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Aidan Randle-Conde | Université Libre de Bruxelles | Belgium

View Blog | Read Bio

Gauge transformation

“Welcome to CMS,” my friend said, “it’s exactly the same as ATLAS, except the fluctuations are downward.” It was a light hearted, almost flippant remark and to an extent it summarised my feelings about the two experiments. So when I moved from the ATLAS experiment to the CMS experiment the biggest changes were not related to the physics. After all, we see the same physics, publish very similar results and analyse the same beams colliding over and over again. The big news that both experiments celebrate the most is, of course, the new boson. ATLAS saw a little more events than they expected in the main channels, and CMS saw a little fewer, and otherwise they both saw the same effect, confirming that it was real.

Aidan at ATLAS

Aidan at CMS

Same experience, different detectors. Nothing really changes!

What really changes is everything surrounding the work. I’ve moved across the world a few times to follow my career, first to California where we analysed collisions at SLAC, and then to CERN to work on ATLAS. This time I moved to ULB in Brussels, the capital of Europe, and that meant a new home, a new nation, a new university, and a new experiment. In fact the only thing that stayed the same were the protons. For me that’s perfect, after all the last thing I want to do is stagnate, doing the same thing day after day. A change like this is refreshing, gives a chance to open up new horizons and reinvent oneself a little. Having those tiny little protons be the only source of continuity is actually quite reassuring in a way. That’s what I’m here for, after all. To keep studying those protons I’ll let everything else around me change and welcome the state of flux.

So as well as all those “auxiliary” changes I decided to change the physics topic as well. I have previously searched for the Higgs boson, starting up and leading a new analysis from scratch before handing it over to the ATLAS machine. This time I’m looking for the Z prime boson, which has a clean signature and if it is seen, it is seen very soon after taking new data. There are several models out there, but given the relative ease and speed of discovery it’s more a matter of “Find now, ask questions later!” Within the first few weeks of taking data we will be poring over the results, looking for any hints of new physics, competing in a head to head race with ATLAS and with each other to find the peak first. If if exists, we’ll find it, and it’ll shake our view of physics at the TeV scale. This is a very different kind of physics for me, and at first it was not I felt particularly comfortable pursuing. I was used to having an airtight model that told me what to expect and how much of it to expect and even where to expect it. This time the data is telling the story and that’s a tricky idea to get used to. Then again this whole transition is about changing my outlook, so why not change analysis style too?

Grand Place

Finding the best table in Brussels and having dinner with a visiting friend.

For those who noticed my absence, I’m sorry! It’s taken a few months from the start of a job search in a very difficult job market, applying to positions on three different experiments, in four different countries. The move from one place to another is never particularly “clean” either, as there are loose ends from my old job, and it takes a while to get started in my new position. Then there are all those small changes, like a different ID card, a different currency, a slightly different style of French. I’ve let it take longer than I should have before returning to blogging because to be honest the break has been a very welcome one. CERN is a very busy place with long days and huge demands. Moving to Brussels was hard work at first, but now I find myself with more space, more time and more opportunities to catch up with everything in my life that was put on the back-burner. A decade of photos to sort, all those books I bought and put on the shelf, the half-finished ideas that got archived for when I got around to it. Contributing to this blog again is part of the grand plan. There are so many topics I want to touch on, and I set a very high bar with the Advent Calendar last year! I also want to look beyond science to the pursuit of knowledge itself and its implications on theology (something I never felt comfortable tackling when working for a US institute.)

The way I see it, moving experiment is just like a gauge transformation. No matter what happens, any physical phenomenon must be the same after a gauge transformation. This kind of transformation is a subtle mathematical change that has no classical analog. By making a phenomenon gauge invariant we can introduce new forces that mop up all the differences, so that ultimately, we all see the same thing, no matter how we look at it. In this case, what stays the same is the underlying nature of those colliding protons. That’s the gauge invariance, and everything else, the movement from place to place, from one experiment to another, are just the fields swooshing about as we perform our own personal gauge transformations. It turns out life is complex.

  • Ken Bloom

    Didn’t know you had moved over. Welcome!

  • Thanks! I hope to see you at a CMS Week or similar at some point 🙂