Posted on 04/30/2003 1:05:30 PM PDT by alnitak
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Physicists find 'rebel' particle
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Physicists have found a new subatomic particle, named Ds (2317). It will help them better understand the building blocks of matter.
The particle consists of an unusual combination of more fundamental particles - quarks. Two quarks form Ds (2317) and, curiously, its properties are not what theory predicted. The announcement was made by physicist Antimo Palano to a packed auditorium at the Stanford Linear Accelerator Center (Slac) in the US. The discovery was made by the BaBar international consortium, which operates a detector at Slac that analyses debris from subatomic particle collisions. 'Back to the drawing boards' "Congratulations to BaBar," said Slac's director, Jonathan Dorfan. "The existence of the particle is not a surprise, but its mass is lower than expected. This result will send theorists back to their drawing boards."
Quarks are fundamental particles of which there are six types present in nature. The "up" and "down" quarks are the lightest, and are found within the nuclei of atoms of ordinary matter. There are also the "charm", "strange", as well as the "top" and "bottom" quarks. These are heavier than the up and down quarks. Quarks can also have antiparticles such as anti-down, etc. Heavier quarks were present in the early Universe and are created today in particle accelerators and in collisions of cosmic rays with atoms in the Earth's atmosphere. The Ds (2317) combines a charm quark with another heavy quark - an anti-strange quark. 'From unexpected directions' Physicists are hailing its discovery as important because it has unexpected properties that will provide insight into the force that binds the quarks together. This force, unlike most others in nature, becomes stronger as the distance between the two quarks increases. Marcello Giorgi, from the University of Pisa, Italy, who leads the BaBar collaboration, said: "Sometimes, the most exciting discoveries come from unexpected directions. There has been a buzz of excitement in the experiment in the past few weeks.
"We have discovered a new charm particle in an experiment designed to probe the difference between matter and antimatter using bottom quarks." Bob Cahn, a BaBar collaborator from Lawrence Berkeley National Laboratory, US, added: "The unexpected mass will make us look again at the forces between quarks and will stimulate new interest in charm-quark systems." And Dr Raymond Orbach, director of the US Energy Department's Office of Science, said: "The BaBar experiment continues to produce important new knowledge adding to our fundamental understanding of the structure of matter." |
You mean this guy?
It's not surprising that I'm not up to date in this exotic field, but I didn't expect to be totally blindsided by something. How long has this been going on? I assume this is the reason that no free quarks exist in nature. Still, it's a darn curious thing.
Since the universe was 10-5 seconds old, when the hadrons formed. ;^)
The theory was worked out in the 1960's. The key features of QCD are confinement and asymptotic freedom. Confinement means that the quarks are confined to hadrons, as you mentioned. Asymptotic freedom means that as the quarks get closer and closer together, the strong-force interaction between them asymptotically approaches zero, i.e. they behave as free particles as far as the strong force is concerned. (They still interact electromagnetically, etc.)
Both of these features are exhibited by a force that is directly proportional to distance. Asymptotic freedom is obvious--the force goes to zero at zero distance--but confinement is less obvious. That arises from the fact that the quarks have finite masses. If the force is proportional to distance, you can only pull a quark and an antiquark so far apart before you put in enough energy to pry a new quark-antiquark pair out of the vacuum. The color charges cancel those of the quarks you're pulling apart, and they "hadronize": the new quark pairs up with the old antiquark, the new antiquark pairs up with the quark, and you have two "colorless" mesons instead of two quarks.
The usual pedagogical analogy is to try to obtain monopoles by pulling a bar magnet apart. It just won't work.
Maybe the Teamsters were doing a preemptive strike in anticipation of this thread. ;^)
They are faculty PHD's in Subatomic Physics and also scriptwriters for "Barney's Playhouse"
Since the universe was 10-5 seconds old, when the hadrons formed. ;^) ========================================================
Well, if you can't be any more specific than that....
</sarcasm mode>
Your reply to PH was simply delightful; succinct and chock-full of fascinating info.
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