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Register a new userScintillation yield from electronic and nuclear recoils in superfluid $^4$He
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Superfluid $^4$He is a promising target material for direct detection of light ($<$ 1 GeV) dark matter. Possible signal channels available for readout in this medium include prompt photons, triplet excimers, and roton and phonon quasiparticles. The relative yield of these signals has implications for the sensitivity and discrimination power of a superfluid $^4$He dark matter detector. Using a 16 cm$^3$ volume of 1.75 K superfluid $^4$He read out by six immersed photomultiplier tubes, we measured the scintillation from electronic recoils ranging between 36.3 and 185 keV$_mathrm{ee}$, yielding a mean signal size of $1.12^{+0.02}_{-0.03}$ phe/keV$_mathrm{ee}$, and nuclear recoils from 53.2 to 1090 keV$_mathrm{nr}$. We compare the results of our relative scintillation yield measurements to an existing semi-empirical model based on helium-helium and electron-helium interaction cross sections. We also study the behavior of delayed scintillation components as a function of recoil type and energy, a further avenue for signal discrimination in superfluid $^4$He.
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Liquid Xenon (LXe) is an excellent material for experiments designed to detect dark matter in the form of Weakly Interacting Massive Particles (WIMPs). A low energy detection threshold is essential for a sensitive WIMP search. The understanding of the relative scintillation efficiency (Leff) and ionization yield of low energy nuclear recoils in LXe is limited for energies below 10 keV. In this paper, we present new measurements that extend the energy down to 4 keV, finding that Leff decreases with decreasing energy. We also measure the quenching of scintillation efficiency due to the electric field in LXe, finding no significant field dependence.
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 $^{83m}$Kr internal conversion electrons is comparable to that from $^{207}$Bi conversion electrons, we obtained the numbers of excitons ($N_{ex}$) and ion pairs ($N_i$) and their ratio ($N_{ex}/N_i$) 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.
This Letter details a measurement of the ionization yield ($Q_y$) of 6.7 keV $^{40}Ar$ atoms stopping in a liquid argon detector. The $Q_y$ of 3.6-6.3 detected $e^{-}/mbox{keV}$, for applied electric fields in the range 240--2130 V/cm, is encouraging for the use of this detector medium to search for the signals from hypothetical dark matter particle interactions and from coherent elastic neutrino nucleus scattering. A significant dependence of $Q_y$ on the applied electric field is observed and explained in the context of ion recombination.
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 $alpha$-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 investigation on the use of xenon in the gas phase as a detector medium in dark matter direct detection experiments.
We measure the liquid argon scintillation response to electronic recoils in the energy range of $2.82$ to $1274.6~{rm keV}$ at null electric field. The single-phase detector with a large optical coverage used in this measurement yields $12.8 pm 0.3 ~ (11.2 pm 0.3)~{rm photoelectron/keV}$ for $511.0$-${rm keV}$ $gamma$-ray events based on a photomultiplier tube single photoelectron response modeling with a Gaussian plus an additional exponential term (with only a Gaussian term). It is exposed to a variety of calibration sources such as $^{22}{rm Na}$ and $^{241}{rm Am}$ $gamma$-ray emitters, and a $^{252}{rm Cf}$ fast neutron emitter that induces quasimonoenergetic $gamma$ rays through a $(n, ngamma)$ reaction with $^{19}{rm F}$ in polytetrafluoroethylene. In addition, the high light detection efficiency of the detector enables identification of the $2.82$-${rm keV}$ peak of $^{37}{rm Ar}$, a cosmogenic isotope in atmospheric argon. The observed light yield and energy resolution of the detector are obtained by the full-absorption peaks. We find up to approximately $25%$ shift in the scintillation yield across the energy range and $3%$ of the energy resolution for the $511.0$-${rm keV}$ line. The Thomas-Imel box model with its constant parameter $varsigma=0.033 ^{+0.012} _{-0.008}$ is found to explain the result. For liquid argon, this is the first measurement on the energy-dependent scintillation yield down to a few ${rm keV}$ at null field and provides essential inputs for tuning the argon response model to be used for physics experiments.
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