1,347 research outputs found
Coherent Neutral Current Neutrino-Nucleus Scattering at a Spallation Source; a Valuable Experimental Probe
The coherent contribution of all neutrons in neutrino nucleus scattering due
to the neutral current is examined considering the Spallation Neutron Source
(SNS) as a source of neutrinos. SNS is a prolific pulsed source of electron and
muon neutrinos as well as muon antineutrinos.Comment: 15 LaTex pages, 14 figures, 3 Table
Backward Raman compression of x-rays in metals and warm dense matters
Experimentally observed decay rate of the long wavelength Langmuir wave in
metals and dense plasmas is orders of magnitude larger than the prediction of
the prevalent Landau damping theory. The discrepancy is explored, and the
existence of a regime where the forward Raman scattering is stable and the
backward Raman scattering is unstable is examined. The amplification of an
x-ray pulse in this regime, via the backward Raman compression, is
computationally demonstrated, and the optimal pulse duration and intensity is
estimated.Comment: 4 pages, 3 figures, submitted to PR
Inter-valley plasmons in graphene
The spectrum of two-dimensional (2D) plasma waves in graphene has been
recently studied in the Dirac fermion model. We take into account the whole
dispersion relation for graphene electrons in the tight binding approximation
and the local field effects in the electrodynamic response. Near the
wavevectors close to the corners of the hexagon-shaped Brillouin zone we found
new low-frequency 2D plasmon modes with a linear spectrum. These "inter-valley"
plasmon modes are related to the transitions between the two nearest Dirac
cones.Comment: 4 pages, 2 figures; submitted in PR
Suppression of Landau damping via electron band gap
The pondermotive potential in the X-ray Raman compression can generate an
electron band gap which suppresses the Landau damping. The regime is identified
where a Langmuir wave can be driven without damping in the stimulated Raman
compression. It is shown that the partial wave breaking and the frequency
detuning due to the trapped particles would be greatly reduced.Comment: 4 pages, 5 figure
XENON10/100 dark matter constraints in comparison with CoGeNT and DAMA: examining the Leff dependence
We consider the compatibility of DAMA/LIBRA, CoGeNT, XENON10 and XENON100
results for spin-independent (SI) dark matter Weakly Interacting Massive
Particles (WIMPs), particularly at low masses (~ 10 GeV), assuming a standard
dark matter halo. The XENON bounds depend on the scintillation efficiency
factor Leff for which there is considerable uncertainty. Thus we consider
various extrapolations for Leff at low energy. With the Leff measurements we
consider, XENON100 results are found to be insensitive to the low energy
extrapolation. We find the strongest bounds are from XENON10, rather than
XENON100, due to the lower energy threshold. For reasonable choices of Leff and
for the case of SI elastic scattering, XENON10 is incompatible with the
DAMA/LIBRA 3 region and severely constrains the 7-12 GeV WIMP mass
region of interest published by the CoGeNT collaboration.Comment: 23 pages, 9 figures. Version 2: more careful treatment of XENON10
efficiencies, expanded discussion. A response to arXiv:1006.2031 is found in
the Appendi
A survey of energy loss calculations for heavy ions between 1 and 100 keV
The original Lindhard-Scharff-Schi{\o}tt (LSS) theory and the more recent
Tilinin theory for calculating the nuclear and electronic stopping powers of
slow heavy ions are compared with predictions from the SRIM code by Ziegler.
While little discrepancies are present for the nuclear contribution to the
energy loss, large differences are found in the electronic one. When full ion
recoil cascade simulations are tested against the elastic neutron scattering
data available in the literature, it can be concluded that the LSS theory is
the more accurate.Comment: Presented at the 10th International Symposium on Radiation Physics,
17-22 September, 2006, Coimbra, Portugal; style corrections, small change to
fig.
Theory of plasmon decay in dense plasmas and warm dense matter
The decay of the Langmuir waves in dense plasmas is not accurately predicted
by the prevalent Landau damping theory. A dielectric function theory is
introduced, predicting much higher damping than the Landau damping theory. This
strong damping is in better agreement with the experimentally observed data in
metals. It is shown that the strong plasmon decay leads to the existence of a
parameter regime where the backward Raman scattering is unstable while the
forward Raman scattering is stable. This regime may be used to create intense
x-ray pulses, by means of the the backward Raman compression. The optimal pulse
duration and intensity is estimated
Measurement of the quenching factor of Na recoils in NaI(Tl)
Measurements of the quenching factor for sodium recoils in a 5 cm diameter
NaI(Tl) crystal at room temperature have been made at a dedicated neutron
facility at the University of Sheffield. The crystal has been exposed to 2.45
MeV mono-energetic neutrons generated by a Sodern GENIE 16 neutron generator,
yielding nuclear recoils of energies between 10 and 100 keVnr. A cylindrical
BC501A detector has been used to tag neutrons that scatter off sodium nuclei in
the crystal. Cuts on pulse shape and time of flight have been performed on
pulses recorded by an Acqiris DC265 digitiser with a 2 ns sampling time.
Measured quenching factors of Na nuclei range from 19% to 26% in good agreement
with other experiments, and a value of 25.2 \pm 6.4% has been determined for 10
keV sodium recoils. From pulse shape analysis, the mean times of pulses from
electron and nuclear recoils have been compared down to 2 keVee. The
experimental results are compared to those predicted by Lindhard theory,
simulated by the SRIM Monte Carlo code, and a preliminary curve calculated by
Prof. Akira Hitachi.Comment: 21 pages, 13 figure
MIMAC-He3 : A Micro-TPC Matrix of Chambers of He3 for direct detection of Wimps
The project of a micro-TPC matrix of chambers of \hetrois for direct
detection of non-baryonic dark matter is presented. The privileged properties
of He3 are highlighted. The double detection (ionization - projection of
tracks) is explained and its rejection evaluated. The potentialities of
MIMAC-He3 for supersymmetric dark matter search are discussed.Comment: to appear in Proc. of the 9th International Conference on Topics in
Astroparticle and Underground Physics (TAUP 2005), Zaragoza, Sept. 200
Negative Particle Planar and Axial Channeling and Channeling Collimation
While information exists on high energy negative particle channeling there
has been little study of the challenges of negative particle bending and
channeling collimation. Partly this is because negative dechanneling lengths
are relatively much shorter. Electrons are not particularly useful for
investigating negative particle channeling effects because their material
interactions are dominated by channeling radiation. Another important factor is
that the current central challenge in channeling collimation is the
proton-proton Large Hadron Collider (LHC) where both beams are positive. On the
other hand in the future the collimation question might reemerge for
electron-positron or muon colliders. Dechanneling lengths increase at higher
energies so that part of the negative particle experimental challenge
diminishes. In the article different approaches to determining negative
dechanneling lengths are reviewed. The more complicated case for axial
channeling is also discussed. Muon channeling as a tool to investigate
dechanneling is also discussed. While it is now possible to study muon
channeling it will probably not illuminate the study of negative dechanneling.Comment: 15 pages, 1 figure, docx fil
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