Yesterday, I was visiting Brandeis University, where I gave a colloquium on the Large Hadron Collider [LHC]. It was such a gorgeous
June April day outside that I felt quite lucky to see a substantial audience, which I think reflects a sense in the wider physics community that the excitement surrounding the LHC no longer reflects merely its future, but also its present.
I also enjoyed a research talk given by a Harvard postdoc, Matt Reece. He had some things to say about which variants of supersymmetry can now largely be excluded by LHC data, both directly from existing searches for superpartner particles, and indirectly from the search for the Standard Model Higgs particle (the simplest possible form that the Higgs particle might take), assuming the hints of a Higgs particle with a mass of 125 GeV/c2 turn out to be the real deal. He also made a nice little back-of-the-envelope calculation in his introduction, showing how that the hierarchy (the same one for which we have a hierarchy problem) between the incredible weakness of gravity and the strengths of the other forces is required for there to be large objects (i.e. planets, stars) that are held together by gravity, but prevented from collapse into a black hole by the effect of electromagnetism.
These days, at every place I visit — and Brandeis was no exception — the question of the Higgs particle always comes up. No surprise; it’s the hottest topic in particle physics right now. And the quality of the evidence always gets discussed. Dr. Reece was of course asked his opinion by someone in the room. So I get a chance to hear a lot of viewpoints.
One of the things that I have found puzzling is that almost all of the other particle physics and string theory bloggers not only are of the opinion that the Higgs particle has definitely been found, but also claim that almost all other particle physicists think so too. I honestly just can’t understand how they can say this. I find plenty of theorists who say things like “well, if I didn’t already have a strong theoretical reason to believe the Higgs particle exists, I wouldn’t be very confident in the evidence that is in the current data.” Meanwhile, many senior experimenters regale me with stories of past errors and biases, some of which you find in the history books, and some of which you can’t. All of this is anecdotal; I can’t tell you how opinion is really distributed. But clearly a substantial fraction of the community — maybe a minority, but not a small one — are much less confident than most of the bloggers. It’s not a question of nay-saying — I haven’t heard anyone argue there’s no evidence at all for a Higgs at 125 — but many physicists feel that the evidence is too weak at this stage for any certainty. Of course we all expect the uncertain situation to be resolved in 2012.
One of the other great pleasures of visiting other universities is that I always get to hear about interesting research directions being pursued that I’d not been following. (The theorists at Brandeis were all doing neat stuff that unfortunately would take way too long to describe here. ) And then, as the day comes to a close, I always hear some good stories. My favorite this time was of an ATLAS experimentalist describing how easy it is to get lost while crawling around, installing or fixing things, inside the vast muon system of the ATLAS detector (one of the two general purpose detectors at the LHC.) Can you imagine getting lost inside your own experiment?! Well, this one’s the size of an eight-story office building, but hasn’t got hallways, elevators, big EXIT signs, or even an obvious THIS WAY UP. Meanwhile, your GPS device doesn’t work down there either!