Extraction of the s-wave pi N scattering lengths from data on pionic atoms

For many years a combined analysis of pionic hydrogen and deuterium atoms has been known as a good tool to extract information on the isovector and especially on the isoscalar s-wave pN scattering length. However, given the smallness of the isoscalar scattering length, the analysis becomes useful only if the pion–deuteron scattering length is controlled theoretically to a high accuracy comparable to the experimental precision. To achieve the required few-percent accuracy one needs theoretical control over all isospin-conserving three-body pNN !pNN operators up to one order before the contribution of the dominant unknown (N†N)2pp contact term. This term appears at next-to-next-to-leading order in Weinberg counting. In addition, one needs to include isospin-violating effects in both two-body (pN) and three-body (pNN) operators. In this talk we discuss the results of the recent analysis where these isospin-conserving and -violating effects have been carefully taken into account. Based on this analysis, we present the up-to-date values of the s-wave pN scattering lengths.

Isospin breaking in pion–deuteron scattering and the pion–nucleon scattering lengths

In recent years, high-accuracy data for pionic hydrogen and deuterium have become the primary source of information on the pion–nucleon scattering lengths. Matching the experimental precision requires, in particular, the study of isospin-breaking corrections both in pion– nucleon and pion–deuteron scattering. We review the mechanisms that lead to the cancellation of potentially enhanced virtual-photon corrections in the pion–deuteron system, and discuss the subtleties regarding the definition of the pion–nucleon scattering lengths in the presence of electromagnetic interactions by comparing to nucleon–nucleon scattering. Based on the p±p channels we find for the virtual-photon-subtracted scattering lengths in the isospin basis a1/2/ g= (170.5±2.0) · 10−3M−1p and a3/2/ g= (−86.5±1.8) · 10−3M−1p .

ROSINA/DFMS capabilities to measure isotopic ratios in water at comet 67P/Churyumov–Gerasimenko

The likelihood that comets may have delivered part of the water to Earth has been reinforced by the recent observation of the earth-like D/H ratio in Jupiter-family comet 103P/Hartley 2 by Hartogh et al. (2011). Prior to this observation, results from several Oort cloud comets indicated a factor of 2 enrichment of deuterium relative to the abundance at Earth. The European Space Agency’s Rosetta spacecraft will encounter comet 67P/Churyumov-Gerasimenko, another Jupiter-family comet of likely Kuiper belt origin, in 2014 and accompany it from almost aphelion to and past perihelion. Onboard Rosetta is the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) which consists of two mass spectrometers and a pressure sensor [Balsiger et al. 2007]. With its unprecedented mass resolution, for a space-borne instrument, the Double Focusing Mass Spectrometer (DFMS), one of the major subsystems of ROSINA, will be able to obtain unambiguously the ratios of the isotopes in water from in situ measurements in the coma around the comet. We will discuss the performance of this sensor on the basis of measurements of the terrestrial hydrogen and oxygen isotopic ratios performed with the flight spare instrument in the lab. We also show that the instrument on Rosetta is capable of measuring the D/H even in the very low density water background released by the spacecraft. This capability demonstrates that ROSINA should obtain very sensitive measurements of these ratios in the cometary environment. These measurements will allow detection of fractionation as function of the distance from the nucleus as well as fractionation due to mechanisms that are correlated with heliocentric distance.

Triple isotope (δD, δ17O, δ18O) study on precipitation, drip water and speleothem fluid inclusions for a Western Central European cave (NW Switzerland)

