NPAC (Nuclear/Particle/Astro/Cosmo) Forum

Dark Matter is one of the grand questions of our era. Composing up to 25% of our universe, its cosmological impacts and gravitational evidence appear robust. Not surprisingly, the search for direct detection via a non-gravitational force is now a massive enterprise. Only one experiment (DAMA/LIBRA) has claimed direct detection in the lab by searching for the hypothesized annual rate modulation of the Dark Matter Halo model. CoGeNT is a table top experiment that leverages novel advances in kilogram-scale germanium detectors, thus enabling the study of extremely low-energy ionization events. Armed with the world's lowest energy threshold, CoGeNT set forth to rule out some of DAMA's final hiding places only to be surprised by a statistically-limited annual modulation signal beyond that of known backgrounds. While far from a discovery of dark matter, the CoGeNT results raise important and exciting questions. We will present the latest results from CoGeNT and plans for the future.

Host: 
Karsten Heeger
Speaker: Mike Miller University of Washington, CENPA

 

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Room and Building: 
5280 Chamberlin Hall
During its first three years of operations, since August 2008, the Large Area Telescope on board the Fermi spacecraft (Fermi-LAT) has detected more than 30 GRBs in the ~30 MeV - 300 GeV energy range, and has set upper limits on the E>100 MeV emission on hundreds of GRBs occurring in its field of view. These results revealed new and puzzling features in the temporal and spectral behavior of GRBs, such as a delayed onset of the high-energy (E>100 MeV) emission with respect to the lower-energy (keV/MeV) signal detected by the Gamma-Ray Burst Monitor (Fermi-GBM), the presence of an extra spectral component in addition to the Band function, an extended emission lasting significantly longer than the lower-energy keV/MeV prompt emission, and the presence of spectral cutoffs at tens-of-MeV energies. We will present these discoveries and their theoretical implications, focusing both on individual cases and also in the context of a systematic and unbiased study performed towards the first Fermi-LAT GRB catalog. In addition, constraints on any energy dependence of the speed of light placed with GRB observations will be presented.
Host: 
Segev BenZvi
Speaker: Vlasios Vasileiou LUPM, Universite de Montpellier, Montpellier, France

 

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Room and Building: 
4274 Chamberlin Hall

Present observations, especially in the gamma ray band, appear to confirm the need for source spectra of cosmic rays steeper than suggested by current theories. This trend is also required by observations of the anisotropy on large scales which in the TeV range is at the level of $sim 10^{-3}$ and appear to stay roughly constant with energy up to around the knee region. Steep spectra are very difficult to explain unless one invokes poorly understood effects in particle scattering or probably the presence of neutrals in the medium where the shock propagates. I will discuss these issues with particular emphasis on the process of particle acceleration in partially ionized media.

Host: 
Paolo Desiati
Speaker: Pasquale Blasi Osservatorio Astrofisico di Arcetri (Florence, Italy)

 

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Room and Building: 
4274 Chamberlin

Dark Matter particles can be captured in the core of the Sun or the Earth, or in the Galactic center, by interacting with the nuclei in the medium. The capture rate depends on the composition of the medium, dark matter mass and its local density. If the captured dark matter annihilate or decay into the Standard Model particles, there is a possibility of producing neutrinos which can be detected via muon tracks or showers. I will present theoretical predictions for the indirect detection of the dark matter particles via neutrino signals due to their annihilations in the core of the Sun/Earth and in the Galactic center. I will discuss how measurements of muons and/or showers by IceCube and KM3NeT may be able to distinguish between different dark matter models, such as gravitino, Kaluza-Klein particle or leptophilic dark matter.

Host: 
Reina Maruyama
Speaker: Ina Sarcevic University of Arizona

 

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Room and Building: 
4274 Chamberlin Hall
Nuclear power production having the merit of very little greenhouse gas emissions accumulates high-level radioactive waste. Currently final storage solutions in deep geological formations are in preparation in many countries having a nuclear fuel cycle to safely keep the spent nuclear fuel for up to a million years. Nuclear reactors using a fast neutron spectrum can fission essentially all long-lived actinides (e.g. Plutonium) and thus transmute the long-lived actinide nuclides into generally short lived fission products. Generation IV nuclear reactor concepts and accelerator driven systems (ADS)are currently in development that foresee a closed fuel cycle. The majority of the fissile nuclides (Uranium, Plutonium) shall be used for power generation and only fission products will be put into final storage that needs to last for only 1000 years because of the shorter nuclear half-lives. For the transmutation of high-level radioactive waste a lot of research and development is still required. One aspect is the precise knowledge of nuclear data for reactions with fast neutrons. Nuclear reactions relevant for transmutation are investigated at the photoneutron source nELBE at Helmholtz-Zentrum Dresden-Rossendorf in Dresden, Germany.&lt;br&gt;<br>
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Supported by the german Federal Ministery for Education and Research under contract 02NUK13A and by the EURATOM FP7 project &amp;quot;ERINDA&amp;quot;.&lt;br&gt;<br>
Host: 
Karsten Heeger
Speaker: Arnd Junghans Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf

 

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Room and Building: 
5310 Chamberlin
Host: 
Simona Toscano
Speaker: Mischa Malkov UCSB

