Quantum field theorist Professor Matt Strassler, whom I mentioned previously and who’s been spending a few days at the Perimeter Institute, takes issue with the science in this BBC science report of “hints” of dark matter in his latest post.
Meanwhile, a bit more insight into the CRESST dark matter situation (see yesterday’s post). There have already been silly press articles. The BBC article says
- Researchers at the Cresst experiment in Italy say they have spotted 67 events in their detectors that may be caused by dark matter particles called Wimps.
No, that’s not what they said. (Not surprisingly, there are other serious scientific errors in the BBC article.) The CRESST paper said they see 67 events that look like a dark matter particle hitting an atomic nucleus in the detector, but some number of them — probably most of them — are caused by backgrounds. That is, they know there are other sources, perfectly conventional, for many of these events.
To be fair, he has questions about the data analysis by the CRESST team too. But the BBC journalist in question was also responsible for the “somewhat excited” report of a potentially ground-breaking result from the Tevatron accelerator in April. And that turned out to be a false alarm.
Interestingly, the sceptical voice then was the Guardian’s tame particle physicist Jon Butterworth, a more hands-on type of physicist.
Another recent BBC report, by a different journalist, claimed
Results from the Large Hadron Collider (LHC) have all but killed the simplest version of an enticing theory of sub-atomic physics.
Researchers failed to find evidence of so-called “supersymmetric” particles, which many physicists had hoped would plug holes in the current theory.
Theorists working in the field have told BBC News that they may have to come up with a completely new idea.
Today was the last day of the Lepton Photon conference, and the Mumbai monsoon let rip in a big way. The noise of rain was so loud at lunch that you could hardly hear the Supersymmetry theorists weeping into their curries after the results reported by LHCb this morning.
Actually they weren’t quite doing that, despite the fact that the LHCb talk from this morning by Gerhard Raven from Amsterdam dealt their favourite theory a blow. He reported a beautiful measurement of a specific decay of the Bs meson (a hadron containing a beauty quark and a strange quark). This agreed very well with the Standard Model, which despite the confidence of some theorists does not include supersymmetry. Less precise measurements had been a bit away from the standard model, and the difference could have been supersymmetry. More hopes dashed. SUSY is even more slippery than the Higgs though, and rumours of her death are exaggerated.
Matt Strassler offered a slightly more polemic response
Ok, today I’ve posted the article you’ve been waiting for: What does the LHC have to say, so far, about supersymmetry?[Here's an article about supersymmetry and what it predicts, and another about standard ways to look for signs of it at the Large Hadron Collider, under certain assumptions; if you want to review the known particles and forces first, you can read about them here.]
If you’ve been reading the press, you may have seen statements such as “the air is getting thin for supersymmetry” or “we’re painting supersymmetry into a corner”. And recently on Cosmic Variance some broad statements about supersymmetry being in serious trouble were made by experimentalist John Conway (before being somewhat watered down after I raised an objection.)
The problem with trying to answer a question like this one — What do LHC results imply for Theory X — is that it is ill-posed. An experiment searches for a phenomenon — not a theory. If a theory always predicts a certain phenomenon, then an experiment can search for that phenomenon, and, in finding it or not, give a definitive thumbs-up or -down to the theory. But often a theory has many versions, and although it will have a general set of predictions — supersymmetry, for instance, predicts superpartner particles — its details can look quite different to an experiment, depending on the version. [For instance, in supersymmetry, whether or not one sees the classic supersymmetry signature depends on the masses of the superpartner particles, on whether there are extra types of particles that are not required by the theory but might just be there anyway, etc.] So any given experimental result is just one important but incomplete piece of information, one that constrains some versions of the theory but not others. Typically, to entirely rule out a general theory like supersymmetry requires a large number of experimental searches for many different phenomena.
Conversely, though, many different theories may predict the same phenomenon. So an experiment that looks for but fails to find a certain phenomenon doesn’t just rule out just one version of one theory. It typically rules out several versions of many different types of theories.
And if it does find that phenomenon, it does not tell you which of those different types of theories it comes from. Remember that, when the LHC makes its first discovery! You’ll likely see claims from physicists in the press about what the discovery means that aren’t really merited by the data.
Indeed. In the meantime, here’s a good introduction to the Standard Model of Particle Physics from Cern News – it’s the first in a series of videos.
Of course, there may be further wrinkles ahead…
And Matt Strassler’s been thinking about some possible wrinkles.
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