higgs, Higgs, HIGGS!

3 07 2012

Update: Both the ATLAS and CMS experiments confirm combined signals from different channels at “5 sigma”!! That means there is about a 1 in 2,000,000 probability this is just a random event (although this kind of analysis can’t rule out what are called “systematic” errors). Nobody is sticking their head out to say “This IS the Higgs” but it really looks like it is. Pinning down the details will likely take a while, but they’ve got every right to open the champagne! As Peter Higgs said “I’m glad it happened in my lifetime!”

The internet is rife with chatter about tomorrow’s announcement at CERN: confirmation of strong statistical evidence of a particle with Higgs boson-like properties exists. OK, that sounds like an incredibly wordy let down. Why can’t we just say “Higgs discovered!”? And, for that matter, why is there so much fuss about the Higgs boson?

I guess it doesn’t hurt to call something a “God Particle” – which is damn silly if ask you me. The journalists might like it but the religious people won’t, and for that matter atheists probably won’t either. Hmm, sounds everyone would be upset by that name!

But, back on track. Simply put, the Higgs boson is what gives the subatomic particles like electrons and quarks (which make up the neutrons and protons in the nuclei of atoms) their mass. And that is a really big deal! Mass is one of the single most important properties of matter. Without it, we’d all zip around at the speed of light. So hunting down the Higgs has been a big deal for a long time.

Particles acquire mass through their interaction with the Higgs bosons. The Higgs field (which the Higgs particles tell the other particles about) permates all space. As a particle moves through it you can think of it as being slowed down by the field as Higgs bosons cluster around it – some people like to give the analogy of clumpy molasses. Different subatomic particles are affected in different ways by the field, so some particles appear more massive than others.

So that tells us what it does, but why is finding the Higgs boson so difficult? Why can’t we just say it’s been found? Simply because we can’t actually detect the Higgs boson directly. They’re far to elusive for us to do that. Think of them as the lesser-spotted-black-backed-southern-migrating-hoji-mawatsit bird of the particle physics world. Yeah, you don’t get to see too many of them.

But what you do see is the things they turn into. And that’s the key. One the best ways of finding the Higgs is that it can decay into two photons (photons are the particles than transmit light). But there are plenty of other possibilities, all of which are mimicked by many other interactions in the subatomic world. So finding the Higgs boson is a needle in a haystack operation. You have to look through hundreds of trillions of events in the hopes of finding what you want.

To put this in perspective, how big is a trillion? Well it would take you 50 years to count to a billion, and trillion is a thousand times larger. So it’s likely no surprise to anyone that analyzing all this data has been as much a triumph of computing power as it has been an engineering marvel to build the LHC itself.

What can we expect tomorrow? At the present time, the physicists have a signal that their confident in, and I suspect that is how the announcement tomorrow will be framed. But it’s far too early to exactly specify the type of particle it corresponds to – there is still a lot more work to be done on that. But the mass of the particle (around 130 times the mass of a single proton) is about what is expected for the Higgs boson.

From a personal perspective, it’s great to see the Higgs finally being uncovered. During grad school, which is over 15 years ago for me now, I had good friends that were working on the ATLAS project at the LHC. It’s amazing to think about how much planning it has taken to get to this stage. The LHC has taken billions of dollars and thousands of the brightest people on the planet over a decade to put together. It is a marvel of technological and intellectual achievement!

Just stop and think about things – isn’t it incredible that as a species we have been able to probe the very nature of the Universe to this degree? We’ve almost uncovered the mechanism through which the reality that we live in gets one of its most fundamental properties – mass! It really is almost unbelievable.

OK, feet back on the ground: Where does particle physics go from here? There’s a lot of important work on pinning down details of the Higgs, but beyond that? Is there the political will to build anything bigger than the LHC? I think not. At 10 billion dollars it’s likely the most expensive ground-based civilian scientific experiment ever (although the Hubble Space Telescope cost more over its mission lifetime because of the high cost of spaceflight). Since the LHC is largely a world-wide collaboration, it’s interesting to look at how much a billion dollars a year (i.e. 10 billion dollars over 10 years) is as fraction of the world economy. In short, 1/70,000th. That puts things in perspective.

But particle physicists are all to well aware of this. There is, fortunately, some hope for the future of accelerator design that could bring down the cost of accelerators. Laser wakefield acceleration, where particles are accelerated by “surfing” on an electric field, hold great promise for the future. In theory, the acceleration produced by the 27km long LHC could be achieved in a few hundred meters using laser technology. But this technology is probably decades away from being realized.

There are still many great questions to be answered in particle physics. What about the beautiful idea of supersymmetry? Where is the elusive dark matter particle that we believe makes 5/6 of the mass in the Universe? Both of these questions are probably as important as finding the Higgs itself.

So I think of tomorrow’s announcement as the beginning of something and not the end. It’s an incredible achievement for us to have got this far (hey, and we all paid for it with tax dollars too!) but there is still so much more to learn!

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