Speaker
Description
Neutrinoless double beta decay (0νββ) is a hypothetical nuclear process in which two neutrons in a nucleus transform into two protons and two electrons without emitting electron antineutrinos. Its observation would demonstrate lepton number violation in weak processes and confirm that neutrinos are Majorana particles. Next-generation 0νββ searches using candidate isotopes aim to reach half-life sensitivities beyond 1028 years. nEXO is a proposed experiment targeting this regime using 136Xe in a liquid xenon (LXe) time projection chamber (TPC). The LXe TPC is housed within a vacuum insulated cryostat and shielded by a 12.3 m diameter, 12.8 m high tank containing 1.5 kilotonnes of ultra-pure water, instrumented with 125 photomultiplier tubes (PMTs). The water tank and the PMT array form the nEXO water Cherenkov muon veto system, also known as the Outer Detector (OD).
To ensure the long-term stability and performance of OD, a monitoring and calibration system is under development. In this system laser light is delivered via optical fibers to optical modules, called DORY, deployed inside the water tank. Each DORY module consists of a PTFE plug and sphere that together form the diffuser. The diffuser is housed inside a pressure enclosure composed of a glass dome window and inner and outer flanges. The DORY modules emit light isotropically, enabling water quality monitoring and PMT timing calibration.
The design and first prototype of DORY have been completed, and we are currently characterizing its light emission profile. DORY characterization setup employs a motorized two-axis rotary stage on which the module is mounted, enabling 4π angular coverage. A fixed PMT records the light intensity at each orientation of the module, producing a map of its emission profile. In parallel, we are planning DORY upgrade and developing the installation strategy for deployment in the water tank. We are also exploring the potential use of the same module in the PICO experiment.
In this talk, I will present the design and current development status of DORY, discuss the upgrades identified during the prototyping phase, describe DORY characterization setup, and present simulation results used to optimize the system parameters. I will also show the first measurements of the module’s light emission profile.