Eccentricities of Double Neutron Star Binaries

Recent pulsar surveys have increased the number of observed double neutron stars (DNS) in our galaxy enough so that observable trends in their properties are starting to emerge. In particular, it has been noted that the majority of DNS have eccentricities less than 0.3, which are surprisingly low for binaries that survive a supernova explosion that we believe imparts a significant kick to the neutron star. To investigate this trend, we generate many different theoretical distributions of DNS eccentricities using Monte Carlo population synthesis methods. We determine which eccentricity distributions are most consistent with the observed sample of DNS binaries. In agreement with Chaurasia & Bailes (2005), assuming all double neutron stars are equally as probable to be discovered as binary pulsars, we find that highly eccentric, coalescing DNS are less likely to be observed because of their accelerated orbital evolution due to gravitational wave emission and possible early mergers. Based on our results for coalescing DNS, we also find that models with vanishingly or moderately small kicks (sigma < about 50 km/s) are inconsistent with the current observed sample of such DNS. We discuss the implications of our conclusions for DNS merger rate estimates of interest to ground-based gravitational-wave interferometers. We find that, although orbital evolution due to gravitational radiation affects the eccentricity distribution of the observed sample, the associated upwards correction factor to merger rate estimates is rather small (typically 10-40%).Comment: 9 pages, 8 figures, accepted by ApJ. Figures reduced and some content changed, references adde

Through-going Muons in the LUX Dark Matter Search

Dark matter makes up most of the mass of the universe, and yet the true nature of this mysterious substance remains unknown. The LUX experiment uses a detector consisting of target xenon nuclei to search for Weakly Interacting Massive Particles, a promising dark matter candidate. The LUX detector is a 370 kg dual-phase xenon time projection chamber. Incident radiation interacts with xenon atoms, resulting in a recoil nucleus or electron that causes both ionization and excitation of Xe along the recoil track. De-excitation of Xe results in the emission of 175 nm scintillation light, and the properties of this scintillation can be used to determine the nature of the incident radiation - possibly identifying WIMP dark matter.LUX has placed world-leading limits on the WIMP-nucleon interaction cross section. The rarity of such interactions requires a thorough understanding of backgrounds in order to implement appropriate background-reducing measures and an effective event-rejection methodology. The LUX water tank surrounds the xenon detector and serves as an active shield, reducing background radiation but also identifying high energy cosmic ray muons that can lead to the production of a highly undesirable neutron background. Since signals created by neutrons may appear very similar to those of WIMPs, care must be taken to not only reduce neutron backgrounds as much as possible, but to also understand any neutron backgrounds that may be present.The goal of this dissertation was to develop a method to identify cosmic ray muons that traverse both the LUX Xe detector and water tank, and to measure a muon flux at the LUX detector depth. The xenon gas-liquid interface served as a fiducial surface through which muon flux was measured. Simultaneous signals between Xe and water detectors were analyzed, and xenon pulse shapes were used to determine the energy and track geometry of the interaction. Muons passing the Xe liquid surface exhibited a particular signature in their pulse shape; this signature was used to identify through-going muons and calculate muon flux.In a previous work, muon flux measurements were taken at sites above the LUX detector, and muon transport models were used to predict vertical muon flux as 4.40 x 10^-9 muons s^-1 cm^-2 at the LUX detector depth. In this work, a flux of 4.60 +/- 0.33_(stat) x 10^-9 muons s^-1 cm^-2 is measured through the LUX water tank and xenon detector liquid surface. The resulting neutrons expected to be seen during the full LUX exposure is ~1 x 10^-1. While expected the background contribution from muon-induced neutrons poses little problem for the LUX WIMP search, an understanding of this background becomes increasingly important as target volumes grow for future generation experiments

Through-going Muons in the LUX Dark Matter Search

Dark matter makes up most of the mass of the universe, and yet the true nature of this mysterious substance remains unknown. The LUX experiment uses a detector consisting of target xenon nuclei to search for Weakly Interacting Massive Particles, a promising dark matter candidate. The LUX detector is a 370 kg dual-phase xenon time projection chamber. Incident radiation interacts with xenon atoms, resulting in a recoil nucleus or electron that causes both ionization and excitation of Xe along the recoil track. De-excitation of Xe results in the emission of 175 nm scintillation light, and the properties of this scintillation can be used to determine the nature of the incident radiation - possibly identifying WIMP dark matter.LUX has placed world-leading limits on the WIMP-nucleon interaction cross section. The rarity of such interactions requires a thorough understanding of backgrounds in order to implement appropriate background-reducing measures and an effective event-rejection methodology. The LUX water tank surrounds the xenon detector and serves as an active shield, reducing background radiation but also identifying high energy cosmic ray muons that can lead to the production of a highly undesirable neutron background. Since signals created by neutrons may appear very similar to those of WIMPs, care must be taken to not only reduce neutron backgrounds as much as possible, but to also understand any neutron backgrounds that may be present.The goal of this dissertation was to develop a method to identify cosmic ray muons that traverse both the LUX Xe detector and water tank, and to measure a muon flux at the LUX detector depth. The xenon gas-liquid interface served as a fiducial surface through which muon flux was measured. Simultaneous signals between Xe and water detectors were analyzed, and xenon pulse shapes were used to determine the energy and track geometry of the interaction. Muons passing the Xe liquid surface exhibited a particular signature in their pulse shape; this signature was used to identify through-going muons and calculate muon flux.In a previous work, muon flux measurements were taken at sites above the LUX detector, and muon transport models were used to predict vertical muon flux as 4.40 x 10^-9 muons s^-1 cm^-2 at the LUX detector depth. In this work, a flux of 4.60 +/- 0.33_(stat) x 10^-9 muons s^-1 cm^-2 is measured through the LUX water tank and xenon detector liquid surface. The resulting neutrons expected to be seen during the full LUX exposure is ~1 x 10^-1. While expected the background contribution from muon-induced neutrons poses little problem for the LUX WIMP search, an understanding of this background becomes increasingly important as target volumes grow for future generation experiments