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Physicists have helped discover a new state of matter that may shed light on the fabric of the universe

12.01.2004

The University team of 14 is part of a group of 300 physicists from 13 countries known as the ‘Belle collaboration’. They have discovered a sub-atomic particle that they are having difficulty explaining and difficulty fitting with any current theory that attempts to describe matter.

Their research will be published in Physical Review Letters (in press).

“It could mean some of the standard and accepted theories on matter will need to be modified to incorporate some new physics,” says University of Melbourne doctoral student in physics and Belle team member, Mr Craig Everton.

The sub-atomic particle they believe could be a meson. A meson by itself is a relatively obscure particle, but one which is made up of quarks, the basic building blocks of not just life, but everything that exists in this universe – as we know it.

This ‘mystery meson’ weighs about the same as a single atom of helium (a heavy-weight by sub-atomic particle standards) and exists for only about one billionth of a trillionth of a second before it decays to other longer-lived, more familiar particles.

“This may seem extremely short-lived by any human standard, but it is nearly an eternity for a sub-atomic particle this heavy,” says Everton.

The team discovered their meson, technically known as X(3872), using a giant electron collider, or the High Energy Accelerator Research organisation (KEK) in Tsukuba, Japan.

This particular electron collider is three kilometres in circumference and acts as a meson factory, churning out what are known a ‘B mesons’ that are studied by physicists worldwide.

“We are in the business of studying quarks, as it is thought they hold the key to understanding many of the principle elements of how all matter in the universe (including life) is constructed,” says Everton.

“Mesons have little direct bearing on life itself. They exist because they can,” he says.

“But to study quarks we need to understand mesons, and X(3872) has got the international physics community both baffled and excited.

“Particle physics is now beginning to merge together the disciplines of cosmology and astrophysics and give new perspectives on stuff such as the evolution and construction of the universe and the nature of dark matter.”

A normal meson particle is comprised of a quark and an antiquark that are held together by the ‘color’ force, or ‘strong’ force because it is the most powerful force in nature.

The large variety of meson particles that have been found to date reflect the many different ways that these combinations can be accomplished. The mass and the decay properties of X(3872), however, do not match theoretical expectations for any conceivable quark-antiquark arrangement.

Theoretical physicists around the world are considering a number of potential explanations. These include modifications to the theory of the color force, or the possibility that the X(3872) is the first example to be seen of a new type of meson, one that is made from four quarks. That is, two quarks and two antiquarks.

“This new sub-atomic particle will mean either the accepted ‘Standard Model’ for the explanation of matter needs to be modified to incorporate new physics, or it could be the first ever discovery of long sought after 4-quark particle. This would be a relief for many as it would confirm the Standard Model,” says Everton.

The Belle discovery was recently confirmed by researchers with the CDF (Collider Detector at Fermilab) experiment at the Fermi National Accelerator Laboratory in Illinois, home of the Tevatron, the world’s largest electron collider.