On Thursday, researchers unveiled probably the most exact measurement but of a neutrino, cutting down the utmost doable mass of the ghostly specks of matter that permeate our universe.
The end result, published within the journal Science, doesn’t outline the precise mass of a neutrino, simply its higher restrict. However the discovering helps convey physicists nearer to determining simply what’s mistaken with the so-called Normal Mannequin, their greatest — albeit incomplete — concept of the legal guidelines that rule the subatomic realm. A technique physicists know it’s not fairly correct is that it means that the neutrino shouldn’t have any mass in any respect.
At grander scales, studying extra about neutrinos will assist cosmologists fill of their ever hazy image of the universe, together with how galaxies clustered collectively and what influences the expansion of the cosmos because the Large Bang.
“We’re attempting to know why we’re right here,” mentioned John Wilkerson, a physicist on the College of North Carolina, Chapel Hill and an writer of the brand new examine. “And that’s one thing neutrinos might have a key position in.”
Physicists know a number of issues about neutrinos. They’re prolific throughout the cosmos, created nearly anytime atomic nuclei snap collectively or rip aside. However they carry no electrical cost and are notoriously difficult to detect.
Neutrinos additionally are available in three varieties, which physicists describe as flavors. And, oddly, they morph from one taste to a different as they transfer by way of house and time, a discovery acknowledged by the Nobel Prize in Physics in 2015. The underlying mechanism that makes these transformations doable, physicists realized, meant that neutrinos should have some mass.
However solely simply so. Neutrinos are mindboggingly gentle, and physicists don’t know why.
Uncovering the precise values of the mass of neutrinos might result in “some form of portal” to new physics, mentioned Alexey Lokhov, a scientist on the Karlsruhe Institute of Expertise in Germany. “That is, for now, the world’s greatest restrict,” he mentioned of his workforce’s measurement.
Dr. Lokhov and his colleagues used the Karlsruhe Tritium Neutrino, or KATRIN, experiment to slender down the mass of a neutrino. At one finish of the 230-foot-long equipment was a supply of tritium, a heavier model of hydrogen with two neutrons in its nucleus. As a result of tritium is unstable, it decays into helium: One neutron converts right into a proton, which spits out an electron within the course of. It additionally spits out an antineutrino, the antimatter twin of a neutrino. The 2 ought to have equivalent mass.
The mass of the unique tritium is break up among the many merchandise of the decay: the helium, electron and antineutrino. Neither neutrinos nor antineutrinos will be instantly detected, however a sensor on the different finish of the experiment recorded 36 million electrons, over 259 days, shed by the decaying tritium. By measuring the vitality of the electron’s movement, they might not directly deduce the utmost mass doable for the antineutrino.
They discovered that worth to be not more than 0.45 electronvolts, within the items of mass utilized by particle physicists, 1,000,000 occasions lighter than an electron.
The higher sure on the mass was measured for just one taste of neutrino. However Dr. Wilkerson mentioned that nailing down the mass of 1 makes it doable to calculate the remainder.
The most recent measurement pushes the doable mass of the neutrino decrease than the previous limit set in 2022 by the KATRIN collaboration, of not more than 0.8 electronvolts. It’s also practically twice as exact.
Elise Novitski, a physicist on the College of Washington who was not concerned within the work, recommended the KATRIN workforce’s cautious effort.
“It’s actually only a tour de drive,” she mentioned of the experiment and the invention. “I’ve full confidence of their end result.”
The KATRIN workforce is engaged on a fair tighter boundary on the neutrino mass from 1,000 days of information, which it expects to gather by the top of the 12 months. That may give the physicists much more electrons to measure, resulting in a extra exact measurement.
Different experiments can even contribute to a greater understanding of the neutrino’s mass, together with Project 8 in Seattle and the Deep Underground Neutrino Experiment, unfold throughout two physics services within the Midwest.
Astronomers learning the construction of the cosmos at giant, regarded as influenced by the huge assortment of neutrinos flooding the universe, have their very own measurement of the particles’ most mass. However in line with Dr. Wilkerson, the boundaries set by astronomers staring out into the void don’t match up with what particle physicists calculate within the lab, as they scrutinize the subatomic world.
“There’s one thing actually fascinating occurring,” he mentioned. “And the possible resolution to that’s going to be physics past the Normal Mannequin.”
