Neutrino: Our Last Hope

Kara Brower | kara.brower@yale.edu October 1, 2010

Dr. Bonnie Fleming, Horace D. Taft Associate Professor of Physics, is currently conducting experiments at the Fermilab on neutrino oscillations that may improve our understanding of the universe. Fermilab, which is funded through the U.S. Department of Energy, is the world’s second most powerful proton-anti-proton particle accelerator. According to Fleming, these physics-pioneering machines quite literally “smash subatomic particles at near the speed of light.” Out of all these subatomic particles, however, Fleming is most interested in the study of neutrinos.

Neutrinos, often termed “the small neutral ones,” were at first difficult to detect due to their ability to pass through matter without nearly any disturbances. Now, they are being detected everywhere: over 50 trillion collide with the human body from sun emanation every second. Moreover, these subatomic particles may play an important role in current scientific understanding of the creation of matter.

Fleming states, “In the last three years of study, neutrinos were determined to have a small, but non-zero mass,” a discovery that may explain the matter-anti-matter paradox in the universe. For example, in the modern concept of physics, wherever there is matter, there is also accompanying anti-matter. Since energy creates both matter and anti-matter particles, upon collision, they must annihilate each other in a “puff of energy,” as termed by Fleming.

If the ratios between matter and anti-matter were equal, as the Standard Model of Physics predicts them to be, the symmetry of particle distributions would have produced complete annihilation of both species. However, a paradox arises from the fact that these ratios are not equal. Somehow, matter has been favored since the creation of the early universe. Scientists have been trying for decades to find enough differences between matter and anti-matter particles to understand how this inequality arose. Subatomic particles such as protons, electrons, and quarks, have been analyzed extensively but no study has satisfactorially explained why the matter particle exists in higher proportions than its anti-matter counterpart. Studies on neutrinos promise to explain this paradox; Fleming declares the neutrino to be “our last hope” in unraveling this mystery.

Currently, Fleming and her team are studying the properties of neutrinos using their oscillation patterns. Each of the three distinct “flavors” of neutrinoselectron, muon, and taucan spontaneously interconvert by oscillation, as deemed by the “neutrino flavor oscillation phenomenon.” Based on these oscillation properties, Fleming is running four experiments, all of which are in different phases but centralize around one question: “Does the neutrino oscillate at the same rate as its anti-particle?” The answer to this question could perhaps explain the inequality of matter distribution.

One of Fleming’s current experiments, ArgoNeut (Argon Neutrino Test), employs a liquid Argon time-projection chamber (TPC) created from 175 L of liquid argon and three wire planes inside an induced electric field of 500 V/cm. Upon trigger, the neutrino beam NuMi spills into this chamber and measures neutrino and anti-neutrino tracks. The TPC has the ability to record 2,048 hits in 400 microseconds to produce an averaged event, which plots induction, collection, and drift distance relative to time. These plots can then be used to compare neutrino and anti-neutrino tracks and analyze the differences.

This and other novel experiments Fleming is performing have already achieved considerable acclaim. Perhaps the neutrino really is “our last hope,” and may play an important role in our understanding of the universe.

Additional Readings:

S. Avvakumov, “Search for Muon-Neutrino to Electron-Neutrino and Anti-Muon Neutrino to Anti-Electron Neutrino Oscillations at NuTeV,” NuTeV Collaboration, Phys. Rev. Lett., 89:011804, 2002.

A. Meth, “The MiniBooNE Detector,” The MiniBooNE Collaboration. Nucl. Instrument., 2008.