We have performed measurements of scintillation light in liquid neon, observing a signal yield in our detector as high as (3.5 $\pm$ 0.4) photoelectrons/keV. We measure pulse shape discrimination efficiency between electronic and nuclear recoils in liquid neon from 50 and 300 keV nuclear recoil energy. We also measure the \leff\, parameter in liquid neon between 30 and 370 keV nuclear recoil energy, observing an average \leff$=0.24$ above 50 keV. We observe a dependence of the scintillation time distribution and signal yield on the pressure and temperature of the liquid neon.
The scintillation light yield of liquid argon from nuclear recoils relative to electronic recoils has been measured as a function of recoil energy from 10 keVr up to 250 keVr. The scintillation efficiency, defined as the ratio of the nuclear recoil scintillation response to the electronic recoil response, is 0.25 \pm 0.01 + 0.01(correlated) above 20 keVr.
The scintillation properties of liquid helium upon the recoil of a low energy helium atom are discussed in the context of the possible use of this medium as a detector of dark matter. It is found that the prompt scintillation yield in the range of recoil energies from a few keV to 100 keV is somewhat higher than that obtained by a linear extrapolation from the measured yield for an 5 MeV alpha particle. A comparison is made of both the scintillation yield and the charge separation by an electric field for nuclear recoils and for electrons stopped in helium.
We perform a theoretical study of the scintillation efficiency in the low-energy region crucial for liquid-xenon dark-matter detectors. We develop a computer program to simulate the cascading process of the recoiling xenon nucleus in liquid xenon and calculate the nuclear quenching effect due to atomic collisions. We use the electronic stopping power extrapolated from the experimental data to the low-energy region, and take into account the effects of electrons escaping from the electron-ion pair recombination using the generalized Thomas-Imel model fitted to scintillation data. Our result agr…
Detailed Monte-Carlo simulations were used to evaluate the performance of a liquid neon scintillation detector for dark matter and low-energy solar neutrino interactions. A maximum-likelihood event vertex fitter including PMT time information was developed, which significantly improves position resolution over spatial-only algorithms, and substantially decreases the required detector size and achievable analysis energy threshold. The ultimate sensitivity to WIMP dark matter and the pp flux uncertainty are evaluated as a function of detector size. The dependence on the neon scintillation and PM…
Scintillation efficiency of low-energy nuclear recoils in noble liquids plays a crucial role in interpreting results from some direct searches for Weakly Interacting Massive Particle (WIMP) dark matter. However, the cause of a reduced scintillation efficiency relative to electronic recoils in noble liquids remains unclear at the moment. We attribute such a reduction of scintillation efficiency to two major mechanisms: 1) energy loss and 2) scintillation quenching. The former is commonly described by Lindhard's theory and the latter by Birk's saturation law. We propose to combine these two to e…
Using a single-phase liquid argon detector with a signal yield of 4.85 photoelectrons per keV of electronic-equivalent recoil energy (keVee), we measure the scintillation time dependence of both electronic and nuclear recoils in liquid argon down to 5 keVee. We develop two methods of pulse shape discrimination to distinguish between electronic and nuclear recoils. Using one of these methods, we measure a background and statistics-limited level of electronic recoil contamination to be $7.6\times10^{-7}$ between 60 and 128 keV of nuclear recoil energy (keVr) for a nuclear recoil acceptance of 50…
The scintillation efficiency (quenching factor) of fluorine and calcium nuclei recoiling in a CaF-2(Eu) crystal was measured in an energy region relevant to dark matter searches. The recoiling nuclei were obtained via the 19-F(n,n') and 40-Ca(n,n') reactions, where the neutron beam was provided via the d(d,n)3-He reaction. The quenching factor of F and Ca nuclei in the CaF-2(Eu) crystal was found to be 11 ~ 20 %, and 9 ~ 23 % relative to the electron equivalent energy for 53 ~ 192 keV and 25 ~ 91 keV recoil energies, respectively, and the energy dependence was observed. The quenching factor we…
