847 research outputs found
Development of portable NMR polarimeter system for polarized HD target
A portable NMR polarimeter system has been developed to measure the
polarization of a polarized Hydrogen-Deuteride (HD) target for hadron
photoproduction experiments at SPring-8. The polarized HD target is produced at
the Research Center for Nuclear Physics (RCNP), Osaka university and is
transported to SPring-8. The HD polarization should be monitored at both
places. We have constructed the portable NMR polarimeter system by replacing
the devices in the conventional system with the software system with PCI
eXtensions for Instrumentation (PXI). The weight of the NMR system is downsized
from 80 kg to 7 kg, and the cost is reduced to 25%. We check the performance of
the portable NMR polarimeter system. The signal-to-noise (S/N) ratio of the NMR
signal for the portable system is about 50% of that for the conventional NMR
system. This performance of the portable NMR system is proved to be compatible
with the conventional NMR system for the polarization measurement.Comment: 6 page, 8 figures, 2011/Mar/9 Replace Author
Cosmological constraints on dark matter models with velocity-dependent annihilation cross section
We derive cosmological constraints on the annihilation cross section of dark
matter with velocity-dependent structure, motivated by annihilating dark matter
models through Sommerfeld or Breit-Wigner enhancement mechanisms. In models
with annihilation cross section increasing with decreasing dark matter
velocity, big-bang nucleosynthesis and cosmic microwave background give
stringent constraints.Comment: 23 pages, 9 figures; Added reference
Bounds on long-lived charged massive particles from Big Bang nucleosynthesis
The Big Bang nucleosynthesis (BBN) in the presence of charged massive
particles (CHAMPs) is studied in detail. All currently known effects due to the
existence of bound states between CHAMPs and nuclei, including possible
late-time destruction of Li6 and Li7 are included. The study sets conservative
bounds on CHAMP abundances in the decay time range 3x10^2 sec - 10^12 sec. It
is stressed that the production of Li6 at early times T ~ 10keV is
overestimated by a factor ~ 10 when the approximation of the Saha equation for
the He4 bound state fraction is utilised. To obtain conservative limits on the
abundance of CHAMPs, a Monte-Carlo analysis with ~ 3x10^6 independent BBN runs,
varying reaction rates of nineteen different reactions, is performed (see
attached erratum, however). The analysis yields the surprising result that
except for small areas in the particle parameter space conservative constraints
on the abundance of decaying charged particles are currently very close to
those of neutral particles. It is shown that, in case a number of heretofore
unconsidered reactions may be determined reliably in future, it is conceivable
that the limit on CHAMPs in the early Universe could be tightened by orders of
magnitude. An ERRATUM gives limits on primordial CHAMP densities when the by
Ref. Kamimura et al. recently more accurately determined CHAMP reaction rates
are employed.Comment: includes Erratum showing most up to date limits after determination
of the most important reaction rate
A Pair Polarimeter for Linearly Polarized High Energy Photons
A high quality beam of linearly polarized photons of several GeV will become
available with the coherent bremsstrahlung technique at JLab. We have developed
a polarimeter which requires about two meters of the beam line, has an
analyzing power of 20% and an efficiency of 0.02%. The layout and first results
of a polarimeter test on the laser back-scattering photon beam at SPring-8/LEPS
are presented
Revisiting vertical structure of neutrino-dominated accretion disks: Bernoulli parameter, neutrino trapping and other distributions
We revisit the vertical structure of neutrino dominated accretion flows
(NDAFs) in spherical coordinates with a new boundary condition based on the
mechanical equilibrium. The solutions show that NDAF is significantly thick.
The Bernoulli parameter and neutrino trapping are determined by the mass
accretion rate and the viscosity parameter. According to the distribution of
the Bernoulli parameter, the possible outflow may appear in the outer region of
the disk. The neutrino trapping can essentially affect the neutrino radiation
luminosity. The vertical structure of NDAF is like a "sandwich", and the
multilayer accretion may account for the flares in gamma-ray bursts.Comment: 7 pages, 2 figures, Accepted for publication in Astrophysics & Space
Scienc
Primordial nucleosynthesis and hadronic decay of a massive particle with a relatively short lifetime
In this paper we consider the effects on big bang nucleosynthesis (BBN) of
the hadronic decay of a long-lived massive particle. If high-energy hadrons are
emitted near the BBN epoch ( -- ), they
extraordinarily inter-convert the background nucleons each other even after the
freeze-out time of the neutron to proton ratio. Then, produced light element
abundances are changed, and that may result in a significant discrepancy
between standard BBN and observations. Especially on the theoretical side, now
we can obtain a lot of experimental data of hadrons and simulate the hadronic
decay process executing the numerical code of the hadron fragmentation even in
the high energy region where we have no experimental data. Using the light
element abundances computed in the hadron-injection scenario, we derive a
constraint on properties of such a particle by comparing our theoretical
results with observations.Comment: 33 pages, 14 postscript figures, reference added, typo corrected, to
appear in Phys. Rev.
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