Possible Indication of Narrow Baryonic Resonances Produced in the 1720-1790 MeV Mass Region

Signals of two narrow structures at M=1747 MeV and 1772 MeV were observed in the invariant masses M_{pX} and M_{\pi^{+}X} of the pp->ppX and pp->p\pi^{+}X reactions respectively. Many tests were made to see if these structures could have been produced by experimental artefacts. Their small widths and the stability of the extracted masses lead us to conclude that these structures are genuine and may correspond to new exotic baryons. Several attempts to identify them, including the possible "missing baryons" approach, are discussed.Comment: 17 pages including 8 figures and 3 tables. ReVte

Analysis and modeling of magnetocaloric effect near magnetic phase transition temperature

International audienceMagnetocaloric behavior of gadolinium near room temperature can be correctly described by the Weiss molecular field theory especially in the paramagnetic state. In this paper, this approach is generalized for binary rare earth alloys which present as Gd a second order phase transition. The magnetic entropy variation can be calculated as a function of the temperature and the applied field. This model was tested on a laboratory synthesized samples of Gd-Tb. The agreement between calculations and experiments shows that this model can be easily used for these alloys in order to optimize their composition and adjust their Curie temperatures. For first order transition materials, the observed magnetocaloric effect enhancement can be explained by magnetoelastic effects which are due to the spontaneous crystal deformation and the structure transformation. A model based on the phenomenological approach of Bean Rodbell is developed to describe such a behavior. It highlights the link between the nature of magnetic transition and the magnetocaloric effect. It can be identified by only two parameters: T 0 the Curie temperature without deformation and η an order parameter which characterizes the transition nature. In this paper we apply this model to describe the giant magnetocaloric effect exhibited by the new Mn 1-x (Ti 0.5 V 0.5) x As materials

ANALYSE DES NUCLÉONS ÉJECTÉS DANS UNE RÉACTION QUASI ÉLASTIQUE (p, p?) A 400 MeV

Une expérience de coïncidences (p,pγ) a été réalisée avec des protons incidents de 400 MeV sur différentes cibles 24Mg, 27Al, 28Si, 60Ni auprès de 1'accélérateur Saturne

ICASENSE : une application de l'analyse en composantes indépendantes à l'IRM parallèle

Les récentes méthodes d'imagerie IRM parallèle (SENSE et SMASH) nécessitent une bonne connaissance de la sensibilité des antennes. Celle ci est généralement mesurée lors d'une phase de calibration, ou estimée par filtrage adaptatif spatio-temporel si l'on dispose d'une série d'acquisitions (TSENSE). Nous proposons une formulation du problème en termes de séparation aveugle de sources : une analyse en composantes indépendantes (ICA) permet alors d'extraire les informations de sensibilité des antennes à partir d'une seule acquisition. Des résultats de simulations sont présentés, démontrant l'intérêt de cette nouvelle méthode que nous nommerons ICASENSE

\pi N and \eta p deexcitation channels of the N^* and \Delta baryonic resonances between 1470 and 1680 MeV

Two reactions, pp->ppX and pp->p\pi^+X, are used to study the 1.47<M<1.68 GeV baryonic mass range. Three different final states are considered in the invariant masses: N^* or \Delta^+, p\pi^0, and p\eta. The last two channels are defined by software cuts applied to the missing mass of the first reaction. Several narrow structures are extracted with widths \sigma(\Gamma) varying between 3 and 9 MeV. Some structures are observed in one channel but not in others. Such nonobservation may be due either to the spectrometer momenta limits or to the physics (e.g. no such disintegration channel is allowed from the narrow state considered). We tentatively conclude that the broad Particle Data Group (PDG) baryonic resonances N(1520)D13, N(1535)S11, Delta(1600)P33, and N(1675)D15 are collective states built from several narrow and weakly excited resonances, each having a (much) smaller width than the one reported by PDG.Comment: 29 pages, plus 50 (.png) figures Will be published in a slightly reduced size in Phys. Rev.

Subthreshold K+ production in deuteron and alpha induced nuclear reactions

Double differential cross sections have been measured for pi+ and K+ emitted around midraidity in d+A and He+A collisions at a beam kinetic energy of 1.15 GeV/nucleon. The total pi+ yield increases by a factor of about 2 when using an alpha projectile instead of a deuteron whereas the K+ yield increases by a factor of about 4. According to transport calculations, the K+ enhancement depends both on the number of hadron-hadron collisions and on the energy available in those collisions: their center-of-mass energy increases with increasing number of projectile nucleons

Eta-Helium Quasi-Bound States

The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from parity conservation and Bose symmetry. The much slower momentum variation observed for the reaction amplitude, as compared to that for the analogous pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the eta-4He system and optical model fits indicate that this probably also the case for eta-3He.Comment: LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to Physics Letters

A NON - CONVENTIONAL TYPE OF PERMANENT MAGNET BEARING

L'utilisation d'aimants disposés en quinconces permet d'obtenir un type particulier de palier magnétique, qui présente des propriétés très intéressantes : entrefer plan, force axiale nulle, et absence de couplage dû aux inhomogeneités d'aimantation. Ces paliers sont bien adaptés aux systèmes tournant très lentement, et à ceux en lévitation magnétique partielle.By using staggering magnets, we obtain a particular type of magneting bearings, owning very interesting properties : plane gap, null axial force, and absence of coupling produced by magnetization non-homogeneities. These bearings are well adapted for low rotational speed Systems, and for partially-magnetic suspensions