Neutrinos Among Us

by Gabrielle DeMarco on October 10, 2011

Approximately 55 miles outside of Hong Kong, deep under the surrounding mountains, rests an important experiment in particle physics. The Daya Bay Reactor Neutrino Experiment churned to life beneath China this summer. The ultra-sophisticated experiment was years in the making and has collaborators around the globe, including right here at Rensselaer.

Professor James Napolitano has been involved since the nascent stages of the experiment, working to design, install, and operate the all-important water purification system surrounding the experiments. And water purification is a huge deal for this experiment.

Contamination of the water by bacteria, gases, or even sunlight can be picked up by the sensitive detectors within the experimental dectectors, resulting in bad data. Even tiny fluctuations in the levels of radiation within the water could ruin the entire experiment because the objects they are looking for produce nearly undetectable amounts of energy. Such traces of energy could easily be lost in background radiation produced by contaminates in the water.

Neutrinos are sub-atomic particles that are electrically neutral. Because they are neutral, they can pass through ordinary matter like rocks, air, or even the human body almost unaffected. In fact, millions of them are currently passing through every square inch of your body as we speak. They are formed by nuclear reactions such as those found in the sun or in nuclear reactors.

All particles have an antiparticle, which is a particle with the same mass, but all other properties reversed. For neutrinos, the only reversible property is their spin. Thus, antineutrinos spin in the direction opposite to that of neutrinos, and this affects the interactions in which they may participate.

The Daya Bay experiment is recording the interactions of antineutrinos as they move away from nuclear reactors in the China Guangdong Nuclear Power Group in Southern China. The nuclear reactions from the reactors provide the antineutrinos for analysis. The antineutrinos move from the power plants through a series of detectors. The detectors cannot directly measure the number of neutrinos produced, instead it must rely on alternate means of getting at the same number. To do this, the detectors are tuned to measure interactions between the neutrinos. Each interaction or smashing of neutrino on neutrino produces a flash of energy that can be read and recorded by the detector.

As the antineutrinos move through the detectors, the number of these interactions will weaken. By comparing the initial energy produced by the interactions upon arrival at the first detector to the amount of energy produced as they wiggle through the final detector scientists will be able to understand how neutrinos interact with matter and evolve over time. The measurements produced by Daya Bay will be the most fine-tuned to date, providing scientists would important details on the role of these important particles.

A deeper understanding of neutrinos will open up important gateways in our understanding of the formation of our universe. Because neutrinos barely interact with other particles, they could be very useful as probes deep into the universe. Many other particles get warped by the environment in deep space causing extreme distortion of data. This means that neutrinos can even be used to probe the dense matter of the sun or the highly compact environment of a collapsing star.