Last week, CERN held its annual workshop at Chamonix to consider the LHC run plan for this year and future years. The results of the workshop, and thus the new run plan, were announced today by CERN management. Over the past few months, there has been much speculation about what the findings would be. One significant rumor turned out not to be true, while another one is true.
Many people had expected that the center-of-mass energy of the LHC would be increased from 7 TeV to 8 TeV in 2011; indeed, experimenters were already starting to make plans for such a scenario. The 1/7 increase in energy would also increase the rate of the production of potential new particles, like the Higgs boson, by something like an equivalent amount, and one thing (among many) that we’ve learned from the Tevatron is that a ten percent-ish improvement really can have a significant impact. However, this will not be happening — the LHC energy will remain at 7 TeV for this year. The accelerator physicists studying the issue came to the conclusion that while the probability of failures that could cause damage to the machine are still low at 8 TeV, those failures could be catastrophic enough to wipe out the run for the entire year. Thus, the overall risk was considered too great.
Now, this non-change in the energy actually changes a lot of things for the experiments! It had been possible that the 2010 run was going to be the last run ever at 7 TeV, and thus the last word on some topics. “Is there a Higgs boson?” is a question that you can attack at any energy, but “What’s the production rate of particle X at 7 TeV collision energy?” can be answered only at, well, 7 TeV. Thus, many topics that appeared to be closed have now been re-opened, and by the end of 2011 can be addressed with at least 30 times more data than we had in 2010. This might make it worth revisiting some questions that were not answered well enough with the 2010 data, and thus might change the plans of some researchers for this year.
Then, there is the rumor that turned out to be true: the year-long shutdown of the LHC that had been planned for 2012 has now been moved to 2013. This is good news for all of us: if you want to discover something, you need as much data as you can get your hands on, and now that data is going to come sooner rather than later. Now, it is true that we’ll still be at a collision energy of 7 or 8 TeV during 2012, rather than the 14 TeV that we’ll have after the 2013 shutdown, and of course that big energy increment is going to help. But at the same time, it is looking more and more like we can “make it up in volume.” The detectors are working very well, the collaborations are turning out results quickly, and it seems likely that the experiments should be able to squeeze every last bit out of the data in the search for new physics. Of course this change of plans does have further implications. We had been figuring that we would need less operational staffing in 2012 because we wouldn’t run, and also that we wouldn’t need to buy so many more computers that year because there wouldn’t be any data to analyze them on. Now this is not true, and we already have to start thinking about a period of operations that’s “only” a year away.
But for now, the focus is on 2011 — with much higher collision rates this year than last year, we are going to be very busy!
