MAJORANA DEMONSTRATOR’s First Detector Units

Stuart Jay Freedman, a physicist in Berkeley Lab’s Nuclear Science Division and professor of physics at the University of California at Berkeley, died November 9, 2012, at the age of 68. Freedman was a world-renowned investigator of fundamental physical laws whose many accomplishments include unique contributions to the study of neutrinos and the weak interaction.

On Wednesday, May 30, the Sanford Underground Research Facility officially opened its Davis Campus, almost a mile deep in the former Homestake gold mine in the Black Hills of South Dakota. The event brought over 60 visitors including officials from federal and state government, scientists from universities and national laboratories, and local and national media. Berkeley Lab is the U.S. Department of Energy’s lead institution for this marked advance in underground science.

The May 30, 2012 dedication of the Davis Campus of the Sanford Underground Research Facility (SURF), 4,850 feet down in South Dakota’s Homestake Mine, marks the official debut of research dedicated to solving some of the most challenging puzzles in 21st-century science. What is the nature of dark matter? What secrets are mysterious neutrinos still hiding? Shielded from cosmic rays by almost a mile of solid rock overhead, supersensitive experiments at the Sanford Lab’s Davis Campus are searching for the answers.

Neutrinos may be even stranger than they seem, if indeed they are the only fermions (particles of matter) that are their own antiparticles. Proof would be a rare form of radioactive decay called neutrinoless double-beta decay, which could only be seen if there’s virtually no background interference. The MAJORANA DEMONSTRATOR now under construction at the Sanford Underground Research Facility in the Black Hills of South Dakota aims to prove these near-perfect conditions can be met.

Some rare cosmic rays pack an astonishing wallop, with energies prodigiously greater than particles in human-made accelerators like the Large Hadron Collider. Their sources are unknown, but gamma-ray bursts are a favored candidate. If so, they should also produce ultra-high-energy neutrinos. Scientists searching for these with IceCube, the giant neutrino telescope at the South Pole to which Berkeley Lab has made key contributions, have found exactly zero. The mystery deepens.

The Daya Bay Reactor Neutrino Experiment collaboration has announced a precise measurement of the last of the unsolved neutrino “mixing angles,” which determine how neutrinos oscillate among different types. The ground-breaking collaboration, led by the United States and China and initiated by Berkeley Lab, is the most sensitive reactor neutrino experiment in the world. The results promise new insight into why enough ordinary matter survived after the big bang to form everything visible in the universe.

Berkeley Lab physicists have played a leading role in designing and building the international Daya Bay Reactor Neutrino Experiment in southern China, which has just begun collecting data on the elusive final measurement needed before the masses of the different kinds of neutrinos can be determined.

Within the past few weeks, the Daya Bay Reactor Neutrino Experiment in China has made rapid strides toward completion of the first of three underground experimental halls for collecting data on the last unknown neutrino “mixing angle.” A mini-slide-show looks at the giant underground experiment’s progress.

From the planet’s core to its surface, heat enables Earth’s magnetic field, spreads the sea floor, and keeps continents on the move. Much of the heat is “radiogenic,” from the radioactive decay of elements in the crust and mantle, but how much? By measuring neutrinos from deep in the Earth, Berkeley Lab scientists and their colleagues at Japan’s KamLAND neutrino detector have published the most precise estimate yet of radiogenic heat.