Of course I was going to write about the LHC restart!

This goat is really proud of the LHC's achievement today.

These goats from Gimmelwald are really proud of the LHC’s achievement today.

Here we go again! I was in the ATLAS control room this morning when the LHC brought 13 TeV proton beams into collisions. It’s a historic achievement. The (simplified) sequence to bring beams into collisions is the following:

  • Inject the protons at 450 GeV into the LHC,
  • Ramp up the energy to 6.5 TeV for each proton beam,
  • Focus the beams,
  • Align the beams such that they are head-on.

As the beams became aligned, we started seeing collisions in ATLAS. This morning, the LHC went through injection and ramp twice. There was a first, unsuccessful attempt. The LHC had to dump the beams and start over.

The ATLAS control room was already very crowded the second time. Once both beams reached 6.5 TeV, there was a measurable drop in the volume of the conversations. The tension was palpable. People were waiting to see if the LHC was going to dump the beams again. But it didn’t, and soon we got collisions. Applause, congratulations and champagne ensued. It was a privilege to be there.

That’s the thing with any official event: it always appears more glorious than it really is. Soon after we got the collisions, the applause and the champagne, my co-workers and I started noticing odd things in the luminosity data we were collecting. Of course, you can only anticipate so many potential problems before you go ahead and try what you built. Our small team was soon overtaken by these odd things as we were trying to make sense of them. As of now, they are still not understood. I can only help so much to understand technical issues, and I feel bad that all the hard work falls on the shoulders of my co-workers. They are outstanding, and they’ll figure it out in a jiffy.

We’re most likely not the only system in ATLAS where new problems were discovered today. Discovering new problems – especially when they are the most puzzling things you’ve seen so far – can make you forget that everything else is working perfectly. That’s why working in detector operations is so unforgiving. While everybody else in the collaboration celebrates how well things are going, you have to react quickly and focus on the things that are not working. You don’t get to pause and rejoice so much.

Anyway, it’s definitely fantastic that we got these collisions. 99% of the infrastructure I’ve been helping with is working, and it’s only going to get more robust and more stable in the next weeks. I also have a renewed appreciation for formal celebrations. They may seem to be superficial formalities sometimes. However, when celebrating is denied, it results in a certain obliviousness to how much has been achieved.

If you want to actually learn things about what happened today, check out Statistical Significance by Ryan. You can also listen to some of my colleagues (Laura, Larry, Tova and Zach) discussing what may be found in Run II in a new podcast called In Particular. Here, you’re only going to get more goats.


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