| The Large Hadron Collider Demistified |
| Blog - Physics | ||||||||||||||||||||
| Written by Nil Valls | ||||||||||||||||||||
| Monday, 12 April 2010 04:16 | ||||||||||||||||||||
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What's the LHC and where is it? LHC stands for Large Hadron Collider, the next generation particle accelerator. It's in a tunnel 27 km (16 mi) of circumference, 100 m (330 ft) underground, located on the Franco-swiss border at the Centre Européenne pour la Recherche Nucléaire (CERN), near Geneva, Switzerland.
What's its mission? To explore a new energy frontier and help us explain many enigmas about the nature of our universe, matter, and the fundamental interactions. In plain terms, how does the LHC work? To make things simple to understand, imagine two concentric circular highways separated by a median, one inside the other. Heavy traffic in the form of car "bunches" moves in opposite directions and really fast on each one. Suppose that the builders of the highways are very curious, and want to see the results of head-on collisions (for the sake of humaneness, let there be no human drivers, all of the cars are remotely controlled). All they need to do is to make the traffic flows cross at some points. Obviously, some cars make it through the crossing points intact (the lucky ones). For the rest, colliding at such high velocities is truly dramatic: First, the car bodies of the involved pair deform, then, things start breaking into small pieces and are shot out in every direction. Well, the LHC works just like that, except that the cars are tiny particles called "protons" and the roads are the "beam pipes." "Dipole magnets" act as the road lines, making the protons follow a circular trajectory and be directed to the interaction point. The collision of two cars (protons) at high energies is dramatic: their constituents break off, deform; they may fuse to other pieces, but ultimately, a spray of particles radiates out in all directions.
Why do you use protons? Other accelerators have collided different type of particles, such as electrons against positrons. Because charged particles lose kinetic energy when their trajectories are forced to bend, heavier particles offer a great advantage, as they don't lose as much energy. Hence, they can be pushed to greater speeds, thus storing more kinetic energy. The predecessor of the LHC, the Tevatron, collides protons against antiprotons, however, antiprotons are very hard to produce. Furthermore, protons have an inner structure of other particles called "quarks" and "gluons" that electrons don't have. This facilitates the study of certain interactions that have been very trendy in the field of particle physics lately. How fast do protons travel and collide against one another inside the LHC? The LHC set an energy record on March 30, 2010. Protons traveled at 99.9999964% the speed of light (299,792,477 meters a second or 186,282 miles a second), which corresponds to an energy of 3.5 trillion electron-volts (TeV). Because there are two beams of protons traveling in opposite directions, the energy of the collisions are doubled (7 TeV). The design energy of the LHC is twice that, i.e. 7 TeV per beam, or 14 TeV center-of-mass energy. At that energy, protons will be traveling at 99.9999991% the speed of light. We hope to achieve this objective within the next two years.
Okay, what is the point in all this? Well, it turns out that scientists don't know all of the ways in which the known and unknown pieces (particles) of the cars (protons) interact. This is important to curious people (like us) who can't sit still until learning the reason for which the universe is like it is. Therefore, scientists and engineers built cylindrical detectors around the interaction points (beam crossings) along the 27 km (16 mi) of the LHC. The cylindrical geometry allows us to capture almost every collision product. With a little bit of work, we can figure out the energy, velocity and mass of almost every piece. Then, with a lot of hard detective work (data analysis) we are able to reconstruct everything that happened from the moment of the collision, namely the "event." According to the Big Band theory, the conditions in the first fractions of a second of our universe were very similar to those found in the collisions of protons at such energies. Then, something bizarre and still unknown to us happened, which lead to the asymmetries that we observe nowadays: for instance, why isn't there just as much antimatter as there is matter? Why do objects have mass, and why is it always fixed for a particular object? Great, but is it really worth spending billions of dollars just to satisfy our curiosity? Absolutely! In the process of designing and building this sort of machines we realize the need for new technologies. The world wide web, for instance, emerged from CERN, as physicists needed a convenient way to share data among themselves. In fact, the Internet as we know it was greatly developed at CERN for the same purpose. Investing in particle beam technology has been crucial in medicine as well, since many therapies and scans are based on the principle of physics involved in accelerators. Alright, but I have more questions... No problem! Feel free to contact me here and I will try to answer them for you!
Comments (1)
1
Tuesday, 22 June 2010 12:09
Tim J.
Sweet, Nil. Thanks for the explanation. Very cool. Hope you're having a good summer so far.
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