Electrons set the stage for neutrino experiments

Neutrinos stands out as the key to lastly fixing a thriller of the origins of our matter-dominated universe, and preparations for 2 main, billion-dollar experiments are underway to disclose the particles’ secrets and techniques. Now, a group of nuclear physicists have turned to the standard electron to supply perception for the way these experiments can higher put together to seize essential info. Their analysis, which was carried out on the U.S. Department of Energy’s Thomas Jefferson National Accelerator Facility and just lately revealed in Nature, reveals that main updates to neutrino fashions are wanted for the experiments to attain high-precision outcomes.

Neutrinos are ubiquitous, generated in copious numbers by stars all through our universe. Though prevalent, these shy particles not often work together with matter, making them very tough to review.

“There is this phenomenon of neutrinos changing from one type to another, and this phenomenon is called neutrino oscillation. It’s interesting to study this phenomenon, because it is not well understood,” mentioned Mariana Khachatryan, a co-lead writer on the research who was a graduate scholar at Old Dominion University in Professor and Eminent Scholar Larry Weinstein’s analysis group when she contributed to the analysis. She is now a postdoctoral analysis affiliate at Florida International University.

One solution to research neutrino oscillation is to construct gigantic, ultra-sensitive detectors to measure neutrinos deep underground. The detectors sometimes comprise dense supplies with massive nuclei, so neutrinos usually tend to work together with them. Such interactions set off a cascade of different particles which can be recorded by the detectors. Physicists can use that information to tease out details about the neutrinos.

“The way that neutrino physicists are doing that is by measuring all particles coming out of the interaction of neutrinos with nuclei and reconstructing the incoming neutrino energy to learn more about the neutrino, its oscillations, and to measure them very, very precisely,” defined Adi Ashkenazi. Ashkenazi is the research’s contact writer who labored on this venture as a analysis scholar in Professor Or Hen’s analysis group on the Massachusetts Institute of Technology. She is now a senior lecturer at Tel Aviv University.

“The detectors are made of heavy nuclei, and the interactions of neutrinos with these nuclei are actually very complicated interactions,” Ashkenazi mentioned. “Those neutrino energy reconstruction methods are still very challenging, and it is our work to improve the models we use to describe them.”

These strategies embrace modeling the interactions with a theoretical simulation known as GENIE, permitting physicists to deduce the energies of the incoming neutrinos. GENIE is an amalgam of many fashions that every assist physicists reproduce sure features of interactions between neutrinos and nuclei. Since so little is understood about neutrinos, it is tough to instantly check GENIE to make sure it’ll produce each correct and high-precision outcomes from the brand new information that can be supplied by future neutrino experiments, such because the Deep Underground Neutrino Experiment (DUNE) or Hyper-Kamiokande.

To check GENIE, the group turned to a humble particle that nuclear physicists know much more about: the electron.

“This exploits the similarities between electrons and neutrinos. We are using electron studies to validate neutrino-nucleus interaction models,” mentioned Khachatryan.

Neutrinos and electrons have many issues in widespread. They each belong to the subatomic particle household known as leptons, so they’re each elementary particles that are not affected by the sturdy pressure.

In this research, the group used an electron-scattering model of GENIE, dubbed e-GENIE, to check the identical incoming power reconstruction algorithms that neutrino researchers will use. Instead of utilizing neutrinos, they used latest electron outcomes.

“Electrons have been studied for years, and the beams of the electrons have very precise energies,” mentioned Ashkenazi. “We know their energies. And when we are trying to reconstruct that incoming energy, we can compare that to what we know. We can test how well our methods work for various energies, which is something you can’t do with neutrinos.”

The enter information for the research got here from experiments performed with the CLAS detector at Jefferson Lab’s Continuous Electron Beam Accelerator Facility, a DOE consumer facility. CEBAF is the world’s most superior electron accelerator for probing the character of matter. The group used information that instantly mirrored the best case to be studied in neutrino experiments: interactions that produced an electron and a proton (vs. a muon and a proton) from nuclei of helium, carbon and iron. These nuclei are just like supplies utilized in neutrino experiment detectors.

Further, the group labored to make sure that the electron model of GENIE was as parallel as attainable to the neutrino model.

“We used the exact same simulation as used by neutrino experiments, and we used the same corrections,” defined Afroditi Papadopoulou, co-lead writer on the research and a graduate scholar at MIT who can be in Hen’s analysis group. “If the model doesn’t work for electrons, where we are talking about the most simplified case, it will never work for neutrinos.”

Even on this easiest case, correct modeling is essential, as a result of uncooked information from electron-nucleus interactions sometimes reconstruct to the proper incoming electron beam power lower than half the time. A very good mannequin can account for this impact and proper the information.

However, when GENIE was used to mannequin these information occasions, it carried out even worse.

“This can bias the neutrino oscillation results. Our simulations must be able to reproduce our electron data with its known beam energies before we can trust they will be accurate in neutrino experiments,” mentioned Papadopoulou.

Khachatryan agreed.

“The result is actually to point out that there are aspects of these energy reconstruction methods and models that need to be improved,” mentioned Khachatryan. “It also shows a pathway to achieve this for future experiments.”

The subsequent step for this analysis is to check particular goal nuclei of curiosity to neutrino researchers and at a broader spectrum of incoming electron energies. Having these particular outcomes for direct comparability will help neutrino researchers in fine-tuning their fashions.

According to the research group, the goal is to attain broad settlement between information and fashions, which can assist guarantee DUNE and Hyper-Kamiokande can obtain their anticipated high-precision outcomes.