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Register a new userLiquid Scintillator Response to Proton Recoils in the 10-100 keV Range
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We study the response of EJ-301 liquid scintillator to monochromatic 244.6 $pm$ 8.4 keV neutrons, targeting the 10-100 keV proton recoil energy interval. Limited experimental information exists for proton light yield in this range, for this or any other organic scintillator. Our results confirm the adequacy of a modified Birks model, common to all organic scintillator formulations, predicting a marked increase in quenching factor as proton energy approaches the few keV regime. The relevance of this behavior within the context of searches for low-mass particle dark matter is mentioned.
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Background: Organic scintillators are widely used for neutron detection in both basic nuclear physics and applications. While the proton light yield of organic scintillators has been extensively studied, measurements of the light yield from neutron interactions with carbon nuclei are scarce. Purpose: Demonstrate a new approach for the simultaneous measurement of the proton and carbon light yield of organic scintillators. Provide new carbon light yield data for the EJ-309 liquid and EJ-204 plastic organic scintillators. Method: A 33~MeV $^{2}$H$^{+}$ beam from the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory was impinged upon a 3-mm-thick Be target to produce a high-flux, broad-spectrum neutron beam. The double time-of-flight technique was extended to simultaneously measure the proton and carbon light yield of the organic scintillators, wherein the light output associated with the recoil particle was determined using $np$ and $n$C elastic scattering kinematics. Results: The proton and carbon light yield relations of the EJ-309 liquid and EJ-204 plastic organic scintillators were measured over a recoil energy range of approximately 0.3 to 1~MeV and 2 to 5~MeV, respectively for EJ-309, and 0.2 to 0.5~MeV and 1 to 4~MeV, respectively for EJ-204. Conclusions: These data provide new insight into the ionization quenching effect in organic scintillators and key input for simulation of the response of organic scintillators for both basic science and a broad range of applications.
This paper describes the liquid scintillator veto system for the COSINE-100 dark matter experiment and its performance. The COSINE-100 detector consists of eight NaI(Tl) crystals immersed in 2200~L of linear alkylbenzene-based liquid scintillator. The liquid scintillator tags between 65 and 75% of the internal $^{40}$K background in the 2--6 keV energy region. We also describe the background model for the liquid scintillator, which is primarily used to assess its energy calibration and threshold.
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.
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.
Germanium is the detector material of choice in many rare-event searches looking for low-energy nuclear recoils induced by dark matter particles or neutrinos. We perform a systematic exploration of its quenching factor for sub-keV nuclear recoils, using multiple techniques: photo-neutron sources, recoils from gamma-emission following thermal neutron capture, and a monochromatic filtered neutron beam. Our results point to a marked deviation from the predictions of the Lindhard model in this mostly unexplored energy range. We comment on the compatibility of our data with low-energy processes such as the Migdal effect, and on the impact of our measurements on upcoming searches.
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