- CoGeNT, for making us drunk with light dark matter.
This experiment created the largest stir in theory this year. CoGeNT, a dark matter detection experiment, announced that it could be seeing dark matter with a relatively light mass, around 10 GeV. The dominating paradigm is dark matter at the weak scale, 100 GeV to 1 TeV, but the CoGeNT result made us stop and think about a wider range theoretical possibilities. Unfortunately, recent exclusion limits results from Xenon10, Xenon100 and CDMS make it highly unlikely that CoGeNT is really observing dark matter. Nevertheless, the lesson we have learned is that dark matter does not have to be where everyone is looking.
- D0, for keeping the hopes for new physics alive.
Good old Tevatron gave us one very intriguing result this year. The D0 collaboration looked into same-sign di-muon events, and found that events with two negative muons occur 1 percent more often that those with two positive muons. This result can be interpreted as CP violation in the B-meson system: the Bbar-mesons oscillate into B-mesons a bit more often than the other way around. The Standard Model predicts such an effect, but the asymmetry should be 100 times smaller that what is observed. Is this new particles contributing to the B-meson mixing? Or did D0 screw up? The jury is still out.
- PSI, for extending the new physics battlefield into atom spectroscopy.
The surprise of the year, no doubt about it. A laser spectroscopy experiment at PSI measured the Lamb shift in muonic hydrogen, and found it to be 5 sigma away from the prediction based on theory and earlier experiments with ordinary hydrogen. Given that simple new physics models cannot provide a consistent explanation, and that QED is doing shamelessly well everywhere else, we all expect that some theoretical or experimental error is at the root of this anomaly. But the possibility that some quirky new physics manifests itself here is still hanging in the air.
- Tevatron, for its tireless Higgs chase.
Tevatron gave us also a completely expected yet very cute result. 10 years ago LEP excluded the Higgs masses below 115 GeV, now Tevatron tells us that Higgs between 156-175 GeV is not the right answer either. Combining that with precision electroweak tests, we deduce that Higgs is cowardly hiding somewhere between 115 and 155 GeV. Poor bastard is thus cornered, and with the LHC joining in the chase he should surrender in no time. Unless he is not there after all...
- LHC, for the overall impression.
After a series of setbacks and delays this year LHC surprised us, for a change, with a stream of good news. We had been told that the first year would be a total mess, as it should take a long time to understand the detectors enough to produce meaningful results. Instead, physics results have been delivered basically from day 1, even in difficult channels like jets + missing energy. LHC already published several important limits, e.g. on 4-quark operators (gracefully called "bounds on compositeness"), or on high-energy high-multiplicity events (under the sexy name of "limits on black hole production"). And much more is due to arrive for the winter conferences. It's easy to predict that the LHC will make it to the 2011 highlights on Resonaances; the only question is whether I will remember it for "important limits" again, or for crazy new discoveries...
Friday, 31 December 2010
It's the end of the year when blogosphere and old-fashioned press alike indulge in a nostalgic mood. Here is my list of the most exciting events of the passing year in the field of particle physics. From the year 2010 I remember (in chronological order):