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Friday, May 10, 2013
Neutrinos are notoriously difficult particles to study: For every 50 billion neutrinos that pass through the MINERvA detector at Fermilab, only about one will interact leaving a trace in our detector, producing particles that we can observe directly.
The likelihood of a neutrino undergoing a quasi-elastic interaction for different values of the momentum transferred to the proton or neutron (Q2) compared to several theoretical models. The data agree best with a model in which the neutrino can interact with multiple protons or neutrons at a time.
In spite of this, we are starting to use neutrinos to learn more about protons and neutrons and how they behave when they’re together inside an atomic nucleus. We already understand a lot about the nucleus: We know that it’s made of protons and neutrons, and we know the number of protons and the number of neutrons in the nucleus for every chemical element. But there is much we still don’t fully understand, especially about what those protons and neutrons are doing inside the nucleus.
We can study the protons’ and neutrons’ behavior in the nucleus the way we might study how people act at a party. Do the party-goers mingle according to the general spirit of the party, or do they break off into pairs? We could determine the party’s nature by sending in very shy folks and observing how quickly they leave and whether they leave through the same door they entered.
In a nucleus, does each proton and neutron react to just the average effect of the others, or do they occasionally pair up? One way to answer this question is to fire neutrinos at nuclei and measure the particles produced when neutrinos do interact with the nuclei of atoms in our detector. By studying those particles, we can try to infer the behavior of the protons and neutrons.”
The energy near the neutrino interaction point in neutrino quasi-elastic events. The data points, in black, are at higher energies on average than the prediction, in red, suggesting that the neutrino really is interacting with multiple protons or neutrons, which are kicked out of the nucleus.
See the full article here.
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