Reflections on a Test Beam

I spent a week at a test beam at CERN, here are my reflections on the experience.

First of all, if you are not working in particle physics, you might wonder what a test beam is.

Imagine a one-week hackathon, but instead of getting some credits for AI usage and being forced to use some startup's shitty SaaS prototype, you get a particle beam from the Proton Synchrotron. If that doesn't sound cool enough, you also get an experimental area enclosed by thick concrete blocks to protect everyone outside from the radiation from the beam, as well as a control room with measurement equipment connected to both the Proton Synchrotron beam data and experimental area equipment.

Inside such a control room, I spent most of the past week, solving hard problems together with incredible engineers and physicists.

With the larger goal of testing the new inner tracker for the high-luminosity upgrade of CMS, we also tested a lot of other subsystems, and got some real physics data. Throughout the week, every 20 seconds two beeps sounded in the control room, signalling a spill: the beam sending particles through our test setup. I still hear the beeps in my head.

Some reflections:

• No matter how prepared you are before, your stuff will break. And if it doesn't break, somebody else's stuff will break, breaking your stuff.
• Debugging and fixing things under extreme time pressure is hard, but also very fun.
• Human communication is inefficient and prone to errors. This might be one of the largest bottlenecks during a test beam.
• Logbooks are good. Hacking at 2am feeling like a boss will not feel good the morning after unless you documented what you did.
• Keeping a good mood, even during bad times, might be the most important skill.

I'll finish this post with some poetry.

Just as computers run to the beat of the clock, humans at test beams run to the periodic double-beeps of beam spills.