Higgs, what is missing now?

[brook]

Hello again everyone

I am not sure if this is the place to ask this question and if I am violating the rules of posting please let me know

Can someone explain to me what the next physical process is going to be to qualify this new Boson as Higgs Boson? Can you let me know what is missing to say definitely it is the Higgs Boson? And if it doesn't turn out to be the one, what of the future? Am sorry I just couldn't ask so clearly cause am not so educated in physics but please let me know the details as much as you can Everything you say, I am sure I would learn from it

Thank you again and may BAUT live forever

[WayneFrancis]

I've been bad and haven't been following hardly any of the releases about the new particle. From what I've read the particle has some of the properties expected for the Higgs but more work needs to be done. I'm eager to hear what people here have to say about it too.

[Shaula]

The main thing to look at is spin. It needs to be spin-0 to be the Higgs. There are also some questions about the less probable decay routes, at the moment the data looks right for the main decay processes but there are some hints that the other channels are not as they should be. This is either new physics or a cruel joke by the universe on particle physicists.

So the main things left to do are:
1) Check the spin
2) Check the decay routes seen against theory.

When the LHC powers up to 14TeV then they will also be checking the self interactions of the particle against what they expect from the Higgs. In the further future there is some excitement building for the idea of a Higgs factory, a muon-muon collider. There are considerable technical challenges to do with this, however.

[Xibalba]

That's really interesting! I've heard that the fact that the particle is not exactly as expected, it might open up ways into supersymmetric particles... How so? I don't really get that.

[Shaula]

Well, one of the options is that if it is not the Higgs it could be one of the missing supersymmetric particles. However other experiments have set very strong limits on the masses of squarks and gluinos so it would not be them. There is a chance it could be a mixed neutralino or slepton, they could be to be in the range 100-150 GeV. If we start finding these superpartners then suddenly supersymmetry looks attractive, the big problem right now is that there is simply no sign of the many particles it needs to complete its zoo.

I think the sleptons are ruled out by the fact that they are charged - that should be obvious in the data. The neutralinos are fermions, I would have thought that that would leave an obvious signature too, but since we have not got the spin of the discovered particle yet I don't think they can be ruled out.

[WayneFrancis]

That's really interesting! I've heard that the fact that the particle is not exactly as expected, it might open up ways into supersymmetric particles... How so? I don't really get that.

I've heard they are receiving about twice as many data points as they would have expected but this might indicate support for a model where there is more then 1 type of Higgs. It was also indicated this is a bit of a problem for super symmetry but not exactly the death blow.

[moozoo]

From what I understand they have ruled out new particles being present over most of the detectable energy range of the LHC except for the one particle found near 125 Gev.
Is that correct?
i.e. we only have one new particle to learn about (or maybe couple of particles close to 125Gev)
Once we know everything about this one particle then we will need to build something bigger, but this time without the SM predicting any being found.

[brook]

Also if someone can comment on how Higgs Boson is related to Dark matter or dark energy? It will be great

[Ivan Viehoff]

Well, one of the options is that if it is not the Higgs it could be one of the missing supersymmetric particles.

I am sure you didn't intend it, but your use of the phrase "one of the missing supersymmetric particles" might possibly suggest to some people that there are some that are not missing, but in fact they all remain missing, where "all" refers to a number that may be as low as zero.

I think at the moment it is a bit like we were trying to confirm rumours of the existence of elephants, and we have now found a very big grey animal. It may turn out that is is not in fact an elephant as the elders intended the word - we haven't been able to check important factors like the possession of a long trunk and big flappy ears. But there weren't any other big gray animals on our list of rumoured beasts yet to be discovered.

[Ivan Viehoff]

Also if someone can comment on how Higgs Boson is related to Dark matter or dark energy?

The discovery of the Higgs Boson, if indeed it turns out to be the HB as understood by the standard model, will shed no light whatsoever on dark matter and dark energy. This is why Woit has termed the discovery by the LHC of the standard model Higgs and nothing else the "nightmare scenario".

