In The Field

Lepton Photon 2009: Shining a light through a wall

While most of the talks here at Lepton Photon have focused on blowing up the Standard Model at high energies — i.e., firing up the LHC — Joerg Jaeckel of the University of Durham in the UK gave an interesting talk on how you can look for new physics at energies of just an electron-volt or so. The LHC might miss particles that only rarely interact with normal matter. And so Jaeckel extolled the virtues of exquisitely sensitive experiments that probe this alternative (and cheaper) ‘low-energy’ frontier.

One classic example is the GammeV experiment at Fermilab, which basically tries to shine a light through an opaque wall. On one side of the wall you can have a source that shoots 10^20 photons per second. On the other is a detector so sensitive that it could catch a single photon per second — a full 20 orders of magnitude sensitivity. Now photons can’t go through walls. But a weakly interacting particle could, something like an axion — a hypothetical dark matter particle. And there are certain rare scenarios where photons could create axions. If that happened, the axion could pass through the wall and create a photon on the other side.

There are plenty of other low-energy experiments — some have looked for slight differences in the way light is polarized in the vacuum, and some have looked for axions in the presence of a strong magnetic field. One has even found hints of an anomaly in the standard model by looking at that way the spin of a muon deviates in a magnetic field.

But these experiments in general get little attention. I suggested to Jaeckel that maybe it’s because the LHC is guaranteed to discover new things, whereas these experiments could end up being as fruitless as the seemingly pointless effort of shining a light on a wall. Jaeckel had a nice analogy. “[The LHC] is digging a broad ditch. With a low-energy experiment, you’re digging a hole. It’s a very deep hole, but you may be drilling in the wrong spot.”


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