MPI fur Kernphysik

Heidelberg, Germany

MPI fur Kernphysik

Heidelberg, Germany
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Bonnivard V.,French National Center for Scientific Research | Combet C.,French National Center for Scientific Research | Daniel M.,University of Liverpool | Funk S.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 10 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2015

Dwarf spheroidal (dSph) galaxies are prime targets for present and future Γ-ray telescopes hunting for indirect signals of particle darkmatter. The interpretation of the data requires careful assessment of their dark matter content in order to derive robust constraints on candidate relic particles. Here, we use an optimized spherical Jeans analysis to reconstruct the 'astrophysical factor' for both annihilating and decaying dark matter in 21 known dSphs. Improvements with respect to previous works are: (i) the use of more flexible luminosity and anisotropy profiles to minimize biases, (ii) the use of weak priors tailored on extensive sets of contamination-free mock data to improve the confidence intervals, (iii) systematic cross-checks of binned and unbinned analyses on mock and real data, and (iv) the use of mock data including stellar contamination to test the impact on reconstructed signals. Our analysis provides updated values for the dark matter content of 8 'classical' and 13 'ultrafaint' dSphs, with the quoted uncertainties directly linked to the sample size; themore flexible parametrizationwe use results in changes compared to previous calculations. This translates into our ranking of potentiallybrightest and most robust targets-namely Ursa Minor, Draco, Sculptor-and of the more promising, but uncertain targets-namely Ursa Major 2, Coma-for annihilating dark matter. Our analysis of Segue 1 is extremely sensitive to whether we include or exclude a few marginal member stars, making this target one of the most uncertain. Our analysis illustrates challenges that will need to be addressed when inferring the dark matter content of new 'ultrafaint' satellites that are beginning to be discovered in southern sky surveys. © 2015 The Authors.

Eliseev S.,MPI fur Kernphysik | Bohm C.,MPI fur Kernphysik | Beck D.,Helmholtz Center for Heavy Ion Research | Blaum K.,MPI fur Kernphysik | And 19 more authors.
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2010

The study of nuclear electron capture (EC) offers an exciting alternative for the determination of the neutrino mass. Whereas only tritium and 187Re can be used in the case of β-decay experiments involving the anti-neutrino, a potentially large number of EC-nuclides can be used in experiments involving the monochromatic neutrino. This alternative to β-decay experiments requires an accurate measurement of QEC-values of appropriate candidates. In the present work we initiate a search for such a candidate and determined the QEC-value of the electron capture in 194Hg by direct mass measurements of 194Hg and 194Au. The new QEC-value of 29(4) keV determined by the ISOLTRAP Penning-trap mass spectrometer at ISOLDE/CERN forbids the K-capture for 194Hg. However, it allows a determination of the neutrino mass by a combination of a micro-calorimetric measurement of the de-excitation spectrum from L-capture in 194Hg and a comparable QEC-value remeasurement by high-precision Penning trap mass spectrometry. © 2010 Elsevier B.V.

Hsu H.-W.,MPI fur Kernphysik | Hsu H.-W.,University of Heidelberg | Kempf S.,MPI fur Kernphysik | Kempf S.,TU Braunschweig | And 9 more authors.
AIP Conference Proceedings | Year: 2010

The stream particles are nanometer-size dust particles ejected from the jovian and the saturnian systems with velocities greater than 100kms -1. Due to their small size, stream particles are more sensitive to the electromagnetic force than to gravity. It has been shown by the simulations that the stream - particle dynamics in interplanetary space should be dominated by the interplanetary magnetic field (IMF) [15]. Based on the measurements by the dust detector on board the Cassini spacecraft, we found that the detection patterns of the stream particles are well correlated with the IMF structures. As the spacecraft crosses the compression regions of the Co - rotation Interaction Regions (CIRs), not only the directionality of the impacts changes with the field direction, but also the impact signal and rate vary with an increase of field strength. By understanding the interaction of stream particles and the solar wind, the data provide important insight to the formation environments of the stream particles and is an unique opportunity to study the dust-moon-magnetosphere system of Jupiter and Saturn. © 2010 American Institute of Physics.

Shu A.,Colorado Center for Lunar Dust and Atmospheric Studies | Shu A.,University of Colorado at Boulder | Shu A.,Laboratory for Atmospheric and Space Physics | Collette A.,Colorado Center for Lunar Dust and Atmospheric Studies | And 24 more authors.
Review of Scientific Instruments | Year: 2012

