As has been reported elsewhere, the LHC is off and running again. Yesterday we saw the first stable beam collisions of the year. So far, collision rates are extremely small, and the detectors are just being roused from their winter slumber, so there is certainly no physics news to report yet. Over the next few days and weeks, the LHC will, fill by fill, increase the number of proton bunches circulating in the machine, and thus the collision rates. Meanwhile, the experiments will check that all of the detector elements are functioning and calibrated, which will allow us to get back to our full menu of work.
So what can we expect in the year to come? Here are a few things that I could think of.
The standard model, again. The LHC has increased the collision energy from 7 to 8 TeV, meaning that once again we have the highest-energy collisions ever created in a controlled experimental environment. One of the first things that happened when we started taking 7 TeV data was a full exploration of the production of known particles, to see that the rates etc. matched the predictions of the well-established and well-tested standard model. Now that we’re at 8 TeV, we’re going to do it all over again. This isn’t going to be making the front page of the newspaper, but it is critical work that must be done; if you can’t show that you understand the “known” physics, you can’t argue that you are seeing any kind of new physics.
OK, so is there a Higgs boson or not? This one will make the front page of the newspaper! As we last saw, CMS and ATLAS (and the Tevatron experiments) have results that suggest that we might be just on the edge of observing the long-awaited Higgs boson. Or perhaps not; everyone agrees that these results might be fluctuations that could well disappear when a larger dataset is analyzed. The expected production rate for a Higgs boson is greater with 8 TeV collisions than 7 TeV, and we hope to record at least three times as much data as we did last year. By the end of 2012, we should finally have an answer to the Higgs question.
The race for Bs. Here is another place where CMS, LHCb and perhaps ATLAS are just on the edge of making a discovery. The decay of the Bs meson to a pair of muons is expected in the standard model at a very low rate. This decay is particularly sensitive to effects from physics beyond the standard model, which could cause the rate to be either higher or lower than that predicted by the SM. It won’t take that much more data for each of the experiments to be able to observe the decay at the predicted rate…if that is indeed what happens. This could well come down to who can process and analyze data most quickly.
How’s that pileup thing working for you? To get more data this year than last year, the LHC will be colliding more protons at a time. Every collision of interest will be accompanied by debris from additional uninteresting collisions. This puts a strain on just about every aspect of the experiment — the volume of the data that must be read out, the complexity of event reconstruction, the requirements on computing resources, and the sophistication of the final data analyses. The sensitivity of many analyses can be degraded by this “pileup” of additional collisions. The experiments will have to be able to control all of these factors to get results out.
Will we ever find anything? It’s true; every search for new particles at the LHC has come up dry so far. We’ll try again this year, with a lot more going for us. Just like with the Higgs, pretty much any new particle will be produced at a higher rate at the higher collision energy, and we’ll also have much more data to look at. And with 2012 being the last year of LHC operations before a two-year long shutdown, we’ll be pulling out all the stops in the searches.
What will be ready for “summer” conferences? The next big public landmark for presenting new results will be the 2012 International Conference on High Energy Physics, which starts on July 4 in Melbourne, Australia. (This is traditionally a summer conference, but in the Southern Hemisphere it will be a winter conference, although it seems winter is mild in Melbourne, at least by Nebraska standards.) There will be about three months of LHC operations before then. What sort of results will be ready in time to show at that forum? Will anyone be able to produce a discovery by that time. I think it’s going to be very challenging, but who knows? (I got asked to co-organize one of the ICHEP parallel tracks, so I will be attending — very exciting! I will be sure to blog and tweet as much as I can from there, assuming my computer works when it is upside down.)
OK, readers — what are you expecting from the LHC this year? We welcome your comments.
