2,660 research outputs found
Six-dimensional nilpotent Lie algebras
We give a full classification of 6-dimensional nilpotent Lie algebras over an
arbitrary field, including fields that are not algebraically closed and fields
of characteristic~2. To achieve the classification we use the action of the
automorphism group on the second cohomology space, as isomorphism types of
nilpotent Lie algebras correspond to orbits of subspaces under this action. In
some cases, these orbits are determined using geometric invariants, such as the
Gram determinant or the Arf invariant. As a byproduct, we completely determine,
for a 4-dimensional vector space , the orbits of \GL(V) on the set of
2-dimensional subspaces of .Comment: Corrected a small error in Theorem 4.
Low-mass dark matter search with the DarkSide-50 experiment
We present the results of a search for dark matter weakly interacting massive particles (WIMPs) in the mass range below 20 GeV=c2using a target of low-radioactivity argon with a 6786.0 kg d exposure. The data were obtained using the DarkSide-50 apparatus at Laboratori Nazionali del Gran Sasso. The analysis is based on the ionization signal, for which the DarkSide-50 time projection chamber is fully efficient at 0.1 keVee. The observed rate in the detector at 0.5 keVee is about 1.5 event=keVee=kg=d and is almost entirely accounted for by known background sources. We obtain a 90% C.L. exclusion limit above 1.8 GeV=c2for the spin-independent cross section of dark matter WIMPs on nucleons, extending the exclusion region for dark matter below previous limits in the range 1.8-6 GeV=c2
The BepiColombo MORE gravimetry and rotation experiments with the ORBIT14 software
The BepiColombomission to Mercury is an ESA/JAXAcornerstone mission, consisting of two spacecraft in orbit around Mercury addressing several scientific issues. One spacecraft is the Mercury Planetary Orbiter, with full instrumentation to perform radio science experiments. Very precise radio tracking from Earth, on-board accelerometer and optical measurements will provide large data sets. From these it will be possible to study the global gravity field of Mercury and its tidal variations, its rotation state and the orbit of its centre of mass. With the gravity field and rotation state, it is possible to constrain the internal structure of the planet. With the orbit of Mercury, it is possible to constrain relativistic theories of gravitation. In order to assess that all the scientific goals are achievable with the required level of accuracy, full cycle numerical simulations of the radio science experiment have been performed. Simulated tracking, accelerometer and optical camera data have been generated, and a long list of variables including the spacecraft initial conditions, the accelerometer calibrations and the gravity field coefficients have been determined by a least-squares fit. The simulation results are encouraging: The experiments are feasible at the required level of accuracy provided that some critical terms in the accelerometer error are moderated. We will show that BepiColombo will be able to provide at least an order of magnitude improvement in the knowledge of Love number k2, libration amplitudes and obliquity, along with a gravity field determination up to degree 25 with a signal-to-noise ratio of 10
Real Time Global Tests of the ALICE High Level Trigger Data Transport Framework
The High Level Trigger (HLT) system of the ALICE experiment is an online
event filter and trigger system designed for input bandwidths of up to 25 GB/s
at event rates of up to 1 kHz. The system is designed as a scalable PC cluster,
implementing several hundred nodes. The transport of data in the system is
handled by an object-oriented data flow framework operating on the basis of the
publisher-subscriber principle, being designed fully pipelined with lowest
processing overhead and communication latency in the cluster. In this paper, we
report the latest measurements where this framework has been operated on five
different sites over a global north-south link extending more than 10,000 km,
processing a ``real-time'' data flow.Comment: 8 pages 4 figure
Study of W± boson in the ALICE muon spectrometer: considerations and analysis using the HLT tool
W± bosons produced in proton-proton collisions can be observed in the ALICE muon spectrometer via their decay into single muons at a transverse momentum, pt ~ Mw/2 40 GeV/c. However the identification of these single muons is complicated by a large amount of muonic background, especially in the low pt region. Therefore, it is necessary to apply precise pt cuts below the region of interest. This can be done by means of the High Level Trigger (HLT). In this paper we present the performance of detecting high pt muons at the HLT level. In order to improve the momentum resolution of the L0 trigger, fast clusterization of the tracking chambers together with L0 trigger matching and fast tracking reconstruction is applied. This will reduce the background in the high pt muon analysis
The radio science experiment with BepiColombo mission to Mercury
BepiColombo is a joint ESA/JAXA mission to Mercury with challenging objectives regarding geophysics, geodesy and fundamental physics. The Mercury Orbiter Radio science Experiment (MORE) is one of the on-board experiments, including three different but linked experiments: gravimetry, rotation and relativity. Using radio observables (range and range-rate) performed with very accurate tracking from ground stations, together with optical observations from the on-board high resolution camera (SIMBIO-SYS) and accelerometer readings from the on-board accelerometer (ISA), MORE will be able to measure with unprecedented accuracy the global gravity field of Mercury and the rotation state of the planet. In this work we present the results of a numerical full-cycle simulation of the gravimetry and rotation experiments of MORE: we discuss the accuracies which can be achieved, focussing in particular on the possible benefits from the use of optical observations in support to the tracking measurements
Study of dimuon production in Indium-Indium collisions with the NA60 experiment
The NA60 experiment at the CERN-SPS is devoted to the study of dimuon
production in heavy-ion and proton-nucleus collisions. We present preliminary
results from the analysis of Indium-Indium collisions at 158 GeV per nucleon.
The topics covered are low mass vector meson production, J/psi production and
suppression, and the feasibility of the open charm measurement from the dimuon
continuum in the mass range below the J/psi peak.Comment: Contribution at XXXXth Rencontres de Moriond, "QCD and High Energy
Hadronic Interactions
First results from the NA60 experiment at CERN
Since 1986, several heavy ion experiments have studied some signatures of the
formation of the quark-gluon plasma and a few exciting results have been found.
However, some important questions are still unanswered and require new
measurements. The NA60 experiment, with a new detector concept that vastly
improves dimuon detection in proton-nucleus and heavy-ion collisions, studies
several of those open questions, including the production of open charm. This
paper presents the experiment and some first results from data collected in
2002.Comment: Paper presented at the XXXVIII Rencontres de Moriond, QCD and High
Energy Hadronic Interactions, Les Arcs, March 22-29, 2003. 4 pages, 6 figure
Meson Production in In-In Collisions and the Puzzle
The NA60 experiment measured dimuon production in In-In collisions at 158
AGeV. This paper presents a high statistics measurement of with
the specific objective to provide insight on the puzzle, i.e. the
difference in the inverse slopes and absolute yields measured by NA49 and
NA50 in the kaon and lepton channel, respectively. Transverse momentum
distributions were studied as a function of centrality. The slope parameter
shows a rapid increase with centrality, followed by a saturation. Variations of
with the fit range of the order of 15 MeV were observed, possibly as a
consequence of radial flow. The meson yield normalized to the number of
participants increases with centrality and is consistently higher than the
yield measured by the NA49 experiment at any centrality.Comment: 4 Pages, 2 Figures. Proceedings of the 20 International
Conference on Ultra-Relativistic Nucleus Nucleus Collision
Per un pugno di libri... scientifici : a divulgation project for high-school students
We discuss the project "Per un pugno di libri... scientifici", aimed at bringing the young generations closer to scientific culture through reading divulgation books about physics. The project, which is addressed to high-school students, is sponsored by INFN and other national and regional research institutions, along with physics departments of some Italian universities
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