Greetings from Barcelona, where the LHCP 2013 conference is underway. I wanted to mention a couple of the opening remarks made by CERN’s Sergio Bertolucci and Mirko Pojer, both of whom spoke about the near-term and medium-term future of the Large Hadron Collider [LHC].
It’s worth taking a moment to review what happened in the LHC’s first run. During its first few years, the LHC was initially intended to run at around 14 TeV of energy in each proton-proton collision, and at a moderate collision rate. But shortly after beams were turned on, and before there were any collisions, there occurred the famous accident of September 19, 2008. The ensuing investigation of the cause revealed flaws in the connections between the superconducting magnets, as well as in the system that protects the machine against the effect of a magnet losing its superconductivity (called a “quench”; quenches are expected to happen occasionally, but they have to be controlled.) To keep the machine safe from further problems, it was decided to run the machine at 7 TeV per collision, and make up (in part) for the lower energy by running at a higher collision rate. Then:
- Late 2009: beams were restarted at 2.2 TeV per collision.
- 2010: a small number of collisions and a few new experimental results were obtained at 7 TeV per collision
- 2011: a large number of collisions (corresponding to nearly 100,000 Higgs particles per experiment [i.e. in ATLAS and CMS]) were obtained at 7 TeV per collision
- 2012: an even larger number of collisions (corresponding to over 400,000 Higgs particles per experiment) were obtained at 8 TeV per collision.
All in all, this “Run 1” of the LHC is widely viewed as enormously successful. For one thing, it showed that (excepting only the flawed but fixable magnet connections) the LHC is an excellent machine and works beautifully. A high collision rate was indeed achieved, and this, combined with the quality of the experimental detectors and the cleverness of the experimental physicists, was sufficient for discovery of and initial study of what is now referred to as a “Standard Model-like Higgs particle”, as well as for ruling out a wide range of variants of certain speculative ideas [here are a couple of examples.]
Currently, the LHC is shut down for repairs and upgrades, in preparation for Run 2, which will begin in 2015. The machine has been warmed up to room temperature (normally its magnets have to be kept at 1.9 Kelvin, i.e 1.9 degrees Celsius above absolute zero), and, among many adjustments, all of those potentially problematic connections between magnets are being improved, to make it safer for the machine to run at higher energy per collision.
So here’s the update — I hesitate to call this “news”, since none of this very surprising to those who’ve been following events in detail. The plan, according to Bertolucci and to Pojer, includes the following
- When Run 2 starts in 2015, the energy per collision will probably be 13 TeV, with the possibility of increasing this toward the design energy of 14 TeV later in Run 2. This was more or less expected, given what was learned about the LHC’s superconducting magnets a few years ago: some of these crucial magnets may have quenches too often when operating at 14 TeV conditions, making the accelerator too inefficient at that energy.
- A big question that is still not decided (and may not be decided until direct experience is gained in 2015) is whether it is better to run with collisions every 50 nanoseconds [billionths of a second], as in 2011-2012, or every 25 nanoseconds, as was the original design for the LHC. The latter is better for the operation of the experimental detectors and the analysis of the data, but poses more challenges for operating the LHC, and may cause the proton beams to be less stable. Studies on this question may be ongoing throughout a good part of 2015.
- Run 2 is currently planned for 2015-2017, but as Pojer reminded us, 2015 will involve starting up the machine at a new energy and collision rate, and so a lot of time in 2015 will be spent on making the machine work properly and efficiently. Somewhat as in 2010, which was a year of pilot running before large amounts of data were obtained in 2011-2012, it is likely that 2015 will also be a year of relatively low data rate. Most of the data in the next run will appear in 2016-2017. The bottom line is that although there will be new data in 2015, one should remember not to expect overly much news in that first year.
Of course the precise dates and plans may shift. Life being what it is, it would not be surprising if some of the challenges are a bit worse than expected; this could delay the start of Run 2 by a few months, or require a slightly lower energy at the start. Nor would it be surprising if Run 2 extends into 2018. But if Run 1 (and the experience at other accelerators) is any guide, then even though some things won’t go as well as hoped, others will go better than expected.