119 research outputs found
A Review of Basic Energy Reconstruction Techniques in Liquid Xenon and Argon Detectors for Dark Matter and Neutrino Physics Using NEST
Detectors based upon the noble elements, especially liquid xenon as well as
liquid argon, as both single- and dual-phase types, require reconstruction of
the energies of interacting particles, both in the field of direct detection of
dark matter (Weakly Interacting Massive Particles or WIMPs, axions, etc.) and
in neutrino physics. Experimentalists, as well as theorists who
reanalyze/reinterpret experimental data, have used a few different techniques
over the past few decades. In this paper, we review techniques based on solely
the primary scintillation channel, the ionization or secondary channel
available at non-zero drift electric fields, and combined techniques that
include a simple linear combination and weighted averages, with a brief
discussion of the applications of profile likelihood, maximum likelihood, and
machine learning. Comparing results for electron recoils (beta and gamma
interactions) and nuclear recoils (primarily from neutrons) from the Noble
Element Simulation Technique (NEST) simulation to available data, we confirm
that combining all available information generates higher-precision means,
lower widths (energy resolution), and more symmetric shapes (approximately
Gaussian) especially at keV-scale energies, with the symmetry even greater when
thresholding is addressed. Near thresholds, bias from upward fluctuations
matters. For MeV-GeV scales, if only one channel is utilized, an
ionization-only-based energy scale outperforms scintillation; channel
combination remains beneficial. We discuss here what major collaborations use.Comment: 42 Pages, 2 Tables, 11 Figures, 13 Equation
Circular Dichroism in Atomic Resonance-Enhanced Few-Photon Ionization
We investigate few-photon ionization of lithium atoms prepared in the
polarized 2() state when subjected to femtosecond light pulses
with left- or right-handed circular polarization at wavelengths between 665 nm
and 920 nm. We consider whether ionization proceeds more favorably for the
electric field co- or counter-rotating with the initial electronic current
density. Strong asymmetries are found and quantitatively analyzed in terms of
"circular dichroism" (). While the intensity dependence of the measured
values is rather weak throughout the investigated regime, a very strong
sensitivity on the center wavelength of the incoming radiation is observed.
While the co-rotating situation overall prevails, the counter-rotating geometry
is strongly favored around 800 nm due to the 2-3 resonant transition,
which can only be driven by counter-rotating fields. The observed features
provide insights into the helicity dependence of light-atom interactions, and
on the possible control of electron emission in atomic few-photon ionization by
polarization-selective resonance enhancement
Using circular dichroism to control energy transfer in multi-photon ionization
Chirality causes symmetry breaks in a large variety of natural phenomena
ranging from particle physics to biochemistry. We investigate one of the
simplest conceivable chiral systems, a laser-excited, oriented, effective
one-electron Li target. Prepared in a polarized p state with |m|=1 in an
optical trap, the atoms are exposed to co- and counter-rotating circularly
polarized femtosecond laser pulses. For a field frequency near the excitation
energy of the oriented initial state, a strong circular dichroism is observed
and the photoelectron energies are significantly affected by the
helicity-dependent Autler-Townes splitting. Besides its fundamental relevance,
this system is suited to create spin-polarized electron pulses with a
reversible switch on a femtosecond timescale at an energy resolution of a few
meV
Nuclear recoil response of liquid xenon and its impact on solar 8B neutrino and dark matter searches
Knowledge of the ionization and scintillation responses of liquid xenon (LXe)
to nuclear recoils is crucial for LXe-based dark matter experiments. Current
calibrations carry large uncertainties in the low-energy region below
keV where signals from dark matter particles of 10 GeV/c masses are
expected. The coherent elastic neutrino-nucleus scattering (CENS) by solar
B neutrinos also results in a continuum of nuclear recoil events below 3.0
keV (99\% of events), which further complicates low-mass dark matter
searches in LXe experiments. In this paper, we describe a method to quantify
the uncertainties of low-energy LXe responses using published calibration data,