 

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Room and Building: 
4274 Chamberlin
The nature of dark matter is one of the key outstanding problems in both particle and astrophysics. If dark matter decays or annihilates into electrons and positrons, it can affect diffuse radiation backgrounds observed in astrophysics. We present a new, more general analysis of constraints on dark matter models. For any decaying dark matter model, constraints on mass and lifetime can be obtained by folding the specific dark matter decay spectrum with a response function. These response functions are derived from full-sky radio surveys and Fermi-LAT gamma-ray observations and apply them to place constraints on some specific dark matter decay models. We also discuss the influence of astrophysical uncertainties on the response function, such as the uncertainties from propagation models and from the spatial distribution of the dark matter. <br>
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Moreover, an anisotropy analysis of full-sky emission gamma-ray and radio maps is performed to identify possible signatures of annihilating dark matter. We calculate angular power spectra of the cosmological background of synchrotron emission from dark matter annihilations into electron-positron pairs. We compare the power spectra with the anisotropy of astrophysical and cosmological radio backgrounds, from normal galaxies, radio-galaxies, galaxy cluster accretion shocks, the cosmic microwave background and Galactic foregrounds. In addition, we develop a numerical tool to compute gamma-ray emission from such electrons and positrons diffusing in the smooth host halo and in substructure halos with masses down to earth mass. We show that, unlike the total gamma-ray angular power spectrum observed by Fermi-LAT, the angular power spectrum from the inverse Compton scattering is exponentially suppressed below an angular scale determined by the diffusion length of electrons and positrons.
Host: 
Peter Timbie
Speaker: Le Zhang UW-Madison/Hamburg University/DESY

 

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Room and Building: 
4274 Chamberlin Hall
The Large Area Picosecond Photodetector Development Collaboration is comprised of groups from three national laboratories, five U.S. universities, and two small U.S. companies working on a three-year project to develop a new generation of economical, large area (400 cm2) microchannel plate photomultipliers that can be tailored for a wide variety of applications in particle physics, medical imaging, and high energy astrophysics. In parallel with the development of the detector, a readout technology based on a switched capacitor array waveform sampling chip with time resolution in the 10 picosecond range is being developed that would allow particle identification by time-of-flight in the multi-GeV energy range. The basic photomultiplier incorporates a bialkali photocathode and a glass capillary microchannel plate pair functionalized by atomic layer deposition (ALD) to produce photoelectrons from incident visible light photons and produce gains of greater 106. Borosilicate glass capillary plates with pore size of 20-40 microns provide an inexpensive substrate compared to the standard lead-glass used in commercial microchannel plates. ALD allows the resistive and secondary emissive functions of the plates to be fabricated separately and economically. The collaboration is characterizing a variety of candidate materials for the coatings in order to optimize the gain and stability of the microchannel plates. Plates with gain of 50,000-70,000 at 1000V. bias have been produced on 33mm diameter substrates. The first 20cm by 20cm square glass capillaries were recently delivered to the project. Two alternatives for assembly and hermetic sealing of the photodetector are being pursued in parallel: a traditional ceramic housing with a strip line anode structure with embedded pins for signal output and high voltage connection, and an all borosilicate glass housing with a silk-screened silver strip line anode readout. The latter represents a potentially very inexpensive method of tube fabrication. An external printed circuit board with a matching strip line layout provides a means of transmitting the signal to the waveform sampling chips while maintaining a 50 ohm impedance from strip line to front-end input. The talk will review the history and current status of the project, summarize potential applications of the photodetector, and outline plans for the future development and production of the photomultiplier.
Host: 
Teresa Montaruli
Speaker: Bob Wagner Argonne

 

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Room and Building: 
4274 Chamberlin Hall
High-resolution x-ray spectroscopy is a powerful tool for studying the evolving universe. Current x-ray missions have high-resolution grating spectrometers; however, non-dispersive spectrometers with improved spectral resolution around 6 keV will enable imaging spectroscopy of extended sources, such as supernova remnants and galaxy clusters. Arrays of microcalorimeters with superconducting transition-edge sensors (TESs) are capable of filling this need.

TES microcalorimeters measure the temperature change that occurs when individual photons are absorbed. In laboratory demonstrations, our TES devices achieve energy resolutions of ~2 eV at 6 keV. The X-ray Microcalorimeter Spectrometer (XMS) is a proposed instrument that will utilize these TES devices in a kilopixel-scale array that would go onboard the International X-ray Observatory (IXO). This instrument will be able to provide superior high-throughput, non-dispersive spectroscopy with high resolution and imaging capabilities in the 0.1 - 10 keV energy range.

In this talk I will introduce science drivers for the XMS instrument. I will then describe the XMS detector technology and the transition from individual pixels to large-scale arrays. I will conclude by showing state-of-the-art results as well as preliminary laboratory tests of a concept for the XMS anti-coincidence detector, which will be used to reject background events generated by cosmic rays.
Host: 
Reina Maruyama
Speaker: Catherine Bailey NASA Goddard Space Flight Center

 

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Room and Building: 
5310
Host: 
Stefan Westerhoff
Speaker: Andrew Smith Argonne National Laboratory

 

Available Downloads:

Room and Building: 
4274 Chamberlin Hall

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