Deuterium (δD) and oxygen (δ18O) isotopes are powerful tracers of the hydrological cycle and have been extensively used for paleoclimate reconstructions as they can provide information on past precipitation, temperature and atmospheric circulation. More recently, the use of δ17O excess derived from precise measurement of δ17O and δ18O gives new and additional insights in tracing the hydrological cycle whereas uncertainties surround this proxy. However, 17O excess could provide additional information on the atmospheric conditions at the moisture source as well as about fractionations associated with transport and site processes. In this paper we trace water stable isotopes (δD,δ17O and δ18O) along their path from precipitation to cave drip water and finally to speleothem fluid inclusions for Milandre cave in northwestern Switzerland. A two year-long daily resolved precipitation isotope record close to the cave site is compared to collected cave drip water (3 months average resolution) and fluid inclusions of modern and Holocene stalagmites. Amount weighted mean δD,δ18O and δ17O are -71.0‰, -9.9‰, -5.2‰ for precipitation, -60.3‰, -8.7‰, -4.6‰ for cave drip water and -61.3‰, -8.3‰, -4.7‰ for recent fluid inclusions respectively. Second order parameters have also been derived in precipitation and drip water and present similar values with 18 per meg for 17O excess whereas d-excess is 1.5‰ more negative in drip water. Furthermore, the atmospheric signal is shifted towards enriched values in the drip water and fluid inclusions (Δ of ~ + 10‰ for δD). The isotopic composition of cave drip water exhibits a weak seasonal signal which is shifted by around 8 - 10 months (groundwater residence time) when compared to the precipitation. Moreover, we carried out the first δ17O measurement in speleothem fluid inclusions, as well as the first comparison of the δ17 O behaviour from the meteoric water to the fluid inclusions entrapment in speleothems. This study on precipitation, drip water and fluid inclusions will be used as a speleothem proxy calibration for Milandre cave in order to reconstruct paleotemperatures and moisture source variations for Western Central Europe.

Imperial Eyes. Van Dycks Porträtmalerei als globale Technologie

Zu Beginn des 17. Jahrhunderts hatte sich die Malerei in Antwerpen vor allem durch Rubens als Medium einer zunehmend global verbundenen Welt etabliert. Doch auch zahlreiche von Van Dycks Porträts sind Zeugnisse eines oft hochgradig ambivalenten Kosmopolitismus. Neben Gemälden von international agierenden Antwerpener Händlern und Gelehrten fertigte der Künstler auch in Genua und England Porträts der adligen Elite an, in welchen sich deren globale Erfahrungen und Ambitionen spiegelten. Van Dyck reagierte in der Inszenierung der Marchesa Elena Grimaldi Cattaneo, mit einem schwarzen Sklaven, wie in der des Earl of Denbigh, zwischen einheimischen und exotischen Elementen, auf spezifische Anforderungen an das repräsentative Porträt im Zeitalter des disenclavement. Diese Anforderungen werden besonders deutlich in dem für eine geplante Expedition nach Madagaskar entstandenen Porträt des Earls of Arundel und dessen Frau Alethea Talbot. Das Gemälde verbindet Elemente herrschaftlicher, merkantilistischer und intellektueller Selbststilisierung mit einer Reduktion auf wenige, innovative Elemente. Die majestätische Inszenierung des Paars ist nur in einem globalen Kontext zu erklären, so dass sich die Frage nach der Funktion des in mehreren Werkstattkopien erhaltenen Gemäldes stellt. Hatte Van Dyck in seiner Komposition eine Lösung gefunden, die im Kontext des englischen Hofes, möglicherweise als Teil eines Festes, wie auch für potentielle Investoren, sowie die verarmte Landbevölkerung, die in der Indentur ihre einzige Hoffnung sah, gleichermaßen überzeugend wirkte? Die Hybris in dem überlebensgroßen Porträts des Paares, das mit leuchtend heller Haut, in kostbar glänzende Stoffe gekleidet und mit modernen Messinstrumenten in den Händen dargestellt ist, lässt es als ideales Medium der globalen Ambitionen des Paars erscheinen.

Cometary Isotopic Measurements

Isotopic ratios in comets provide keys for the understanding of the origin of cometary material, and the physical and chemical conditions in the early Solar Nebula. We review here measurements acquired on the D/H, N-14/N-15, O-16/O-18, C-12/C-13, and S-32/S-34 ratios in cometary grains and gases, and discuss their cosmogonic implications. The review includes analyses of potential cometary material available in collections on Earth, recent measurements achieved with the Herschel Space Observatory, large optical telescopes, and Rosetta, as well as recent results obtained from models of chemical-dynamical deuterium fractionation in the early solar nebula. Prospects for future measurements are presented.

Scintillation efficiency of liquid argon in low energy neutron-argon scattering

Experiments searching for weak interacting massive particles with noble gases such as liquid argon require very low detection thresholds for nuclear recoils. A determination of the scintillation efficiency is crucial to quantify the response of the detector at low energy. We report the results obtained with a small liquid argon cell using a monoenergetic neutron beam produced by a deuterium-deuterium fusion source. The light yield relative to electrons was measured for six argon recoil energies between 11 and 120 keV at zero electric drift field.