Using ROOT’s Virtual Monte-Carlo (VMC) interface allows a high energy physics simulation to be built (almost) independently of the transport package used. One can write a single simulation and alter which Monte-Carlo transport package (Geant3, Geant4, FLUKA) is utilized in the simulation by altering a single line of code. This allows one to test a simulation’s results against other transport packages in a hassle-free and dependable manner. I first adopted this approach while at CERN, working on a simulation intended to verify Geant3’s treatment of delta-rays and found anomalous behaviour. A quick change to the Geant4 transport package resulted in correct behaviour, leaving me to wonder just how this might affect ALICE’s inner tracking system (More on that later). After getting ROOT, geant3, FLUKA, geant4 and the relevant VMC packages to compile and run nicely on Scientific Linux and Ubuntu, I decided to have another go at setting up the VMC environment in MacOS 10.6 (Snow Leopard) on my home machine. Snow Leopard is a genuine 64-bit operating system (uname -m reports x86_64, system type is macosx64) so one might expect some troubles in the compilation process. Fortunately the process was relatively simple in the end. One must install the developer tools (or XCode) that come with the Snow Leopard install DVD, as well as gfortran. Read more…
Well, I managed to get accepted into the CERN Summer Student Programme for 2009. Thank goodness. It’s two and a half months of lectures and projects at CERN in Geneva. This is about the best opportunity for a young physicist and should really open a lot of doors for future studies. Unfortunately the LHC itself will not be operational by the time I arrive so no actual data to mess with, but there will be a full-scale simulation conducted in July that will provide some excellent data for my thesis. And the money is great too! 
February 26th, 2009
Angus
From now on I am going to write an entry each week explaining complex physical phenomenon, hopefully in a way in which anyone (even my mother…) can understand, as long as they put their mind to it. As many diagrams as necessary will be produced, however the number of formulae per entry is limited to one. For this week’s entry I have chosen “Jet Suppression in Heavy Ion Collisions” as it is something that has a rather daunting name but can be understood reasonably easily with the aid of diagrams.
First things first: “Heavy Ion Collisions” are what modern particle accelerators (RHIC or the doomsday device that is the Large Hadron Collider at CERN, Geneva) are all about. Basically, two atoms (or to be specific: ions, which are basically atoms with some electrons stripped off) of a “heavy” element such as lead or gold are bashed against each other at very high energy (basically, speeds that are 99.99% of the speed of light, 300 000km/s).
Doing this allows us to see what’s inside the atoms. On the first level, atoms consist of a nucleus and electrons. Inside the nucleus there are protons (positively charged) and neutrons (uncharged). But why stop there? Inside a proton or neutron there are 3 particles known as quarks. These are (as far as we know) the most elementary building blocks of matter. These are shown in the diagram on the left. The quarks are held together by gluons, which can be thought of as the glue that group the quarks and give the proton or neutron its structure. Read more…
The greatest thing about the Stellenbosch Institute of Advanced Study (STIAS) is undoubtedly the catering. It makes conferences a pleasure. I’ve never eaten so well so consistently before. I’ve eaten better food, but if one was to take the time averaged taste factor$<f>$ then it would be far higher than my usual veggie hotdog lifestyle. Anyway, the conference in question was a 4 day workshop on lasers and accelerators. The topics ranged from using lasers to accelerate electrons to GeV energy levels to using lasers in fusion reactions for energy production (unfortunately way away from being viable at the moment). It’s always nice to see a completely different section of physics and the speakers did an excellent job in giving those of us who had little idea on the applications of lasers an overview and an understanding on how and why people are building such enormous lasers.
The PS3 is quite something. It currently runs my simple Metropolis algorithm of the Ising model 22x faster than my Core2 6450 (not a beast of a machine but still). Although I have my suspicions that the more complicated (and memory hungry) Wang-Landau algorithm that I’m trying to implement will not be quite as successful. It requires more communication between the cores and that might cause some headaches. Unless one successfully splits the density of states up into sections and processes these independently, but then one must be sure to avoid systematic statistical errors
Quantum Mechanics:
Schrodinger’s Time-Dependent Equation:
$ihbarfrac{partial}{partial t}left|Psi(t)right>=Hleft|Psi(t)right>$
Planck Constant:
$h =6.62606896(33) times 10^{-34}mbox{J}cdotmbox{s} = 4.135 667 33(10) times10^{-15}mbox{eV}cdotmbox{s}.$
Reduced Planck Constant:
$hbar equiv frac{h}{2pi} = 1.054 571 628(53)times10^{-34} mbox{J}cdotmbox{s} = 6.582 118 99(16) times10^{-16} mbox{eV}cdotmbox{s}$
Heisenberg’s Uncertainty Principle:
$Delta x Delta p ge frac{hbar}{2}$
I’ve written an essay on quantum computing. It’s not great but there’s a lot of content in it. If you’re interested in quantum computers I suggest you also have a look at the references at the end of the essay. Note you should understand some quantum mechanics or at least Hilbert spaces before attempting to read this, or it will all seem like nonsense. One, Zero and So Much More