LHC: “we have observed a new particle consistent with a Higgs boson. But which one?”

That’s what they’ll be trying to work out over the next few years.  Matt Strassler’s probably the man to go to for more on the options ahead.  But, for now, the news from Cern is that they have, almost certainly, found “that damned elusive particle“, a Higgs boson.  Earlier this morning one of the six theoreticians who predicted the field/boson, Peter Higgs, instructed his family to start chilling the champagne, and Stephen Hawking has conceded that he has lost his $100 bet.  As an aside, noted previously, here’s a fascinating Guardian interview with Peter Higgs from 2007.

From the BBC report

Prof Rolf Heuer, director-general of Cern, commented: “As a layman I would now say I think we have it.”

“We have a discovery – we have observed a new particle consistent with a Higgs boson. But which one? That remains open.

“It is a historic milestone but it is only the beginning.”

Here’s the moment of the announcement, via the Irish Times report.

And Cern’s John Ellis answers the question “What is the Higgs boson?”

The Guardian live-blog has now closed, but has lots of information and links.  Including this from Brian Cox

This is without doubt in my opinion the biggest scientific discovery of my lifetime and without doubt one of the biggest scientific discoveries of all time, so I’m tremendously excited… This day will go down as one of the great days in the history of science I think, and that’s not overly hyperbolic.

This is a prediction that was made almost 50 years ago. And the prediction is that the universe, everywhere, empty space, everywhere you look, every little cubic centimetre of space in front of you and inside your body and across the universe, is rammed full of Higgs particles, and everything that makes up your body, the little subatomic particles in your hand, are bouncing off them, and that’s how they get their mass.

And more than that the theory said that these Higgs particles condensed out into empty space less than a billionth of a second after the universe began. It sounds very esoteric and fundamental. But what we’ve shown today is that’s right. That’s actually how the universe works. So it’s one of the central planks of our understanding of how everything in the universe works.

And even though, throughout my whole career as a particle physicist of 20 years now, this theory has been there, I think the realisation that it’s actually right is quite shocking, actually; I’m quite shocked that such a strange thing has been shown to be true.

It’s also worth noting the quote from Stephen Hawking on his lost bet.

This is an important result and should guarantee Higgs the Nobel prize but it is a pity in a way because the great advances in physics have come from experiments that gave results we didn’t expect.

As I’ve mentioned before, here’s a good introduction to the Standard Model of Particle Physics from Cern News – it’s the first in a series of videos.

Of course, there may still be further wrinkles ahead…

Final point to note, again, from the earlier BBC report

Scientists will have to look at how the Higgs decays – or transforms – into other, more stable particles after being produced in collisions at the LHC.

Dr Pippa Wells, a member of the Atlas experiment, said that several of the decay paths already showed deviations from what one would expect of the Standard Model Higgs.

For example, a decay path where the Higgs transforms into two photon particles was “a bit on the high side”, she explained.

These could get back into line as more statistics are added, but on the other hand, they may not.

“We’re reaching into the fabric of the Universe at a level we’ve never done before,” said Prof Incandela.

“We’re on the frontier now, on the edge of a new exploration. This could be the only part of the story that’s left, or we could open a whole new realm of discovery.”

2012 looks set to be a vintage year for particle physics”, indeed.

Adds Niall has a good background post on the announcement here.

And from the Guardian’s tame particle physicist, Jon Butterworth, who’s a member of the ATLAS team.

So today has been amazing. Today we saw a completely objective, repeatable, observation of something fundamentally new.

Say that again. Twice.

And it’s existence was predicted by mathematical understanding of previous data, coupled with some prejudices about aesthetics, symmetry and how a decent universe ought to hang together. I don’t know about you, but this amazes me.

Now, it looks like the Higgs boson. Or a Higgs boson. But it might not be. It has the right electric charge (i.e. none). It seems to appear about as often as it should in some decay modes. It is definitely a boson. But it is supposed to give mass to all fundamental particles, and we haven’t seen it do anything with fermions (quarks and leptons) yet, just bosons.

So it looks like a Higgs. But we need to look more carefully.

And there might be more of these things out there…

These are great times.

Indeed.

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