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Scientists Study Nuclei and Leptons for Future Neutrino Experiments

A research team from the PRISMA+ cluster of excellence at the Johannes Gutenberg University Mainz (JGU) has successfully computed the way in which atomic nuclei of the calcium element act under collisions with electrons.

Graphic of two molecules colliding

Image Credit: FlashMovie/

The results coincide well with the available experimental data. A computation based on a basic theory has accurately explained experiments for a nucleus almost equal to the weight of calcium for the first time.

Specifically relevant is the potential that such calculations could have to explain neutrino experiments. The study results were published in the renowned journal Physical Review Letters.

The new publication was released by the research team headed by Professor Sonia Bacca, Professor for theoretical nuclear physics in the cluster of excellence PRISMA+. The study was performed in association with Oak Ridge National Laboratory.

Professor Bacca is skilled in successfully estimating several properties of atomic nuclei, drawing them from the reactions among their constituents, such as nucleons, quantifiable within chiral effective field theory.

The goal of Bacca’s research is to offer a concrete connection between experimental and basic theory of quantum chromodynamics. In physics, this kind of process is known as an “ab initio calculation,” where “ab initio” means “from the beginning” in Latin.

The same theory can also explain the cross-section of the atomic nuclei probed using external fields such as interacting with electrons or other particles. This process is important to comprehend the existing data and explain future experiments, for instance, in neutrino physics, a key focus of the PRISMA+ research program.

Calcium 40 is our test system, so to speak. With our new ab initio method we were able to calculate very precisely what happens with electron scattering and how the Calcium atomic nucleus behaves.

Dr Joanna Sobczyk, Study First Author and Post Doctorate, Johannes Gutenberg University Mainz

Understanding Neutrinos

Neutrinos are evasive particles capable of continuously penetrating the Earth but are challenging to detect and analyze. However, by using new planned experiments like DUNE in the United States, researchers look to analyze their basic properties—for instance, the phenomenon by which one kind of neutrino transforms into another, known as neutrino oscillation.

We are very pleased that we have succeeded in basically showing that our method works reliably. Now a new era begins, where the ab initio methods can be used to describe the scattering of leptons—these include electrons and neutrinos—on nuclei, even for 40 nucleons.

Sonia Bacca, Professor of Theoretical Nuclear Physics, Cluster of Excellence PRISMA+

To achieve this, researchers require key data obtained from theoretical calculations. Particularly the question of how the neutrinos interact with the atomic nuclei in the detector.

The experimental data collected regarding the neutrinos scattering on atomic nuclei seem to be rare. So, the researchers initially turned toward scattering another lepton—the electron—that has experimental data.

This is considered a significant success, as so far, there was no possible way to perform such calculations for elements as heavy as calcium, composed of 40 nucleons.

The team is looking forward to analyzing the element Argon and its interaction with the neutrinos after successfully completing the process for calcium. Argon is expected to play a vital role as a target in the scheduled DUNE experiment.

One of the nicest features of our approach is that it allows us to rigorously quantify uncertainties associated with our calculation. Uncertainty quantification is very time-consuming, but extremely important in order to be able to appropriately compare theory against experiment.

Dr. Bijaya Acharya, PRISMA+ postdoc, co-author of the study

Journal Reference:

Sobczyk, J. E., et al. (2021) Ab Initio Computation of the Longitudinal Response Function in 40Ca. Physical Review Letters.

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