In the Daya Bay Reactor Neutrino Experiment 960 20-cm-diameter waterproof photomultiplier tubes are used to instrument three water pools as Cherenkov detectors for detecting cosmic-ray muons. Of these 960 photomultiplier tubes, 341 are recycled from
the MACRO experiment. A systematic program was undertaken to refurbish them as waterproof assemblies. In the context of passing the water leakage check, a success rate better than 97% was achieved. Details of the design, fabrication, testing, operation, and performance of these waterproofed photomultiplier-tube assemblies are presented.
In 2012 the Daya Bay experiment made an unambiguous observation of reactor antineutrino disappearance over kilometer-long baselines and determined that the neutrino mixing angle $theta_{13}$ is non-zero. The measurements of Daya Bay have provided the
most precise determination of $theta_{13}$ to date. This whitepaper outlines the prospects for precision studies of reactor antineutrinos at Daya Bay in the coming years. This includes precision measurements of sin$^2 2theta_{13}$ and $Delta m^2_{ee}$ to $<$3%, high-statistics measurement of reactor flux and spectrum, and non-standard physics searches.
Thin flexible sheets of high-permeability FINEMET foils encased in thin plastic layers have been used to shield various types of 20-cm-diameter photomultiplier tubes from ambient magnetic fields. In the presence of the Earths magnetic field this type
of shielding is shown to increase the collection efficiency of photoelectrons and can improve the uniformity of response of these photomultiplier tubes.
