Pedagoguery

The most powerful microscope in the world is set to begin operating later this year. Measuring 8.6 kilometers in diameter, it is a ring of superconducting electromagnets surrounding a circular tube which contains a vacuum situated underground at the border between Switzerland and France near Geneva. It is the Large Hadron Collider, or LHC, and it's goal is to plumb the tiniest bits of matter to (among other things) help us explain why mass exists.

The LHC will be the most powerful particle accelerator yet built. It will be the first to be able to accelerate particles into the TeV range (one trillion electron Volts, or 10¹² electron Volts). To compare, the energy contained within the mass of a proton is about one thousandth of a TeV, while the most massive confirmed particle in the Standard Model is the Top quark, at 0.171 TeV.

The LHC will collide protons. (Protons are in the class of particles called hadrons, thus the name of the collider). Protons are produced and fed into a small accelerator called the Proton Synchrotron. From there, they are fed into a larger accelerator called the Super Proton Synchrotron or SPS. At this point, they will be traveling at 99.99975% of the speed of light. The SPS will feed bunches of protons into opposite directions into the main accelerator, the LHC, which will further boost them to 99.9999991% of the speed of light – a 16-fold increase in energy. Over 2800 bunches of protons will be circulating within the LHC at any one time, and the streams will cross at four different locations within the collider, crossing over 31 million times per second. At each crossing, scientists expect to see about 20 collisions, each generating about 1.5 megabytes of data. That's nearly one billion MB of data, or one Petabyte per second. As cheap as computer storage is these days, that much will quickly overwhelm available storage, so the biggest challenge the builders of the LHC had to face is how to discard the majority of data that is not of interest. What scientists are really interested is evidence of the Higgs particle, which they expect to produce every 2.5 seconds at full beam intensity.

At each of the four collision points is a detector. These detectors are massive structures, which is necessary for them to detect the high energy particles and decay products produced in the collision. The first one is called the CMS, or Compact Muon Solenoid. It is a general purpose detector. The LHCb, however, is tuned to look for bottom quarks and anti-quarks. It's goal is to try to determine why the universe has a slight overabundance of matter as compared to anti-matter. The ATLAS (A Toroidal LHC AparatuS) is a second general purpose detector, which is based on huge toroidal magnets as opposed to the more standard barrel-shaped solenoid. Finally, there is ALICE (A Large Ion Collider Experiment) studies the proton-proton collisions as a reference point for later studying collisions of lead nuclei. These collisions produce primordial fireballs called a quark-gluon plasma, which mirror conditions in the very early universe.

Data is filtered through a sophisticated set of criteria. Of the 31 million events per second, the first trigger selects 100,000 events per second based on isolated features in the data. The rest are discarded. The second trigger looks at the events as a whole and selects 100 events per second and sends those onto the analysis grid. This grid is a collection of computers, both at CERN (the agency in charge of the LHC), and at universities around the world. The data first hits something called Tier 0, which is a set of thousands of computers at CER, where the data is immediately archived. This data is then made available to the Tier 1 sites over 10-gigabit-per-second optical lines. Tier 1 consists of major laboratories all over the world. The Tier 1 sites then make the data available to the Tier 2 sites at universities and institutes world over, where data analysis is performed.

The engineering and scientific expertise that went into building the LHC is nothing short of phenomenal, and it will hopefully provide a fount of new information on the fundamental building blocks of matter for some time to come.

Next time, our galaxy is on a collision course with the Andromeda galaxy. What will happen when we get there?