Production of Electron Neutrinos at Nuclear Power Reactors and the Prospects for Neutrino Physics

High flux of electron neutrinos(\nue) is produced at nuclear power reactors through the decays of nuclei activated by neutron capture. Realistic simulation studies on the neutron transport and capture at the reactor core were performed. The production of \chr51 and \fe55 give rise to mono-energetic \nue's at Q-values of 753 keV and 231 keV and fluxes of $8.3 \times 10^{-4}$ and $3.0 \times 10^{-4}$ \nue/fission, respectively. Using data from a germanium detector at the Kuo-Sheng Power Plant, we derived direct limits on the \nue magnetic moment and the radiative lifetime of \mu_{\nu} < 1.3 \times 10^{-8} ~ \mub and $\rm{\tau_{\nu} / m_{\nu} > 0.11 s / eV}$ at 90% confidence level (CL), respectively. Indirect bounds on $\rm{\tau_{\nu} / m_{\nu}^3}$ were also inferred. The \nue-flux can be enhanced by loading selected isotopes to the reactor core, and the potential applications and achievable statistical accuracies were examined. These include accurate cross-section measurements, studies of mixing angle $\theta_{13}$ and monitoring of plutonium production.Comment: 5 pages, 3 figures, 7 table

Minimizing Unsatisfaction in Colourful Neighbourhoods

Colouring sparse graphs under various restrictions is a theoretical problem of significant practical relevance. Here we consider the problem of maximizing the number of different colours available at the nodes and their neighbourhoods, given a predetermined number of colours. In the analytical framework of a tree approximation, carried out at both zero and finite temperatures, solutions obtained by population dynamics give rise to estimates of the threshold connectivity for the incomplete to complete transition, which are consistent with those of existing algorithms. The nature of the transition as well as the validity of the tree approximation are investigated.Comment: 28 pages, 12 figures, substantially revised with additional explanatio

J/Psi Propagation in Hadronic Matter

We study J/$\psi$ propagation in hot hadronic matter using a four-flavor chiral Lagrangian to model the dynamics and using QCD sum rules to model the finite size effects manifested in vertex interactions through form factors. Charmonium breakup due to scattering with light mesons is the primary impediment to continued propagation. Breakup rates introduce nontrivial temperature and momentum dependence into the J/$\psi$ spectral function.Comment: 6 Pages LaTeX, 3 postscript figures. Proceedings for Strangeness in Quark Matter 2003, Atlantic Beach, NC, March 12-17, 2003; minor corrections in version 2, to appear in J. Phys.

Heavy Quarkonia and Quark Drip Lines in Quark-Gluon Plasma

Using the potential model and thermodynamical quantities obtained in lattice gauge calculations, we determine the spontaneous dissociation temperatures of color-singlet quarkonia and the `quark drip lines' which separate the region of bound $Q\bar Q$ states from the unbound region. The dissociation temperatures of $J/\psi$ and $\chi_b$ in quenched QCD are found to be 1.62$T_c$ and $1.18T_c$ respectively, in good agreement with spectral function analyses. The dissociation temperature of $J/\psi$ in full QCD with 2 flavors is found to be 1.42$T_c$. For possible bound quarkonium states with light quarks, the characteristics of the quark drip lines severely limit the stable region close to the phase transition temperature. Bound color-singlet quarkonia with light quarks may exist very near the phase transition temperature if their effective quark mass is of the order of 300-400 MeV and higher.Comment: 8 pages, 2 figures, in LaTex, invited talk presented at the International Conference on Strangeness in Quark Matter, UCLA, March 26-31, 200

Real space first-principles derived semiempirical pseudopotentials applied to tunneling magnetoresistance

In this letter we present a real space density functional theory (DFT) localized basis set semi-empirical pseudopotential (SEP) approach. The method is applied to iron and magnesium oxide, where bulk SEP and local spin density approximation (LSDA) band structure calculations are shown to agree within approximately 0.1 eV. Subsequently we investigate the qualitative transferability of bulk derived SEPs to Fe/MgO/Fe tunnel junctions. We find that the SEP method is particularly well suited to address the tight binding transferability problem because the transferability error at the interface can be characterized not only in orbital space (via the interface local density of states) but also in real space (via the system potential). To achieve a quantitative parameterization, we introduce the notion of ghost semi-empirical pseudopotentials extracted from the first-principles calculated Fe/MgO bonding interface. Such interface corrections are shown to be particularly necessary for barrier widths in the range of 1 nm, where interface states on opposite sides of the barrier couple effectively and play a important role in the transmission characteristics. In general the results underscore the need for separate tight binding interface and bulk parameter sets when modeling conduction through thin heterojunctions on the nanoscale.Comment: Submitted to Journal of Applied Physic

Strain Effects on Point Defects and Chain-Oxygen Order-Disorder Transition in 123-Structure Cuprate Superconductors

The energetics of Schottky defects in 123 cuprate superconductor series, $\rm REBa_2Cu_3O_7$ (where RE = lanthandies) and $\rm YAE_2Cu_3O_7$ (AE = alkali-earths), were found to have unusual relations if one considers only the volumetric strain. Our calculations reveal the effect of non-uniform changes of interatomic distances within the RE-123 structures, introduced by doping homovalent elements, on the Schottky defect formation energy. The energy of formation of Frenkel Pair defects, which is an elementary disordering event, in 123 compounds can be substantially altered under both stress and chemical doping. Scaling the oxygen-oxygen short-range repulsive parameter using the calculated formation energy of Frenkel pair defects, the transition temperature between orthorhombic and tetragonal phases is computed by quasi-chemical approximations (QCA). The theoretical results illustrate the same trend as the experimental measurements in that the larger the ionic radius of RE, the lower the orthorhombic/tetragonal phase transition temperature. This study provides strong evidence of the strain effects on order-disorder transition due to oxygens in the CuO chain sites.Comment: In print Phys Rev B (2004

Anomalous J/psi suppression and charmonium dissociation cross sections

We study $J/\psi$ suppression in Pb+Pb collisions at CERN-SPS energies in hadronic matter with energy- and temperature-dependent charmonium dissociation cross sections calculated in the quark-interchange model of Barnes and Swanson. We find that the variation of J/$\psi$ survival probability from peripheral to central collisions can be explained as induced by hadronic matter absorption in central collisions.Comment: 30 pages, 8 figures, LaTex, changed for the latest NA50 dat