Seasonal Variation Effects on Possible Dark Matter Signals in the LZ Experiment at Sanford Lab

Author: Jack Genovesi, Department of Physics

Co-Author: Dr. Xinhua Bai, Department of Physics

Co-Author: Dr. Gleb Sinev, Department of Physics

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

The leading hypothesis of dark matter in our galaxy predicts Weakly Interacting Massive Particles (WIMPs), which will soon be probed by the LUX-ZEPLIN (LZ) experiment at Sanford Lab in Lead, SD. The introduction of WIMPs attempts to describe the astronomically observed anomalous galactic rotation by stating the existence of a relatively massive neutral particle that interacts gravitationally, but does not interact visibly via the emission of light, hence it would explain its “dark matter” nature. LZ is an ultra-low background two-phase xenon time projection chamber, which can observe even very rare radioactive decays and hopefully directly discover WIMP interactions for the first time. An anticipated unique feature in the WIMP signal compared to background noise, such as radioactivity, will be the annual modulation of the galactic WIMP flux. This seasonal effect is due to the Earth’s orbit around the sun in which Earth will be travelling into the galactic WIMP wind during our summer or out of it during winter, thus the WIMP detection rate on Earth would seasonally increase, and decrease, respectively. In our simulation study we take a frequentist approach using a large number of simulated LZ experiments each with 1000 days live-time to probe LZ’s sensitivity to observe such an annual modulation if finding WIMP signals, which would be the smoking gun for direct dark matter detection. We considered various velocity distributions of WIMPs in our galaxy, such as the Standard Halo Model (SHM) and an extended SHM++. We take these details into consideration to correctly identify a WIMP footprint against backgrounds such as radioactivity or solar neutrinos.