In the 21st century, particle physics and cosmology have come together in a unified quest to understand the fundamental constituents of the Universe and how they evolved after the Big Bang. A radically new picture has emerged in the past two decades, in which the energy content of the Universe today consists of only 4% ordinary matter, with the rest divided among two mysterious components, dark matter and dark energy. The LBNL Physics Division carries out research that spans the full range of particle physics and cosmology, from studies of sub-atomic particles created in accelerator collisions that decay almost instantly, to large-scale cosmological structures observed in galaxy surveys looking back billions of years in cosmic time.
Physics Division scientists conduct research at leading facilities all over the world. At the ATLAS experiment, located at the Large Hadron Collider in Geneva, Switzerland, we seek to understand the origin of mass and the nature of the Higgs boson, as well as searching for new particles beyond the Standard Model of particle physics. In an underground experiment located near Daya Bay, China, we measure the subtle oscillations of neutrinos from one type to another. Almost one mile underground, in the Homestake mine in South Dakota, we are looking for the signals of dark matter particles colliding with xenon atoms in the LUX detector. At Fermilab, near Chicago, we are collaborating on the design and construction of a new experiment called Mu2e that will look for the very rare transformation of a muon into an electron that, if observed, would be an immediate signal of physics beyond the Standard Model.
The 2011 Nobel Prize in Physics was awarded to LBNL scientist Saul Perlmutter for his ground breaking discovery, made using Type Ia supernovae, that the expansion of the universe is accelerating. To continue the study of dark energy, the LBNL Supernova Cosmology Project takes data on telescopes around the world and in space, using the Hubble Space Telescope, while the Supernova Factory studies nearby Type Ia Supernova using a dedicated spectrograph in Hawaii.
Another technique to study dark energy, called baryon acoustic oscillations, is being pursued by the BOSS experiment. BOSS uses the Sloan telescope on a mountaintop near Alamogordo, New Mexico to methodically map the positions of 1.5 million galaxies and study the expansion history of the Universe over the past 6 billion years. A follow up experiment, BigBOSS will measure 20 million galaxies and reach back 10 billion years, or more.
To study the earliest moments of the Universe, we use the cosmic microwave background and its polarization. The CMB comes to us from every direction with very nearly the same intensity. The first measurements of the tiny deviations from anisotropy were made by the COBE experiment, led by 2006 Nobel Laureate George Smoot. Currently, the PolarBear experiment in Chile is studying the polarization of the CMB.
In addition to these experiments we carry out theoretical work on a wide range of topics. We also host the Particle Data Group, which publishes a new version of the definitive reference for particle physics, the Report on Particle Properties, every two years.