University of Minnesota
School of Physics & Astronomy


Why Neutrinos Matter?

Satish Desai
Satish Desai
Symmetry Magazine

Satish Desai is a research associate working on the NOvA experiment, which is searching for the rate of neutrino oscillations. Desai’s role on the experiment is to oversee the reconstruction of simulated data. After managing quality assurance for the NOvA Module factory, which was staffed by several hundred University of Minnesota Students, Desai has moved on to measuring neutrino cross-sections. Desai uses data from NOvA’s near detector which is located near the neutrino beam at Fermilab, outside Batavia, IL, and compares it to data at the far-detector located in Ash River, Minnesota.

The purpose of measuring the cross sections is to find the probability that a neutrino will interact in the detector, and whether such an interaction would produce a proton, neutron, or a more exotic particle like a pion. Desai is also trying to understand how much of the neutrino’s initial energy will go into creating another particle like a proton.

Desai says understanding these probabilities will help physicists find the initial energies of the neutrinos, which are unknown interaction by interaction. They are hoping to find a way to connect the actual observables back to that incoming neutrino energy. “Using the actual observables that we have in our detector, we can go back and find the original energy of the neutrino. That’s an important part of our flagship measurement, the rate of neutrino oscillation, because that will depend on the neutrino’s energy.” Desai says this information will also help physicists fill in their model of the nucleus, which is not yet complete.

Nova has functionally identical near and far detectors, so it doesn’t need to know as much about the probabilities. Future detectors may not have identical detectors, so they will need a more complete understanding of these neutrino interaction rates.

Desai is also interested in charge-parity (CP) violation in neutrinos. Physicists know that CP violation must occur to explain the asymmetry of matter and antimatter in the Universe. If matter and anti-matter were symmetric, we could not exist, because matter would be annihilated by anti-matter. A charge conjugation is way of looking at a given interaction, changing all the particles into their antiparticles. “With a charge conjugation, an electron hitting an atom and creating particles would become an anti-electron hitting an anti-atom and creating anti-particles. If the two reactions happen at the same rate, it respects charge conjugation symmetry. If not, it violates it.” Physicists are looking for a way in which matter acts differently than anti-matter. NOvA and its successor experiments will address whether charge-parity violation happens with neutrinos. “We know something like this happens with quarks but the effect is too small to explain the asymmetry in the Universe. If it were the case with neutrinos then they are common enough that that could explain the asymmetry.”

Desai says it is going to take a long time to get enough data to be able to make any interesting statements about CP Violations. NOvA expects its first physics results sometime in 2015. The experiment will run six years in total, with three years in neutrino mode, three years in anti-neutrino mode.