Lab finds evidence of tinier part of matter
NEWPORT NEWS — Scientists at the Thomas Jefferson National Accelerator Facility have evidence of a new subatomic particle called a pentaquark.
Before your eyes glaze over, know that pentaquarks could help physicists understand the basic building blocks of matter.
"It's completely new physics," said Melanie O'Byrne, Jefferson Lab's science writer. Scientists may have to add a new limb on the family tree of subatomic particles.
First, a quick lesson in particle physics.
Everything around us is composed of tiny particles called atoms, which have a nucleus surrounded by electrons. Inside the nucleus are even smaller particles - neutrons and protons, which are made up of even tinier units called quarks.
In normal matter — the air we breathe, the water we drink, the newspaper you are reading — quarks come in sets of three units. But since the mid-1960s, some scientists have suspected that quarks can combine differently, such as in groups of five.
Quarks are too small to see, even with a microscope. So scientists have to use atom-smashing devices, such as the Continuous Electron Beam Accelerator Facility at Jefferson Lab, to study how the quarks interact.
A Japan-based group of scientists announced their pentaquark research in October, followed by a Russian group. At the Department of Energy's Jefferson Lab, a group of scientists from various countries decided to examine data from a 1999 experiment to see if they could find the same phenomenon as the Japanese.
"At first I was very skeptical," said Ken Hicks, an Ohio University professor who was part of the Jefferson Lab experiment. "There's a general bias against this type of particle existing because so many people have searched for it and not found anything."
In an underground cavern known as Experimental Hall B, scientists fired an electron beam through a target made up of a heavy version of hydrogen called deuterium. A cylindrical detector about 30 feet wide picked up volumes of information about how the subatomic particles reacted. Scientists then spent months sifting through computer data, pulling out evidence of pentaquarks.
Jefferson Lab will submit its findings in about two weeks to Physical Review Letters, a journal published by the American Physical Society. The journal recently published the Japanese group's findings, but Jefferson Lab's work will include more evidence, Hicks said.
Pentaquarks have short lives lasting a tiny fraction of a second. Hicks doubts that the pentaquark research will lead to a practical application in his lifetime.
That does not mean it is insignificant. Physics books may have to add the pentaquark as an exotic addition to the variety of subatomic particles. Over time, past discoveries in particle physics have led to breakthroughs in cancer treatment.
"It's not going to overturn the apple cart," he said. "But it's still an important step forward in our understanding of the forces between quarks."
Some scientific observers are still taking a wait-and-see approach. Andrew Sandorfi, senior physicist at Brookhaven National Laboratory in New York, said he will have "guarded excitement" about the research until the Japanese and Jefferson Lab groups follow-up with more experiments.
"I'm not generally a betting man, but in this case I would bet it will turn out that they're right," he said.