Particle detectors that use liquid xenon (LXe) as detection medium are among the leading technologies in the search for dark matter weakly interacting massive particles (WIMPs). A key enabling element has been the low-energy detection threshold for recoiling nuclei produced by the interaction of WIMPs in LXe targets. In these detectors, the nuclear recoil energy scale is based on the LXe scintillation signal and thus requires knowledge of the relative scintillation efficiency of nuclear recoils, Leff. The uncertainty in Leff at low energies is the largest systematic uncertainty in the reported…
Ionization and scintillation produced by nuclear recoils in gaseous xenon at approximately 14 bar have been simultaneously observed in an electroluminescent time projection chamber. Neutrons from radioisotope $α$-Be neutron sources were used to induce xenon nuclear recoils, and the observed recoil spectra were compared to a detailed Monte Carlo employing estimated ionization and scintillation yields for nuclear recoils. The ability to discriminate between electronic and nuclear recoils using the ratio of ionization to primary scintillation is demonstrated. These results encourage further inves…
In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches. PSD in LXe was based on the observation that scintillation light from electron events was emitted over a longer period of time than that of nuclear recoil events, and our method used a simple ratio of early to total scintillation light emission in a single scintillation event. Requiring an efficiency of 50% for nuclear recoil retention we reduced the electron background to 7.7\pm1.1(stat)\pm1.2 0.6(sys)\times10-2 at energies between 4.8 and 7.2 keVee …
The bright scintillation of pure CsI operated at liquid-nitrogen temperature makes of this material a promising dark matter and neutrino detector. We present the first measurement of its quenching factor for nuclear recoils. Our findings indicate it is indistinguishable from that for sodium-doped CsI at room temperature. Additional properties such as light yield, afterglow, scintillation decay properties for electron and nuclear recoils, and energy proportionality are studied over the \mbox{108-165 K} temperature range, confirming the vast potential of this medium for rare-event searches.
We report an in-situ measurement of the nuclear recoil (NR) scintillation decay time constant in liquid xenon (LXe) using the XMASS-I detector at the Kamioka underground laboratory in Japan. XMASS-I is a large single-phase LXe scintillation detector whose purpose is the direct detection of dark matter via NR which can be induced by collisions between Weakly Interacting Massive Particles (WIMPs) and a xenon nucleus. The inner detector volume contains 832 kg of LXe. $^{252}$Cf was used as an external neutron source for irradiating the detector. The scintillation decay time constant of the result…
The energy and electric field dependence of pulse shape discrimination in liquid xenon have been measured in a 10 gm two-phase xenon time projection chamber. We have demonstrated the use of the pulse shape and charge-to-light ratio simultaneously to obtain a leakage below that achievable by either discriminant alone. A Monte Carlo is used to show that the dominant fluctuation in the pulse shape quantity is statistical in nature, and project the performance of these techniques in larger detectors. Although the performance is generally weak at low energies relevant to elastic WIMP recoil searche…
Scintillation response of cryogenic CsI to few-keV and sub-keV nuclear recoils
University of Chicago（芝加哥大学）；Donostia International Physics Center (DIPC)（多诺西亚国际物理中心）；Ikerbasque, Basque Foundation for Science（伊克尔巴斯基克，巴斯克科学基金会）；Instituto de Física Corpuscular, CSIC & Universitat de València（粒子物理研究所，西班牙国家科学研究委员会与瓦伦西亚大学）
Neutron capture-induced nuclear recoils have emerged as an important tool for detector calibrations in direct dark matter detection and coherent elastic neutrino-nucleus scattering (CE$ν$NS). $\texttt{nrCascadeSim}$ is a command-line tool for generating simulation data for energy deposits resulting from neutron capture on pure materials. Presently, silicon, germanium, neon, and argon are supported. While the software was developed for solid state detector calibration, it can be used for any application which requires simulated neutron capture-induced nuclear recoil data.
