Sunday 6 December 2009

Back on track... what's next?

Unless you just came back from a trip to Jupiter moons you know that the LHC is up and running again. This time, each commissioning step can be followed in real time on blogs, facebook, or twitter, which demonstrates that particle physics has made a huge leap since the last year, at least in technological awareness. After the traumatic events of the last Fall (LHC meltdown, moving to New Jersey) I'm still a little cautious to wag my tail. But the LHC is back on track, no doubt about it, and one small step at a time we will reach high energy collisions early next year.

So what does this mean, in practice?
In the long run - everything.
In the short run - nothing.

The long run stands for 3-4 years. By that time, the LHC should acquire enough data for us to understand the mechanism of electroweak symmetry breaking. Most likely, Higgs will be chased down and its mass and some of its properties will be measured. If there is new physics at the TeV scale we will have some general idea of its shape, even if many details will still be unclear. The majority (all?) of currently fashionable theories will be flushed down the toilet, and the world will never be the same again.

In the short run, though, nothing much is bound to happen. In 2010 the LHC will run at 7 TeV center of mass energy (birds singing that there won't be an energy upgrade next year), which makes its reach rather limited. Furthermore, the 100 inverse picobarns that the LHC is planning produce next year is just one hundredth of what Tevatron will have acquired by the end of the end of 2010. These two facts will make it very hard to beat the existing constraints from Tevatron, unless in some special, very lucky circumstances. So the entire 2010 is going to be an engineering run; things will start to rock only in 2012, after the shutdown in 2011 brings the energy up to 10 TeV and increases the luminosity.


Unless, by the end of 2010 Tevatron has a 2-3 sigma indication of a light Higgs boson. In that case, I imagine, CERN might consider the nuclear option. The energy is not that crucial for chasing a light Higgs - the production cross section at 7 TeV is only a factor of two smaller than at 10 TeV, and moreover the background at 7 TeV is also smaller. So CERN might decide to postpone the long shutdown and continue running at 7 TeV for as long as it takes to outrace Tevatron and claim the Higgs discovery. That scenario is not impossible in my opinion, and it would be very attractive for bloggers because it promises blood. But even that, in any case, is more than one year away.

In the meantime, we have to look elsewhere for excitement. Maybe the old creaking Tevatron will draw the lucky number? Or maybe astrophysicists will find a smoking gun in the sky? Or, as I was dreaming early this year, the dark matter particle will be detected. Or maybe it already was? But that wild rumor deserves a separate post ;-)


Anonymous said...

you mean CDMS? have they seen anything? *really*?!

cormac o raifeartaigh said...

lovely succinct overview, many thanks