Low temperature magnetic transition of chromite in ordinary chondrites

International audienceWe present low temperature magnetic data (thermal demagnetization, hysteresis) obtained on thirty three ordinary chondrite meteorites. A magnetic transition is observed in the 40–80 K range (average 66 K), and is interpreted as a ferrimagnetic to paramagnetic phase transition. We present quantitative analyses of changes in magnetization across the magnetic phase transition and chemical elemental analyses to argue that chromite, a common accessory mineral in meteorites, is the mineral undergoing the phase transition, and not troilite or tetrataenite as proposed in previous studies. Moreover, we observe a correlation between the measured Curie temperature and chemical composition of chromites in ordinary chondrites. Low temperature magnetic measurement are thus a sensitive indicator of chromite composition in these meteorites, and as such a possible proxy to the understanding of their thermal metamorphism

Localization and characterization of buried magnetic structures using a multi-scale tomography application to archaeological structures on Fox-Amphoux site

International audienceWe want to characterize and localize the depth of archaeological structures from the measurement of magnetic potential anomalies above ground to have a non-destructive test of an archaeological site and to suggest a strategy of excavation. A class of tomography methods used in potential field theory are based on cross-correlation technique (Patella), Euler method or generalized Hilbert transform (Nabighian). New class of tomography methods is based on real continuous wavelet transform for characterizing and localizing “homogeneous” buried sources (magnetic, electric and gravity). These last methods use the properties of the Poisson kernel (real by definition), and the wavelet theory. We relax here, the assumption on sources and introduce a method that we call “multi-scale tomography”. Our approach is based on the harmonic extension of observated magnetic field to produce a complex source by the use of a complex Poisson kernel solution of the Laplace equation for complex potential field. A phase and modulus are defined. We show that the phase provides additional information on the total magnetic inclination and the structure of sources, while the modulus allows us to characterize its spatial location, depth and “effective degree”. Results of excavation of Roman kilns of Fox Amphoux site (Var, France) are then compared to the estimates

Multi-scale or multipolar tomography development of electrical or magnetic SP data: Applications on archeological prospecting

1 p.International audienceRecent tomography methods developped in potential field theory are based on monopolar or dipolar probability tomography methods (Patella 1997, Mauriello and Patella 1999. These kinds of algorithms needs to have a knowledge of the source, in particular its multipolar order (ie: dipole, monopole, quadripole,...etc). A new method based on the complex continuous wavelet transform (CCWT ) allows to obtain a multipolar tomography of the subsurface at different spatial scales, without ''apriori" information of the source. This method used the potential theory combined to dilation, covariance and phase properties of the CCWT (Saracco et al 2004, Moreau et al 1997). This multi-scale or multipolar tomography has been used to characterize and localize with success in depth, degree and orientation, potential sources from surface measurements of anomalies SP data in different applications (e.g. subsurface hydrogeophysics; hydrodynamic flux circulations modelling hydrothermal system or to define electrical precursors in volcanic risk; or in magnetic survey). The presentation of this method compared to other methods will be presented on noisy and synthetic magnetic and electrical data. Results on real SP data will be presented in archeological prospecting and volcano risk

Experimental verification of the “Burns” hypothesis for the formation of Meridiani Planum sediments through weathering of sulfide-rich deposits.

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Gallium Crystal Chemistry in Synthetic Goethites

The distribution of Ga and Al atoms within the octahedral sheets of synthetic goethites has been investigated by XRD and Ga K-edge XANES and EXAFS spectroscopies. XRD results indicate a solid solution between goethite (α-FeOOH) and GaGoe4 (40 mol% of Ga). The XANES data indicate the presence of 6Ga in the solid solution. The fitting procedures for EXAFS spectra show no evidence of preferential octahedral site substitutions for Ga

Study of coherent J/ψJ/\psi production in lead-lead collisions at sNN \sqrt{{\mathrm{s}}_{\mathrm{NN}}} = 5 TeV

International audienceCoherent production of J/ψ mesons is studied in ultraperipheral lead-lead collisions at a nucleon-nucleon centre-of-mass energy of 5 TeV, using a data sample collected by the LHCb experiment corresponding to an integrated luminosity of about 10 μb$^{−1}$. The J/ψ mesons are reconstructed in the dimuon final state and are required to have transverse momentum below 1 GeV. The cross-section within the rapidity range of 2.0 < y < 4.5 is measured to be 4.45 ± 0.24 ± 0.18 ± 0.58 mb, where the first uncertainty is statistical, the second systematic and the third originates from the luminosity determination. The cross-section is also measured in J/ψ rapidity intervals. The results are compared to predictions from phenomenological models.[graphic not available: see fulltext

Measurement of χc1_{c1}(3872) production in proton-proton collisions at s \sqrt{s} = 8 and 13 TeV

International audienceThe production cross-section of the χ$_{c1}$(3872) state relative to the ψ(2S) meson is measured using proton-proton collision data collected with the LHCb experiment at centre-of-mass energies of $\sqrt{s}$ = 8 and 13 TeV, corresponding to integrated luminosities of 2.0 and 5.4 fb$^{−1}$, respectively. The two mesons are reconstructed in the J/ψπ$^{+}$π$^{−}$ final state. The ratios of the prompt and nonprompt χ$_{c1}$(3872) to ψ(2S) production cross-sections are measured as a function of transverse momentum, p$_{T}$, and rapidity, y, of the χ$_{c1}$(3872) and ψ(2S) states, in the kinematic range 4 < p$_{T}$< 20 GeV/c and 2.0 < y < 4.5. The prompt ratio is found to increase with p$_{T}$, independently of y. For the prompt component, the double ratio of the χ$_{c1}$(3872) and ψ(2S) production cross-sections between 13 and 8 TeV is observed to be consistent with unity, independent of p$_{T}$ and centre-of-mass energy.[graphic not available: see fulltext

Search for the doubly charmed baryon Ξcc+ {\varXi}_{cc}^{+} in the Ξc+π−π+ {\varXi}_c^{+}{\pi}^{-}{\pi}^{+} final state

International audienceA search for the doubly charmed baryon ${\varXi}_{cc}^{+}$ is performed in the ${\varXi}_c^{+}{\pi}^{-}{\pi}^{+}$ invariant-mass spectrum, where the ${\varXi}_c^{+}$ baryon is reconstructed in the pK$^{−}$π$^{+}$ final state. The study uses proton-proton collision data collected with the LHCb detector at a centre- of-mass energy of 13 TeV, corresponding to a total integrated luminosity of 5.4 fb$^{−1}$. No significant signal is observed in the invariant-mass range of 3.4–3.8 GeV/c$^{2}$. Upper limits are set on the ratio of branching fractions multiplied by the production cross-section with respect to the ${\varXi}_{cc}^{++}$→ (${\varXi}_c^{+}$→ pK$^{−}$π$^{+}$)π$^{+}$ decay for different ${\varXi}_{cc}^{+}$ mass and lifetime hypotheses in the rapidity range from 2.0 to 4.5 and the transverse momentum range from 2.5 to 25 GeV/c. The results from this search are combined with a previously published search for the ${\varXi}_{cc}^{+}$→${\varLambda}_c^{+}$K$^{−}$π$^{+}$ decay mode, yielding a maximum local significance of 4.0 standard deviations around the mass of 3620 MeV/c$^{2}$, including systematic uncertainties. Taking into account the look-elsewhere effect in the 3.5–3.7 GeV/c$^{2}$ mass window, the combined global significance is 2.9 standard deviations including systematic uncertainties.[graphic not available: see fulltext