followed by case studies to evaluate the impact of yield uncertainties on
B searches and low-mass dark matter sensitivity in a typical ton-scale
LXe experiment. We conclude that naively omitting yield uncertainties leads to
overly optimistic limits by factor for a 6 GeV/c WIMP mass. Future
nuclear recoil light yield calibrations could allow experiments to recover this
sensitivity and also improve the accuracy of solar B flux measurements
A Review of NEST Models, and Their Application to Improvement of Particle Identification in Liquid Xenon Experiments
Liquid xenon is a leader in rare-event physics searches. Accurate modeling of
charge and light production is key for simulating signals and backgrounds in
this medium. The signal- and background-production models in the Noble Element
Simulation Technique (NEST) are presented. NEST is a simulation toolkit based
on experimental data, fit using simple, empirical formulae for the average
charge and light yields and their variations. NEST also simulates the final
scintillation pulses and exhibits the correct energy resolution as a function
of the particle type, the energy, and the electric fields. After vetting of
NEST against raw data, with several specific examples pulled from XENON,
ZEPLIN, LUX/LZ, and PandaX, we interpolate and extrapolate its models to draw
new conclusions on the properties of future detectors (e.g., XLZD's), in terms
of the best possible discrimination of electron(ic) recoil backgrounds from a
potential nuclear recoil signal, especially WIMP dark matter. We discover that
the oft-quoted value of 99.5% discrimination is overly conservative,
demonstrating that another order of magnitude improvement (99.95%
discrimination) can be achieved with a high photon detection efficiency (g1 ~
15-20%) at reasonably achievable drift fields of 200-350 V/cm.Comment: 24 Pages, 6 Tables, 15 Figures, and 15 Equation
Applying Superfluid Helium to Light Dark Matter Searches: Demonstration of the HeRALD Detector Concept
The SPICE/HeRALD collaboration is performing R&D to enable studies of sub-GeV
dark matter models using a variety of target materials. Here we report our
recent progress on instrumenting a superfluid He target mass with a
transition-edge sensor based calorimeter to detect both atomic signals (e.g.
scintillation) and He quasiparticle (phonon and roton) excitations. The
sensitivity of HeRALD to the critical "quantum evaporation" signal from He
quasiparticles requires us to block the superfluid film flow to the
calorimeter. We have developed a heat-free film-blocking method employing an
unoxidized Cs film, which we implemented in a prototype "HeRALD v0.1" detector
of 10~g target mass. This article reports initial studies of the atomic
and quasiparticle signal channels. A key result of this work is the measurement
of the quantum evaporation channel's gain of , which will
enable He-based dark matter experiments in the near term. With this gain
the HeRALD detector reported here has an energy threshold of 145~eV at 5 sigma,
which would be sensitive to dark matter masses down to 220~MeV/c.Comment: 14 pages, 9 figure
Conversion of Iodide to Hypoiodous Acid and Iodine in Aqueous Microdroplets Exposed to Ozone
Halides are incorporated into aerosol sea spray, where they start the catalytic destruction of ozone (O3) over the oceans and affect the global troposphere. Two intriguing environmental problems undergoing continuous research are (1) to understand how reactive gas phase molecular halogens are directly produced from inorganic halides exposed to O3 and (2) to constrain the environmental factors that control this interfacial process. This paper presents a laboratory study of the reaction of O3 at variable iodide (I–) concentration (0.010–100 μM) for solutions aerosolized at 25 °C, which reveal remarkable differences in the reaction intermediates and products expected in sea spray for low tropospheric [O3]. The ultrafast oxidation of I– by O3 at the air–water interface of microdroplets is evidenced by the appearance of hypoiodous acid (HIO), iodite (IO2–), iodate (IO3–), triiodide (I3–), and molecular iodine (I2). Mass spectrometry measurements reveal an enhancement (up to 28%) in the dissolution of gaseous O3 at the gas–liquid interface when increasing the concentration of NaI or NaBr from 0.010 to 100 μM. The production of iodine species such as HIO and I2 from NaI aerosolized solutions exposed to 50 ppbv O3 can occur at the air–water interface of sea spray, followed by their transfer to the gas-phase, where they contribute to the loss of tropospheric ozone
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