Physicists Announce First Results From Daya Bay’s Final Dataset

The Daya Bay Neutrino Experiment has created the most precise measurement yet of theta13, an essential parameter for comprehending how neutrinos transform their “taste.”

BEIJING; BERKELEY, CA; and UPTON, NY- Over approximately nine years, the Daya Bay Reactor Neutrino Experiment captured an unprecedented five and a half million communications from subatomic particles called neutrinos.

Currently, the international team of physicists of the Daya Bay collaboration has reported the first result from the experiment’s full dataset: the most exact measurement yet of theta13, an essential parameter for understanding how neutrinos transform their “taste.” The result, introduced today at the Neutrino 2022 conference in Seoul, South Korea, will help physicists explore some of the most significant mysteries bordering the nature of universe and the matter.

What are Neutrinos?

Neutrinos are subatomic particles that are famously elusive and significantly abundant. They endlessly bombard the entire Earth’s surface at nearly the speed of light. However, seldom interact with matter. They can travel through a light year’s worth of lead without disturbing a single atom.

One of the specifying characteristics of these ghost-like particles is their ability to oscillate between three unique “flavors”: muon neutrino, tau neutrino, and an electron neutrino. The Daya Bay Reactor Neutrino Experiment was designed for investigating the properties that determine the probability of those oscillations, or what is known as mixing angles and mass splittings.

The Neutrino Experiment at the Daya Bay Reactor

Just one of the three mixing angles stayed unknown when Daya Bay was developed in 2007: theta13. So, Daya Bay was developed to determine theta13 * with higher sensitivity than any other experiment.

Operating in Guangdong (China), the Daya Bay Reactor Neutrino Experiment includes large, cylindrical particle detectors immersed in water swimming pools in 3 underground caves. The eight detectors pick up light signals produced by antineutrinos streaming from close-by nuclear power plants. Antineutrinos are the antiparticles of neutrinos and are generated in abundance by nuclear reactors.

Daya Bay was constructed through an international effort and a first-of-its-kind partnership for a significant physics project between China and the USA. The Beijing-based Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences leads China’s function in the collaboration, while the United State Department of Energy’s (DOE) Lawrence Berkeley National Laboratory and Brookhaven National Laboratory co-lead U.S. involvement.

To define the value of theta13, Daya Bay scientists detected neutrinos of a specific flavor-in this case, electron antineutrinos- in each of the underground caverns. Two caves are near the nuclear reactors, and the third cavern is farther away, giving ample distance for the antineutrinos to oscillate. By comparing the variety of electron antineutrinos grabbed by the near and far detectors, physicists determined how several transformed tastes and, consequently, theta13 value.

Daya Bay physicists created the world’s first conclusive dimension of theta13 in 2012 and subsequently improved upon the dimension’s precision as the experiment continued taking information. After nine years of operation and completion of information collection in December 2020, outstanding detector performance, and dedicated information analysis, Daya Bay has far exceeded expectations.

Dealing with the complete dataset, physicists have now gauged the value of theta13 with a precision two and a half times which was greater than the experiment’s layout objective. Nothing else existing or planned experiment is expected to reach such a charming level of precision.

“We had several evaluation teams that scrutinized painstakingly the entire dataset, carefully taking into account the evolution of detector performance over the nine years of operation,” stated Daya Bay co-spokesperson Jun Cao of IHEP. “The teams took advantage of the big dataset not only to refine the choice of antineutrino occasions but also to enhance the decision of backgrounds. This dedicated effort permits us to reach an unrivaled level of precision.”

Discovery after experience

The precision dimension of theta13 will enable physicists to more easily determine other parameters in neutrino physics and create more accurate designs of subatomic particles and their interaction.

By investigating the interactions and properties of antineutrinos, physicists may gain insight into the universe’s imbalance of matter and antimatter. Physicists believe that antimatter and matter were created in equal amounts at the time of the Big Bang.

However, if that were the case, these two opposites should have annihilated, leaving behind only light. Some distinction between both must have tipped the equilibrium to explain the preponderance of matter (and lack of antimatter) in the universe today.

“We expect there might be some distinction between neutrinos and antineutrinos,” stated Berkeley physicist and Daya Bay co-spokesperson Kam-Biu Luk. We have never discovered differences between particles and antiparticles for leptons, the type of particles that includes neutrinos.

We have only detected distinctions between particles and antiparticles for quarks. However, the differences we see with the quarks are not enough to describe why there is more matter than antimatter in the universe. It is feasible that neutrinos might be the smoking gun.”

The most recent evaluation of Daya Bay’s final dataset also offered physicists a precise dimension of the mass splitting. This property dictates neutrino oscillations frequency.

“The measurement of mass splitting was not one of Daya Bay’s genuine design objectives. However, it became accessible thanks to the relatively huge value of theta13,” Luk stated. “We determined the mass splitting to 2.3% with the final Daya Bay dataset, an enhencement over the 2.8% precision of the previous Daya Bay measurement.”

The international Daya Bay collaboration expects to report more findings from the last dataset, including updates to previous dimensions.

Daya Bay results to precisely measure and compare the properties of neutrinos and antineutrinos will be utilized by the Next-generation neutrino experiments, such as the Deep Underground Neutrino Experiment (DUNE). Presently under construction, DUNE will provide physicists with the world’s most intense neutrino beam, underground detectors divided by 800 miles, and the chance to study the behavior of neutrinos like never before.

“As one of many physics objectives, DUNE expects to gauge theta13 nearly as precisely as Daya Bay eventually,” said Brookhaven experimental physicist and Daya Bay collaborator Elizabeth Worcester. “This is amazing because we will then have precise theta13 measurements from different oscillation channels, which will rigorously evaluate the three-neutrino version. Until DUNE gets to that high precision, we can utilize Daya Bay’s precise theta13 measurement as a constraint to allow the search for differences between neutrino and antineutrino properties.”

Scientists will also utilize the big theta13 value and reactor neutrinos to determine which of the three neutrinos is the lightest. “The exact theta13 measurement of Daya Bay improves the mass-ordering sensitivity of the Jiangmen Underground Neutrino Observatory (JUNO), which will finish construction in China next year,” stated Yifang Wang, JUNO spokesperson, and IHEP director. “Moreover, JUNO will attain sub-percent level precision on the mass splitting gauged by Daya Bay in numerous years.”

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