Theia: An advanced optical neutrino detector

Abstract

New developments in liquid scintillators, high-efficiency, fast photon detectors, and chromatic photon sorting have opened up the possibility for building a large-scale detector that can discriminate between Cherenkov and scintillation signals. Such a detector could exploit these two distinct signals to observe particle direction and species using Cherenkov light while also having the excellent energy resolution and low threshold of a scintillator detector. Situated in a deep underground laboratory, and utilizing new techniques in computing and reconstruction techniques, such a detector could achieve unprecedented levels of background rejection, thus enabling a rich physics program that would span topics in nuclear, high-energy, and astrophysics, and across a dynamic range from hundreds of keV to many GeV. The scientific program would include observations of low-and high-energy solar neutrinos, determination of neutrino mass ordering and measurement of the neutrino CP violating phase δ, observations of diffuse supernova neutrinos and neutrinos from a supernova burst, sensitive searches for nucleon decay and, ultimately, a search for NeutrinoLess Double Beta Decay (NLDBD) with sensitivity reaching the normal ordering regime of neutrino mass phase space. This paper describes Theia, a detector design that incorporates these new technologies in a practical and affordable way to accomplish the science goals described above. We consider two scenarios, one in which Theia would reside in a cavern the size and shape of the caverns intended to be excavated for the Deep Underground Neutrino Experiment (DUNE) which we call Theia 25, and a larger 100 ktonne version (Theia 100) that could achieve an even broader and more sensitive scientific program.

Characterization of water-based liquid scintillator for Cherenkov and scintillation separation

“…Given that scanning the multi-dimensional likelihood space using MC simulations is extremely compute-intensive, ρ i j are calculated off-line using the analytical form of the scintillation time profile model Eqn. (6). The total uncertainty, σ i , on a parameter i, is given by [1]:…”

“…The ratio of Cherenkov to scintillation light would also offer a powerful handle for particle and event identification, while a clean Cherenkov signal would facilitate the ring-imaging necessary for long-baseline neutrino physics. A detector with these capabilities would have favorable signal to background ratio across a broad spectrum of physics topics [5][6][7][8].…”

Cherenkov and Scintillation Separation in Water-Based Liquid Scintillator using an LAPPD

“…This work considers three samples of WbLS, formed by combining linear alkylbenzene (LAB) and 2,5 diphenyloxazole (PPO), a common solvent-fluor pair in neutrino detectors [47,48], with water. It is a candidate target material for upcoming optical detectors, including ANNIE [36], AIT-NEO [37], and Theia [38]. This work considers WbLS mixtures prepared with scintillator loaded at the 1%, 5%, and 10% levels.…”

“…In contrast, this work demonstrates the effectiveness of fast photodetectors, such as the LAPPD, in achieving high Cherenkov purity at the MeV scale. This capability is advantangeous to achieve the physics goals of a hybrid detector such as Theia [38], several of which depend on direction reconstruction using Cherenkov light.…”

“…Most notably, the ANNIE collaboration plans to deploy both WbLS and LAPPDs to aid in vertex reconstruction and improve neutron detection efficiency [36]. Future detectors, such as AIT-NEO [37] and Theia [38], may also utilize WbLS and LAPPDs, as well as photon sorting devices, such as dichroicons. The measurements presented here constitute the first combination of multiple of these technologies, and provide insight for their incorporation into larger apparatus.…”