A hypervelocity dust accelerator for studying micrometeorite impacts has been constructed at the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS) at the University of Colorado. Based on the Max-Planck-Institüt für Kernphysik (MPI-K) accelerator, this accelerator is capable of emitting single particles of a specific mass and velocity selected by the user. The accelerator consists of a 3 MV Pelletron generator with a dust source, four image charge pickup detectors, and two interchangeable target chambers: a large high-vacuum test bed and an ultra-high vacuum impact study chamber. The large test bed is a 1.2 m diameter, 1.5 m long cylindrical vacuum chamber capable of pressures as low as 10-7 torr while the ultra-high vacuum chamber is a 0.75 m diameter, 1.1 m long chamber capable of pressures as low as 10 -10 torr. Using iron dust of up to 2 microns in diameter, final velocities have been measured up to 52 km/s. The spread of the dust particles and the effect of electrostatic focusing have been measured using a long exposure CCD and a quartz target. Furthermore, a new technique of particle selection is being developed using real time digital filtering techniques. Signals are digitized and then cross-correlated with a shaped filter, resulting in a suppressed noise floor. Improvements over the MPI-K design, which include a higher operating voltage and digital filtering for detection, increase the available parameter space of dust emitted by the accelerator. The CCLDAS dust facility is a user facility open to the scientific community to assist with instrument calibrations and experiments. © 2012 American Institute of Physics.

Bunyatyan A.,MPI fur Kernphysik | Bunyatyan A.,Yerevan Physics Institute
Proceedings - 38th International Symposium on Multiparticle Dynamics, ISMD 2008 | Year: 2012

Small-angle detectors at the LHC give access to a broad physics programme within and beyond the Standard Model. We present here some studies of forward physics processes related to underling event, multi-parton interactions and low-x QCD dynamics.

Mocker A.,University of Stuttgart | Bugiel S.,University of Stuttgart | Auer S.,AM Associates | Baust G.,MPI fur Kernphysik | And 20 more authors.
Review of Scientific Instruments | Year: 2011

Investigating the dynamical and physical properties of cosmic dust can reveal a great deal of information about both the dust and its many sources. Over recent years, several spacecraft (e.g., Cassini, Stardust, Galileo, and Ulysses) have successfully characterised interstellar, interplanetary, and circumplanetary dust using a variety of techniques, including in situ analyses and sample return. Charge, mass, and velocity measurements of the dust are performed either directly (induced charge signals) or indirectly (mass and velocity from impact ionisation signals or crater morphology) and constrain the dynamical parameters of the dust grains. Dust compositional information may be obtained via either time-of-flight mass spectrometry of the impact plasma or direct sample return. The accurate and reliable interpretation of collected spacecraft data requires a comprehensive programme of terrestrial instrument calibration. This process involves accelerating suitable solar system analogue dust particles to hypervelocity speeds in the laboratory, an activity performed at the Max Planck Institut fr Kernphysik in Heidelberg, Germany. Here, a 2 MV Van de Graaff accelerator electrostatically accelerates charged micron and submicron-sized dust particles to speeds up to 80 km s-1. Recent advances in dust production and processing have allowed solar system analogue dust particles (silicates and other minerals) to be coated with a thin conductive shell, enabling them to be charged and accelerated. Refinements and upgrades to the beam line instrumentation and electronics now allow for the reliable selection of particles at velocities of 1-80 km s-1 and with diameters of between 0.05 m and 5 m. This ability to select particles for subsequent impact studies based on their charges, masses, or velocities is provided by a particle selection unit (PSU). The PSU contains a field programmable gate array, capable of monitoring in real time the particles' speeds and charges, and is controlled remotely by a custom, platform independent, software package. The new control instrumentation and electronics, together with the wide range of accelerable particle types, allow the controlled investigation of hypervelocity impact phenomena across a hitherto unobtainable range of impact parameters. © 2011 American Institute of Physics.

Mocker A.,University of Stuttgart | Mocker A.,University of Colorado at Boulder | Grun E.,MPI fur Kernphysik | Grun E.,University of Colorado at Boulder | And 5 more authors.
Journal of Applied Physics | Year: 2012

In-situ measurements, the direct interception and analysis of dust particles by spacecraft-based instrumentation, provide insights into the dynamical, physical and chemical properties of cosmic dust. The most sensitive detection methods for dust particles in space are based on impact ionization. Laser ionization is used for the test, development, and calibration of impact ionization instruments and to complement laboratory based particle impact experiments. A typical setup uses a 355 nm Nd-YAG laser with a pulse length of about 5 ns. It is necessary to investigate the properties of both processes with respect to their comparability. A study was performed to find out to what extent laser ionization can be used to simulate impact ionization. The findings show that laser ionization and impact ionization show similarities, which can be used to test the functionality of dust impact detectors, especially time-of-flight instruments. Our paper provides information on what extent these similarities hold and where their limits are. © 2012 American Institute of Physics.

