110639465
The LHCb Run Control
LHCb has designed and implemented an integrated Experiment Control System. The Control System uses the same concepts and the same tools to control and monitor all parts of the experiment: the Data Acquisition System, the Timing and the Trigger Systems, the High Level Trigger Farm, the Detector Control System, the Experiment's Infrastructure and the interaction with the CERN Technical Services and the Accelerator. LHCb's Run Control, the main interface used by the experiment's operator, provides access in a hierarchical, coherent and homogeneous manner to all areas of the experiment and to all its sub-detectors. It allows for automated (or manual) configuration and control, including error recovery, of the full experiment in its different running modes. Different instances of the same Run Control interface are used by the various sub-detectors for their stand-alone activities: test runs, calibration runs, etc. The architecture and the tools used to build the control system, the guidelines and components provided to the developers, as well as the first experience with the usage of the Run Control will be presented
60504028
LHCb distributed computing and the grid
The current architecture of the LHCb distributed system for Monte Carlo data production is described, together with details of the implementation and performance of a regional site at INFN-CNAF. An overview is given of the current and planned use of Grid technology from the European Datagrid Project (EDG), and of the development of an experiment-specific user interface to Grid services.
126243169
The selection crate for the L0 calorimeter trigger
39676478
High rate packets transmission on ethernet LAN using commodity hardware
We report on measurements performed to test the reliability of high rate data transmission over copper Gigabit Ethernet for the LHCb online system. High reliability of such transmissions will be crucial for the functioning of the software trigger layers of the LHCb experiment, at the CERN's LHC accelerator. The technological challenge in the system implementation consists of handling the expected high data throughput of event fragments using, to a large extent, commodity equipment. We report on performance evaluations (throughput, error rates and frame drop) of the main components involved in data transmission: the Ethernet cable, the PCI bus and the operating system (the latest kernel versions of Linux). Three different platforms have been used.
121570479
Compatibility and possible implications of the experimental results on solar neutrinos
Abstract The effect of varying the assumed value of the cross-section for the proton-proton fusion weak reaction of the solar cycle on the solar neutrino problem is discussed. It is shown that an increase of about 20% of the relevant astrophysical factor fields compatibility (within the present experimental accuracy) of the available results with theory and among themselves.
110405827
Storage management solutions and performance tests at the INFN Tier-1
Performance, reliability and scalability in data access are key issues in the context of HEP data processing and analysis applications. In this paper we present the results of a large scale performance measurement performed at the INFN-CNAF Tier-1, employing some storage solutions presently available for HEP computing, namely CASTOR, GPFS, Scalla/Xrootd and dCache. The storage infrastructure was based on Fibre Channel systems organized in a Storage Area Network, providing 260 TB of total disk space, and 24 disk servers connected to the computing farm (280 worker nodes) via Gigabit LAN. We also describe the deployment of a StoRM SRM instance at CNAF, configured to manage a GPFS file system, presenting and discussing its performances.
15769380
Modeling the magnetic field in the protostellar source NGC 1333 IRAS 4A
Context. Magnetic fields are believed to play a crucial role in the process of star formation. Aims. We compare high-angular resolution observations of the submillimeter polarized emission of NGC 1333 IRAS 4A, tracing the magnetic field around a low-mass protostar, with models of the collapse of magnetized molecular cloud cores. Methods. Assuming a uniform dust alignment efficiency, we computed the Stokes parameters and synthetic polarization maps from the model density and magnetic field distribution by integrations along the line-of-sight and convolution with the interferometric response. Results. The synthetic maps are in good agreement with the data. The best-fitting models were obtained for a protostellar mass of 0.8 M� ,o f age 9× 10 4 yr, formed in a cloud with an initial mass-to-flux ratio ∼2 times the critical value. Conclusions. The magnetic field morphology in NGC 1333 IRAS 4A is consistent with the standard theoretical scenario for the formation of solar-type stars, where well-ordered, large-scale, rather than turbulent, magnetic fields control the evolution and collapse of the molecular cloud cores from which stars form.
