Fresh Evidence Supports Higgs Boson Discovery 42
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.
Re:More than one Higgs Boson? (Score:5, Informative)
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? (Score:5, Informative)
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.
link (Score:5, Informative)
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... [nature.com]
Re:More than one Higgs Boson? (Score:3, Informative)
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? (Score:5, Informative)
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? (Score:3, Informative)
Re:The science is not settled on this. (Score:5, Informative)
They have strong indications [atlas.ch] 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 [arxiv.org].
Re:More than one Higgs Boson? (Score:4, Informative)
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.