In our story about how protons find their way into the LHC, we spent a fair bit of time emphasizing the importance of the machine's luminosity, which is a rough measure of how many collisions it produces per unit of time. The greater the luminosity, the more data that physicists will have to work with, and the greater the chance that they'll catch a rare event that hints at some fundamentally new physics. The LHC was designed to have a very high luminosity, which is even more exciting to many physicists than the machine's record-setting 7TeV collision energies.

But, at least to begin with, the people running the collider were very cautious with their new machine. Protons get injected into the main LHC ring in bunches and the first runs of the hardware kept the bunch number low. This allowed some time to measure and tweak the performance of the hardware, ensuring that everything was working properly before it was pushed by the addition of more proton bunches. Somewhere around the start of August, as the graph above indicates, that caution came to an end, and the luminosity of the LHC started to rise dramatically as more proton bunches were injected for each run. In recent days, each physics run has produced a large vertical leap in the total number of collisions recorded.

The luminosity of colliders is, for reasons physicists seem loath to explain, measured in units called inverse barns (typically, the numbers are in the inverse pico- and femtobarn range). After barely registering a fraction of an inverse picobarn for several months, the numbers have shot up over the past few weeks, and have now reached nearly 3.5 pb-1. For context, however, the Tevatron's long operational history has allowed it collect about 10 inverse femtobarns; the LHC won't get to a fb-1 until sometime later next year.

The other thing to note is that there's a growing difference between the luminosity delivered to the detectors and the amount that's actually been recorded. That's because, as the luminosity increases, it outstrips the ability of the LHC's network and storage grids to capture it. With the increased luminosity, the hardware and software at the detectors need to start filtering out well understood events, enabling researchers to focus on those most likely to tell us something new. As the luminosity increases further, the gap between the two should grow larger.