Friday, February 19, 2010

Signs of spring

Could it be that springtime is near, not just in Earth's climate (in the Northern hemisphere at least!), but also in experimental particle physics?

It has been a long, trying winter, with few really exciting observations since the early 1970's. Experiments at Fermilab, SLAC, and CERN confirmed and refined the so-called "Standard Model" of particle physics, for which Nobel prizes were duly dished out during the 70's, 80's, 90's, and even into the last decade. The tau lepton and top quark were confirmed (c. 1975 and 1995, respectively), filling out most of the missing pieces of the bestiary, with the Higgs boson remaining the one stubborn holdout.

These are terrifically important results, don't get me wrong. Four decades is not a long time to test and verify such a complex theory as the Standard Model. Nevertheless it has been frustrating for theorists, who - we can be honest here - find the Standard Model rather clunky and unloveable, and feel certain that it must be incomplete. Candidates to extend it abound, from supersymmetry to technicolor to strings, but very little data exists to constrain them. The cancellation of the SSC in 1993 was a major disappointment; arguably, the most fruitful development to emerge from particle physics laboratories during this period was the World Wide Web, invented at CERN in 1989 (just 21 years ago - but it feels like a century!).

However, all that may be poised to change. The Large Hadron Collider at CERN is finally almost ready to take data, and it should be powerful enough to go beyond the Standard Model. At the very least it should discover the Higgs or, failing that, blast a big hole in the Model.

But what prompted me to write this post was a recent, tantalizing result on dark matter. This is the mysterious matter which seems to comprise 75% or so of the mass of the universe, but which has never been directly seen.

At least until now - perhaps. An experiment called "CDMS II", utilizing fantastically sensitive detectors buried in a mine in Minnesota, reported in December the detection of two possible dark matter collisions (the paper came out in Science last week). Unfortunately, this was not enough events to confidently claim a discovery; the researchers estimated a 75% probability of being due to dark matter, rather than background noise.

Although not definitive, this is very exciting since it would be the first detection ever of a particle from beyond the Standard Model. Indeed, the most favored dark matter candidate at present is the so-called "Lightest Supersymmetric Particle", and theorists would love to get their hands on any concrete information about this creature.

So there's still, speaking literally, nothing to report. But there are gathering signs of promise everywhere. Punxsatawney Phil may have predicted a long winter this year - but what does a groundhog know about particle physics anyway?

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