Speaker
Carlos Faham
(Brown University)
Description
The Large Underground Xenon (LUX) experiment and LZ (LUX-ZEPLIN) experiments are dark matter search experiments based on ultra-low background liquid xenon time projection chambers. In collaboration with the experiments, Hamamatsu Photonics has developed a series of very low background photomultiplier tubes (PMTs), culminating in a new fully operational 3-inch diameter PMT (R11410MOD) that has U/Th radioactivity less than 1 mBq per PMT, representing a significant improvement over existing photodetectors. The LUX experiment relies on photon counting with 122 2-inch Hamamatsu R8778 PMTs for detecting the energy and position of all interactions in the active xenon space. Thus, it requires PMTs with single photon sensitivity and high quantum efficiency at 178 nm in order to detect low-energy depositions from dark matter. The PMTs need to have low intrinsic radioactivity levels since they are located in the active region of the experiment, and low-energy scatters in the xenon from radioactive decay byproducts can mimic a positive dark matter signal. Results from performance tests and radioactivity measurements for the Hamamatsu R8778 PMTs, and their impact on LUX, will be presented. Results from the developmental Hamamatsu R11410MOD PMTs, and their projected impact on next-generation dark matter experiments, will also be shown.
Author
Carlos Faham
(Brown University)
