31995433
Data Handling and Transfer in the LHCb Experiment
This paper focuses on the management of raw event data files containing the electronic response to particle collisions in the LHCb detector at the LHC storage ring at CERN. The typical file life cycle is presented, starting from writing of raw event streams into files to transfer to the CERN tape storage system and to the offline GRID distributed processing infrastructure. A distributed solution centered on a dedicated database is implemented to address the raw event data management needs. The solution is integrated with the data acquisition system software chain and with the experiment control system. The software architecture and hardware configurations are explained together with the testing methods, current development status and future plans.
129617632
The Durham Extensive Air Shower Array
120919376
The Durham air shower array - III: Evaluation of the array's response to showers
Abstract A Monte Carlo investigation of the Durham air shower array is described in which the systematic biases introduced into air shower data recorded by the experiment are evaluated.
121598426
High-energy muons in extensive air showers
SummaryA study has been made of the density of high-energy muons (10<Eμ<300 GeV) as a function of the distance from the axis of extensive air showers in the size range 2·105<Ne<3·106,i.e. showers produced by primary cosmic rays in a decade of energy centered on 5·1015 eV. The results for muons above 50 GeV agree with those from the Lodz-Moscow group, but those for muons above 200 GeV are a little different from the only other experimental results: those of Acharyaet al. Comparison with predictions favours a CKP-type model with a «normal» comparison. The simple scaling model with any composition does not give a good fit to the data, but no doubt modifications could be made, principally an increase in the mean transverse momentum, which would restore agreement.RiassuntoSi è effettuato uno studio della densità dei muoni (10<Eμ<300 GeV) in funzione della distanza dall’asse di sciami d’aria estesi nell’intervallo di grandezza 2·105<Ne<<3·106, cioè sciami prodotti da raggi cosmici del primario in un decadimento di energia centrato su 5 · 1015 eV. I risultati per muoni al di sopra di 50 GeV sono in accordo con quelli del gruppo di Lodz-Moscow, ma quelle per muoni al di sopra di 200 GeV sono un po’ differenti dagli unici altri risultati sperimentali: quelli di Acharyaet al. Confronti con produzioni sono a favore del modello del tipo CKP con una composizione « normale ». Il modello a variazione di scala semplice con qualsiasi composizione non dà un buon adattamento ai dati, ma, senza dubbio, modificazioni potrebbero essere fatte, principalmente un aumento nell’impulso trasversale medio, che ripristinerebbero l’accordo.
5719579
DIRAC: A Community Grid Solution
The DIRAC system was developed in order to provide a complete solution for using the distributed computing resources of the LHCb experiment at CERN for data production and analysis. It allows a concurrent use of over 10K CPUs and 10M file replicas distributed over many tens of sites. The sites can be part of a Computing Grid such as WLCG or standalone computing clusters all integrated in a single management structure. DIRAC is a generic system with the LHCb specific functionality incorporated through a number of plug-in modules. It can be easily adapted to the needs of other communities. Special attention is paid to the resilience of the DIRAC components to allow an efficient use of non-reliable resources. The DIRAC production management components provide a framework for building highly automated data production systems including data distribution and data driven workload scheduling. In this paper we give an overview of the DIRAC system architecture and design choices. We show how different components are put together to compose an integrated data processing system including all the aspects of the LHCb experiment - from the MC production and raw data reconstruction to the final user analysis.
5729393
High-Speed Data-Injection for Data-Flow Verification at LHCb
The High Level Trigger (HLT) and Data Acquisition System select about 2 kHz of events out of the 40 MHz of beam crossings. The selected events are consolidated into files in onsite storage and then sent to permanent storage for subsequent analysis on the Grid. For local and full-chain tests a method to exercise the data-flow through the High Level Trigger is needed in the absence of real data. In order to test the system as much as possible under identical conditions as for data-taking, the solution would be to inject data at the input of the HLT at a minimum rate of 2 kHz. This is done via a software implementation of the trigger system which sends data to the HLT. The application has to simulate that the data it sends come from real LHCb readout-boards. Data can come from several input streams, which are selected according to probabilities or frequencies. Therefore the emulator offers runs which are not only identical data-flows coming from a sequence on tape, but physics-like pseudo-indeterministic data-flow, including lumi events and candidate b-quark events. Both simulation data and previously recorded real data can be re-played through the system in this manner. As the data rate is high (100 MB/s), care has been taken to optimize the emulator for throughput from the Storage Area Network. The emulator can be run in stand-alone mode, but even more interesting is that it can emulate any partition of LHCb in parallel with the real hardware partition. In this mode it is fully integrated into the standard run-control. The architecture, implementation, and performance results of the emulator and full tests will be presented. This emulator is a crucial part of the ongoing data-challenges in LHCb. Results from these Full System Integration Tests (FEST) will be presented, which helped to verify and benchmark the entire LHCb data-flow.