7757480
The Challenge of Sub-Keplerian Rotation for Disk Winds
Strong magnetization makes the disks surrounding young stellar objects rotate at rates that are too sub-Keplerian to enable the thermal launching of disk winds from their surfaces unless the rate of gas diffusion across field lines is dynamically fast. This underappreciated implication of disk magnetization poses a considerable challenge for disk-wind theory.
17633573
Gravitational Collapse of Magnetized Clouds. II. The Role of Ohmic Dissipation
We formulate the problem of magnetic field dissipation during the accretion phase of low-mass star formation, and we carry out the first step of an iterative solution procedure by assuming that the gas is in free fall along radial field lines. This so-called "kinematic approximation" ignores the back reaction of the Lorentz force on the accretion flow. In quasi-steady state and assuming the resistivity coefficient to be spatially uniform, the problem is analytically soluble in terms of Legendre's polynomials and hypergeometric confluent functions. The dissipation of the magnetic field occurs inside a region of radius inversely proportional to the mass of the central star (the "Ohm radius"), where the magnetic field becomes asymptotically straight and uniform. In our solution the magnetic flux problem of star formation is avoided because the magnetic flux dragged in the accreting protostar is always zero. Our results imply that the effective resistivity of the infalling gas must be higher by at least 1 order of magnitude than the microscopic electric resistivity, to avoid conflict with measurements of paleomagnetism in meteorites and with the observed luminosity of regions of low-mass star formation.
18590
The Chemistry of the early universe
The process of molecule formation in the primor- dial gas is considered in the framework of Friedmann cosmo- logical models from redshift z =1 0 4 to z =0 . First, a com- prehensive analysis of 87 gas phase reaction rates (both col- lisional and radiative) relevant in the physical environment of the expanding universe is presented and critically discussed. On this basis, calculations are carried out of the abundance of 21 molecular species as function of redshift, for different values of the cosmological parameters 0, and H0, evaluating con- sistently the molecular heating and cooling due to H2 ,H D and LiH molecules. One of the major improvements of this work is the use of a better treatment of H recombination that leads to a reduction of a factor 2-3 in the abundance of electrons and H + at freeze-out, with respect to previous studies. The lower residual ionization has a negative effect on the chemistry of the primordial gas in which electrons and protons act as cat- alysts in the formation of the first molecules. We find that in the standard model (h =0 :67, 10 =4 :5, 0 =1 and (D/H) =4 :3 10 5 ), the residual fractional ionization at z =1 is (e= H) =3 :0210 4 , and the main molecular species fractional abundances (H2= H) =1 :1 10 6 , (HD=H 2 )=1 :1 10 3 , (HeH + = H) =6 :2 10 13 , (LiH + = H) =9 :4 10 18 and (LiH=LiH + )=7 :6 10 3 . We devise a reduced chemical network that reproduces with excellent accuracy the numerical results of the complete model and allows to follow the chemical compositions and the thermal properties of a primordial gas in the presence of an external radiation field. Finally, we provide accurate cooling functions of H2, HD and LiH in a wide range of density and temperature that can be conveniently used in a variety of cosmological applications.
14593491
Galactic chemical evolution of Lithium: interplay between stellar sources
In this paper we study the evolution of 7Li in the Galaxy considering the contributions of various stellar sources: Type II supernovae, novae, red giant stars, and asymptotic giant branch (AGB) stars. We present new results for the production of 7Li in AGB stars via the hot bottom burning process, based on stellar evolutionary models. In the light of recent observations of dense circumstellar shells around evolved stars in the Galaxy and in the Magellanic Clouds, we also consider the impact of a very high mass-loss rate episode (superwind) before the evolution off the AGB phase on the 7Li enrichment in the interstellar medium. We compare the Galactic evolution of 7Li obtained with these new 7Li yields (complemented with a critical reanalysis of the role of supernovae, novae and giant stars) with a selected compilation of spectroscopic observations including halo and disk field stars as well as young stellar clusters. We conclude that even allowing for the large uncertainties in the theoretical calculation of mass-loss rates at the end of the AGB phase, the superwind phase has a significant effect on the 7Li enrichment of the Galaxy.