To Understand The Universe, Science Calls On The Ultrasmall

A special three-day symposium focusing on the weird subatomic particles that could help answer those compelling questions takes place in Washington, D.C., August 16-18 at the 238th National Meeting of the American Chemical Society (ACS).

Titled "The Chemistry and Physics of Neutrino Experiments," it will include almost two dozen reports on experiments to understand what Nobel Laureate Frederick Reines once termed "the most tiny quantity of reality ever imagined by a human being." Neutrinos ("small neutral ones") are among the subatomic, or elementary, particles that make up all matter. They have no electric charge, virtually no mass, and pass through ordinary matter without causing any disruption. Most neutrinos traveling through Earth come from the Sun, and trillions of solar electron neutrinos pass through every person each second. Although those properties make neutrinos difficult to detect, detecting and understanding them are key scientific pursuits, partly because of the implications for cosmology.

"The neutrino has the smallest observed mass for any elementary particle, but they appear in such astonishing numbers in the universe that they are a large portion of its mass," said Steven Elliott, Ph.D. He is a physicist at Los Alamos National Laboratory in New Mexico. "At the moment, neutrinos may be massive enough to account for more mass in the universe than all stars combined."

Many of the ACS presentations focus on experiments to investigate these particles. Scientists are turning to huge devices — the MiniBooNE detector, the Super Kamiokande, the Sudbury Neutrino Observatory, the Borexino solar neutrino detector and the IceCube detector — that detect neutrinos using large volumes of liquids, like mineral oil, water or even the ice cap at the South Pole.

In the devices, scientists record the radiation of neutrinos generated from particle decay. The science and engineering laboratories must work deep underground to avoid cosmic rays and other ordinary background radiation, which would harm the experiments' results.

"Neutrino experiments are complicated undertakings that take years to design and construct and even longer to operate," says Richard Hahn, Ph.D., co-organizer of the ACS symposium and a scientist with Brookhaven National Laboratory (BNL) in Upton, N.Y. "The results tell us about fundamental physics, but developing the experiments is multidisciplinary, requiring expertise in physics but also other areas like organic, inorganic and nuclear chemistry."

Traveling near the speed of light, these tiny particles come in three varieties or "flavors," and they all routinely change from one type to another, a phenomenon known as oscillation. Because of their feeble interaction with all matter, understanding neutrinos and their effects on a universal scale has posed a challenge to nuclear chemists and physicists for decades.

Using these large detectors, scientists are looking to uncover some of the neutrino's basics. Elliott, for example, hopes to determine its mass using a technique called double beta decay. Previous research has determined a 'relative mass scale' of the neutrino, but a precise measurement is necessary to better understand the universe's development of structure, Elliott says.

Scientists are also trying to resolve the question of the universe's asymmetry — one of the greatest unsolved issues in physics, says Minfang Yeh, Ph.D., co-organizer of the ACS symposium and a scientist with Hahn at BNL. Almost everything observable from Earth seems to be made of matter, but based on experimental particle interactions, physicists believe that The Big Bang created equal amounts of matter and antimatter. Yeh imagines the apparent disappearance of antimatter could involve discrepancies in how neutrinos and anti-neutrino oscillate, or change flavors.

"Scientists think maybe the conversion mechanism could lead us to the understanding of the imbalance," Yeh said. "If there's a difference between a neutrino and an antineutrino, maybe theoretically that's one source of the asymmetry between matter and anti-matter in the universe." Yeh adds that neutrinos could be a solution to another mystery — dark matter, an energy that makes up almost one-quarter of the universe's mass. Like neutrinos, non-baryonic dark matter has virtually no interaction with ordinary matter. Unlike neutrinos, its existence hasn't been proven but is inferred by measuring the effects of its gravity.

One device that could probe the mystery of asymmetry is a proposed 500 kT Water Cherenkov detector. The massive detector will investigate differences between neutrinos and antineutrinos from 4,850-feet underground in South Dakota. Weighing 500 kilotons, it will detect neutrinos from a beam of particles sent from Fermilab's proton accelerator in Illinois.

Another device, Fermilab's MiniBooNE detector, records neutrino oscillations and consists of a 40-foot diameter spherical tank holding 800 tons of mineral oil. It is covered on the inside by 1,520 8-inch phototubes.