Continuing our first set of guest blogs at Chris Lintott’s Universe, this is the second
part of Alice’s trip around CERN. The first part is here.
The talk began with a description of the international co-operation involved, the 20 member states, and the Big Question they are investigating: “How Nature Really Works”. The lecturer described their branch of science as “Astro-Particle Physics”, or the origin of matter. The list of topics he put up at the beginning sounded so interesting that I just have to put up a list: particle physics, neutrino oscillation, lead nuclei collisions, anti-hydrogen radiation and spectroscopy, radioactive isotopes and neutron beams, accelerators and detectors.
The lecturer went on to focus on one of these: the accelerators and decectors. He claimed that the antihydrogen produced is the first that exists in the Universe since the “grand shoot-out” between matter and antimatter that occurred in the first minutes after the Big Bang, and that it is not yet confirmed whether it will show the same spectroscopic lines as hydrogen. This made us all sit up and frown because we’d had a lecture claiming that antimatter is exactly the same as matter, just with the charges reversed – that a galaxy we see through our telescopes could be antimatter, that the person sitting next to us could be antimatter; the only way we could tell is if we touched these things. Unfortunately all the antihydrogen so far created has far too much kinetic energy for it to be useful, and research is currently underway to see how to cool it. (We all wanted to know how it can be contained before it meets matter and they annihilate each other! I am still wondering. I also wonder if aliens have ever created antimatter or recreated the Big Bang, too, in a galaxy far, far away . . .)
We then focussed on one major experiment to come in 2008, the Large Hadron Collider. Particle accelerators such as the LHC were compared to electron microscopes: both can “see” smaller things than visible light. The particles they accelerate gain kinetic energy up until a point at which the kinetic energy can be interpreted as an increase in mass (E = mc2). Electrons accelerated by CERN, for example, have reached 20,000 times the mass of an ordinary electron. They then hit He(l) nuclei. This generates new particles – so new matter is created out of kinetic energy.
Energy and momentum have to be conserved. If very big particles are created, they may just “flip away” little ones, so it is necessary to make the heavy ones collide with each other. One method of detection is Cherenkov radiation – distorted atoms left behind a trail, like a visual sonic boom. In the LEP detector, the only thing that is not absorbed is muons. They can see them falling down like rain. The tour guide, later, talked a lot about muons . . .
In a previous CERN experiment, when an electron and a positron, they created a new pair of quarks. The lecturer spoke about quarks changing ‘flavour’ from up to down, for example in the creation of C14 in the Earth’s upper atmosphere, and the weak nuclear force and how it allows changes of particle (quark) identity, and the sizes of neutrinos and generations of matter which literature can describe better than I can. This was given as an explanation for matter rather than antimatter surviving in the Universe. (I’ve heard quite a few of those, most of which were stated to be the established truth! The most intriguing to date claimed that Dirac’s equation suggests that, for antimatter, time runs backwards*, and that antimatter decays faster than matter, hence the one in a billion matter particles left over after all the annihilations . . .)
* Someone told me two weeks ago that that’s tachyons, not antimatter.
Coming up over the weekend : The experiment itself