Fresh Evidence Supports Higgs Boson Discovery

An anonymous reader writes Researchers at CERN have discovered the first evidence for the direct decay of the Higgs boson into fermions, a strong indication that the particle found two years ago is the Higgs boson. From the article: "Assistant professor of physics at MIT and leader of the international effort, Markus Klute, said that his team was trying to establish if the particle that was discovered in 2012 was really consistent with the Higgs boson that was found in the Standard Model, and not one of many Higgs bosons, or an a particle that looks like it but has a different origin." Their researchers also found that the bosons also decay to fermions (fermions include all quarks and leptons) in a way that is consistent with the Standard Model Higgs. 'We have now established the main characteristics of this new particle, in its coupling to fermions and to bosons, and its spin-parity structure; all of these things are consistent with the Standard Model,' Klute says." CERN has also announced the LHC restart schedule.

Comments

Type 13

[jfdavis668]

Well, I guess Earth isn't a type 13 planet after all.

More than one Higgs Boson?

[timrod]

Here's what I don't understand, which is probably because I wasn't a physics major.

I thought the idea behind the Higgs Boson was this one particle that explained away a lot of different things in physics if you inserted it into the equation, but that no one could actually prove existed - and thus the idea was that if it did exist, physics was validated and if not, they'd be going back to the drawing board.

The way I've always heard it talked about, there was only one Higgs boson that either existed or did not exist - anything different wouldn't be considered a Higgs boson, but a different particle altogether since there was a specific definition as to what constituted a Higgs boson.

So, how can there be more than one Higgs boson?

Re:More than one Higgs Boson?

[AchilleTalon]

In the energy range of the LHC the Higgs boson is not the only new particle that could have been discovered. You cannot automatically tag the particle a Higgs boson unless you observe and measure some of its characteristics, which is exactly what is done here, to prove it is actually a Higgs boson and not another exotic particle from another exotic theory. The Standard Model is far to be the only existing one and the LHC is also seeking for physics beyond the Standard Model. The few characteristics originally observed from the early announcement were insufficient to make certain it was a Higgs boson, that's why it was originally called a Higgs-like particle.

Re:More than one Higgs Boson?

[Charliemopps]

It depends on the model. In "The standard model" there is one Higgs boson. There are other models where there are more. This is a strong confirmation of the Standard model which is where the real story is. A lot of models for the universe just died. When the LHC restarts we should get some really interesting data.

Re:More than one Higgs Boson?

[craklyn]

One cannot measure a Higgs boson directly since it promptly decays. Consequently, it's necessary to identify particles it decays into.

Quarks and leptons are measurable objects in detectors, but quarks and leptons are also created in other processes that are much more likely to occur. This creates a large background which must be subtracted from the Higgs boson decay's signal. These channels are harder to measure due to the significant background.

The other channels of Higgs decay that were identified first included Higgs bosons decaying into gauge bosons. The probability of this occuring is not so large, but such decays can result in 4 leptons (e.g. two electrons plus two muons, four electrons, or four muons), and that has a very clean, measurable signal with very low background.

Re:More than one Higgs Boson?

[craklyn]

This is kind of like if you're walking through the woods and you discover piles of bear shit as you go. The bear shit implies there's at least one bear in the woods, but it does not preclude that there could be multiple bears responsible for it.

The Higgs field is a solution to the question of why some fundamental particles have mass. Theoretically, such a field is well-motivated. If such a field exists, it implies there is at least one massive, spin-zero particle that we have decided to call the Higgs boson. There are various extensions to our models, such as the so-called "Higgs two-doublet model" which SUSY extends, where more than one Higgs exists.

Re:More than one Higgs Boson?

[cciechad]

See this. Best explanation on how the higgs particle may vary. http://profmattstrassler.com/a...

Re:More than one Higgs Boson?

[pjt33]

FWIW, the mass of the Higgs is less than that of the top quark, but considerably more than that of the other quarks.