If the Higgs turns out to be rather different than what we expected, then maybe that will point the way to some new physics, and maybe to explaining the phenomena of apparent missing matter and cosmology not doing what we predict.

[Shaula]

From what I understand they have ruled out new particles being present over most of the detectable energy range of the LHC except for the one particle found near 125 Gev.

Remember the LHC is running at about half power right now.

[ShinAce]

Remember the LHC is running at about half power right now.

I thought it did see full power. Initially at 3.5 Tev per beam(when the quench happened) and now at 4 Tev per beam. It's not until the 'long slumber' that it will get the upgrades(read: rebuild going into 2014-2015) to get up to 7 Tev per beam. Just because the ultimate idea has been in the books for a while, doesn't mean it's running at half power. I can see people reading that and going "Well then, why don't we crank it up?". The answer is, we can't. But we will, in 2015. That's asking someone for a lot of patience when the science is being done now, at this energy level.

Before the LHC was powered on, people were already hearing about the Higgs boson search. What are we expecting to find this time(ie, the 2015 LHC)? As far as I know, there aren't any new particles that are expected to appear.

[antoniseb]

I thought it did see full power. ...

I assume by "power" you guys are referring to "top proton energy". I don't know if the number of protons will stay the same as they go toward 7 TeV per beam.

[ShinAce]

For sure, I'm talking about energy/nucleon. I heard with the upgrade that the bunch spacing is to stay the same. However, I don't know if bunches increase in particle count.

[brook]

so if Higgs can only explain about just the 4% the matter we know about the Universe, which doesn't include dark matter and dark energy, why do physicists call it fundamental to the whole universe( matter +dark matter+dark energy)? I am sure they have a reason someone please help I heard some Physicists say it is the " Bang" in the big bang. Am a bit confused. Please help

[Shaula]

The point is that at the moment there is no other mass generation mechanism. The 4% figure is horribly misleading too in that it implies that the Higgs mechanism is insignificant. The main points to bear in mind are:

1) The Higgs mechanism provides a fundamental way to generate the mass for massive vector bosons
2) The Higgs mechanism is critical to explaining how electroweak unification works
3) Similar to the strong force (the strong force holds colour charged quarks together but a second order effect known as the residual strong force holds non-colour-charged nucleaons together too) it is perfectly possible that a 'residual' Higgs effect is the fundamental mechanism for fermionic mass generation. The important thing is having some mechanism that generates mass in the first place.

People saying Higgs is not important because of the 4% number is ridiculous. It is very much like saying that any physics to do with baryonic mass is unimportant because it makes up 5% of the whole universe.

No physicist I have ever spoken to (I am one and work in a room full of them!) has ever said that the Higgs is the bang in the big bang. It is part of fundamental standard model physics, not an explanation for everything.

[lpetrich]

As to measuring the putative Higgs particle's spin, I think that that will be done by looking for an imprint of the LHC proton beams' directions on the likely directions of the outgoing particles. If there is zero imprint, that is, isotropic decay, that will mean that the putative Higgs particle has spin 0. However, making that test will require collecting more events to get good statistical significance.

The Standard Model predicts its Higgs particle's decays with no free parameters. However, extensions of the Standard Model like the Minimal Supersymmetric Standard Model (MSSM) have some additional parameters, and some of them affect their Higgs particles' masses and decay rates. The MSSM predicts more than the single Higgs particle of the SM: three neutral ones and both signs of a charged one. One of the neutral ones is relatively light and SM-like -- and with a range of expected masses that the recently-observed particle falls right into.

-

As to the origin of mass, the Higgs particle makes it by having a nonzero lowest-energy field value. So every particle that interacts with it continually experiences its presence, and that drags those particles and gives those particles their masses. Without the Higgs particle, every other Standard-Model particle would be massless.

