1,793 research outputs found
Metastable helium molecules as tracers in superfluid liquid He
Metastable helium molecules generated in a discharge near a sharp tungsten
tip operated in either pulsed mode or continuous field-emission mode in
superfluid liquid He are imaged using a laser-induced-fluorescence
technique. By pulsing the tip, a small cloud of He molecules is
produced. At 2.0 K, the molecules in the liquid follow the motion of the normal
fluid. We can determine the normal-fluid velocity in a heat-induced counterflow
by tracing the position of a single molecule cloud. As we run the tip in
continuous field-emission mode, a normal-fluid jet from the tip is generated
and molecules are entrained in the jet. A focused 910 nm pump laser pulse is
used to drive a small group of molecules to the vibrational state.
Subsequent imaging of the tagged molecules with an expanded 925 nm probe
laser pulse allows us to measure the velocity of the normal fluid. The
techniques we developed demonstrate for the first time the ability to trace the
normal-fluid component in superfluid helium using angstrom-sized particles.Comment: 4 pages, 7 figures. Submitted to Phys. Rev. Let
A Path to the Direct Detection of sub-GeV Dark Matter Using Calorimetric Readout of a Superfluid He Target
A promising technology concept for sub-GeV dark matter detection is
described, in which low-temperature microcalorimeters serve as the sensors and
superfluid He serves as the target material. A superfluid helium target has
several advantageous properties, including a light nuclear mass for better
kinematic matching with light dark matter particles, copious production of
scintillation light, extremely good intrinsic radiopurity, a high impedance to
external vibration noise, and a unique mechanism for observing phonon-like
modes via liberation of He atoms into a vacuum (`quantum evaporation'). In
this concept, both scintillation photons and triplet excimers are detected
using calorimeters, including calorimeters immersed in the superfluid. Kinetic
excitations of the superfluid medium (rotons and phonons) are detected using
quantum evaporation and subsequent atomic adsorption onto a microcalorimeter
suspended in vacuum above the target helium. The energy of adsorption amplifies
the phonon/roton signal before calorimetric sensing, producing a gain mechanism
that can reduce the techonology's recoil energy threshold below the calorimeter
energy threshold. We describe signal production and signal sensing
probabilities, and estimate electron recoil discrimination. We then simulate
radioactive backgrounds from gamma rays and neutrons. Dark matter - nucleon
elastic scattering cross-section sensitivities are projected, demonstrating
that even very small (sub-kg) target masses can probe wide regions of as-yet
untested dark matter parameter space
Spatial methods for event reconstruction in CLEAN
In CLEAN (Cryogenic Low Energy Astrophysics with Noble gases), a proposed
neutrino and dark matter detector, background discrimination is possible if one
can determine the location of an ionizing radiation event with high accuracy.
We simulate ionizing radiation events that produce multiple scintillation
photons within a spherical detection volume filled with liquid neon. We
estimate the radial location of a particular ionizing radiation event based on
the observed count data corresponding to that event. The count data are
collected by detectors mounted at the spherical boundary of the detection
volume. We neglect absorption, but account for Rayleigh scattering. To account
for wavelength-shifting of the scintillation light, we assume that photons are
absorbed and re-emitted at the detectors. Here, we develop spatial Maximum
Likelihood methods for event reconstruction, and study their performance in
computer simulation experiments. We also study a method based on the centroid
of the observed count data. We calibrate our estimates based on training data
A Consistent Dark Matter Interpretation For CoGeNT and DAMA/LIBRA
In this paper, we study the recent excess of low energy events observed by
the CoGeNT collaboration and the annual modulation reported by the DAMA/LIBRA
collaboration, and discuss whether these signals could both be the result of
the same elastically scattering dark matter particle. We find that, without
channeling but when taking into account uncertainties in the relevant quenching
factors, a dark matter candidate with a mass of approximately ~7.0 GeV and a
cross section with nucleons of sigma_{DM-N} ~2x10^-4 pb (2x10^-40 cm^2) could
account for both of these observations. We also comment on the events recently
observed in the oxygen band of the CRESST experiment and point out that these
could potentially be explained by such a particle. Lastly, we compare the
region of parameter space favored by DAMA/LIBRA and CoGeNT to the constraints
from XENON 10, XENON 100, and CDMS (Si) and find that these experiments cannot
at this time rule out a dark matter interpretation of these signals.Comment: 8 pages, 6 figure
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