The LUX Surface Facility at the Sanford Laboratory permits the full testing of the assembly and operation of the LUX detector above ground, prior to installation in the Davis Laboratory underground. The facility infrastructure also allows the commissioning of the underground detector transport and the detector installation, using the same vertical support structure that is used for deployment in the large Davis Laboratory water tank. The facility houses a class 1,000 clean room for detector assembly operations.
The LUX experiment subsystem testing at the Surface Facility includes the electronics chain and 122 photomultiplier tubes inside the detector, the cryogenic systems, the xenon gas purification/circulation and the automated recovery safety systems. It also allows the validation of the cryostat and feed through in water. The Surface Facility can be used for testing other large-scale, low background detectors.
Background and Water Shield at Surface Facility
Events associated with cosmic and radioactive backgrounds at the Surface Facility present challenges to the detector operation and data taking. Specific steps must be taken to reduce the gamma ray event rate from natural radioactive backgrounds, and to reduce the effect of the high-energy interactions from cosmic muons in the detector. Without shielding, the event rate due to gammas and neutrons in the detector, is 10 kHz, which is too high by two orders of magnitude for standard detector operation. A 1 meter thick shield of water reduces the detector?s event rate to 100 Hz. This tank still considerably smaller than that in the Davis Laboratory. High-energy cosmic muons are expected at the rate of 50 Hz throughout the detector, and the water shield does not stop muons significantly. By momentarily turning the detector on when muons traverse the detector volume, the effect of muons activity in the detector can be reduced considerably.