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.
62560089
DIRAC: reliable data management for LHCb
DIRAC, LHCb's Grid Workload and Data Management System, utilizes WLCG resources and middleware components to perform distributed computing tasks satisfying LHCb's Computing Model. The Data Management System (DMS) handles data transfer and data access within LHCb. Its scope ranges from the output of the LHCb Online system to Grid-enabled storage for all data types. It supports metadata for these files in replica and bookkeeping catalogues, allowing dataset selection and localization. The DMS controls the movement of files in a redundant fashion whilst providing utilities for accessing all metadata. To do these tasks effectively the DMS requires complete self integrity between its components and external physical storage. The DMS provides highly redundant management of all LHCb data to leverage available storage resources and to manage transient errors in underlying services. It provides data driven and reliable distribution of files as well as reliable job output upload, utilizing VO Boxes at LHCb Tier1 sites to prevent data loss. This paper presents several examples of mechanisms implemented in the DMS to increase reliability, availability and integrity, highlighting successful design choices and limitations discovered.
58846599
DIRAC data management: consistency, integrity and coherence of data
The DIRAC Data Management System (DMS) relies on both WLCG (Worldwide LHC Computing Grid Project) Data Management services (LCG File Catalogues, Storage Resource Managers and File Transfer System (FTS)) and LHCb specific components (Bookkeeping database). The complexity of both the DMS and its interactions with numerous WLCG components as well as the instability of facilities concerned, has frequently turned into unexpected problems in data moving and/or data registration, preventing a coherent picture of datasets. Several developments in LHCb have been made in order to avoid data corruptions, missing data incoherence and inconsistences among Catalogues and physical storage both through safety measures at data management level (failover mechanism, check sums, roll back mechanism) and extensive background checks. In this paper all the tools developed for checking data integrity and consistency will be presented as well as a Storage Usage agent, whose aim is to produce an up-to-date accounting of all LHCb storage usage using the LFC mirror database. The goal of this activity is the development of a generic tool suite able to categorize, analyze and systematically cure the disparate problems affecting the DMS in order to maintain a consistent picture of the main catalogues (Bookkeeping and LFC) and the Storage Elements.
60523028
DIRAC: data production management
The LHCb Computing Model describes the dataflow for all stages in the processing of real and simulated events, and defines the role of LHCb associated Tier-1 and Tier-2 computing centers. The WLCG 'Dress Rehearsal' exercise aims to allow LHC experiments to deploy the full chain of their Computing Models, making use of all underlying WLCG services and resources, in preparation for real data taking. During this exercise simulated RAW physics data, matching the properties of eventual real data, will be uploaded from the LHCb Online storage system to Grid enabled storage. This data will then be replicated to LHCb Tier-1 centers and subsequently processed (reconstructed and stripped). The product of this processing is user analysis data that are distributed to all LHCb Tier-1 centers. DIRAC, LHCbs Workload and Data Management System, supports the implementation of the Computing Model in a data driven, real time and coordinated fashion. In this paper the LHCb Computing Model will be reviewed and the DIRAC components providing the needed functionality to support the Computing Model will be detailed. An evaluation of the preparedness for real data taking will also be given.
60746151
LHCb data management on the computing grid
The LHCb detector is one of the four experiments being built to harness the proton-proton collisions provided by the Large Hadron Collider (LHC) at the European Organisation for Nuclear Research (CERN). The data rate expected, when the LHC experiments are fully operational, eclipses that of any previous scientific experiments and has motivated the adoption of a grid computing paradigm to store and process the data. Managing PetaBytes of data in a distributed environment provides a rich set of challenges related to scalability, reliability and performance. This thesis will present the data management requirements for executing the workload of the LHCb collaboration. We present the systems designed that support all aspects of the grid data management for LHCb, from data transfer, to data integrity, and efficient data access. The distributed computing environment is inherently unstable and much focus has been made on providing systems that are robust and resilient to observed failures.
62238242
Data stream handling in the LHCb experiment
This paper presents the event data handling in the LHCb experiment, starting from the acceptance of events by the software trigger farm to making the data available for offline reprocessing. In the data acquisition system, events accepted by the High Level Trigger farm are assembled into streams according to their type. Each stream will be written to disk as a 2 GB file for optimal storage and ease of reconstruction. Under nominal conditions about 2 such files will be produced per minute. The life cycle and state transitions of each file are managed by means of a dedicated database. These files must be copied to the tape storage and simultaneously be made available online to various calibration and monitoring tasks. Additionally, to initiate the start of the offline re-processing all file parameters must be propagated to the offline Grid data analysis system. This system has been designed for extreme robustness and reliability with redundancy in almost every component and supports various fail-over mechanisms. The software, hardware, and protocols designed for this purpose will be discussed in detail. Performance figures of data-challenges done in 2007 will be shown.
