Physicists discover new form of matter (Die Welt)

Physicists discover new form of matter

The "Pentaquark" consists of five quarks — researchers want to create even larger "molecules" from quarks.

Newport News — Physicists in Japan and in the United States independently discovered a new exotic form of matter — a particle consisting of five quarks, which they call a "pentaquark". Scientists have searched for this elementary particle for a quarter century. In the SPring-8 research center in Aioi near Osaka and in the Thomas Jefferson National Lab in Newport News, Virginia they succeeded in creating and in detecting this new form of matter.

Quarks are fundamental building blocks of matter. Protons and neutrons present in the atomic nuclei of the ordinary matter around us are made of three quarks each. Quarks may thus be considered as the "backbone" of the material world. Physicists also already knew about elementary particles made from two quarks — so-called mesons.

The Standard Model, as the generally accepted theory of modern particle physics, does not forbid the existence of quintuples of quarks. Physicists are now using powerful particle accelerators in an attempt to fuse a quark triplet and a quark doublet to a quark quintuplet.

"One could say that, for the first time, a molecule of quarks was created," says particle physicist Frank Wilzcek of the Massachusetts Institute of Technology in Boston. "This is really a milestone in physics."

To this date, the properties of the quarks remain a mystery. While all other forces in nature, such as gravitation or the attractive force created by electrical charge, decrease with increasing distance between the partners, the quarks' attractive force increases the further they are pulled apart from each other. This "strong attraction" of the quarks has as consequence that they cannot be isolated from each other. The three quarks in a proton may swirl around each other, however they are shackled to each other by invisible "springs" so that even the most gigantic forces are not enough to separate them. This is the reason why a single isolated quark has never been observed.

The fusing of quark douplets and triplets to a pentaquark requires an enormous experimental effort. The Japanese scientists can claim to be "first". However, shortly after their success, researchers at the Jefferson Lab were also successful in creating the pentaquark which, as expected, is 5/3 times heavier than a proton. Armed with these new insights scientists hope to come to a better understanding of quark properties, and perhaps create even larger "quark molecules".

The confirmation of this discovery by two groups, working with very different experimental arrangements, makes it very likely that this success is real. And this could be worth the Nobel Prize. Says physicist Peter Barnes of the Los Alamos National Laboratory: "It has the potential of being something really important."

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