Bulletin of the American Physical Society
3rd Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 54, Number 10
Tuesday–Saturday, October 13–17, 2009; Waikoloa, Hawaii
Session EG: Nuclear Astrophysics I |
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Chair: Dan Bardayan, Oak Ridge National Laboratory Room: Kings 2 |
Friday, October 16, 2009 9:00AM - 9:15AM |
EG.00001: Suppression of the stellar enhancement factor and reaction rates far from stability Thomas Rauscher Nuclei in astrophysical plasmas occur in excited states because they are in thermal equilibrium with the stellar plasma. This modifies the reaction cross sections and has important consequences for the determination of stellar reaction rates. The application of detailed balance implies that stellar effects are less pronounced in the direction of positive Q-value and that measurements should preferably be performed in this reaction direction. However, we show that the general Q-value rule does not apply for a number of cases due to the suppression of low-energy transitions in the exit channel by an additional barrier (Coulomb or centrifugal). Additionally, it has to be realized that the validity of detailed balance cannot be taken for granted in all cases. This is well known for nuclei at stability having isomeric states but may also become problematic in nuclei with low level densities. Another complication with low level densities is that the Hauser-Feshbach model cannot be applied anymore to predict reaction cross sections. Resonant and direct reactions also become important. Preliminary results of a new large-scale prediction of astrophysical reaction rates across the nuclear chart including both the compound and the direct mechanism will be shown. [Preview Abstract] |
Friday, October 16, 2009 9:15AM - 9:30AM |
EG.00002: Hoyle Reloaded: A fix for the Cosmological Lithium Problem? Richard Cyburt, Maxim Pospelov There is a significant discrepancy between the current theoretical prediction of the cosmological lithium abundance, mostly produced as $^7$Be during the Big Bang, and its observationally inferred value. We investigate whether the resonant enhancement of $^7$Be burning reactions may alleviate this discrepancy. We identify one narrow nuclear level in $^9$B, $E_{5/2^+} \simeq 16.7$ MeV that is not sufficiently studied experimentally, and being just $\sim 200$ keV above the $^7$Be+d threshold, may lead to the resonant enhancement of $^7$Be$(d,\gamma$)$^9$B and $^7$Be$(d,p)\alpha\alpha$ reactions. We determine the relationship between the domain of resonant energies $E_r$ and the deuterium separation width $\Gamma_d$ that results in the significant depletion of the cosmological lithium abundance and find that $ (E_r, ~\Gamma_{d}) \simeq (170-220,~10-40)$ keV can eliminate current discrepancy. Our results also imply that before dedicated nuclear experimental and theoretical work is done to clarify the role played by this resonance, the current conservative BBN prediction of lithium abundance should carry significantly larger error bars, [$^7$Li/H]$_{\rm BBN}$$= (2.5-6)\times 10^{-10}$. [Preview Abstract] |
Friday, October 16, 2009 9:30AM - 9:45AM |
EG.00003: The Impact of Reaction Rate Uncertainties (and other nuclear physics inputs) on Nucleosynthesis in the Neutrino-p Process Carla Frohlich, X. Tang, J.W. Truran The neutrino-p ($\nu p$) process has been shown to be an important nucleosynthesis process, occurring in core collapse supernovae, that contributes to the synthesis of nuclei in the mass region 64$\le$A$\le$120. Such a nucleosynthesis process (in addition to the r- and s-processes) is needed to explain the observed abundance patterns in this mass region - particularly in very low metallicity stars. The $\nu p$-process consists of a sequence of (p,$\gamma$) and (n,p) or $\beta ^+$ reactions, where the slowest reactions set the timescale. Nucleosynthesis studies of such events as the $\nu p$-process typically involve the use of reaction networks that include several thousand nuclei and associated reaction cross sections and lifetimes, most of which are only known theoretically. A majority of the nuclei involved are unstable and hence pose a challenge for experimental nuclear physicists. With improvements in existing facilities such as NSCL at MSU and ATLAS at ANL and with a future FRIB facility, experimental investigations of reaction rates and other nuclear quantities involving unstable nuclei will become feasible. In this talk, we will demonstrate how uncertainties in the reaction rates influence the resulting nucleosynthesis. In addition, we will identify important reactions and nuclei to be studied experimentally with upcoming techniques at the new facilities. [Preview Abstract] |
