LHC Run 2 – reaching the top of the learning curve

As the LHC Physics conference gets underway in St Petersburg, it’s a good time to take stock of where things stand with Run 2.

 For all those involved with operating the LHC and its experiments in this new energy and intensity regime, 2015 was always going to be a learning curve. And learning we most certainly are. The main objective for this year has always been to set up the machine and experiments for production running at high energy and high intensity in 2016, 17 and 18.  That said, the experiments have all been able to collect quality data at 13 TeV, with the first Run 2 papers and conference presentations being written and delivered this summer.

It would be unfair of me, however, to give the impression that it’s all been plain sailing. As well as the highs: smooth recommissioning of the machine, physics getting underway, and a successful transition to 25-nanosecond bunch spacing, we’ve also had our fair share of lows. There have been no show-stoppers, but rather a series of more minor issues that have slowed things down. Sensitivity of the quench-protection system, now fully understood and due to be rectified in the September technical stop, has cost us time. Synchrotron radiation and electron clouds become more of an issue at the energy we’re now running at, so we have to learn how to live with that. And the infamous Unidentified Falling Objects – UFOs – are back, though there is now strong evidence that these decrease with time. All in all, as time goes on, the LHC’s performance gets better, and I believe it is shaping up well to deliver good beam for the rest of 2015 and through the production phase of Run 2 starting in 2016.

For the experiments, most things have gone smoothly, but many of you will be aware that the cryogenic system supplying the CMS magnet has been having some difficulty. As a result, a fraction of the data CMS has taken this year is at zero-field. As I write, the system seems to be stable, but it’s clear that there are contaminants in the cold box that supplies the magnet with liquid helium, and this will therefore need a thorough clean. Interim measures are being taken during the technical stop, aimed at finding a way to continue to operate the magnet with an acceptable duty cycle. All being well, CMS will be able to take data satisfactorily with field on until the end of the 2015 physics programme, postponing the cleaning operation until the winter stop in order to be ready for the start of 2016.

To conclude, I’d like to congratulate everyone concerned in getting us to where we are today: on the threshold of the first LHC Physics conference with 13 TeV data on display. Along with the continuing flow of exciting results from Run 1, such as the combined ATLAS-CMS result on Higgs couplings presented today, there’s much good physics to digest already from Run 2. And as we approach the top of the learning curve, there’s the promise of very much more to come.

Rolf Heuer