Physics & Astronomy News

"Symmetry-guided large-scale shell-model theory" Launey, Dytrych, and Draayer. Prog. Part. Nucl. Phys. 89 (2016) 101-136

his detailed review focuses on a symmetry-guided strategy that utilizes exact as well as partial symmetries for enabling a deeper understanding of and advancing ab initio (or "from first principles") studies for determining the microscopic structure of atomic nuclei. It discusses extensions of nuclear theory beyond current limitations toward heavier nuclei and larger model spaces, as well as explorations of simple patterns in nuclei and how they emerge from first principles. We review symmetry-based techniques that prove useful in our ab initio symmetry-adapted no-core shell-model theory, as well as in various modern nuclear models, such as ab initio lattice effective field theory, ab initio hyperspherical harmonics method, SU(3) and symplectic models, Richardson and Gaudin's exact pairing model, and cluster models with a focus on the resonating-group method. We discuss important implications of these approaches that have advanced our knowledge of emergent phenomena in nuclei, including enhanced collectivity, giant resonances, shape coexistence, and pairing, together with halo and cluster substructures.

"Analytical model for ion stopping power and range in the therapeutic energy interval for beams of hydrogen and heavier ions" Donahue and Newhauser et, al. Phys. Med. Biol. 61 (2016) 6570–6584

Many different approaches exist to calculate stopping power and range of protons and heavy charged particles. These methods may be broadly categorized as physically complete theories (widely applicable and complex) or semi-empirical approaches (narrowly applicable and simple). However, little attention has been paid in the literature to approaches that are both widely applicable and simple. We developed simple analytical models of stopping power and range for ions of hydrogen, carbon, iron, and uranium that spanned intervals of ion energy from 351keV u−1 to 450 MeV u−1 or wider. The analytical models typically reproduced the best-available evaluated stopping powers within 1% and ranges within 0.1mm. The computational speed of the analytical stopping power model was 28% faster than a full-theoretical approach. The calculation of range using the analytic range model was 945 times faster than a widely-used numerical integration technique. The results of this study revealed that the new, simple analytical models are accurate, fast, and broadly applicable. The new models require just 6 parameters to calculate stopping power and range for a given ion and absorber. The proposed model may be useful as an alternative to traditional approaches, especially in applications that demand fast computation speed, small memory footprint, and simplicity.

"Event ontology in quantum mechanics and downward causation" Gambini and Pullin, International Journal of quantum foundations 2, 89 (2016)

We show that several interpretations of quantum mechanics admit an ontology of objects and events. This ontology reduces the breach between mind and matter. When humans act, their actions do not appear explainable in mechanical terms but through mental activity: motives, desires or needs that propel them to action. These are examples of what in the last few decades have come to be called "downward causation". Basically, downward causation is present when the disposition of the whole to behave in a certain way cannot be predicted from the dispositions of the parts. The event ontology of quantum mechanics allow us to show that systems in entangled states present emergent new properties and downward causation.

"Decays of the Three Top Contributors to the Reactor ν¯e High-Energy Spectrum, Rb92, Y96gs, and Cs142, Studied with Total Absorption Spectroscopy", Rasco, Zganjar, Blackmon, et, al. Phys. Rev. Lett. 117, 092501

Abstract We report total absorption spectroscopy measurements of Rb92, Y96gs, and Cs142 β decays, which are the most important contributors to the high energy ν¯e spectral shape in nuclear reactors. These three β decays contribute 43% of the ν¯e flux near 5.5 MeV emitted by nuclear reactors. This ν¯e energy is particularly interesting due to spectral features recently observed in several experiments including the Daya Bay, Double Chooz, and RENO Collaborations. Measurements were conducted at Oak Ridge National Laboratory by means of proton-induced fission of U238 with on-line mass separation of fission fragments and the Modular Total Absorption Spectrometer. We observe a β-decay pattern that is similar to recent measurements of Rb92, with a ground-state to ground-state β feeding of 91(3)%. We verify the Y96gs ground-state to ground-state β feeding of 95.5(20)%. Our measurements substantially modify the β-decay feedings of Cs142, reducing the β feeding to Ba142 states below 2 MeV by 32% when compared with the latest evaluations. Our results increase the discrepancy between the observed and the expected reactor ν¯e flux between 5 and 7 MeV, the maximum excess increases from ∼10% to ∼12%.

