Stars, like our own Sun, produce energy through nuclear fusion. In this process, two light atomic nuclei combine to form one or more heavier atomic nuclei and additional sub-atomic particles, such as neutrons. In a new study, researchers explore muon capture to get valuable insights into stellar hydrogen burning.
What is a Muon?
Muon is one of the fundamental subatomic particles, the most basic building blocks of the universe, as described in the Standard Model of Particle Physics. It resembles electrons but is 207 heavier. Muons belong to the leptons group, meaning they are not made of even smaller pieces of matter. Like other members of the lepton group, the muon is influenced by three of the four fundamental forces in the universe.
When a muon binds with a hydrogen isotope called a deuteron composed of one proton and one neutron, it forms a system of two neutrons. This process is similar to proton-proton fusion, where two protons combine to create a deuteron.
The muons that reach the Earth result from particles in the atmosphere colliding with cosmic rays or the high-energy protons and atomic nuclei that move through space just below the speed of light. Muons exist only 2.2 microseconds before decaying into an electron and two kinds of neutrinos. Since they move near the speed of light, muons can travel far before finally decaying.
Investigating Muon Capture
A team of nuclear theorists conducted a novel study focusing on muon capture on the deuteron. The group involves the University of Pisa collaborating with the Istituto Nazionale Fisica Nucleare in Italy, the Theory Center at the Thomas Jefferson National Accelerator Facility, and Washington University in St. Louis.
The research team, led by Leah Ceccarelli, investigated the muon capture rate to describe the interaction among nucleons and their interactions with the muon. This was made possible by using advanced models derived from chiral effective field theory.
The experts focus on estimating theoretical uncertainty, for which four sources were identified. These include model dependence, chiral-order convergence for the weak nuclear current, uncertainty in the single-nucleon axial form factor, and the numerical technique for solving bound and scattering systems.
Ceccarelli and her colleagues adopted a theoretical framework that enabled the identification of principal sources of uncertainties. The effectiveness of this approach was then compared with the results in previous studies. It was revealed that there is an uncertainty of approximately 2%, lower than experimental errors.
The study conducted by the researchers supports the ongoing efforts to enhance the accuracy of muon capture measurements. It also holds the key to using the same theoretical framework for studying proton-proton fusion and other processes. This could help scientists model the hydrogen-burning phase of stars and understand solar neutrino fluxes.
In the future, the researchers plan to include muon capture processes on helium-3 and lithium-6 and compare them with the results from previous studies. They also aim to apply this framework to investigate other weak processes relevant to solar standard models and neutrino fluxes.
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