The Higgs nonzero-field lowest-energy state can be explained with an analogy of a marble in a bowl. In a "normal" one, the marble will settle down in the center, and if you push it, it will oscillate back and forth around the center. But in a bowl with a hump in the center, like a juice-squeezer bowl, the marble will settle down in the trough around the central hump, at nonzero distance from the center. It will oscillate inward and outward, but move at constant speed in the trough. That trough-motion mode is called a "Goldstone mode", and in elementary particles, it would show up as a massless mode. Peter Higgs and others discovered that such massless modes could disappear into photonlike fields that were made massive from symmetry breaking, thus avoiding excess massless particles.

-

As to the mass of baryonic matter, the mass that we observe in the world around us and in ourselves, about 98% of it is due to a side effect of an effect called color confinement. From their mutual interactions, quarks' and gluons' interactions with each other become very strong at distances much above 10^(-15) m, the size of a nucleon (proton or neutron). So they can't get much further apart from each other than about that distance. That's what gives nucleon that size. Since gluons are massless and up and down quarks are not much more massive than an electron, most of quarks' and gluons' energy in nucleons is kinetic and interaction energy. Thus, by E = mc^2, most of the mass of nucleons comes from that energy.

In summary, about 98% of nucleons' masses is due to color-confinement-induced quark and gluon kinetic and interaction energy, 1% due to electromagnetic effects, and 1% due to quark (rest) masses. The electron's mass is 0.05% that of a nucleon. Nuclear binding energies are typically a little less than 1% of a nucleon mass, electron binding energies in atoms much less, and molecular binding energies even less.

However, electrons, up quarks, and down quarks all get their masses by the Higgs mechanism, and their mass values are important in determining the structure of the baryonic parts of our Universe.

In our Universe, baryonic matter has only about 5% of its total mass, with most of the rest being dark matter and dark energy. The favorite candidates for dark matter do not get their masses from the Higgs mechanism, and the nature of dark energy is even more obscure, though unlikely to get mass from the Higgs mechanism. The inflation-making field in the early Universe likewise likely does not get its mass from the Higgs mechanism.

So only about 0.05% of the Universe's total mass is Higgs-generated. About 5% of it is generated by color confinement, and the rest is obscure.

[Shaula]

However, electrons, up quarks, and down quarks all get their masses by the Higgs mechanism.

I hate to nitpick but I would like to say that I think that this should read "It is believed that electrons..."

In Electroweak theory the symmetry that is broken, the basic structure of what is going on is understood and there are several mechanisms proposed to actually allow the Higgs mechanism to be realised. When it comes to fermions all that has been proposed is that there is some mystery coupling of the fields, of some unknown strength, relating to a broken symmetry of unknown form, that leads to the same basic results.

Basically it would be a shock if there was a totally new mass generation mechanism for fermions but the theory has been hard to advance without some knowledge of the Higgs boson. Hopefully we are now at the stage where we can get that and the Higgs mechanism for fermions can be fully worked out. But until then it is not a fully formed and rigorous theory.

[xylophobe]

Is it theorized that the Higgs would have an anti-Higgs particle?

If so what would be the resultant particles/photons?

What is the half-life of a Higgs boson?

[ShinAce]

Is it theorized that the Higgs would have an anti-Higgs particle?

If so what would be the resultant particles/photons?

What is the half-life of a Higgs boson?

The Higgs boson is the anti Higgs. Like the photon, it is its own antiparticle. It carries no electric charge, nor color charge, and has zero spin. All of this information has been available on wiki prior to the discovery.

[lpetrich]

The Higgs-particle mean lifetime?

From LHC Higgs Cross Section Working Group - CrossSections < LHCPhysics < TWiki, the Standard-Model decay width of the Higgs particle is about 3 MeV.

That means a mean life of about 2*10^-22 seconds, and multiplying it by c, 7*10^-14 m, not much more than the size of a nucleon.

[brook]

Are there other Mass generation mechanisms proposed other than the Higgs Mechanism? Has there been any experiments done to test those mechanisms?

[lpetrich]

Theories like Higgsless models, including Technicolor (physics), Topcolor, Top quark condensate, Preons, and Unparticle physics (from Wikipedia).