Slashdot Mirror
New Particle Found, the Bottom-Most Bottomonium
PhysicsDavid writes "Collaborators on the BaBar experiment at the Stanford Linear Accelerator Center have detected and measured, for the first time after a 30-year search, the lowest energy particle of the 'bottomonium' family, called the eta-sub-b. Bottomonium consists of a bottom quark and an anti-bottom quark bound together by the strong force. The discovery fills in a missing piece of quark physics that will help reveal the nature and behavior of the quarks and the strong force."
When a bottom quark and an anti-bottom quark are pulled together by the strong force, they form a quark âoeatomâ-much like an electron and a proton come together under the electromagnetic force to create a hydrogen atom.
Anti-quarks don't behave like anti-matter, despite sharing that awesome prefix.
They exist in groups of two or three that create a neutral color charge. For example, a particle can consist of red, green, and blue or of blue and anti-blue.
They just have to be "color"-neutral so (red, green, blue) and (red, anti-red) are both allowed.
Who ordered that?
It is a doublet, also known as a meson. They're not long-lived, but they exist.
I have no idea why they didn't use the word 'meson' in the article. Bottomonium is a type of quarkonium, which is a type of meson.
Genocide Man -- Life is funny. Death is funnier. Mass murder can be hilarious.
Our stable particles are made of triplets. There are all kinds of doublets in the particle zoo; the fact that they are unstable makes them observable (since we usually detect not the particle but its decay).
I'm aging rapidly, I bought a new game and had no idea if my machine was good for it.
The same way protons and electrons avoid crashing into each other. The energy states are discontinuous and do not include zero. Once the bottomonium meson reaches its lowest state, it can't lose any more energy, so it can't get close enough to annihilate.
Genocide Man -- Life is funny. Death is funnier. Mass murder can be hilarious.
No, the antibottom quark is the bottom quark's antiparticle. It's just that antimatter doesn't work quite the way science fiction stories make it sound.
They will annihilate after some time (the particle's lifetime), but they can be bound together for some time before that happens. Another good example is the \pi^0 (neutral pion), which is made of up and anti-up (or down and anti-down) quarks. It decays after some time to two photons.
I don't know what is the lifetime of this \eta_b particle or its main decay branch (I haven't RTF BaBar's A and I'm not a QCD specialist), but it should be very short, and the main decay channel should be hadronic (ie, particle jets).
Bottom (and top and up and all the colours) are arbitrary names chosen by the scientists who discovered/theorized these particles. The names do not describe the properties of the particles in any way. You'll have to go ask them why they picked these names, but personally I think it's because they got bored of Greek and Latin.
The interesting question, IMHO, is: Was this particle predicted by anybody else's research?
Yes. It's called the standard model. It's not surprising that it was found ... it would have been more surprising if it hadn't been found eventually.
Actually, the top and bottom quarks were originally named truth and beauty. They were renamed to top and bottom because the original names were thought to be silly. Names like top and bottom count as sensible in the context of quantum mechanics.
I believe it was Niels Bohr who said that if you do not find quantum mechanics confusing you do not really understand it. But then, he didn't really understand it either :D (There's still more to learn/discover...)
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
The Earth orbits the Sun and does not get annihilated by being sucked into the middle of the sun despite being attracted to it by gravity. For the (sort of) the same reason bound states of matter/anti-matter particles can exist without the particles combining and annihilating each other.
The strong force is one of the four fundamental forces. They are gravitation, EM force, weak force and strong force.
Actually, under the right circumstances, anti-particles don't immediately self-destruct. Electrons and positrons (anti-electrons) can form an atom-like species, too, with half-lives on the order of 10^-7 to 10^-10 seconds. Way back in 1971, an entire review of positronium chemistry (ie chemistry of positron and electron as an ato-like species) was published in Angewandte Chemie, a major chemistry journal. (Page 179 for the international edition, published in English.) It's not my area of study, but I came across the review once when looking for something else in the same issue.
Abstract: In this progress report, the properties and behavior of the positron (positive electron, anti-electron) and of the positronium, a hydrogen atom containing a positron instead of a proton, are considered from the chemist's viewpoint. Examples are given to demonstrate the development of positronium chemistry, in aqueous solution and in the gaseous, liquid, and solid phases, with its problems and possibilities.
Not only did Gell-Mann like the sound of the word, but it was also because they came in triplets. The line from Joyce is "Three quarks for Muster Mark"
General Relativity: Space-time tells matter where to go; Matter tells space-time what shape to be.
No, anti-matter pretty much does work the way most Sci-Fi portrays it. However, quarks, while being what matter is composed of, are not matter in and of themselves and thus can behave differently.