Department of Physics and Astronomy

Permanent link for this collectionhttps://hdl.handle.net/2022/22354

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Browsing Department of Physics and Astronomy by Subject "Astrophysics"

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    Evolution of Li, Be and B in the Galaxy
    (American Astronomical Society, 2001-10) Valle, Giada; Ferrini, Federico; Galli, Daniele; Shore, Steven N.
    In this paper we study the production of Li, Be and B nuclei by Galactic cosmic ray spallation processes. We include three kinds of processes: (i ) spallation by light cosmic rays impinging on interstellar CNO nuclei (direct processes); (ii ) spallation by CNO cosmic ray nuclei impinging on interstellar p and 4He (inverse processes); and (iii ) α–α fusion reactions. The latter dominate the production of 6,7Li. We calculate production rates for a closed-box Galactic model, verifying the quadratic dependence of the Be and B abundances for low values of Z. These are quite general results and are known to disagree with observations. We then show that the multi-zone multi-population model we used previously for other aspects of Galactic evolution produces quite good agreement with the linear trend observed at low metallicities without fine tuning. We argue that reported discrepancies between theory and observations do not represent a nucleosynthetic problem, but instead are the consequences of inaccurate treatments of Galactic evolution.
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    Improved Spin-Dependent WIMP Limits from a Bubble Chamber
    (American Association for the Advancement of Science, 2008-04) Behnke, Ed; Levine, Ilan
    Bubble Chambers provided the dominant particle detection technology in accelerator experiments for several decades, eventually falling into disuse with the advent of other techniques. We report here on the first period of operation of an ultra-clean, room-temperature bubble chamber containing 1.5 kg of superheated CF3I, a target maximally sensitive to spin-dependent and -independent Weakly Interacting Massive Particle (WIMP) couplings. An exposure in excess of 250 kg-days is obtained, with a live-time fraction reaching 80%. This illustrates the ability to employ bubble chambers in a new realm, the search for dark matter particles. Improved limits on the spin-dependent WIMP-proton scattering cross section are extracted from this first period. An extreme intrinsic insensitivity to the backgrounds commonly limiting these experiments (a rejection factor for photon-induced electrons of ~10^−10) has been measured in operating conditions leading to the detection of low-energy nuclear recoils such as those expected from WIMPs.
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    A Search for Periodicities in the 8B Solar Neutrino Flux Measured by the Sudbury Neutrino Observatory
    (American Physical Society, 2005-10) Levine, Ilan
    A search has been made for sinusoidal periodic variations in the 8B solar neutrino flux using data collected by the Sudbury Neutrino Observatory over a 4-year time interval. The variation at a period of one year is consistent with modulation of the 8B neutrino flux by the Earth’s orbital eccentricity. No significant sinusoidal periodicities are found with periods between 1 day and 10 years with either an unbinned maximum likelihood analysis or a Lomb-Scargle periodogram analysis. The data are inconsistent with the hypothesis that the results of the recent analysis by Sturrock et al., based on elastic scattering events in Super-Kamiokande, can be attributed to a 7% sinusoidal modulation of the total 8B neutrino flux.