Experimenting with mirror nuclei reveals new information about protons and neutrons' interior architecture.
Scientists
are holding up a'mirror' to protons and neutrons in order to learn more about
the components that make up our observable cosmos. The MARATHON experiment at
the US Department of Energy's Thomas Jefferson National Accelerator Facility
found fresh insights into the architecture of the so-called mirror nuclei,
helium-3, and triton, by comparing them. On February 9th, 2022, the findings
were published in Physical Review Letters.
The
fundamental particles quarks and gluons, which make up a large portion of the
stuff we perceive in the cosmos, are buried deep within the protons and
neutrons that make up atomic nuclei. The existence of quarks and gluons was
originally demonstrated half a century ago by Nobel Prize-winning research at
the DOE's Stanford Linear Accelerator Center (now known as SLAC National
Accelerator Laboratory).
Deep
inelastic scattering has entered a new era because to these remarkable
experiments. High-energy electrons that travel deep inside protons and neutrons
probe the quarks and gluons within them.
"What
we mean by deep inelastic scattering is that nuclei attacked with electrons in
the beam break up quickly, disclosing the nucleons inside," explained
Gerassimos (Makis) Petratos, a professor at Kent State University and the
MARATHON experiment's spokesperson and contact person.
The
momenta — a quantity that comprises the electrons' mass and velocity – are
measured by the massive particle detector systems that capture the electrons
that originate from these collisions.
Deep
inelastic scattering studies have been carried out in numerous laboratories
throughout the world since those first tests five decades ago. Nuclear
physicists have gained a better knowledge of the role of quarks and gluons in
the structures of protons and neutrons as a result of these investigations.
Experiments are still being conducted to fine-tune this procedure in order to
get ever more specific information.
Nuclear
physicists compared the results of deep inelastic scattering tests in two
mirror nuclei for the first time in the recently finished MARATHON experiment
to learn about their structures. The physicists concentrated on the nuclei of
helium-3 and tritium, a hydrogen isotope. Tritium has two neutrons and one
proton, whereas helium-3 has two protons and one neutron. The consequence of
transforming all protons into neutrons and neutrons into protons would be
tritium if you could'mirror' transform helium-3. They're called mirror nuclei
because of this.
Two
state of the art particle detector systems, the High Resolution Spectrometers
in Jefferson Lab’s Experimental Hall A, were instrumental in collecting data in
the MARATHON experiment. Credit: Thomas Jefferson National Accelerator Facility |
"We employed the simplest mirror nuclei system that exists, tritium and helium-3," said David Meekins, a Jefferson Lab staff scientist and a co-spokesperson for the MARATHON experiment.
"It turns out that we can access the structural functions of protons relative to neutrons by measuring the ratio of cross sections in these two nuclei." These two numbers could be linked to the distribution of up and down quarks inside nuclei, according to Petratos.
The
MARATHON experiment was first developed in a summer workshop in 1999 and was
finally carried out in Jefferson Lab's Continuous Electron Beam Accelerator
Facility, a DOE user facility, in 2018. The MARATHON experimental
collaboration's more than 130 individuals overcame numerous obstacles to
complete the experiment.
MARATHON,
for example, required high-energy electrons, which were made possible by the 12
GeV CEBAF Upgrade Project, which was completed in 2017, as well as a customised
tritium target system.
"Clearly, the aim was the most difficult aspect of this specific trial. "Because tritium is a radioactive gas, we had to put safety first," Meekins added. "That's part of the lab's mission: there's nothing so vital that we can't put safety first."
In
Experimental Hall A, 10.59 GeV (billion electron-volt) electrons were fired at
four different targets. Helium-3 and three hydrogen isotopes, including
tritium, were among the targets. The left and right High-Resolution
Spectrometers in the hall were used to gather and measure the emitted
electrons.
After
the data was collected, the team worked together to properly examine the
information. The original data was published in the final article so that other
organisations could utilise the model-free data in their own analysis. It also
included Petratos' analysis, which is based on a theoretical model with minor
adjustments.
"We wanted to make it clear that here is the measurement we took, this is how we did it, this is the scientific extraction from the measurement, and this is how we accomplished it," Meekins says. "We don't have to worry about favouring one model over another because the data can be used by anyone."
The
findings contain greater electron momenta measurements of these mirror nuclei
than previously accessible, in addition to a precise calculation of the
proton/neutron structure function ratios. This high-quality data collection
also allows for more extensive investigations to answer other nuclear physics
concerns, such as why quarks are distributed differently inside nuclei than
free protons and neutrons (a phenomenon known as the EMC Effect) and other studies
of particle architectures in nuclei.
The
MARATHON spokesmen were quick to credit the final outcomes to the hard work of
collaboration members when addressing the findings.
"The success of this experiment is due to the exceptional group of people who participated in the trial, as well as the assistance we received from Jefferson Lab," said Mina Katramatou, a Kent State University professor and co-spokesperson for the MARATHON project. "A terrific group of young physicists, including early career postdoctoral researchers and graduate students, worked on this experiment as well." “There were five graduate students who got their theses research from this data,” Meekins confirmed. “And it’s good data, we did a good job, and it was hard to do.”
Reference: Journal PHYSICALREVIEW LETTERS
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