Improving the Search for Dark Matter with the Upcoming LUX-ZEPLIN (LZ) Experiment at Sanford Lab

Author: Madan Timalsina, Department of Physics

Mentor & Co-Author: Dr. Juergen Reichenbacher, Department of Physics

The 2nd generation direct detection dark matter experiment LZ will perform the most sensitive direct search for weakly-interacting massive particles (WIMPs). LZ will operate 4850 feet underground at the Sanford Underground Research Facility (SURF) in Lead, South Dakota. LZ uses a two-phase xenon detector with ~7 tons target mass. WIMPs 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.

Calibrations with neutron sources, such as DD-generator, AmLi, Cf-252 and Y/Be, will be used to map out the NR signal region and gamma-ray sources to map out the electron recoil (ER) background region. Before initial deployments of neutron calibration sources their precise fluxes and energies have to be characterized for which we will employ our new He-3 based SDSMT neutron telescope. Our evaluations of calibration, background and WIMP signal simulations, prior to LZ getting real data, demonstrated that we will have a quick, competitive analysis turn-over, as LZ gets its first real data soon. Further, we already developed a procedure to ascertain the time-dependent electron lifetime in the liquid xenon, which is needed to correct all data. We also studied the major neutron NR backgrounds, such as radiogenic neutrons generated by (alpha, n) reactions on the inner Teflon layer (inserted for better light collection, but source of alpha-rays from radon daughter plate-out), spontaneous fission of e.g. U-238 as well as cosmic- induced neutrons from muons.