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Neutrinos are the most abundant yet most elusive massive particles in the universe. They rarely interact with matter and oscillate into different identities over time. In order to understand these ghostly particles in greater detail, understanding and modeling their feeble interaction with various detector materials used in giant detectors is critical. Neutrino oscillation experiments seek to improve and constrain models used in their simulations to match the reality as closely as possible.
The MINERvA experiment continues to provide measurements relevant to these experiments to help scientists better model these interactions and implement in their simulation. This week’s Wine and Cheese Seminar at Fermilab features a talk from the MINERvA collaboration, presenting its measurement of the total probability that a muon type neutrino (or antineutrino) interacts with the protons and neutrons inside the MINERvA detector via something called charged-current interaction.
The signature of the charged-current interaction is the neutrino changing into a charged muon (a heavier cousin of electron) by the exchange of a charged W boson. In the process, the neutrino transfers some of its energy and momentum to the recoil proton or neutron. Depending on the energy and momentum transfer, the recoiled particle can experience one of the following processes: It remains intact; becomes what is called an excited state and decays into other particles; or breaks up into individual constituents and coalesces immediately to form other particles. A measurement of the probability of the interaction happening by any of these channels is what is known as the inclusive cross section.
When only a small amount of energy is transferred from the neutrino to the proton or neutron, the probability for this charged-current interaction is largely independent of the initial neutrino energy. This provides an alternative method to estimate the number of neutrinos per unit area through the detector, referred to by physicists as neutrino flux, as a function of neutrino energy. This method also provides a valuable tool to complement other methods for determining neutrino flux. The new MINERvA measurement employed this method to extract the neutrino flux and used the extracted flux to measure the inclusive scattering cross sections as the function of initial neutrino energy.
Dipak Rimal is a physicist at the University of Florida.