Wednesday, July 4, 2012

What it means - and what it doesn't

(from the front page of today's www.cern.ch)

You may have heard by now... researchers at the ATLAS and CMS experiments at CERN have announced today that they've discovered the God Particle. I wasn't surprised by the announcement, but I did come home from my morning run to find text messages from family members asking for explanations.
First off, let me point out that the researchers themselves are, while excited, much more hesitant to refer to the announcement as revolutionary. The media has made a run of it, but not the scientists themselves.
So what does it mean?
In the Standard Model of particle physics, the best understanding we have to date of the subatomic world, the Higgs field was predicted decades ago to be the mechanism by which other particles have mass (think of wading through a river with your clothes on - the farther across you get, the wetter the fabric is and the heavier you are because of it). In our understanding of the universe, every field is associated with a particle (in more technical terms, the particle is basically a bunched-up bit of the field), so the Higgs field has to be associated with a Higgs boson, and the Higgs boson has to have certain characteristics. And while this Higgs particle is important, and a key feature of the Standard Model, it's not really anything like a "God particle." It's one more piece in the puzzle, one more particle in the Standard Model pantheon.
Now, to the "discovery" of today's announcement. Aside from noting that discovery of the Higgs is not the be-all-end-all of science (what about dark matter? dark energy? unification of gravity with the other fundamental forces?), the data presented today needs to be taken with some hesitation. While the term often thrown around is "five sigma" - meaning that the signal has about a one in a million chance of being just noise - the CERN announcement and the associated figures doesn't show any individual 5-sigma data. That certainty of discovery only comes when taking all of the data together. The fact that CMS, ATLAS, and the Tevatron data from before the shutdown all seem to indicate a new particle in this particular mass region is convincing, though.
But what precisely was discovered? Here's another trick that the media are playing on you. The CERN (and Tevatron) researchers didn't discover the Higgs particle. What they discovered was an as-yet unknown particle with a mass of about 125 GeV. It could be the Higgs. It could be something completely different. What's necessary now is to go through as much data as possible to determine whether the new particle behaves like we theoretically expect the Higgs to behave. Does it have all the right characteristics? We don't know yet. We know that we've looked elsewhere and not seen anything, and we know that in this particular region the data look promising. But that's all.
So what does it all mean? The take-home message is this: they've found something, and it's pretty convincing, but nobody knows for sure what it is. And even if it is the Higgs, it's not the end of science.

2 comments:

  1. "the CERN announcement and the associated figures doesn't show any individual 5-sigma data. "

    The individual sigma per decay channel is not 5. What they show is the total sigma, from all measured Higgs decays, which is 5 sigma. This 5 sigma is for each individual experiment.

    The analysis was done independently from ATLAS and CMS, without any data from Tevatron.

    In the next 2-3 weeks ATLAS and CMS will combine their data.

    ReplyDelete
    Replies
    1. It is convincing, but it's not the headline-grabbing amazingness that the media has made it out to be. That's my basic point.

      Delete

Think carefully before you post. I reserve the right to moderate any comments posted to my blog.