W mass from fully leptonic and mixed decays at LEP

This article describes the determination of the W boson mass through the mixed hadronic-leptonic and fully leptonic channels at LEP. The results are preliminary and refer to the data collected up to 1998. The combined LEP W mass value for (mixed)-leptonic events is m/sub w /=(80.310+or-0.060) GeV/c/sup 2/. This value, combined with the result from the hadronic channel, gives m/sub w/=(80.339+or-0.055) Ge V/c/sup 2/. (4 refs)

Measuring performances of linux hypervisors

Virtualization is a now proven software technology that is rapidly transforming the IT landscape and fundamentally changing the way people make computations and implement services. Recently, all major software producers (e.g., Microsoft and RedHat) developed or acquired virtualization technologies. Our institute (http://www.cnaf.infn.it) is a Tier1 for experiments carried on at the Large Hadron Collider at CERN (http://lhc.web.cern.ch/lhc/) and is experiencing several benefits from virtualization technologies, like improving fault tolerance, providing efficient hardware resource usage and increasing security. Currently, the virtualization solution we adopted is xen, which is well supported by the Scientific Linux distribution, widely used by the High-Energy Physics (HEP) community. Since Scientific Linux is based on RedHat ES, we felt the need to investigate performances and usability differences with the new kvm technology, recently acquired by RedHat. The case study of this work is the Tier2 site for the LHCb experiment hosted at our institute; all major grid elements for this Tier2 run on xen virtual machines smoothly. We will investigate the impact on performance and stability that a migration to kvm would entail on the Tier2 site, as well as the effort required by a system administrator to deploy the migration

Multiple Parton Interactions, top--antitop and W+4j production at the LHC

The expected rate for Multiple Parton Interactions (MPI) at the LHC is large. This requires an estimate of their impact on all measurement foreseen at the LHC while opening unprecendented opportunities for a detailed study of these phenomena. In this paper we examine the MPI background to top-antitop production, in the semileptonic channel, in the early phase of data taking when the full power of $b$--tagging will not be available. The MPI background turns out to be small but non negligible, of the order of 20% of the background provided by W+4j production through a Single Parton Interaction. We then analyze the possibility of studying Multiple Parton Interactions in the W+4j channel, a far more complicated setting than the reactions examined at lower energies. The MPI contribution turns out to be dominated by final states with two energetic jets which balance in transverse momentum, and it appears possible, thanks to the good angular resolution of ATLAS and CMS, to separate the Multiple Parton Interactions contribution from Single Parton Interaction processes. The large cross section for two jet production suggests that also Triple Parton Interactions (TPI) could provide a non negligible contribution. Our preliminary analysis suggests that it might be indeed possible to investigate TPI at the LHC.Comment: Typos fixed. Published in JHE

Lesson learned from the recovery of an orphan source inside a maritime cargo: analysis of the nuclear instrumentations used, and measures realized during the operations

In this paper, the authors analyze the case study of the recovery of an orphan source of 60Co inside a maritime cargo full of metal wastes in the Italian Harbor of Genova carried out by the Italian Fire Fighters. Orphan radioactive sources or Radiological Dispersal Devices are a critical security issue in large geographical areas, and they result in a safety concern for people who may become accidentally exposed to ionizing radiation. The abandonment of orphan sources can usually be related to three factors: human errors, cost reasons (in order to avoid the payment of disposal procedures), or malevolent purposes (like the production of dirty bombs). The present data concern the nuclear safety measures implemented during the recovery event and the pool of procedures carried out in order to reduce the risks for the involved harbor operators. Following data collection and analysis, an important lesson about the management of such events and scenarios can be learned

Variability in pH, fCO2, oxygen and flux of CO2 in the surface water along a transect in the Atlantic sector of the Southern Ocean

Underway sampling and measurements of pH, fCO2, oxygen and Chlorophyll a (Chl a) were performed in the surface waters from Cape Town (South Africa) to Queen Maud Land (Antarctica) in the Atlantic sector of the Southern Ocean during the austral summer 1997/1998. From direct measurements of these parameters and from calculated fCO2 the oceanic carbon dioxide system was studied and related to hydrological and biological parameters. fCO2 was in general undersaturated relative to the atmosphere and showed a large variability with values ranging from 313 to 377 μatm with a mean value of 346±13 μatm. The undersaturation was more pronounced in areas associated with fronts where high Chl a and high pH in situ values were observed. Using shipboard wind speed data, estimates of the CO2 flux were made along the transect and during three mesoscale surveys on the northward return transect in the area of the Spring Ice Edge (SIE), the Winter Ice Edge (WIE) and in the Antarctic Polar Front (APF). The undersaturation observed during the transect caused the ocean to act as a sink for CO2 with a mean sea–air flux for the entire transect of −3±5 mmol m−2 d−1 with a large variability between −20 mmol m−2 d−1 (oceanic uptake) to 1.3 mmol m−2 d−1 (oceanic source). The lowest fCO2 values (largest oceanic uptake of CO2) were found at the southern boundary of the APF at 53°S, which coincided with a supersaturation in oxygen and high pH values. Oxygen concentrations were measured from 50°S to 63°S and varied between 324 and 359 μmol kg−1 with a mean value of 347±9 μmol kg−1. In general only small deviations from equilibrium oxygen saturation were observed (mean value=99±2%). However, in the SIE oxygen was clearly undersaturated, probably an effect of upwelling of oxygen poor deep water which had not yet been compensated for by biological production. Three weeks later, the ice edge had retreated in the SIE region and the Chl a concentration had increased three-fold, suggesting the start of a phytoplankton bloom. This was also seen in the oxygen concentration which had increased and showed supersaturation. This coincided with an increased oceanic uptake of CO2 in the SIE during the mesoscale survey

Electroweak Physics, Experimental Aspects

Collider measurements on electroweak physics are summarised. Although the precision on some observables is very high, no deviation from the Standard Model of electroweak interactions is observed. The data allow to set stringent limits on some models for new physics.Comment: Plenary Talk at the UK Phenomenology Workshop on Collider Physics, Durham, 199

Enhancing Radiation Detection by Drones through Numerical Fluid Dynamics Simulations

This study addresses the optimization of the location of a radioactive-particle sensor on a drone. Based on the analysis of the physical process and of the boundary conditions introduced in the model, computational fluid dynamics simulations were performed to analyze how the turbulence caused by drone propellers may influence the response of the sensors. Our initial focus was the detection of a small amount of radioactivity, such as that associated with a release of medical waste. Drones equipped with selective low-cost sensors could be quickly sent to dangerous areas that first responders might not have access to and be able to assess the level of danger in a few seconds, providing details about the source terms to Radiological-Nuclear (RN) advisors and decision-makers. Our ultimate application is the simulation of complex scenarios where fluid-dynamic instabilities are combined with elevated levels of radioactivity, as was the case during the Chernobyl and Fukushima nuclear power plant accidents. In similar circumstances, accurate mapping of the radioactive plume would provide invaluable input-data for the mathematical models that can predict the dispersion of radioactivity in time and space. This information could be used as input for predictive models and decision support systems (DSS) to get a full situational awareness. In particular, these models may be used either to guide the safe intervention of first responders or the later need to evacuate affected regions