New Delhi, Apr 14 (PTI) A study has set a maximum value, or upper limit, that a neutrino -- the lightest sub-atomic particle -- weighs under 0.45 electronvolts, which is at least a million times lighter than an electron.
Findings of the study, published in the journal Science, takes scientists closer towards understanding the fundamental laws of nature.
The KArlsruhe TRItium Neutrino, or KATRIN, experiment is an international collaboration of scientists looking to work out the "absolute mass" of a neutrino.
Considered the lightest particles in the universe, neutrinos are formed during nuclear reactions -- when nucleus of two atoms merge (fusion) or a nucleus of an atom breaks apart (fission). A neutrino is not a charged particle.
The researchers explained that neutrinos act as "cosmic architects" by influencing how galaxies are formed and spread in the universe.
Given their active role in shaping the visible structures in the universe, a precise measurement of a neutrino's mass is, therefore, essential for a complete understanding of the fundamental laws of nature, the team said.
The newly set maximum value halves the previous one of 0.9 electrovolts, also calculated by the KATRIN team in a 2022 study published in the journal Nature.
"For this result we have analysed five measurement campaigns, totalling approximately 250 days of data collection from 2019 to 2021 -- about a quarter of the total data expected from KATRIN," author Kathrin Valerius from Karlsruhe Institute of Technology, Germany, said.
"With each campaign, we have gained new insights and further optimized the experimental conditions," author Susanne Mertens from the Max Planck Institute for Nuclear Physics, Germany, said.
For assessing the mass of neutrinos, the ongoing KATRIN experiment looks at the beta decay of 'tritium'. Beta decay is a type of radioactive decay in which a nucleus gives out an electron or a positron (positively charged electron).
Tritium is an isotope of a hydrogen atom, carrying the same number of protons but differing in the number of neutrons. However, owing to the excess number of neutrons, tritium is unstable and radioactive in nature.
Analysing the energy of the electrons emitted from the decay of tritium allows for a direct measurement of a neutrino's mass, the researchers said.
Technical instruments required for the experiment include a 70-metre-long beamline housing an intense source of tritium, and a high-resolution spectrometer (to separate the emitted particles) with a diameter of 10 metres.
"Stemming from 36 million electrons collected in 259 measurement days, a substantial reduction of the background level, and improved systematic uncertainties, this result tightens KATRIN's previous bound by a factor of almost two," the authors wrote.
"On the basis of the first five measurement campaigns, we derived a best-fit value, resulting in an upper limit of (less than) 0.45 electronvolts," the authors wrote.