Friday, October 16, 2009 9:45AM - 10:00AM |
EG.00004: Looking for Dark Matter with the CDMS Detectors Mark Kos The Cryogenic Dark Matter Search (CDMS) has the world's best sensitivity to Weakly Interacting Massive Particle (WIMP) interactions. By independently measuring phonon and ionization energy, CDMS distinguishes electromagnetic backgrounds from possible WIMP nuclear recoil events. CDMS consists of five towers of Ge and Si detectors. Recently a SuperTower has been installed with larger Ge detectors and improved phonon readout. I will present the experiment's most recent results and discuss operation of the new detectors. [Preview Abstract] |
Friday, October 16, 2009 10:00AM - 10:15AM |
EG.00005: LUX dark matter search: expected sensitivity Peter Sorensen The LUX 300~kg two-phase Xe detector aims to detect or exclude dark matter in the form of Weakly Interacting Massive Particles (WIMPs) with scalar cross section (per nucleon) as low as $7\times10^{-46}$~cm$^2$. This is equivalent to $\sim 0.5$~events/100~kg/month in a 100~kg fiducial volume. The LUX design is set to ensure $<1$ background event / 10~months live, which could potentially be characterized as a WIMP interaction. Based on above-ground calibrations and data from the XENON10 experiment, LUX expects to reject up to 99.9\% of the dominant electron-recoil background at detector threshold ($\sim5$~keVr), with 50\% acceptance for nuclear recoils. This talk will discuss the projected sensitivity of the LUX experiment for elastic and inelastic dark matter scenarios. [Preview Abstract] |
Friday, October 16, 2009 10:15AM - 10:30AM |
EG.00006: LUXSim: A GEANT4-based Simulation Framework for the Large Underground Xenon Detector Melinda Sweany The Large Underground Xenon (LUX) detector is a 100 kg target mass WIMP detector capable of achieving a cross section sensitivity of 7x10$^{-42}$cm$^2$ for a 100 GeV WIMP. LUX will commence operations in early 2010 at the Sanford Underground Lab in Lead, South Dakota. The most important consideration in building LUX is the minimization and characterization of neutron backgrounds that could emulate a WIMP signal. In order to accurately determine the level of background, we require a precise simulation of radioactive sources embedded within the detector components. Traditionally in GEANT4 simulations, particle beams have been distinct from the detectors, as is typical in high energy or medical applications. We are developing a GEANT4 simulation framework, LUXSim, capable of generating primary particles within detector components from independently specified activities of radionuclei. Geometry classes are also recast so that tracking information within individual components, such as energy depositions, is easily stored without specifying each as a sensitive detector. In addition, LUXSim includes built-in commands for changing detector type, activities within components, and the level of information storage for each detector component, so that recompilation is not necessary. The basic class structure of LUXSim will be described, including examples of usage, and preliminary results will be presented. [Preview Abstract] |
Friday, October 16, 2009 10:30AM - 10:45AM |
EG.00007: The LUX Dark Matter Search Program Kenneth Clark LUX (Large Underground Xenon) is a two-phase Time Projection Chamber that will instrument 350 kg of Xenon, 100 kg of which will form a fiducially active target for WIMP interactions. It will be deployed at the Sanford Underground Lab at the Homestake Mine in Lead, South Dakota, where the Early Implementation Program is providing space at the 4850 feet level for LUX. The first detector with 120 photomultiplier tubes is being constructed and is projected to start collecting data in early 2010. Prior to this installation, a prototype detector with a reduced fiducial volume has been in operation in an above ground environment. Results from this detector, along with discussion of the full LUX sensitivity will be presented. [Preview Abstract] |
Friday, October 16, 2009 10:45AM - 11:00AM |
EG.00008: Measuring the ultra-high energy comic ray flux with the Telescope Array Middle Drum detector Thomas Sonley The Telescope Array (TA) Experiment, located 200 kilometers southwest of Salt Lake City, Utah, is the largest Ultra-High Energy cosmic ray detector in the northern hemisphere. TA is a follow up to the High Resolution Fly's Eye (HiRes) and AGASA experiments, and seeks to gain insight into cosmic ray acceleration by measuring the flux of cosmic rays with energies over $10^{18}$ eV. The detector consists of 507 scintillator counters distributed in a square grid with 1.2 km spacing. Three fluorescence detector stations sit on the corners of a ~30 km equilateral triangle overlooking the array of surface detectors, and provide full hybrid coverage with the scintillator array above 10 EeV. Telescope Array underwent commissioning in 2007 and began routine data collection operations at the beginning of 2008. One of the three fluorescence stations, the Middle Drum (MD) site, is instrumented with detectors previously used at the HiRes-1 site. The inclusion of the MD site makes possible a direct comparison between the fluorescence energy scales and spectra between TA and HiRes. We will present a progress report on the analysis of the TA data collected by the MD site. [Preview Abstract] |