Summer 2016 Graduates

On Friday, August 5th, LSU Physics & Astronomy welcomed 6 new PhD, 6 MS and 1 BS graduates who conferred their Degrees at the Pete Maravich Assembly Center.

"The Variable Star V Sculptoris," Journal of the American Association of Variable Star Observers (JAAVSO), vol. 44, p. 50, (2016). Published by Landolt, A. U

Multicolor photometry is presented for V Scl and six nearby sequence stars.

"Intermittent Multi-Color Photometry for V1017 Sagittarius," Journal of the American Association of Variable Star Observers, vol. 44, p. 45, (2016). Published by Landolt, A. U.

UBVRI photoelectric photometry is presented for the dwarf nova V1017 Sgr.

Gravitational Waves Detected from Second Pair of Colliding Black Holes

The LIGO Scientific Collaboration and the Virgo collaboration identify a second gravitational wave event in the data from Advanced LIGO detectors. On December 26, 2015 at 03:38:53 UTC, scientists observed gravitational waves-ripples in the fabric of spacetime-for the second time. The gravitational waves were detected by both of the twin Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors, located in Livingston, Louisiana, and Hanford, Washington, USA.

Publication: Rob Hynes et al, present a multi-wavelength study of the low-mass X-ray binary Sco X-1 in "Kepler K2 Observations of Sco X-1: Orbital Modulations and Correlations with Fermi GBM and MAXI" in Monthly Notices of the Royal Astronomical Society.

Rob Hynes, Brad Schaefer, undergrad Zach Baum, Ching-Cheng Hsu, Mike Cherry et al. present a multi-wavelength study of the low-mass X-ray binary Sco X-1 in "Kepler K2 Observations of Sco X-1: Orbital Modulations and Correlations with Fermi GBM and MAXI" in Monthly Notices of the Royal Astronomical Society. Read more

Graduate Student Spotlight: Chris Johnson, LSU Department of Physics & Astronomy

LSU Physicists Discover Extreme Light From Frozen Argon

"Comments on Optical Photometry and the Generation of Standard Stars” Published by Arlo U. Landolt. Society of the Pacific Conference Series, vol. 503, (2016).

Comments will be made on situations encountered in the process of observational optical photometry and the establishing of standard star sequences.

Department of Physics and Astronomy Spring 2016 Graduates

Thirteen LSU Physicists and Graduate Students Among Team to Receive Special Breakthrough Prize

BATON ROUGE - A Special Breakthrough Prize in Fundamental Physics will recognize the scientists and engineers contributing to the momentous detection of gravitational waves from two black holes colliding over a billion light years away. Thirteen physicists and graduate students from LSU, who conduct research where the detections were made at the Laser Interferometer Gravitational-Wave Observatory, or LIGO, in Livingston, La., will be among the recipients of this prestigious honor.

New Publication: "Scaled plane-wave Born cross sections for atoms and molecules," H. Tanaka, M. J. Brunger, L. Campbell, H. Kato, M. Hoshino, and A. R. P. Rau. Rev. Mod. Phys. 88, 025004 (45 pp) (2016).

The Born approximation, as applied and extended by Bethe in the 1930s, has been dominant and useful for calculating scattering cross sections of electrons from atoms and molecules.

Wayne Newhauser and Rui Zhang's paper "The physics of proton therapy" made PMB's highlights of 2015

PMB is the top journal of medical physics. The accolade is for papers that were among "the most influential research published in PMB in 2015."

"Giant magneto-optical Raman effect in a layered transition metal compound" Ward Plummer, Jiandi Zhang, PNAS 2349-2353, doi: 10.1073/pnas.1601010113

solids. It usually involves electron-mediated process, involving photon, electron and phonon interactions. In principle, manipulating electrons, for instance by applying a magnetic field, should affect Raman phonon intensity, yet there is no direct experimental measurement. Recently Prof. Ward Plummer and Prof. Jiandi Zhang, through a collaboration with Prof. Qingming Zhang' s group at Renmin University in Beijing, China, reported the first realization of the idea in a prototype material, MoS2. From monolayer and bilayer to bulk MoS2 they observed a dramatic modification of Raman phonon intensity induced by magnetic field. Such a giant magneto-optical effect appearing at a monoatomic layer level and its technological implications for magnetic-optical devices should inspire a new branch of inelastic light scattering. For detail, read the related published article in Proceedings of the National Academy of Sciences.

Searching the Sky for the Wobbles of Gravity