641 research outputs found
N* and Meson Resonances in J/psi decays
Over sixty million J/psi events have been collected by the BES Collaboration
at the Beijing Electron-Positron Collider (BEPC). J/psi decays provide an
excellent place for studying excited nucleons and hyperons -- N*, ,
and resonances, as well as meson resonances, including
possible glueballs and hybrids. Physics objectives, recent results and future
prospects of light hadron spectroscopy at BEPC are presented.Comment: Invited talk at the 7th International Workshop on Production,
Properties and Interaction of Mesons, Cracow, Poland, May 23-28, 200
The cranking formula and the spurious behaviour of the mass parameters
We discuss some aspects of the approach of the mass parameters by means of
the simple cranking model. In particular, it is well known that the numerical
application of this formula is often subject to ambiguities or contradictions.
It is found that these problems are induced by the presence of two derivatives
in the formula. To overcome these problems, we state a useful ansatz and we
develop a number of simple arguments which tend to justify the removal of these
terms. As soon as this is done, the formula becomes simpler and easier to
interpret. In this respect, it is shown how the shell effects affect the mass
parameters. A number of numerical tests help us in our conclusions.Comment: version 3 corrigendum of the ansatz of section V, corrigendum of the
legend of Fig3. Submission = text file + 5 figure
Variation in the synthesis of microcystin in response to saline and osmotic stress in Microcystis ruginosa PCC7806
The growth and synthesis of microcystin in Microcystis aeruginosa PCC7806 was studied in cells grown in the presence of NaCl or with sucrose. The saline stress caused a decrease in the transcript levels of mcyD, one of the genes involved in microcystin synthesis, which was correlated with a decrease in the content of microcystin-LR in the cells. The cells treated with sucrose also had reduced levels of mcyD transcripts and contents of microcystin-LR
Pairing in 4-component fermion systems: the bulk limit of SU(4)-symmetric Hamiltonians
Fermion systems with more than two components can exhibit pairing condensates
of much more complex structure than the well-known single BCS condensate of
spin-up and spin-down fermions. In the framework of the exactly solvable SO(8)
Richardson-Gaudin model with SU(4)-symmetric Hamiltonians, we show that the BCS
approximation remains valid in the thermodynamic limit of large systems for
describing the ground state energy and the canonical and quasiparticle
excitation gaps. Correlations beyond BCS pairing give rise to a spectrum of
collective excitations, but these do not affect the bulk energy and
quasiparticle gaps.Comment: 13 pages; 2 figures; 1 tabl
Lowest-lying Tetra-Quark Hadrons in Anisotropic Lattice QCD
We present a detailed study of lowest-lying hadrons in
quenched improved anisotropic lattice QCD. Using the and
diquark-antidiquark local and smeared operators, we attempt to isolate the
signal for and states in two flavour
QCD. In the chiral limit of light-quark mass region, the lowest scalar
state is found to have a mass, MeV, which is slightly
lower than the experimentally observed . The results from our
variational analysis do not indicate a signature of a tetraquark resonance in
I=1 and I=2 channels. After the chiral extrapolation the lowest
state is found to have a mass, MeV. We analysed the
static potential extracted form a tetraquark Wilson loop and illustrated
the behaviour of the state as a bound state, unbinding at some critical
diquark separation. From our analysis we conclude that scalar system
appears as a two-pion scattering state and that there is no spatially-localised
state in the light-quark mass region.Comment: 9 pages, 10 figure
Rotational states in deformed nuclei: An analytic approach
The consequences of the spontaneous breaking of rotational symmetry are
investigated in a field theory model for deformed nuclei, based on simple
separable interactions. The crucial role of the Ward-Takahashi identities to
describe the rotational states is emphasized. We show explicitly how the rotor
picture emerges from the isoscalar Goldstone modes, and how the two-rotor model
emerges from the isovector scissors modes. As an application of the formalism,
we discuss the M1 sum rules in deformed nuclei, and make connection to
empirical information.Comment: 19 pages, 9 figure
Searching for the light dark gauge boson in GeV-scale experiments
We study current constraints and search prospects for a GeV scale vector
boson at a range of low energy experiments. It couples to the Standard Model
charged particles with a strength <= 10^-3 to 10^-4 of that of the photon. The
possibility of such a particle mediating dark matter self-interactions has
received much attention recently. We consider searches at low energy high
luminosity colliders, meson decays, and fixed target experiments. Based on
available data, searches both at colliders and in meson decays can discover or
exclude such a scenario if the coupling strength is on the larger side. We
emphasize that a dedicated fixed target experiment has a much better potential
in searching for such a gauge boson, and outline the desired properties of such
an experiment. Two different optimal designs should be implemented to cover the
range of coupling strength 10^-3 to 10^-5, and < 10^-5 of the photon,
respectively. We also briefly comment on other possible ways of searching for
such a gauge boson.Comment: 33 pages, 5 figures; v2: corrected discussion of Upsilon decays,
updates to discussion of fixed-target experiments and QED constraints,
numerous minor changes, references added; v3: typo corrected relative to the
JHEP published versio
Manganese pigmented anodized copper as solar selective absorber
The study concerns the optical and structural properties of layers obtained by a new efficient surface treatment totally free of chromium species. The process is made up of an anodic oxidation of copper in an alkaline solution followed by an alkaline potassium permanganate dipping post-treatment. Coatings, obtained at the lab and pilot scales, are stable up to 220 °C in air and vacuum, present low emissivity (0.14 at 70 °C) and high solar absorptivity (0.96), i.e. a suitable thermal efficiency (0.84 at 70 °C)
- …