Atomic nuclei and leptons: Milestone in the calculation of cross
sections
Precise theoretical predictions relevant for future neutrino experiments


Date:
August 10, 2021
Source:
Johannes Gutenberg Universitaet Mainz
Summary:
A team has succeeded in computing how atomic nuclei of the Calcium
element behave in collisions with electrons. Results agree very well
with available experimental data. For the first time, a calculation
based on a fundamental theory is capable of correctly describing
experiments for a nucleus as heavy as Calcium. Of particular
relevance is the potential that such calculations could have in
the future to interpret neutrino experiments.



FULL STORY ==========================================================================
A team in the PRISMA+ cluster of excellence at the Johannes Gutenberg University in Mainz succeeded in computing how atomic nuclei of the
Calcium element behave in collisions with electrons. Results agree
very well with available experimental data. For the first time,
a calculation based on a fundamental theory is capable of correctly
describing experiments for a nucleus as heavy as Calcium. Of particular relevance is the potential that such calculations could have in the
future to interpret neutrino experiments. The journal Physical Review
Letters reports on the achieved milestone in its current volume.


==========================================================================
The new publication stems from the group lead by Prof. Sonia Bacca,
Professor for theoretical nuclear physics in the cluster of excellence
PRISMA+ , in collaboration with Oak Ridge National Laboratory. Bacca
works with great success in predicting various properties of atomic
nuclei deriving them from the interactions among their constituents
-- the nucleons -- which can be described within chiral effective
field theory. Her research aims at providing a solid connection
between experimental observations and the underlying theory of quantum chromodynamics. In physics, such a procedure is described as an "ab initio calculation," where "ab initio" means "from the beginning" in Latin.

Also cross sections of atomic nuclei probed by external fields, for
example through the interaction with electrons or other particles, can
be described within the same theory. This procedure is key to explaining existing data and interpreting future experiments, for example in neutrino physics -- an important focus of the PRISMA+ research program.

Understanding neutrinos Neutrinos are elusive particles that are
constantly penetrating our Earth but are very difficult to detect and understand. With new planned experiments, such as the DUNE experiment in
the USA, scientists want to investigate their fundamental properties,
for example, the phenomenon in which one type of neutrinos transform
into another -- called in technical jargon, neutrino oscillation. In
order to achieve that, they need important information from theoretical calculations. Specifically, the relevant question is: How do neutrinos
interact with atomic nuclei in the detector? Since experimental data
on the scattering of neutrinos on atomic nuclei are rare, the team
of researchers first looked at the scattering of another lepton -- the
electron -- for which experimental data are available. "Calcium 40 is our
test system, so to speak," explains Dr. Joanna Sobczyk, postdoc in Mainz
and first author of the study. "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." This is a great success:
Until now it was not possible to carry out such calculations for an
element as heavy as Calcium, which consists of 40 nucleons.

"We are very pleased that we have succeeded in basically showing that
our method works reliably," says Sonia Bacca. "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." "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," comments Dr. Bijaya Acharya, PRISMA+ postdoc and
also co-author of the study.

After they were able to show the potential of their method for Calcium,
the research team wants to look at the element Argon and its interaction
with neutrinos in the future. Argon will play an important role as a
target in the planned DUNE experiment.

========================================================================== Story Source: Materials provided by
Johannes_Gutenberg_Universitaet_Mainz. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. J. E. Sobczyk, B. Acharya, S. Bacca, G. Hagen. Ab Initio
Computation of the Longitudinal Response Function in Ca40. Physical
Review Letters, 2021; 127 (7) DOI: 10.1103/PhysRevLett.127.072501 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210810143042.htm

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