118694154
Production of Dimuons by Pions and Protons at Fermilab
In this lecture I shall describe an experiment in progress1 at the Fermi National Accelerator Laboratory (FNAL) to study the production of μ+μ− pairs in hadron-hadron collisions. So far, we have used beams of 225 — GeV π+, π− and protons incident on carbon and tin targets for most of the data. In an earlier run, a 150 GeV positive beam was used with a beryllium target. The results I report of the 150 GeV run are final; those at 225 GeV are preliminary.
119204101
Small-scale structure of the interstellar medium towards rho Oph stars: diffuse band observations
We present an investigation of small-scale-structure in the distribution of large molecules/dust in the interstellar medium through observations of diffuse interstellar bands (DIBs). High signal-to-noise optical spectra were recorded towards the stars rho Oph A, B, C and DE using the University College London Echelle Spectrograph (UCLES) on the Anglo-Australian Telescope. The strengths of some of the DIBs are found to differ by about 5-9 % between the close binary stars rho Oph A and B, which are separated by a projected distance on the sky of only ~344 AU. This is the first star-system in which such small-scale DIB strength variations have been reported. The observed variations are attributed to differences between a combination of carrier abundance and the physical conditions present along each sightline. The sightline towards rho Oph C contains relatively dense, molecule-rich material and has the strongest \lambda\lambda 5850 and 4726 DIBs. The gas towards DE is more diffuse and is found to exhibit weak C_2 (blue) DIBs and strong yellow/red DIBs. The differences in diffuse band strengths between lines of sight are, in some cases, significantly greater in magnitude than the corresponding variations among atomic and diatomic species, indicating that the DIBs can be sensitive tracers of interstellar cloud conditions.
7049031
Small-scale structure in the interstellar medium: time-varying interstellar absorption towards κ Velorum
Ultra-high spectral resolution observations of time-varying interstellar absorption towards κ Vel are reported, using the Ultra-High Resolution Facility on the Anglo-Australian Telescope. Detections of interstellar Ca i, Ca ii, K i, Na i and CH are obtained, whilst an upper limit on the column density is reported for C_2. The results show continued increases in column densities of K i and Ca i since observations ∼4 yr earlier, as the transverse motion of the star carried it ∼10 au perpendicular to the line of sight. Line profile models are fitted to the spectra and two main narrow components (A and B) are identified for all species except CH. The column density N(K i) is found to have increased by 82^(+10)_(−9) per cent between 1994 and 2006, whilst N(Ca i) is found to have increased by 32 ± 5 per cent over the shorter period of 2002–2006. The line widths are used to constrain the kinetic temperature to T_(k,A) < 671^(+18)_(−17) K and T_(k,B) < 114^(+15)_(−14) K. Electron densities are determined from the Ca i/Ca ii ratio, which in turn place lower limits on the total number density of n_A ≳ 7 × 10^3 cm^(−3) and n_B ≳ 2 × 10^4 cm^(−3). Calcium depletions are estimated from the Ca i/K i ratio. Comparison with the chemical models of Bell et al. confirms the high number density, with n = 5 × 10^4 cm^(−3) for the best-fitting model. The first measurements of diffuse interstellar bands (DIBs) towards this star are made at two epochs, but only an upper limit of ≲ 40 per cent is placed on their variation over ∼9 yr. The DIBs are unusually weak for the measured E(B − V) and appear to exhibit similar behaviour to that seen in Orion. The ratio of equivalent widths of the λ5780 to λ5797 DIBs is amongst the highest known, which may indicate that the carrier of λ5797 is more sensitive to ultraviolet radiation than to local density.
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.
14431702
Diffuse interstellar bands in z < 0.6 Ca ii absorbers
The diffuse interstellar bands (DIBs) probably arise from complex organic molecules whose strength in local galaxies correlates with neutral hydrogen column density, N(H i), and dust reddening, E(B−V). Because Ca ii absorbers in quasar (QSO) spectra are posited to have high N(H i) and significant E(B−V), they represent promising sites for the detection of DIBs at cosmological distances. Here we present the results from the first search for DIBs in nine Ca ii-selected absorbers at 0.07 < zabs < 0.55. We detect the 5780-A DIB in one line of sight at zabs= 0.1556; this is only the second QSO absorber in which a DIB has been detected. Unlike the majority of local DIB sight-lines, both QSO absorbers with detected DIBs show weak 6284-A absorption compared with the 5780-A band. This may be indicative of different physical conditions in intermediate redshift QSO absorbers compared with local galaxies. Assuming that local relations between the 5780-A DIB strength and N(H i) and E(B−V) apply in QSO absorbers, DIB detections and limits can be used to derive N(H i) and E(B−V). For the one absorber in this study with a detected DIB, we derive E(B−V) = 0.23 mag and log N(H i) ≥ 20.9, consistent with previous conclusions that Ca ii systems have high H i column densities and significant reddening. For the remaining eight Ca ii-selected absorbers with 5780-A DIB non-detections, we derive E(B−V) upper limits of 0.1–0.3 mag.