Antihelium Discovered By STAR 94
Medevilae writes with this excerpt from ScienceBlog:
"Eighteen examples of the heaviest antiparticle ever found, the nucleus of antihelium-4, have been made in the STAR experiment at RHIC, the Relativistic Heavy Ion Collider at the US Department of Energy's Brookhaven National Laboratory. ... Ordinary nuclei of helium atoms consist of two protons and two neutrons. Called alpha particles when emitted in radioactive decays, they were found in this form by Ernest Rutherford well over a century ago. The nucleus of antihelium-4 (the anti-alpha) contains two antiprotons bound with two antineutrons. ... 'It’s likely that antihelium will be the heaviest antiparticle seen in an accelerator for some time to come,' says STAR Collaboration member Xiangming Sun of Berkeley Lab’s NSD. 'After antihelium the next stable antimatter nucleus would be antilithium, and the production rate for antilithium in an accelerator is expected to be well over two million times less than for antihelium.'"
Re:Okay, I get some of this . . . (Score:5, Informative)
An anti-neutron is like a neutron, but instead of being composed of an up quark and two down quarks, it is composed of an anti-up quark and two anti-down quarks. Each of the quarks has an electrical charge -- they add in such a way that the sum is zero. For an anti-neutron, the quarks have the opposite charges as before, but they still all add to zero.
Re:Okay, I get some of this . . . (Score:4, Informative)
"Ordinary" neutrons would annihilate anti-protons if they got sufficiently close, i.e., to form a nucleus. On a semi-related note, I remember reading that charge-reversal isn't the only property of antimatter; it can also be thought of like quantum spin-reversal or time-reversal (ordinary matter going backwards in time). Weird stuff.
Re:Here comes the alchemy (Score:4, Informative)
http://en.wikipedia.org/wiki/Synthesis_of_noble_metals#Gold_synthesis_from_Mercury [wikipedia.org]
We already have made gold....
Re:Okay, I get some of this . . . (Score:4, Informative)
On a semi-related note, I remember reading that charge-reversal isn't the only property of antimatter; it can also be thought of like quantum spin-reversal or time-reversal (ordinary matter going backwards in time).
That's really the most correct way to think about it. Take the electron, for instance. It always repels other electrons, period. If you get an electron going backward in time, it still repels other electrons, but because time is flipped around it looks like an attraction. It is not just charge but ALL the properties of the particle which are reversed.
In the case of a neutron, imagine it not as a neutral particle but as an electric dipole (tripole really, but for simplicity imagine it's a dipole). When you get sufficiently far away from it, the net electric field is pretty much zero. It's not until you look at it very closely that you see the two opposite charges. Now, you can reverse those charges and still, at big distances it looks like there's no field. But you did in fact reverse the charges.