be written out; the steering is integrated with the new configuration (presented separately), and topological and global triggers have been added. This paper will present details of the final design and its implementation, the principles behind it, and the requirements and constraints it is subject to. The experience gained from technical runs with realistic trigger menus will be described.
At the ATLAS experiment, the Detector Control System (DCS) is used to oversee detector conditions and supervise the running of equipment. It is essential that information from the DCS about the ...status of individual sub-detectors be extracted and taken into account when determining the quality of data taken and its suitability for different analyses. DCS information is written to the ATLAS conditions database and then summarised to provide a status flag for each sub-detector and displayed on the web. We discuss how this DCS information should be used, and the technicalities of making this summary.
Quantum-chemical ab
initio calculations were performed for the electronic ground state and several low-lying excited states of the Ne
3
+ molecular ion. Large parts of the potential energy surfaces, ...including the global minimum of the ground state, were treated by means of multi-reference many-body perturbation theory, starting from the SCF wave function of neutral Ne
3. For the inductive local minima of the ground state at C
∞v and C
2v geometries, the multi-configuration coupled electron-pair approach was used, together with an extended basis set. In agreement with the best previous calculations, we obtain a symmetric linear (D
∞h) equilibrium geometry for the Ne
3
+ ground state, with a bond distance of 3.55 a.u. and a binding energy of 0.10 eV relative to Ne
2
+ and Ne. In addition to this global minimum, two local minima exist, which correspond to a Ne
2
+ ion in its electronic ground state (
R
e=3.27 a
.u.) binding a Ne atom by inductive forces. Both these minima are very shallow (0.07 and 0.03 eV for the C
∞v and C
2v structures). Potential energy surfaces for several low-lying excited states of Ne
3
+ were calculated as well and their properties, e.g. adiabatic and vertical excitation energies, local minima, and dissociation channels, are discussed.
First results from the DELPHI pixel detector Becks, K.H.; Brunet, J.M.; Caccia, M. ...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment,
05/1998, Letnik:
409, Številka:
1-3
Journal Article, Conference Proceeding
Recenzirano
In 1996 the DELPHI experiment at LEP has upgraded its silicon tracker. In the forward region, pixel detectors were installed. The pixel commissioning and the first results are reported.
The status of the DELPHI very forward ministrip detector Adam, W; Bosio, C; Chochula, P ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/1996, Letnik:
379, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We present the results of final acceptance tests of the DELPHI VFT ministrip detector before and during detector assembly. Dedicated tests were carried out to detect substandard channels, measure the
...S
N
performance and test the assembled detector for electronic failures.
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