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Wednesday, July 04, 2012

A New Particle has been Discovered -- Chances are, it is the Higgs Boson

It's Higgs boson day today here at the conference. There's a live feed to the press conference from CERN, the schedule has been rearranged to accommodate it, etc. I can't say I'm as excited about it as some of the people here -- they are quite abuzz -- but it is kind of cool. [Update: In the press conference, they are very clear to say they have found something -- a boson of some sort -- but they emphasize they can't yet say it's Higgs. But it seems clear they think that's exactly what they've found. Update: I'm sitting next to two Nobel prize winners, George Smoot and Kurt Wüthrich -- not sure how that happened, Smoot sat next to me yesterday too, but anyway -- the latter is upset at the press conference. He thinks it is too soon to make the announcement, and a simple press release saying we found something, but not sure what it is would have better conveyed what they actually know at this point. In short, though it may turn out to be correct, he thinkis it is being oversold at this point (in part to satisfy the money interests behind the discovery.]

Update: They are having a panel discussion among laureates, and with scietists from CERN (through a video link). Here's the kind of thing I'm hearing:

David Gross

Not revolutionary, we’ve had other equally important confirmations of the standard model, but this closes the last gap in the standard model.

It is “a” Higgs, if not “the” Higgs -- hope not the simplest Higgs. Great day for humanity.

Only have 2% of the data they will eventually collect.

George Smoot

Also want to congratulate the theorists, seeing power of an idea and the standard model. Poetry in a certain sense. In past, he was critical that the theorists stuck too tightly to simple, most elegant version of the standard model, pushed for alternatives, but they (theorists) appear to be right. People should celebrate, and congratulate CERN for being careful (CERN found a candidate particle consistent with Higgs bosons, etc., but don’t say they found it – that’s what we have to see). Difficulty is that we found what we expect, but must be careful to validate, won’t really understand for 2-3 years. Try not to rush to judgment…

Carlo Rubbia

Question the value of the cross-section results being given. 2 sigma difference between results, theory. Important element to consider. Is the factor of 2 important? Is it statistical error, or does it tell us there’s a new physics there.

Standard model gives an exact value, but there is a disagreement with empirical results. Need to discuss this among this group of scientists (we are linked to CERN – they are answering – not sure who, but saying within statistical error – but need more data to clear this up – very important to do this)

Getting down into the weeds about the exact type of Higgs they may have found, questions about super-symmetry.

CERN scientist: we found a boson, not sure it’s the boson.

End of update.

A new particle has been discovered -- chances are, it is the Higgs boson, EurekAlert: The long and complicated journey to detect the Higgs boson, which started with one small step about 25 years ago, might finally have reached its goal. This was reported by LHC particle accelerator scientists today at the European Laboratory for Particle Physics, CERN, near Geneva.
The Higgs boson is the final building block that has been missing from the "Standard Model," which describes the structure of matter in the universe. The Higgs boson combines two forces of nature and shows that they are, in fact, different aspects of a more fundamental force. The particle is also responsible for the existence of mass in the elementary particles. ...
Most of us experience the world as a diverse and complex place. But the physicists among us are not content with visible reality. They are striving to get to the bottom of that reality and to see whether it is, as they think, based on the absolute simplicity displayed by the early universe. They expect to observe a range of particles that are different "ensembles" of a handful of elementary particles. The scientists are hoping to see a unification of the four fundamental forces of nature that act on these particles (the weak force responsible for radioactivity, electromagnetic force, the strong force responsible for the existence of protons and neutrons, and gravitation).
The first step in the journey to unify the forces was completed with the almost certain discovery of the Higgs particle: The union of two elementary forces – the electromagnetic and weak force, to become the electroweak force.
One aspect of the Higgs boson, named after the Scottish physicist Peter Higgs, manifests itself in the giving of mass to the weak force carriers – the "W" and "Z" particles. (The electromagnetic force carrier, the photon, remains massless.) ...
The likelihood of creating the Higgs boson in a single collision is similar to that of randomly extracting a specific living cell from the leaf of a plant, out of all the plants growing on Earth. To cope with this task,... scientists ... developed unique particle detectors... These detectors have been adapted to detect muon particles. In some of the very rare collisions that produce Higgs particles, the footprint of the Higgs particle – that which is recorded in the detectors – is four energetic muons. Thus, the detection of such muons provides circumstantial evidence for the existence of the Higgs particle. ...
The calculations carried out by scientists in recent weeks ... have revealed, with a high degree of statistical significance, a new particle with a mass similar to the expected mass of the Higgs. The wording is purposely cautious, leaving room for the possibility that a new particle other than the Higgs can be found within this mass range. The probability that this is, indeed, a new particle, is quite low. (But if it were, in truth, a different particle, say some physicists, things will start to get "really interesting.") ...

More here:

... The Higgs boson is the final piece of the Standard Model of particle physics, an amazing theoretical edifice that has stood the test of time for more than three decades now. The Standard Model features two kinds of particles. There are "fermions," the particles of matter, which take up space (you can't pile them on top of each other). Then there are "bosons," the force particles, which can pile up. The four forces include gravity, electromagnetism, the strong nuclear force, and the weak nuclear force. That last one-- the weak force--is the most messy and complicated of the forces. And the Higgs boson (or really the Higgs field from which it arises) is the reason why.
For the other forces (gravity, electromagnetism, strong), the force carrying particles all have precisely zero mass. That's not an accident; according to modern physics, the very existence of these forces reflects a deep symmetry of Nature's laws, and this symmetry demands that the force-carrying particles remain massless. For the weak force, the force-carrying particles are called the W and Z bosons, and they have quite substantial masses. The reason why (we believe) is that the underlying symmetry has been broken by the Higgs field.
The Higgs field breaks this hidden symmetry because it fills space--it has a nonzero value absolutely everywhere. You move through it as you go through your day, and you would still be moving through it if you were flying through interstellar space. It's invisible and hard to interact with, but it's there. And it doesn't only give mass to the W and Z bosons; it's also responsible for giving mass to all of the fermions that make up matter. Electrons, muons, quarks--all these particles get mass because of the Higgs. It's kind of a big deal. ...

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