Introduction

In recent years, physicists around the world have been on a quest to uncover evidence of a rare nuclear process known as neutrinoless double beta (0νββ) decay. This phenomenon involves the simultaneous transformation of two neutrons into two protons within a nucleus, but unlike the conventional double beta decay, this process does not produce neutrinos.

Significance of Neutrinoless Double Beta Decay

The implications of detecting neutrinoless double beta decay would be monumental for our understanding of the universe. It would support the idea that neutrinos and their counterparts, antineutrinos, are essentially the same particle—a proposition first posited by the renowned Italian physicist Ettore Majorana in 1937.

The AMoRE Experiment

The Advanced Mo-based Rare Process Experiment (AMoRE) collaboration, a dedicated team of international scientists, has taken on the task of searching for this elusive decay using specialized molybdate scintillating crystals operated at extremely low temperatures, near absolute zero. Their latest findings, published in Physical Review Letters, set new constraints for future research aiming to observe this rare decay process.

Neutrino Properties and Their Importance

The neutrino is one of the fundamental particles outlined in the Standard Model of particle physics, conceptualized by Wolfgang Pauli nearly a century ago. Despite being the most widely abundant particle in the cosmos, many of its characteristics, including its mass, remain mysterious.

The Role of Molybdenum-100

The core mission of the AMoRE experiment is to measure neutrino mass and explore the profound questions surrounding the balance of matter and antimatter in the universe. To pursue this goal, the collaboration focused on molybdenum-100 (100Mo), a radioactive isotope of molybdenum with an atomic number of 42.

Challenges in Detection

Due to the extremely low probability of observing this decay, an extensive amount of molybdenum isotopes is required to capture potential decay signals against a backdrop of noise. This is a common challenge for experiments studying double beta decay, including those undertaken by AMoRE.

Experimental Setup

For their latest experiment, the team prepared several kilograms of molybdenum enriched in 100Mo, using scintillating crystals that emit both heat and light upon particle interaction. Their detection system, encased in a specialized low-temperature setup, was situated 700 meters underground at the Yangyang Underground Laboratory in South Korea—shielded from cosmic rays and other environmental interference.

Results and Future Directions

During our AMoRE-I run, we achieved unprecedented sensitivity for detecting neutrinoless double beta decay of molybdenum-100 but, unfortunately, we did not observe any significant signals. Our background-only results allowed us to set improved limits on the half-life of Mo-100 decay.

Looking Ahead to AMoRE-II

This groundbreaking study has laid the groundwork for future explorations of this elusive process, providing a clearer direction for subsequent research. The AMoRE collaboration is already gearing up for its next phase of experimentation at a new facility in Korea called Yemilab, which boasts an even deeper location of 1000 meters underground.

The next phase, AMoRE-II, is in the final stages of preparation and is expected to start collecting data in about a year. We face considerable challenges in utilizing approximately 100 kilograms of molybdenum-based crystal detectors while maintaining ultra-low temperature conditions and minimizing background noise. However, AMoRE-II aims to be one of the most sensitive searches for neutrinoless double beta decay worldwide.

Conclusion

As researchers continue to delve into the mysteries of neutrinos, the pursuit of understanding the fundamental differences—or similarities—between matter and antimatter remains at the forefront of modern physics. Stay tuned as AMoRE pushes the boundaries of what's possible in nuclear physics!