18,723 research outputs found
New Prospects in Fixed Target Searches for Dark Forces with the SeaQuest Experiment at Fermilab
An intense, 120 GeV proton beam incident on an extremely long, iron target
generates enormous numbers of light-mass particles that also decay within that
target. If one of these particles decays to a final state with a hidden gauge
boson, or if such a particle is produced as a result of the initial collision,
then that weakly interacting, hidden-sector particle may traverse the remainder
of the target and be detected downstream through its possible decay to an
, , or final state. These conditions can be
realized through an extension of the SeaQuest experiment at Fermilab, and in
this initial investigation we consider how it can serve as an ultrasensitive
probe of hidden vector gauge forces, both Abelian and non-Abelian. A light,
weakly coupled hidden sector may well explain the dark matter established
through astrophysical observations, and the proposed search can provide
tangible evidence for its existence --- or, alternatively, constrain a "sea" of
possibilities.Comment: 14 pages, 8 figures; improved sensitivity analysis and cross-checks;
small shifts in the expected limits; conclusions unchanged; refs. adde
Nuclear pairing from microscopic forces: singlet channels and higher-partial waves
Background: An accurate description of nuclear pairing gaps is extremely
important for understanding static and dynamic properties of the inner crusts
of neutron stars and to explain their cooling process.
Purpose: We plan to study the behavior of the pairing gaps as a
function of the Fermi momentum for neutron and nuclear matter in all
relevant angular momentum channels where superfluidity is believed to naturally
emerge. The calculations will employ realistic chiral nucleon-nucleon
potentials with the inclusion of three-body forces and self-energy effects.
Methods: The superfluid states of neutron and nuclear matter are studied by
solving the BCS gap equation for chiral nuclear potentials using the method
suggested by Khodel et al., where the original gap equation is replaced by a
coupled set of equations for the dimensionless gap function defined
by and a non-linear algebraic equation for the
gap magnitude at the Fermi surface. This method is
numerically stable even for small pairing gaps, such as that encountered in the
coupled partial wave.
Results: We have successfully applied Khodel's method to singlet () and
coupled channel ( and ) cases in neutron and nuclear matter. Our
calculations agree with other ab-initio approaches, where available, and
provide crucial inputs for future applications in superfluid systems.Comment: 18 pages and 9 figure
The 1979 X-ray outburst of Cen X-4
X-ray observations of the first major outburst (since its initial discovery in 1969) of the "classical" transient X-ray source Cen X-4 were obtained with the Ariel 5 All-Sky Monitor. The flare light curve exhibits a double-peaked maximum at a level of approximately 4 times the Crab nebula, and its duration and characteristic decay time scale are the shortest yet observed from the class of "soft" X-ray transients. A total X-ray output of approximately 3 x 10 to the 43rd power ergs, a factor of approximately 20 less than that of the 1969 outburst is estimated. In addition, evidence is found for a regular modulation of the flux during the decline phase at a period of 8.2 plus or minus 0.2 hours. The existing data are consistent with a source model involving episodic mass exchange from a late-type dwarf onto a neutron star comparison in a relatively close binary system
Microscopic Restoration of Proton-Neutron Mixed Symmetry in Weakly Collective Nuclei
Starting from the microscopic low-momentum nucleon-nucleon interaction V{low
k}, we present the first systematic shell model study of magnetic moments and
magnetic dipole transition strengths of the basic low-energy one-quadrupole
phonon excitations in nearly-spherical nuclei. Studying in particular the
even-even N=52 isotones from 92Zr to 100Cd, we find the predicted evolution of
the predominantly proton-neutron non-symmetric state reveals a restoration of
collective proton-neutron mixed-symmetry structure near mid-shell. This
provides the first explanation for the existence of pronounced collective
mixed-symmetry structures in weakly-collective nuclei.Comment: 5 Pages, 3 figure
Search for plasma oscillations stimulated by a pre-bunched electron beam from the Rensselaer linear accelerator
Argon plasma oscillations stimulated by high energy pre-bunched electron beam from linear accelerato
Gamma-ray bursts during neutron star formation. Gamma-ray bursts and transient X-ray sources
Discussions are presented of the associations between cosmic gamma ray bursts and transient X-ray sources, and the release of gravitational binding energy during the formation of neutron stars. The model for studying the associations is described along with the release of neutrinos during the collapse of white dwarfs
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