In a groundbreaking announcement on Thursday, scientists have revealed a new limit on the mass of neutrinos, the elusive and enigmatic particles that could unlock some of the universe's greatest mysteries. This latest finding, which halves the previous estimate, is a significant step forward in the long-standing quest to understand these tiny ghost particles.
Since the concept of neutrinos was first proposed nearly a century ago, the scientific community has been on a relentless pursuit to uncover their properties, particularly their mass. According to Thierry Lasserre, a physicist at France's Alternative Energies and Atomic Energy Commission, the mass of neutrinos plays a crucial role in influencing the structures that compose our cosmos. As the most abundant particles in the universe, neutrinos weave a complex thread that connects the infinitesimally small to the vast expanse of the universe.
These invisible particles have been traversing the universe since the Big Bang, which occurred approximately 13.8 billion years ago. The sheer number of neutrinos is staggering; estimates suggest there are about a billion neutrinos for every atom in the cosmos. However, their incredibly low mass and lack of electric charge mean that neutrinos rarely interact with matter. In fact, trillions of these ghostly particles are thought to pass through the human body every second without us even noticing.
Since 2019, over a hundred scientists from six countries have been collaborating on the KATRIN project, based at Germany's Karlsruhe Institute of Technology, in a bid to uncover the mysteries surrounding neutrinos. In a recent study published in the journal Science, the KATRIN collaboration announced that the mass of a neutrino cannot exceed 0.45 electron volts, a figure that is less than a billionth of the mass of a proton found within atomic nuclei. This new upper limit is approximately half of the mass estimate released in 2022, following their initial measurements.
The KATRIN experiment utilizes a massive spectrometer to examine the decay of tritium, a radioactive isotope of hydrogen that emits both electrons and neutrinos. The study employs a 70-meter-long (230-foot-long) apparatus dominated by a 200-ton spectrometer, operating in a vacuum. By measuring the energy of the emitted electrons, researchers can infer vital information about the neutrinos. Achieving accurate results requires measuring a substantial number of electrons; KATRIN's first results in 2022 involved measuring six million electrons, while the more precise figure announced recently was derived from a total of 36 million measurements. By the end of this year, the team anticipates having collected data on around 250 million electrons, marking a pivotal moment in their research.
Determining the mass of neutrinos is crucial for addressing several unresolved questions in cosmology. Despite their light mass, neutrinos have been integrated into various models that aim to explain dark energy, the mysterious force believed to be accelerating the expansion of the universe. It is estimated that roughly 95% of the universe consists of dark energy and dark matter, leaving only 5% for all known matter.
Looking ahead, the KATRIN collaboration is planning to establish a new detection system named TRISTAN to search for a new class of neutrinos known as sterile neutrinos. These hypothetical particles are thought to have significantly more mass than typical neutrinos and do not interact with matter. Some researchers speculate that sterile neutrinos could potentially be linked to dark matter, further broadening our understanding of the universe's composition.
As scientists continue to unravel the mysteries of neutrinos, this ongoing research not only deepens our understanding of the cosmos but also paves the way for future discoveries that could transform our comprehension of the universe.