Friday, October 16, 2009 11:00AM - 11:15AM |
EG.00009: Search for WIMPs dark matter by means of thin NaI(Tl) scintillator Ken-Ichi Fushimi The segmented detector system made of inorganic crystal is applied to serach for WIMPs dark matter. The NaI(Tl) crystal has great advantages to search for WIMPs dark matter;. \begin{enumerate} \item 100\% of natural abundance of odd $A$ nuclei ($^{23}$Na and $^{127}$I). \item $^{127}$I has a low energy excited state at 57.6keV which is excited by spin-dependent interaction. \end{enumerate} The prototype detector of thin NaI(Tl) was tested. The energy resolution and the low energy threshold will be reported. The future prospect of WIMPs dark matter search by various detector will be discussed. [Preview Abstract] |
Friday, October 16, 2009 11:15AM - 11:30AM |
EG.00010: Neutron production by cosmic ray muons at the Sudbury Neutrino Observatory James Loach Neutrons produced by cosmic ray muon interactions can be a significant background in sensitive underground experiments. The Sudbury Neutrino Observatory (SNO) is an efficient and well-calibrated neutron detector capable of measuring the rate and characteristics of thermal neutrons produced by muon interactions in its heavy water target, light water shielding and surrounding rock. The location of the detector, beneath a rock overburden 5900 meters water equivalent, implies that the muon flux is particularly low in rate and high in energy. SNO's measurements, with their unique target materials and high energy muons, are important for benchmarking Monte Carlo codes that will be used to predict muon-induced neutron fluxes in future low background experiments. [Preview Abstract] |
Friday, October 16, 2009 11:30AM - 11:45AM |
EG.00011: Equation of State for Asymmetric Nuclear Matter at Finite Temperatures with the Variational Method Hajime Togashi, Hiroaki Kanzawa, Masatoshi Takano, Kazuhiro Oyamatsu, Kohsuke Sumiyoshi The free energies of uniform nuclear matter at various densities, temperatures and proton fractions are calculated with the variational method, toward a new nuclear equation of state (EOS) for supernova simulations. Following the method by Schmidt and Pandharipande, the expectation value of the two-body Hamiltonian with the AV18 potential is calculated in the two-body cluster approximation. The averaged occupation probabilities of the single particle states in the Jastrow trial wave function at finite temperature are parameterized by the proton and neutron effective masses. The energy caused by the UIX three-body potential is treated somewhat phenomenologically so as to obtain the realistic nuclear EOS at zero temperature. The entropy is also expressed with the averaged occupation probabilities, and then the free energy is minimized with respect to the effective masses. The proton fraction dependence of the obtained thermodynamic quantities is discussed. [Preview Abstract] |
Friday, October 16, 2009 11:45AM - 12:00PM |
EG.00012: Equation of State for Non-uniform Nuclear Matter by the Variational Method with Thomas-Fermi Calculations Hiroaki Kanzawa, Masatoshi Takano, Kazuhiro Oyamatsu, Kohsuke Sumiyoshi Toward a new equation of state (EOS) for supernova (SN) simulations based on the realistic nuclear forces, the EOS for non-uniform nuclear matter is constructed in the Thomas-Fermi (TF) approximation. The energy of uniform nuclear matter used in the TF calculation is obtained by a simplified variational method with the AV18 and UIX potentials. The parameters associated with the nuclear three-body force are fixed so that the TF calculation for atomic nuclei reproduces the gross behavior of their experimental masses and radii. With use of this TF method, the EOS of non-uniform nuclear matter, which is assumed to be composed of a Coulomb lattice of single species of nucleus immersed in a uniform electron gas (with neutrons dripped out of the nuclei), are calculated for various baryon densities and proton fractions at zero temperature. The obtained thermodynamic quantities of non-uniform matter are compared with those of Shen-EOS. [Preview Abstract] |
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