Plastic scintillators are widely used in industry, medicine and scientific research, including nuclear and particle physics. Although one of their most common applications is in neutron detection, experimental data on their response to low-energy nuclear recoils are scarce. Here, the relative scintillation efficiency for neutron-induced nuclear recoils in a polystyrene-based plastic scintillator (UPS-923A) is presented, exploring recoil energies between 125 keV and 850 keV. Monte Carlo simulations, incorporating light collection efficiency and energy resolution effects, are used to generate ne…
TetraPhenyl Butadiene is the wavelength shifter most widely used in combination with liquid Argon. The latter emits scintillation photons with a wavelength of 127 nm that need to be downshifted to be detected by photomultipliers with glass or quartz windows. TetraPhenyl Butadiene has been demonstrated to have an extremely high conversion efficiency, possibly higher than 100 % for 127 nm photons, while there is no precise information about the time dependence of its emission. It is usually assumed to be exponentially decaying with a characteristic time of the order of one ns, as an extrapolatio…
Radiative alpha-capture, ($α,γ$), reactions play a critical role in nucleosynthesis and nuclear energy generation in a variety of astrophysical environments. The St. George recoil separator at the University of Notre Dame's Nuclear Science Laboratory was developed to measure ($α,γ$) reactions in inverse kinematics via recoil detection in order to obtain nuclear reaction cross sections at the low energies of astrophysical interest, while avoiding the $γ$-background that plagues traditional measurement techniques. Due to the $γ$-ray produced by the nuclear reaction at the target location, recoil…
Organic liquid scintillators are used in a wide variety of applications in experimental nuclear and particle physics. Boron-loaded scintillators are particularly useful for detecting neutron captures, due to the high thermal neutron capture cross section of $^{10}$B. These scintillators are commonly used in neutron detectors, including the DarkSide-50 neutron veto, where the neutron may produce a signal when it scatters off protons in the scintillator or when it captures on $^{10}$B. Reconstructing the energy of these recoils is complicated by scintillation quenching. Understanding how nuclear…
Digital pulse shape discrimination has become readily available to distinguish nuclear recoil and electronic recoil events in scintillation detectors. We evaluate digital implementations of pulse shape discrimination algorithms discussed in the literature, namely the Charge Comparison Method, Pulse-Gradient Analysis, Fourier Series and Standard Event fitting. In addition, we present a novel algorithm based on a Laplace Transform. Instead of reducing the performance of these algorithms to a single Figure of Merit, we evaluate them as function of recoil energy. Specifically, using commercial EJ-…
The response of a NE-213 liquid-scintillator detector has been measured using tagged neutrons from 2--6 MeV originating from an Am/Be neutron source. The neutron energies were determined using the time-of-flight technique. Pulse-shape discrimination was employed to discern between gamma-rays and neutrons. The behavior of both the fast (35 ns) and the combined fast and slow (475 ns) components of the neutron scintillation-light pulses were studied. Three different prescriptions were used to relate the neutron maximum energy-transfer edges to the corresponding recoil-proton scintillation-light y…
Liquid Xe TPCs are among the most popular choices for double beta decay and WIMP dark matter searches. Gaseous Xe has intrinsic advantages when compared to Liquid Xe, specifically, tracking capability and better energy resolution for double beta decay searches. The performance of gaseous Xe can be further improved by molecular additives such as trimethylamine(TMA), which are expected to (1) cool down the ionization electrons, (2) convert Xe excitation energy to TMA ionizations through Penning transfer, and (3) produce scintillation and electroluminescence light in a more easily detectable wave…
The study of the neutron response and n-gamma discrimination for small (18x26x8) mm3 liquid scintillator BC501A (Bicron) detector was carried out by digital charge comparison method. Three ranges of neutron energies were used: uniform distribution from 0.95 MeV to 1.23 MeV, continuous spectra of AmBe source and monoenergetic 16.2 MeV neutrons. The obtained results are compared with those for cylindrical liquid scintillation detector (40 mm diameter, 60 mm length) at the same energies of neutrons. A dramatic fall of the neutron response function at 400 keVee for small detector at 16.2 MeV neutr…
A new measurement of the quenching factor for low-energy nuclear recoils in CsI[Na] is presented. Past measurements are revisited, identifying and correcting several systematic effects. The resulting global data are well-described by a physics-based model for the generation of scintillation by ions in this material, in agreement with phenomenological considerations. The uncertainty in the new model is reduced by a factor of four with respect to an energy-independent quenching factor initially adopted as a compromise by the COHERENT collaboration. A significantly improved agreement with Standar…
Directional sensitivity is one of the most important aspects of WIMP dark matter searches. Yet, making the direction of nuclear recoil visible with large target masses is a challenge. To achieve this, we are exploring a new method of detecting directions of short nuclear recoil tracks in high-pressure Xe gas, down to a few micron long, by utilizing columnar recombination. Columnar recombination changes the scintillation and ionization yields depending on the angle between a track and the electric field direction. In order to realize this, efficient cooling of electrons is essential. Trimethyla…
We present a comprehensive analysis of electronic recoil vs. nuclear recoil discrimination in liquid/gas xenon time projection chambers, using calibration data from the 2013 and 2014-16 runs of the Large Underground Xenon (LUX) experiment. We observe strong charge-to-light discrimination enhancement with increased event energy. For events with S1 = 120 detected photons, i.e. equivalent to a nuclear recoil energy of $\sim$100 keV, we observe an electronic recoil background acceptance of $<10^{-5}$ at a nuclear recoil signal acceptance of 50%. We also observe modest electric field dependence of …