Re:More than one Higgs Boson?

[azav]

OK. So what makes these particles if they instantly decay? If they instantly decay, then there must be a Higgs factory all over the universe rapidly churning these babies out

If the Higgs decays, then how do the bosons keep their mass when it is gone?

Re:More than one Higgs Boson?

[pjt33]

I'm not a real physicist, but by coincidence I happen to be reading a good book about the LHC and the Higgs field at the moment. (The Particle at the End of the Universe, by Sean Carroll: highly recommended). The explanation given, as I understand it, is that what really matters isn't particles but fields: particles are what we perceive when a field has a concentration of energy in one* place. (* Except that we're talking quantum mechanics here, so the Gabor-Heisenberg-Weyl uncertainty principle applies).

Re:More than one Higgs Boson?

[radtea]

So, how can there be more than one Higgs boson?

Physicists have a funny way of talking about theoretical entities, particularly these days when theory almost always leads experiment. We have years or decades to talk about theoretical entities, and that leads to a strange nomenclature.

"The Higgs" is actually a class of particles. In the "bare" electro-weak theory none of the particles have masses. The only way to give them mass is to break one of the internal symmetries of the theory, and one "natural" way of doing that was invented by Peter Higgs and others in the form of a massive scalar field that takes on a non-zero vacuum expectation value as energy decreases (this is the famous "Mexican hat" potential.)

Suppose we arrived on Earth from Mars and were observing the inhabitants, and we wondered how emergency vehicles would get through busy traffic. One of our number--call it Sggih--theorizes that humans, being visually-oriented, might use a flashing light to warn motorists of an emergency vehicle. Others might elaborate on this and suggest that both a flashing light and a loud noise would be use. All of these types of local warning mechanisms might go under the name of Sggih, with the original one being the "minimal Sggih mechanism" and the other ones going under different names.

In the meantime, there are those who think that humans are telepathic, or use radios, or some other non-local signalling mechanism.

Then one day in the course of observation a Martian--and let's say Martians are deaf, the air being so thin there--sees an emergency vehicle with a flashing light on top zipping through traffic. Horray! The Sggih mechanism is correct! At least probably... it may be that wasn't an emergency vehicle but some kind of advertising stunt. And if it is the Sggih, which one is it? Further research is required to determine if humans use the minimal Sggih mechanism or one of the more complex elaborations...

This work is in the vein of that further research, and the outcome strongly suggests that of the various theoretical possibilities, nature is actually using the minimal Higgs and that is what has been seen, rather than some unexpected but similar exotic particle.

All of this is good news for those of us who are unenthused by supersymmetry and other more-or-less exotic extensions to the Standard Model.

Re:The science is not settled on this.

[jythie]

More evidence supporting something does not necessarily mean the issue is 'settled', but it does add weight to the interoperation and puts an increased burden on detractors to defend their position.

link

[HybridST]

There was a link to a paper in phys.org's coverage yesterday. I read the coverage but I haven't had time to check the paper out.

The story:
m.phys.org/news/2014-06-evidence-higgs-boson-fermions.html

The paper:
http://www.nature.com/nphys/jo...

Re:The science is not settled on this.

[HybridST]

Undergrad so take this with a grain of salt.

They found something that looks like a higgs, smells like a higgs, and even quacks like a higgs while looking in the higgs-pond. They, afaict, have not yet measured its quantum-spin as being zero which would confirm it's indeed a higgs.

If the higgs-like object that was discovered is truly A higgs, it may or may not be THE higgs of the standard model. The newly discovered decay channel of the higgs-like object seems to point toward the standard model and a few other frameworks which others here know in far greater detail than I.

Now they need to measure the spin...

Re:The science is not settled on this.

[ByteSlicer]

They have strong indications that the particle is spin-0.
In the plot, blue is the expected data for spin-0, red for spin-2. The black line is derived from measurements and nicely corresponds with the peak of spin-0.
See also here.