I know what you are thinking. The LHC is back in action, at the highest energies ever! Where are the results? Where are all the blog posts?
Back in action, yes, but restarting the LHC is a very measured process. For one thing, when running at the highest beam energies ever achieved, we have to be very careful about how we operate the machine, lest we inadvertently damage it with beams that are mis-steered for whatever reason. The intensity of the beams — how many particles are circulating — is being incrementally increased with successive fills of the machine. Remember that the beam is bunched — the proton beams aren’t continuous streams of protons, but collections that are just a few centimeters long, spaced out by at least 750 centimeters. The LHC started last week with only three proton bunches in each beam, only two of which were actually colliding at an interaction point. Since then, the LHC team has gone to 13 bunches per beam, and then 39 bunches per beam. Full-on operations will be more like 1380 bunches per beam. So at the moment, the beams are of very low intensity, meaning that there are not that many collisions happening, and not that much physics to do.
What’s more, the experiments have much to do also to prepare for the higher collision rates. In particular, there is the matter of “timing in” all the detectors. Information coming from each individual component of a large experiment such as CMS takes some time to reach the data acquisition system, and it’s important to understand how long that time is, and to get all of the components synchronized. If you don’t have this right, then you might not be getting the optimal information out of each component, or worse still, you could end up mixing up information from different bunch crossings, which would be disastrous. This, along with other calibration work, is an important focus during this period of low-intensity beams.
But even if all these things were working right out of the box, we’d still have a long way to go until we had some scientific results. As noted already, the beam intensities have been low, so there aren’t that many collisions to examine. There is much work to do yet in understanding the basics in a revised detector operating at a higher beam energy, such as how to identify electrons and muons once again. And even once that’s done, it will take a while to make measurements and fully vet them before they could be made public in any way.
So, be patient, everyone! The accelerator scientists and the experimenters are hard at work to bring you a great LHC run! Next week, the LHC takes a break for maintenance work, and that will be followed by a “scrubbing run”, the goal of which is to improve the vacuum in the LHC beam pipe. That will allow higher-intensity beams, and position us to take data that will get the science moving once again.
