Jeffrey K. Nelson
Professor of Physics

Experimental High Energy Group
Department of Physics
College of William and Mary
P.O. Box 8795
Williamsburg, VA 23187-8795

phone: (757) 221-3579

fax: (757) 221-3540

Neutrino Physics

My group studies subatomic particles called neutrinos.

Neutrinos, a category of leptons, have no electric charge and do not feel the strong interactions that bind the quarks into protons and neutrons. Consequently neutrinos usually pass directly through matter without any sign of their passage. Our only chance to detect them is on the rare occasions when they interact with an atomic nucleus with the weak nuclear force. The only evidence of their interaction is the subatomic debris resulting from these collisions. This makes neutrino experiments very challenging. We need to use massive detectors and very intense neutrino beams to ensure that we see enough interactions to make precision measurements.

Modern neutrino research focuses on their strange ability to spontaneously change from one neutrino type to one of the other two types of neutrinos. This happens as they travel over distances of 100 km to 10,000 km. It had been predicted theoretically that if neutrinos were massive, and consisted of mixed quantum mechanical states, they would change their type. This process is known as neutrino oscillations and refutes the previous assumption that neutrinos were massless. The mass difference between the two oscillating neutrino types and three quantum mixing parameters affect the distances for these oscillations. These neutrino oscillation parameters are fundamental physical constants in the same way that the mass and charge of the electron are fundamental.

Neutrino research, because of the scale, cost and associated duration for construction of the experimental facilities, is "big science." We often think of any particular experiment's construction in the same way that an astronomer thinks of a new observatory. Here are two experiments that my group is contributing to.

Neutrino Oscillation Measurements with the MINOS detectors

The goal of the MINOS experiment is to confirm the neutrino oscillation hypothesis, to measure the neutrino mass splitting, and to determine neutrino oscillation parameters. It measures a neutrino beam produced at Fermilab near Chicago with detectors near its source (near detector) and 735 km away (far detector). The 5,400-ton MINOS far detector was built in the Soudan Underground Laboratory. We measure neutrino energies in the near detector and use them to predict the neutrino energies at the far detector. By comparing the data to expectations we can search for neutrino oscillations.

Within MINOS, we recently completed our second year in a planned five year program. We have already provided improved measurements of the neutrino oscillation parameters. In addition to papers on the technology of MINOS, we have also published papers exploiting the fact that it is the first magnetized deep-underground detector to study cosmogenic neutrinos and cosmic rays.

Neutrino Interaction and Nuclear Physics with the MINERvA Detector

The goal of the MINERvA collaboration is to perform precision studies of neutrino interactions on nuclei. Past experiments collected modest samples on different nuclei than, for example, the iron used in the MINOS detectors. MINERvA will have a variety of targets ranging from helium to lead. These targets will enable the systematic study of the effects of different nuclei on neutrino-nucleus interactions.

Since we do not directly detect neutrinos, knowledge of the debris that comes out after a neutrino interacts in a nucleus is our only way to determine the neutrino's properties. Precision neutrino data from MINERvA will be critical for the MINOS oscillation measurements to reach their best possible precision. Uncertainties in neutrino scattering are also the leading source of error on a number of newly proposed neutrino experiments.

We are leading the development program on the 30,000 scintillator detectors in MINERvA in collaboration with Univ. of Rochester, Hampton Univ., and Fermilab. We are planning to assembly over 60% of the detector assemblies on campus. We hope to commission the detector in 2009.

In addition to the MINERvA detector construction we are also working make set of calibrations tests using miniature versions of MINERvA placed in beams at JLAB and Fermilab. The first of these was run in spring 2007. A larger Fermilab run is planned for 2008 and we are prototyping these detectors at W & M.

Some links

Recent Publications

Further reading

Remember, 2+2=7 for sufficiently large values of 2