The LUX-ZEPLIN (LZ) experiment will enable a neutrinoless double $\beta$ decay search in parallel to the main science goal of discovering dark matter particle interactions. We report the expected LZ sensitivity to ${}^{136}\mathrm{Xe}$ neutrinoless double $\beta$ decay, taking advantage of the significant ($>600$ kg) ${}^{136}\mathrm{Xe}$ mass contained within the active volume of LZ without isotopic enrichment. After 1000 live-days, the median exclusion sensitivity to the half-life of ${}^{136}\mathrm{Xe}$ is projected to be $1.06\times {10}^{26}$ years (90% confidence level), similar to existing constraints. We also report the expected sensitivity of a possible subsequent dedicated exposure using 90% enrichment with ${}^{136}\mathrm{Xe}$ at $1.06\times {10}^{27}$ years.

• Received 12 December 2019
• Accepted 2 June 2020

DOI:https://doi.org/10.1103/PhysRevC.102.014602