Talks & Events
KICP Friday Noon Seminars
Current & Future KICP Seminars
Past KICP Seminars
New mass windows and detection prospects for primordial black hole dark matter
Recent developments have opened up new possible windows where primordial black holes (PBHs) can make up all of dark matter (DM). In the first half of the talk, I will describe how microlensing of X-ray pulsars could help to probe the asteroid-mass window. In the second half, I will discuss how stable (nearly) extremal PBHs with masses below traditional evaporation bounds could populate all of DM. These extremal PBHs could give rise to energetic signals when present-day binaries merge.
Understanding neutrino background implications in LXe-TPC dark matter searches using 127Xe electron captures
Dark matter searches using dual-phase xenon time projection chambers (LXe-TPC) rely on the discrimination between electronic recoils (background) and nuclear recoils (signal) based on the ratio of ionization electrons to scintillation photons produced by the interaction in the liquid xenon. This discrimination is calibrated at low energies using tritium β-decays. However, neutrino and Compton scatters from inner-shell electrons of xenon atoms result in the emission of Auger electrons and x-rays in addition to the primary recoiling electron, and thus have a different event topology than β-decays and valence-shell electron recoils. Due to their low kinetic energy and large numbers, these secondary particles can deposit larger amounts of energy within a small radius, which is uncharacteristic of valence electron recoils and is more akin to nuclear recoils. This affects the profile of the neutrino-electron scattering background in a way that is, so far, uncalibrated and unaccounted for in LXe-TPC dark matter searches, and presents the possibility of a false discovery claim. To investigate the significance of this effect, electrons capture decays of 127Xe are used to simulate the vacancies produced by inner-shell e-ν scatters in the Xenon Electron-recoil L-shell Discrimination Analyzer (XELDA) detector. The 127Xe source produces a high-purity sample of inner-shell vacancies accompanied by an Auger cascade that can easily be isolated from the prompt γ's emitted in the decay. In this talk, I will present preliminary results from a cross-calibration of the XELDA detector using both 127Xe EC-decays and 3H β-decays. The observed discrepancy reduces the efficiency with which neutrino-induced electron recoils can be rejected in large-scale LXe-TPC dark matter searches, such as LUX-ZEPLIN and DARWIN.
The Origin of Multiphase Galaxy Outflows
Star-forming galaxies are often observed to host outflows - gas that is flowing away from the galaxy in phases ranging from cold molecular clouds to hot X-ray emitting plasma. While these multiphase outflows are routinely observed, theoretically constraining their origin and evolution has proven difficult. Explaining the prevalence and velocities of the cool ionized phase (T~10^4 K) in particular poses a challenge. In this talk, I will discuss a potential dual origin for this cool gas. Through a series of extremely high-resolution simulations run with the GPU-based Cholla code, I will show that in high star formation surface density systems, dense disk gas can be pushed out by the collective effect of clustered supernovae, explaining the low-velocity material. Subsequent shredding and mixing of these clouds creates gas with intermediate densities and temperatures that is prone to radiative cooling, allowing momentum to transfer between phases and producing high velocity cool gas. In addition to explaining the nature of outflows themselves, these multiphase winds could potentially be a source of the cool photo-ionized gas that is found in abundance in galaxy halos.
X-ray Search for Axions from Nearby Isolated Neutron Stars
We performed a search for axion-like particles (ALPs) in the nearby isolated neutron stars and interpreted the recently observed excess in X-ray by an axion model. These ALPs can be produced from the hot cores of the neutron stars at temperatures around 10^8 K and be converted into X-ray photons within the magnetosphere of the neutron stars. The dominant production modes are the nucleon bremsstrahlung and Cooper pair-breaking-formation processes. These ALPs and the produced photons carry energies of order the core temperature or the superfluid gaps and are therefore much hotter than the surface temperature of around 10^6 K. X-ray dim isolated neutron stars are excellent targets due to low background in the signal range of 1-100 keV. We fit the axion model to an X-ray excess in 2-8 keV observed by XMM-Newton and Chandra and discuss prospects of confirming or ruling out the axion interpretation by future measurements of NuSTAR.
Near Future of Dark Matter Searches: Go Big, or Go Low
The identification of dark matter is presently one of the greatest challenges in science, fundamental to our understanding of the Universe. There are a number of experiments and R&D projects planned in the near future aiming to directly detect dark matter particles, and they largely fall into two categories: larger iterations of previous experiments; and novel techniques that seek to drive sensitivity towards low mass particles. One of the former, the LUX-ZEPLIN (LZ) experiment has grown out of its two precursors with the goal of constructing a next generation dark matter detector at Sanford Underground Research Facility (SURF) in South Dakota, with 7 tonnes of fully active liquid xenon. LZ has been designed to explore much of the parameter space available for WIMP models, with excellent sensitivity for WIMP masses between a few GeV and a few TeV. In this talk I will present an overview of the LZ detector design, current project status and timeline.
As for the latter, we explore the use of a novel technique, the Snowball chamber, in the search for low-mass dark matter. This chamber uses supercooled water as the target, employing an exotic phase transition of metastable water in a similar fashion to a bubble chamber in reverse, but with enhanced low energy threshold (sub-keV) and background discrimination as a function of thermodynamic conditions. I will discuss the potential of this new technology to drastically expand detector sensitivity in the sub-GeV range, opening up a new parameter space currently out of reach.