Could the Moon Hold the Key to Proton Decay?
Proton decay, a hypothetical type of particle decay, has long eluded observation, presenting one of physics’ enduring mysteries. A recent study by an international team of researchers suggests using samples from the Moon to search for evidence of proton decay, potentially advancing our understanding of the laws of nature.
In this discussion, Dr. Patrick Stengel, a postdoctoral fellow in the Cosmology group of the INFN Ferrara Division, elaborates on the study’s motivation, significant findings, and the implications of confirming proton decay.
Motivation Behind the Study
The study began around 2018 with lead author Dr. Sebastian Baum and others exploring the use of paleodetectors, a proposed method for examining particles over vast geological time frames. Discussions with Dr. Joshua Spitz, a co-author interested in paleodetectors for dark matter exploration, led to the realization that finding proton decay on Earth is hindered by atmospheric neutrinos.
“About a year after completing the paper on atmospheric neutrinos, Spitz proposed examining mineral samples from the Moon,” Dr. Stengel told Universe Today. “The lack of atmosphere on the Moon suppresses the flux of cosmic-ray-induced neutrinos compared to Earth. This suppression makes it possible, in principle, to search for proton decay using lunar samples.”
For the study, the researchers proposed a hypothetical concept using paleo-detectors that would involve collecting mineral samples from more than 5 kilometers (3.1 miles) beneath the lunar surface and analyzing them for presence of proton decay, either on the Moon itself or back on Earth. The researchers note these lunar paleo-detector samples could yield proton lifetimes up to 1034 years. For context, the age of the universe is approximately 13.7 x 109 years. Therefore, what are the most significant results from this study?
Significant Findings
Dr. Stengel noted: “For lunar mineral samples buried deep enough to shield from cosmic ray backgrounds, and with sufficient radioactive purity, the sensitivity of the paleodetector to proton decay can compete with the next generation of conventional proton decay experiments.”
Proton decay, first proposed in 1967 by Soviet physicist and Nobel laureate Dr. Andrei Sakharov, is assumed to occur when protons decay into smaller subatomic particles. While proton decay has not been observed, quantum tunneling has been proposed as a mechanism, potentially offering insights into the origin of the universe and life.
Importance of Exploring Proton Decay
“Proton decay is a general prediction of particle physics theories beyond the Standard Model (SM). It is a low-energy predictor of grand unified theories (GUTs), which aim to unify all fundamental forces at high energy levels. For over 50 years, physicists have designed experiments to look for proton decay,” Dr. Stengel explained.
“The discovery of proton decay would be groundbreaking for science and particle physics, providing the first confirmation of physics beyond the SM. Characterizing proton decay signals could reveal fundamental aspects of nature’s underlying theory.”
Future Steps
Collecting lunar samples from at least 5 kilometers deep is a significant challenge. The deepest human-collected sample from the Moon was from Apollo 17, which only reached 300 centimeters (118 inches). The Kola Superdeep Borehole on Earth, at 12.3 kilometers (7.6 miles), required several years to drill.
“We have chosen not to speculate too much about the logistics of conducting such experiments on the Moon, staying within our particle physics expertise. However, the concept is timely given the renewed interest in lunar exploration, with various institutions planning extensive experimental programs,” Dr. Stengel said.
NASA’s Artemis program aims to return astronauts to the Moon, which could facilitate the necessary drilling. Despite the logistical challenges, only 1 kilogram of lunar material is needed to compete with conventional experiments, thanks to the vast exposure time of paleodetectors to potential proton decay.
As scientific interest in paleodetectors grows, this study could prove beneficial for both discovering proton decay and deepening our understanding of the universe. “The paleodetector represents the last frontier in the quest for proton decay,” Dr. Stengel concluded.
How the paleodetector will help scientists potentially discover proton decay in the coming years and decades remains to be seen. This is the essence of scientific inquiry!
Source: Could the Moon Hold the Key to Proton Decay?
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Could the Moon Hold the Key to Proton Decay?