By Gail Gallessich

UCSB Physics Professor Harry Nelson

UCSB Physics Professor Harry Nelson went to Switzerland last month to celebrate receiving the High Energy and Particle Physics Prize of the European Physical Society for 2005. The celebration was at CERN, the world’s largest particle physics laboratory, located near Geneva.

Nelson is part of a team called the “NA31 Collaboration,” a group that performed anti-matter experiments. The award went to the entire group of researchers—73 in all, including only four Americans—who worked on experiments that “showed for the first time direct charge-parity violation in the decays of neutral K mesons,” according to the award citation.

Charge-parity, or CP, violation is thought to be the reason why the universe is made of matter, even though equal amounts of matter and anti-matter should have been created in the Big Bang.

This year’s EPS award to the NA31 Collaboration, which is led by Heinrich Wahl, is the first time an EPS award has been given to a group.

The European Physical Society prize has been awarded since 1989. David Gross, director of the Kavli Institute for Theoretical Physics and winner of the 2004 Nobel Prize in physics, won the EPS prize in 2003.

Nelson explained that in particle physics, unlike theoretical physics, the scientists must work in large teams to carry out experiments. Nelson arrived at CERN in 1987 and helped build the portion of the apparatus that distinguished among the various types of particles that travel at speeds approaching the speed of light.

Nelson is currently working with another group of physicists in the highly competitive international search for “dark matter.” His group is called the Cryogenic Dark Matter Search, or CDMS, and is considered the leading research endeavor on this issue. He explained that reliable data indicate that most of the matter in the universe emits no detectable light. The “dark” matter is inferred, generally, from the gravitational pull that it exerts on the matter that does emit light.

A simple explanation would be that the dark matter consists of protons and other atomic nuclei, which for some reason do not emit light. However, Nelson noted that this explanation is inconsistent with our understanding of the Big Bang, and that the dark matter must consist of a new type of “exotic” particle.