Science and Technology Article

LUX/LZ Dark Matter Experiment & Neutron Calibration

Author:  Madan K. Sharma Timalsina

The LUX Dark Matter Experiment has performed the most sensitive direct search for weakly-interacting massive dark matter particles (so-called WIMPs). The successor experiment LZ will also be located underground at SURF (Sanford Underground Research Facility) in Lead/SD. The LZ central detector will not only be an order of magnitude larger than the existing LUX inner detector, but its sensitivity for direct dark matter searches will be even 100 times better than LUX. If WIMPs exist, they could interact in the cryogenic liquid xenon of the detector's core by bouncing into a xenon nucleus, which will then recoil and produce scintillation light and electric charge. The ratio of the directly detected scintillation light and the delayed charge detection is characteristic for such a nuclear recoil, and differs significantly from an electron recoil produced by undesired background reactions. However, the precise knowledge of the critical ratio value, for which the electron recoil dominated regime transitions into the nuclear recoil dominated regime, is key.
Dedicated neutron calibration sources such as a DD-generator gun, AmLi and AmBe neutron sources, as well as a new mono-energetic Y/Be neutron source are essential tools to precisely map the nuclear recoil region. That way it can be demonstrated what a possible WIMP detection would look like in the LUX/LZ detectors.
The precise neutron fluxes of the various neutron calibration sources have to be measured before the actual deployments of the sources will be performed, in order to assess the detection efficiency in the detector.
A new neutron monitor system, utilizing He-3 proportional counter tubes, is being developed within the framework of the LUX/LZ project.