Behold the pentaquark

[mrz]

Behold the pentaquark
By Dr David Whitehouse
BBC News Online science editor


Physicists have discovered a new class of subatomic particle that will provide unexpected insights into the fundamental building blocks of matter.

Theory predicted where the particle should emerge
The discovery involves quarks - particles that make up the protons and neutrons usually found in the nuclei of atoms.

The new particle is the so-called pentaquark - five quarks in formation. Until now, physicists had only seen quarks packed into two- or three-quark combinations.

They say that the discovery of this new particle should have far-reaching consequences for our understanding of the structure of matter.

Confirmed discovery

Until recently, no firm evidence of pentaquarks existed, even though physicists have searched for these objects for over 30 years.

In 2002, the first tentative evidence of the pentaquark was put forward at an international scientific conference in Japan. Earlier this year a report of this work was submitted for publication to the journal Physical Review Letters.

The report says that pentaquarks were created by blasting carbon atoms with X-rays by a Japanese team, led by Takashi Nakano of Osaka University.

Other evidence for the pentaquark has recently been reported by other experiments, with perhaps the strongest evidence coming from the Jefferson Lab in Virginia, US.

Physicist Ken Hicks of Ohio University, who took part in both the experiment and the confirmatory work at the Jefferson Lab, says it took him two months to convince himself that the pentaquark was real.

We are quarks

More than 99.9% of the mass of everyday objects is contained within the nucleus of atoms. This means that most of your body mass comes from subatomic particles that are made up of quarks.


Carbon atoms were struck with X-rays
There are hundreds of subatomic particles known and most are composites of simpler particles. They all fit into two categories - baryons and mesons.

Baryons are made of three quarks and mesons are comprised of two quarks - a quark and an anti-quark.

For a long time scientists have been puzzled as to why only these quark combinations existed. Some predicted other combinations such as the pentaquark which consists of five quarks, including an anti-quark.

The discovery of the pentaquark, also known as a new exotic baryon state, should have far-reaching consequences for our theory of particle interactions that attempt to explain the structure of matter.


Hmm ik zie het vast weer veels te simpel maar zonder al teveel carbon in je lichaam ben je dus ongevoelig voor "liefde" van anderen? Of is moe worden geen gevolg van liefde? :duizelig:

http://news.bbc.co.uk/2/hi/science/nature/3034754.stm

[mrz]

Pentaquark discovery confounds sceptics
17:08 02 July 03
NewScientist.com news service

A brand new sub-atomic particle called the pentaquark has made its debut at labs in Japan and the US. Unlike ordinary protons and neutrons in atomic nuclei, which contain three quarks, the pentaquark has five.

The result has delighted Russian physicists who predicted the mass of the particle in 1997, but met a lot of scepticism from their peers.

"It was not an easy decision to publish our paper six years ago, but eventually we went ahead despite resistance in the community," says Maxim Polyakov, now at the Ruhr University in Bochum, Germany. "It is a great pleasure that our theory seems to be correct."

The pentaquark may have been common in the Universe just after the Big Bang, 14 billion years ago. And further studies of it could help patch up some holes in the theory of the strong force that glues quarks together in particles like protons and neutrons.

"The discovery is not just getting another animal in a zoo," says Polyakov. "It will seriously influence our understanding of what the ordinary proton and neutron are made of and 'how they work'."


Up and down


Particles that contain quarks fall into two main categories. "Baryons", such as stable protons and neutrons in atomic nuclei, contain three quarks. "Mesons" contain two, a quark and an anti-quark, but they are never stable and vanish in a split second.

Theory does not forbid the existence of a short-lived five-quark particle, and scientists have looked for them in the debris of particle-smasher experiments for decades. Having turned up nothing, they were beginning to think they had missed some rule of nature that bans pentaquarks from forming.


But they got a new lead in 1997, thanks to work by Polyakov, Dmitri Diakonov and Victor Petrov at the Petersburg Nuclear Physics Institute in Russia. They predicted that one particular pentaquark - containing two "up" quarks, two "down" quarks and an "anti-strange" quark - should be about 1.5 times as heavy as a proton.

Now scientists say they have spotted a particle with the right mass and all the hallmarks of a pentaquark. A team led by Takashi Nakano of Osaka University and another led by Ken Hicks at the Jefferson lab in Virginia made a high-energy gamma ray interact with a neutron to create a meson and a pentaquark. The pentaquark survived for only about 10-20 seconds before decaying into a meson and a neutron.

The Japanese results appear this week in Physical Review Letters. Experiments at a Moscow lab have also found evidence for this pentaquark. "The absence of these multiquark particles has bothered physicists for the last forty years," Polyakov told New Scientist. "Now it is over."

But for the moment, physicists say they know very little about the new particle. "The discovery of the pentaquark is really too new," says Hicks. "We haven't had time to think about the implications."


Hazel Muir

http://www.newscientist.com/news/news.jsp?id=ns99993903