20742679
Galaxy Zoo: an independent look at the evolution of the bar fraction over the last eight billion years from HST-COSMOS ?
We measure the redshift evolution of the bar fraction in a sample of 2380 visually selected disc galaxies found in Cosmic Evolution Survey (COSMOS) Hubble Space Telescope (HST ) images. The visual classications used both to identify the disc sample and to indicate the presence of stellar bars were provided by citizen scientists via the Galaxy Zoo: Hubble (GZH) project. We nd that the overall bar fraction decreases by a factor of 2, from 22 5% at z = 0:4 (tlb = 4:2 Gyr) to 11 2% at z = 1:0 (tlb = 7:8 Gyr), consistent with previous analysis. We show that this decrease, of the strong bar fraction in a volume limited sample of massive disc galaxies [stellar mass limit of log(M?=M ) 10:0], cannot be due to redshift-dependent biases hiding either bars or disc galaxies at higher redshifts. Splitting our sample into three bins of mass we nd that the decrease in bar fraction is most prominent in the highest mass bin, while the lower mass discs in our sample show a more modest evolution. We also include a sample of 98 red disc galaxies. These galaxies have a high bar fraction (45 5%), and are missing from other COSMOS samples which used SED tting or colours to identify high redshift discs. Our results are consistent with a picture in which the evolution of massive disc galaxies begins to be aected by slow (secular) internal process at z 1. We discuss possible connections of the decrease in bar fraction to the redshift, including the growth of stable disc galaxies, mass evolution of the gas content in disc galaxies, as well as the mass-dependent eects of tidal interactions.
3675875
Galaxy Zoo: Quantifying Morphological Indicators of Galaxy Interaction
We use Galaxy Zoo 2 visual classifications to study the morphological signatures of interaction between similar-mass galaxy pairs in the Sloan Digital Sky Survey. We find that many observable features correlate with projected pair separation – not only obvious indicators of merging, disturbance and tidal tails, but also more regular features, such as spiral arms and bars. These trends are robustly quantified, using a control sample to account for observational biases, producing measurements of the strength and separation scale of various morphological responses to pair interaction. For example, we find that the presence of spiral features is enhanced at scales ≲ 70 h− 170 kpc, probably due to both increased star formation and the formation of tidal tails. On the other hand, the likelihood of identifying a bar decreases significantly in pairs with separations ≲ 30 h− 170 kpc, suggesting that bars are suppressed by close interactions between galaxies of similar mass. We go on to show how morphological indicators of physical interactions provide a way of significantly refining standard estimates for the frequency of close pair interactions, based on velocity offset and projected separation. The presence of loosely wound spiral arms is found to be a particularly reliable signal of an interaction, for projected pair separations up to ∼100 h− 170 kpc. We use this indicator to demonstrate our method, constraining the fraction of low-redshift galaxies in truly interacting pairs, with M* > 109.5 M⊙ and mass ratio <4, to be between 0.4 and 2.7 per cent.
120618738
Observation of high mass electron-positron pairs produced in proton-proton collisions at the CERN ISR
Abstract In an experiment performed at the CERN Intersecting Storage Rings (ISR), 11 e + e − pairs of high invariant mass value (> 2.5 GeV/c 2 ) have been observed. Of these events, 9 can be interpreted as arising from the reaction p + p → J (3.1) + anything. the cross-section for this reaction is estimated and compared with the result obtained at lower centre-of-mass energies.
120272757
A System of Cylindrical Drift Chambers in a Superconducting Solenoid
Abstract A superconducting solenoid at the CERN ISR has been equipped with a system of high accuracy cylindrical drift chambers. This detector consists of eight layers of field shaped drift cells with a delay line opposite each sense wire to provide coupled two dimensional readout. The design, construction, and operation of this system are discussed. The resolution and performance of the delay lines and sense wires under ISR running conditions are shown.
123901120
A Study of Inclusive Spectra and Two Particle Correlations at Large Transverse Momentum
Abstract The inclusive production of π and η mesons at 90° from proton-proton collisions has been measured at the CERN ISR at centre-of-mass energies between 23.5 and 62.4 GeV. The momentum correlation of charged particles emitted together with a large transverse momentum pion has also been studied, using two magnetic spectrometers each centred at 90°.