18 research outputs found
Measurement of Scintillation and Ionization Yield and Scintillation Pulse Shape from Nuclear Recoils in Liquid Argon
We have measured the scintillation and ionization yield of recoiling nuclei
in liquid argon as a function of applied electric field by exposing a
dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy
pulsed narrow band neutron beam produced at the Notre Dame Institute for
Structure and Nuclear Astrophysics. Liquid scintillation counters were arranged
to detect and identify neutrons scattered in the TPC and to select the energy
of the recoiling nuclei. We report measurements of the scintillation yields for
nuclear recoils with energies from 10.3 to 57.3 keV and for median applied
electric fields from 0 to 970 V/cm. For the ionization yields, we report
measurements from 16.9 to 57.3 keV and for electric fields from 96.4 to 486
V/cm. We also report the observation of an anticorrelation between
scintillation and ionization from nuclear recoils, which is similar to the
anticorrelation between scintillation and ionization from electron recoils.
Assuming that the energy loss partitions into excitons and ion pairs from
Kr internal conversion electrons is comparable to that from Bi
conversion electrons, we obtained the numbers of excitons () and ion
pairs () and their ratio () produced by nuclear recoils from
16.9 to 57.3 keV. Motivated by arguments suggesting direction sensitivity in
LAr-TPC signals due to columnar recombination, a comparison of the light and
charge yield of recoils parallel and perpendicular to the applied electric
field is presented for the first time.Comment: v2 to reflect published versio
Dark Matter in 3D
We discuss the relevance of directional detection experiments in the
post-discovery era and propose a method to extract the local dark matter phase
space distribution from directional data. The first feature of this method is a
parameterization of the dark matter distribution function in terms of integrals
of motion, which can be analytically extended to infer properties of the global
distribution if certain equilibrium conditions hold. The second feature of our
method is a decomposition of the distribution function in moments of a model
independent basis, with minimal reliance on the ansatz for its functional form.
We illustrate our method using the Via Lactea II N-body simulation as well as
an analytical model for the dark matter halo. We conclude that O(1000) events
are necessary to measure deviations from the Standard Halo Model and constrain
or measure the presence of anisotropies.Comment: 36 pages, 13 figure
Measurement of the liquid argon energy response to nuclear and electronic recoils
International audienceA liquid argon time projection chamber, constructed for the Argon Response to Ionization and Scintillation (ARIS) experiment, is exposed to the highly collimated and quasimonoenergetic LICORNE neutron beam at the Institut de Physique NuclĂ©aire dâOrsay (IPNO) in order to study the scintillation response to nuclear and electronic recoils. An array of liquid scintillator detectors, arranged around the apparatus, tag scattered neutrons and select nuclear recoil energies in the [7, 120] keV energy range. The relative scintillation efficiency of nuclear recoils is measured to high precision at null field, and the ion-electron recombination probability is extracted for a range of applied electric fields. Single-scattered Compton electrons, produced by gammas emitted from the deexcitation of Li*7 in coincidence with the beam pulse, along with calibration gamma sources, are used to extract the recombination probability as a function of energy and electron drift field. The ARIS results are compared with three recombination probability parametrizations (Thomas-Imel, Doke-Birks, and PARIS), allowing for the definition of a fully comprehensive model of the liquid argon response to nuclear and electronic recoils down to the few-keV range. The constraints provided by ARIS to the liquid argon response at low energy allow the reduction of systematics affecting the sensitivity of dark matter search experiments based on liquid argon
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DarkSide: Latest results and future perspectives
DarkSide is direct-detection dark-matter experimental project based on radiopure argon. The main goal of the DarkSide program is the detection of rare nuclear elastic collisions with hypothetical dark-matter particles. The present detector, DarkSide-50, placed at Laboratori Nazionali del Gran Sasso (LNGS), is a dualphase time projection chamber (TPC) filled with ultra-pure liquid argon, extracted from underground sources. Surrounding the TPC to suppress the background there are neutron and muon active vetoes. One of argon key features is the capability to distinguish between electron and nuclear recoils, exploiting the different shapes of the signals. DarkSide-50 new results, obtained using a live-days exposure of 532.4 days, are presented. This analysis sets a 90% C.L. upper limit on the dark matternucleon spin-independent cross-section of 1.1 Ă 10-44 cm2 for a WIMP mass of 100 GeV/c2. The next phase of the project, DarkSide-20k, will be a new detector with a fiducial mass of ⌠20 tons, equipped with cryogenic silicon photomultipliers (SiPM)
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Measurement of the ion fraction and mobility of 218Po produced in 222Rn decays in liquid argon
We report measurements of the charged daughter fraction of 218Po as a result of the 222Rn alpha decay, and the mobility of 218Po+ ions, using radon-polonium coincidences from the 238U chain identified in 532 live-days of DarkSide-50 WIMP-search data. The fraction of 218Po that is charged is found to be 0.37 ± 0.03 and the mobility of 218Po+ is (8.6 ± 0.1) Ă 10â4 cmVs2