First results from the Eos detector

Future ktonne-scale, scintillation-based neutrino detectors, such as Theia, plan to exploit new and yet to be developed technologies to simultaneously measure Cherenkov and scintillation

signals in order to provide a rich and broad physics program. These hybrid detectors will be based on fast timing photodetectors, novel liquid scintillators, and spectral sorting. This talk focuses on a currently operating technical demonstrator, called Eos. The novel detector with an approximately 4-tonne target fiducial volume has been constructed during the past year at UC Berkeley and LBNL (Lawrence Berkeley National Laboratory). Eos now provides a test bed for these emerging technologies required for hybrid Cherenkov/Scintillation detectors. Eos deploys calibration sources to verify scintillator and photon detector optical models and performance, to enable an extrapolation to ktonne-scale detectors. The detector was operated with a water target during spring/summer 2024, and is now the first multi-ton scale deployment of the novel water-based liquid scintillator (WbLS). Future phases may include novel organic liquids, and metal loading. This talk presents first results from the WbLS phase of Eos.