Role of the experimental filter in obtaining the Arrhenius plot in multifragmentation reactions

Recently it has been argued that the linear relation between the transverse energy and the apparent probability to emit a fragment proves that the total system is in thermal equilibrium. It is shown, for a specific reaction Xe+Sn at 50 A.MeV, that the same behavior is obtained in the context of Quantum Molecular Dynamical without invoking the idea of equilibrium. The linear dependance is shown to be a detector effect.Comment: 11 pages, 4 Postscript figures. Submitted Phys. Rev. Let

ÉTATS A GRAND NOMBRE DE QUASI-PARTICULE DANS LES ISOTOPES PAIRS DE PLOMB

Une étude par distribution spectrale dans les sous-espaces définis par leur nombre de quasi-particules a été effectuée dans les isotopes pairs de plomb. La comparaison avec des résultats obtenus dans les isotopes d'étain montre que le recouvrement entre les différents sous-espaces est fortement lié à l'interaction résiduelle utilisée. En particulier des états à grand nombre de quasi-particules sont présents à basse énergie. Le problème des états spurieux inhérent à cette méthode, qui sont responsables d'une surestimation du couplage, est abordé et différentes corrections sont proposées aussi bien sur les dimensions, les centroïdes et les largeurs des sous-espaces

On the influence of statistics on the determination of the mean value of the depth of shower maximum for ultra high energy cosmic ray showers

The chemical composition of ultra high energy cosmic rays is still uncertain. The latest results obtained by the Pierre Auger Observatory and the HiRes Collaboration, concerning the measurement of the mean value and the fluctuations of the atmospheric depth at which the showers reach the maximum development, Xmax, are inconsistent. From comparison with air shower simulations it can be seen that, while the Auger data may be interpreted as a gradual transition to heavy nuclei for energies larger than ~ 2-3x10^18 eV, the HiRes data are consistent with a composition dominated by protons. In Ref. [1] it is suggested that a possible explanation of the observed deviation of the mean value of Xmax from the proton expectation, observed by Auger, could originate in a statistical bias arising from the approximated exponential shape of the Xmax distribution, combined with the decrease of the number of events as a function of primary energy. In this paper we consider a better description of the Xmax distribution and show that the possible bias in the Auger data is at least one order of magnitude smaller than the one obtained when assuming an exponential distribution. Therefore, we conclude that the deviation of the Auger data from the proton expectation is unlikely explained by such statistical effect.Comment: To be published in Journal of Physics G: Nuclear and Particle Physic

Prospects for GMRT to Observe Radio Waves from UHE Particles Interacting with the Moon

Ultra high energy (UHE) particles of cosmic origin impact the lunar regolith and produce radio signals through Askaryan effect, signals that can be detected by Earth based radio telescopes. We calculate the expected sensitivity for observation of such events at the Giant Metrewave Radio Telescope (GMRT), both for UHE cosmic rays (CR) and UHE neutrino interactions. We find that for 30 days of observation time a significant number of detectable events is expected above $10^{20}$ eV for UHECR or neutrino fluxes close to the current limits. Null detection over a period of 30 days will lower the experimental bounds on UHE particle fluxes by magnitudes competitive to both present and future experiments at the very highest energies.Comment: 21 pages, 9 figure

First steps towards a target laboratory at GANIL

The development of large-isotopically enriched 208Pb and 209Bi targets and the production of thin carbon films are described. Their use on rotating wheels in heavy-ion fusion reactions with intense 58Fe, 76Ge and 48Ca beams is reported

Sub-Femto-g free fall for space-based gravitational wave observatories : LISA Pathfinder results

We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 +/- 0.1 fm s(-2)/root Hz, or (0.54 +/- 0.01) x 10(-15) g/root Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 +/- 0.3) fm/root Hz, about 2 orders of magnitude better than requirements. At f <= 0.5 mHz we observe a low-frequency tail that stays below 12 fm s(-2)/root Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA.Peer ReviewedPostprint (published version

LISACode : A scientific simulator of LISA

A new LISA simulator (LISACode) is presented. Its ambition is to achieve a new degree of sophistication allowing to map, as closely as possible, the impact of the different sub-systems on the measurements. LISACode is not a detailed simulator at the engineering level but rather a tool whose purpose is to bridge the gap between the basic principles of LISA and a future, sophisticated end-to-end simulator. This is achieved by introducing, in a realistic manner, most of the ingredients that will influence LISA's sensitivity as well as the application of TDI combinations. Many user-defined parameters allow the code to study different configurations of LISA thus helping to finalize the definition of the detector. Another important use of LISACode is in generating time series for data analysis developments

A Three-Point Cosmic Ray Anisotropy Method

The two-point angular correlation function is a traditional method used to search for deviations from expectations of isotropy. In this paper we develop and explore a statistically descriptive three-point method with the intended application being the search for deviations from isotropy in the highest energy cosmic rays. We compare the sensitivity of a two-point method and a "shape-strength" method for a variety of Monte-Carlo simulated anisotropic signals. Studies are done with anisotropic source signals diluted by an isotropic background. Type I and II errors for rejecting the hypothesis of isotropic cosmic ray arrival directions are evaluated for four different event sample sizes: 27, 40, 60 and 80 events, consistent with near term data expectations from the Pierre Auger Observatory. In all cases the ability to reject the isotropic hypothesis improves with event size and with the fraction of anisotropic signal. While ~40 event data sets should be sufficient for reliable identification of anisotropy in cases of rather extreme (highly anisotropic) data, much larger data sets are suggested for reliable identification of more subtle anisotropies. The shape-strength method consistently performs better than the two point method and can be easily adapted to an arbitrary experimental exposure on the celestial sphere.Comment: Fixed PDF erro