Despite being the feeblest and lightest of the known particles, the neutrino is one of the most abundant particles in the Universe and has played a critical role in its evolution. Within standard cosmological models, most of the neutrinos were produced in the Big Bang and completely decoupled from matter after the first second. During that short time it is possible that through the process of Leptogenesis neutrinos helped to produce the matter/anti-matter asymmetry that sets the stage for all of the structures that we see in the universe today. However, these theories generally require the condition that the neutrino is a so-called Majorana particle, acting as its own anti-particle. The search for the extremely rare neutrinoless double-beta $(0 ubetabeta)$ decay is currently the most practical way to address this question. Here we present the results of the first tonne-year exposure search for $0 ubetabeta$ decay of $^{130}$Te with CUORE. With a median half-life exclusion sensitivity of $2.8times10^{25}$ yr, this is the most sensitive search for $0 ubetabeta$ decay in $^{130}$Te to date. We find no evidence for $0 ubetabeta$ decay and set a lower bound of $T_{1/2} > 2.2times10^{25}$ yr at a 90% credibility interval. CUORE is the largest, coldest solid-state detector operating below 100mK in the world. The achievement of 1 tonne-year of exposure demonstrates the long-term reliability and potential of cryogenic technology at this scale, with wide ranging applications to next-generation rare-event searches, dark matter searches, and even large-scale quantum computing.
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