This article first appeared June 11 in Fermilab Today.
With 2 1/2 months of running the Large Hadron Collider's CMS experiment under our belts, our mid-range goals have evolved. Initially we were happy to record any interactions at a collision energy of 7 trillion electron volts. However, it’s important to recall that the beam energy is only one of the important parameters in a particle collider. A second critical parameter is the brightness of the beams, and, in the first few weeks of running, the brightness of the beams was tiny. Under these circumstances, the number of collisions per second was quite modest, and we could record every collision that occurred.
The amount of beam delivered has increased enormously. In the month and a half (45 days) since beginning operations, the amount of beam delivered is more than 10,000 times what we saw on the first day.
However, the beam brightness has steadily increased over the past two and a half months. It currently takes a minute to see as many collisions as we used to see in a day. Very soon, the same number of collisions will take seconds. Those of us of a certain age might remember the old I Love Lucy episode in which she and Ethel wrap candy. It starts out easily, but the rate quickly increases until they can no longer handle it and chaos ensues. This is essentially the situation in which the CMS detector collaborators find themselves.
Of course, this was anticipated. Today’s thousands of collisions per second are a far cry from the designed 800,000,000 collisions per second. To cope with the deluge, CMS designed an extensive trigger system. As the torrent of collisions occurs in the center of the detector, carefully designed electronics inspect them all and select those that are most likely to include a discovery. The LHC is now delivering enough beam that we must utilize the trigger system to record only a portion of the collisions.
This is a unique time in the lifetime of an experiment. About every week, the amount of beam delivered by the LHC doubles. With our trigger electronics doing their job, we look forward to seeing our data set grow in leaps and bounds.
by Don Lincoln