Hsu H.-W.,MPI fur Kernphysik | Hsu H.-W.,University of Heidelberg | Hsu H.-W.,University of Colorado at Boulder | Postberg F.,MPI fur Kernphysik | And 11 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011

We analyze the dynamics and composition of Saturnian stream particles measured by the Cosmic Dust Analyser (CDA) onboard the Cassini spacecraft. To reconstruct the dynamical properties of Saturnian stream particles, we adopt a backward tracing method with in situ solar wind measurements to filter out the influence of the interplanetary magnetic field. Our results show that stream particles from Saturn have sizes ranging from 2 to 8 nm (radius) with ejection velocities between 50 and 200 kms-1. Moreover, the derived "ejection region" of stream particles in the outer part of Saturn's E ring is indicative of the dust charging condition profile in the planet's magnetosphere. By using the Cassini magnetospheric plasma measurements as input, our ejection model considers stochastic charging and well reproduces the dynamical properties of stream particles derived from backward simulations. An updated analysis of CDA stream-particle mass spectra confirms that the silicateous material is the most probable composition of Saturnian stream particles, in contrast to E ring particles whose composition is dominated by water ice. This compositional discrepancy can be reproduced by our model if the different sputter efficiencies of silicateous material and water ice are considered. We suggest that silicateous impurities released from icy grains at the outer E ring are the most probable source of Saturnian stream particles. Finally, we discuss the role of dust particles as a mobile neutral reservoir in Saturn's magnetosphere which may be responsible for certain features in the Cassini O and O2 + measurements. Copyright 2011 by the American Geophysical Union.

Hsu H.-W.,MPI fur Kernphysik | Hsu H.-W.,University of Heidelberg | Kempf S.,MPI fur Kernphysik | Kempf S.,TU Braunschweig | Jackman C.M.,Imperial College London
Icarus | Year: 2010

In January 2004 the dust instrument on the Cassini spacecraft detected the first high-velocity grain expelled from Saturn - a so-called stream particle. Prior to Cassini's arrival at Saturn in July 2004 the instrument registered 801 faint impacts, whose impact signals showed the characteristic features of a high-velocity impact by a tiny grain. The impact rates as well as the directionality of the stream particles clearly correlate with the sector structure of the interplanetary magnetic field (IMF). The Cosmic Dust Analyser (CDA) registered stream particles dominantly during periods when the IMF direction was tangential to the solar wind flow and in the prograde direction. This finding provides clear evidence for a continuous outflow of tiny dust grains with similar properties from the saturnian system. Within the compressed part of co-rotating interaction regions (CIRs) of the IMF, characterized by enhanced magnetic field strength and compressed solar wind plasma, CDA observed impact bursts of faster stream particles. We find that the bursts result from the stream particles being sped up inside the compressed CIR regions. Our analysis of the stream-particle dynamics inside rarefaction regions of the IMF implies that saturnian stream particles have sizes between 2 and 9 nm and exit the saturnian systems closely aligned with the planet's ring plane with speeds in excess of 70 km s-1. © 2009 Elsevier Inc. All rights reserved.

Kempf S.,MPI fur Kernphysik | Kempf S.,TU Braunschweig | Beckmann U.,MPI fur Kernphysik | Schmidt J.,University of Potsdam
Icarus | Year: 2010

Pre-Cassini models of Saturn's E ring [Horányi, M., Burns, J., Hamilton, D., 1992. Icarus 97, 248-259; Juhász, A., Horányi, M., 2002. J. Geophys. Res. 107, 1-10] failed to reproduce its peculiar vertical structure inferred from Earth-bound observations [de Pater, I., Martin, S.C., Showalter, M.R., 2004. Icarus 172, 446-454]. After the discovery of an active ice-volcanism of Saturn's icy moon Enceladus the relevance of the directed injection of particles for the vertical ring structure of the E ring was swiftly recognised [Juhász, A., Horányi, M., Morfill, G.E., 2007. Geophys. Res. Lett. 34, L09104; Kempf, S., Beckmann, U., Moragas-Klostermeyer, G., Postberg, F., Srama, R., Economou, T., Schmidt, J., Spahn, F., Grün, E., 2008. Icarus 193, 420-437]. However, simple models for the delivery of particles from the plume to the ring predict a too small vertical ring thickness and overestimate the amount of the injected dust. Here we report on numerical simulations of grains leaving the plume and populating the dust torus of Enceladus. We run a large number of dynamical simulations including gravity and Lorentz force to investigate the earliest phase of the ring particle life span. The evolution of the electrostatic charge carried by the initially uncharged grains is treated selfconsistently. Freshly ejected plume particles are moving in almost circular orbits because the Enceladus orbital speed exceeds the particles' ejection speeds by far. Only a small fraction of grains that leave the Hill sphere of Enceladus survive the next encounter with the moon. Thus, the flux and size distribution of the surviving grains, replenishing the ring particle reservoir, differs significantly from the flux and size distribution of the particles freshly ejected from the plume. Our numerical simulations reproduce the vertical ring profile measured by the Cassini Cosmic Dust Analyzer (CDA) [Kempf, S., Beckmann, U., Moragas-Klostermeyer, G., Postberg, F., Srama, R., EconoDmou, T., Smchmidt, J., Spahn, F., Grün, E., 2008. Icarus 193, 420-437]. From our simulations we calculate the deposition rates of plume particles hitting Enceladus' surface. We find that at a distance of 100 m from a jet a 10 m sized ice boulder should be covered by plume particles in 105-106 years. © 2009 Elsevier Inc. All rights reserved.

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