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Register a new userPhysics reach of a low threshold scintillating argon bubble chamber in coherent elastic neutrino-nucleus scattering reactor experiments
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The physics reach of a low threshold (100 eV) scintillating argon bubble chamber sensitive to Coherent Elastic neutrino-Nucleus Scattering (CE$ u$NS) from reactor neutrinos is studied. The sensitivity to the weak mixing angle, neutrino magnetic moment, and a light $Z$ gauge boson mediator are analyzed. A Monte Carlo simulation of the backgrounds is performed to assess their contribution to the signal. The analysis shows that world-leading sensitivities are achieved with a one-year exposure for a 10 kg chamber at 3 m from a 1 MW$_{th}$ research reactor or a 100 kg chamber at 30 m from a 2000 MW$_{th}$ power reactor. Such a detector has the potential to become the leading technology to study CE$ u$NS using nuclear reactors.
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A 30-g xenon bubble chamber, operated at Northwestern University in June and November 2016, has for the first time observed simultaneous bubble nucleation and scintillation by nuclear recoils in a superheated liquid. This chamber is instrumented with a CCD camera for near-IR bubble imaging, a solar-blind photomultiplier tube to detect 175-nm xenon scintillation light, and a piezoelectric acoustic transducer to detect the ultrasonic emission from a growing bubble. The time of nucleation determined from the acoustic signal is used to correlate specific scintillation pulses with bubble-nucleating events. We report on data from this chamber for thermodynamic Seitz thresholds from 4.2 to 15.0 keV. The observed single- and multiple-bubble rates when exposed to a $^{252}$Cf neutron source indicate that, for an 8.3-keV thermodynamic threshold, the minimum nuclear recoil energy required to nucleate a bubble is $19pm6$ keV (1$sigma$ uncertainty). This is consistent with the observed scintillation spectrum for bubble-nucleating events. We see no evidence for bubble nucleation by gamma rays at any of the thresholds studied, setting a 90% C.L. upper limit of $6.3times10^{-7}$ bubbles per gamma interaction at a 4.2-keV thermodynamic threshold. This indicates stronger gamma discrimination than in CF$_3$I bubble chambers, supporting the hypothesis that scintillation production suppresses bubble nucleation by electron recoils while nuclear recoils nucleate bubbles as usual. These measurements establish the noble-liquid bubble chamber as a promising new technology for the detection of weakly interacting massive particle dark matter and coherent elastic neutrino-nucleus scattering.
The deployment of a low-noise 3 kg p-type point contact germanium detector at the Dresden-II power reactor, 8 meters from its 2.96 GW$_{th}$ core, is described. This location provides an unprecedented (anti)neutrino flux of 8.1$times 10^{13} ~bar{ u_{e}}/$cm$^{2}$s. When combined with the 0.2 keV$_{ee}$ detector threshold achieved, a first measurement of CE$ u$NS from a reactor source appears to be within reach. We report on the characterization and abatement of backgrounds during initial runs, deriving improved limits on extensions of the Standard Model involving a light vector mediator, from preliminary data.
Coherent elastic neutrino-nucleus scattering (CEvNS) is the dominant neutrino scattering channel for neutrinos of energy $E_ u < 100$ MeV. We report a limit for this process using data collected in an engineering run of the 29 kg CENNS-10 liquid argon detector located 27.5 m from the Oak Ridge National Laboratory Spallation Neutron Source (SNS) Hg target with $4.2times 10^{22}$ protons on target. The dataset yielded $< 7.4$ observed CEvNS events implying a cross section for the process, averaged over the SNS pion decay-at-rest flux, of $<3.4 times 10^{-39}$ cm$^{2}$, a limit within twice the Standard Model prediction. This is the first limit on CEvNS from an argon nucleus and confirms the earlier CsI non-standard neutrino interaction constraints from the collaboration. This run demonstrated the feasibility of the ongoing experimental effort to detect CEvNS with liquid argon.
We report the first measurement of coherent elastic neutrino-nucleus scattering (cevns) on argon using a liquid argon detector at the Oak Ridge National Laboratory Spallation Neutron Source. Two independent analyses prefer cevns over the background-only null hypothesis with greater than $3sigma$ significance. The measured cross section, averaged over the incident neutrino flux, is (2.2 $pm$ 0.7) $times$10$^{-39}$ cm$^2$ -- consistent with the standard model prediction. The neutron-number dependence of this result, together with that from our previous measurement on CsI, confirms the existence of the cevns process and provides improved constraints on non-standard neutrino interactions.
We study the sensitivity of detectors with directional sensitivity to coherent elastic neutrino-nucleus scattering (CE$ u$NS), and how these detectors complement measurements of the nuclear recoil energy. We consider stopped pion and reactor neutrino sources, and use gaseous helium and fluorine as examples of detector material. We generate Standard Model predictions, and compare to scenarios that include new, light vector or scalar mediators. We show that directional detectors can provide valuable additional information in discerning new physics, and we identify prominent spectral features in both the angular and the recoil energy spectrum for light mediators, even for nuclear recoil energy thresholds as high as $sim 50$ keV. Combined with energy and timing information, directional information can play an important role in extracting new physics from CE$ u$NS experiments.
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