Has the Higgs Boson Particle Been Discovered at Cern?

[Vanadium 50]

So how do we know that the new particle is not a combination of a very heavy newly encountered quark and its anti-partner?

Reason one: if this is a ¹S₀ state of a new quarkonium state (bound state of a quark-antiquark pair), there will also be a ³S₁ state that will decay to e+e- and mu+mu- pairs, at a rate where there should be a hundred thousand or more events by now. Such a thing would have been discovered long ago - probably at the Tevatron or HERA, but certainly by the LHC last year.

Reason two: A 65 GeV quark would completely screw up precision electroweak measurements and would have been discovered indirectly years ago.

Reason three: The decay into ZZ* is way too big. Maybe a million times too big. A second-order weak process competing with strong processes? It should be invisible.

 

[Vanadium 50]

The theory predicted a certain mass range in order for the wek force coupling to work out. Yet no "Higgs" could be found in that range. So they switched the range.

What on Earth are you talking about?

The Higgs Boson has to have a mass between 0+epsilon and 1000 GeV, otherwise it has problems doing the job of the Higgs and properly break electroweak symmetry.

Direct searches ruled out the range below 114 GeV and precision electroweak measurements ruled out the range above 200 GeV or so.

It ended up at 126 GeV. So what's the problem?

 

[ApplePion]

"The SM contains three quark families. A forth family would be new physics and therefore beyond the SM." Clearly when I was asking about it being a quark ant-quark pair with a 7th quark I was discussing the possibility that more than 6 quarks exist."This quark would form other combinations, too. None of them was observed."

Yeah, such as this 7th quark with the anti-quark of an 8th quark. How do you know the 8th quark is not so massive that such a neson could not be found at the energies currently used?

 

[ApplePion]

"if this is a 1S0 state of a new quarkonium state (bound state of a quark-antiquark pair), there will also be a 3S1 state that will decay to e+e- and mu+mu- pairs, at a rate where there should be a hundred thousand or more events by now. Such a thing would have been discovered long ago - probably at the Tevatron or HERA, but certainly by the LHC last year>>

What would the mass of the 3S1 state be? Would it be too high to have been created by current experiments?

 

[ApplePion]

Could someone please clarify something for me. In earlier experiments they were looking for and expecting to find the Higgs in a certain mass range. They didn't find it, of course, and began looking in a different range.

What was the reason why they were originally so convinced it had to be in that first range?

 

[lpetrich]

Look at charmonium and bottomonium states for 1S0 - 3S1 splittings. Eta-c vs. J/psi, eta-b vs. upsilon. They are not very large compared to the masses of the particles.

The relative sizes of the effects parallel the electromagnetic case, though with a much larger "fine structure constant".

Overall mass: m
Orbital energy: m*a²
Spin-orbit and spin-spin energy: m*a⁴

a = "fine structure constant" or g²/(4*pi)

If the particles differ in mass, then:

Smaller: m
Larger: M
Overall mass: M
Orbital energy: m*a²
Spin-orbit energy: m*a⁴
Spin-spin energy: m*(m/M)*a⁴

So if the recently-discovered particle was a 1S0 quarkonium state, then it ought to have a related 3S1 quarkonium state with a very close mass value.

 

[ApplePion]

Thanks for your post, lpetrich.

 

[Vanadium 50]

What would the mass of the 3S1 state be?

5 to 6 MeV (not GeV, MeV) above the 1S0. So also ~125 GeV.

It would surely have been seen previously.

 

[mfb]

I would say the observation, at the same mass, of excess events consistent with H->Z,Z(*)-> 4 leptons, by both CMS and Atlas adds a great deal to the reliability of the finding, and the probability that it is 'Higgs like'.

Related to possible measurement errors: Yes, of course.
Related to the total statistical significance: Not unimportant, but the 2photon-channel dominates the combination.

Clearly when I was asking about it being a quark ant-quark pair with a 7th quark I was discussing the possibility that more than 6 quarks exist.

And my statement was that this option is not part of the SM.

"This quark would form other combinations, too. None of them was observed."

Yeah, such as this 7th quark with the anti-quark of an 8th quark.

Or the 7th quark with up, down, strange and (rare) charm and bottom. None of these combinations was observed.

In earlier experiments they were looking for and expecting to find the Higgs in a certain mass range.

Earlier experiments had less energy and therefore not the sensitivity to look in the whole possible mass range. They just hoped to find it where the experiments were sensitive... you always hope to find something with your detector.

 

[Edgardo]

Here is a video from the Fermilab youtube channel explaining the term sigma:

Searching for the Higgs boson and other particles requires scientists to take into account statistics and probability in their analyses. Fermilab physicist Don Lincoln explains these concepts using simple dice.

http://youtu.be/73JeQ2RZnwc

https://www.youtube.com/watch?v=73JeQ2RZnwc

 

[ApplePion]

OK, thanks, Vanadium.

 

[ApplePion]

"Or the 7th quark with up, down, strange and (rare) charm and bottom. None of these combinations was observed."

OK, that is a good point, mfb.

 

[ApplePion]

"Earlier experiments had less energy and therefore not the sensitivity to look in the whole possible mass range. They just hoped to find it where the experiments were sensitive... you always hope to find something with your detector."

I really remember reading that they had a theoretical reason for thinking it would have been in that mass range. Something about making weak force couplings work out.

And I remember very distinctly that they were not just saying that they were looking in that range because that was all the energy that was then available--at the time they were saying they were *expecting* it to be in that range.

 

[Coin]

I am uncertain whether to post this question here or in the BESM forum.

I am curious about the reminders from CERN that, if I understood correctly-- did I understand correctly?-- officially they have found "a spin 0 boson" but they are not going so far as to call it the SM Higgs yet. I assume this is merely caution.

I'm curious though: If this is *not* the SM Higgs (some people say that various channels must be double checked with theory before concluding that's the case) what else do they think it might be?

I assume the only other option (since they did find the spin 0 boson) is one Higgs within some kind of multiple Higgs system? Are there other candidates if the newly found 125GEV boson is not the SM Higgs?

I have repeatedly seen posts on physics blogs saying that supersymmetry has been "excluded" below a certain mass level which keeps bumping up. On the LHC's supersymmetry "exclusions", does that exclude *all* sparticles (i.e. does it exclude Higgsinos?) Can we easily distinguish a Higgs from a Higgsino, i.e., are we sure that we just found a Higgs and not a Higgsino?

 

[Vanadium 50]

A Higgsino is a fermion. This is a boson. So it's not a Higgsino.

 

[Coin]

Ah, I should have been able to figure that out on my own. Thanks! :)

 

[kloptok]

But, as far as I understood, the particle can still be a SUSY Higgs, i.e. the lightest of several "higgsons". I am not sure how a 125 GeV Higgs fits in with the LHC SUSY exclusion data, but I think it is still compatible. This is probably one of the things discussed at ICHEP as we speak. I was at a presentation at my university a few months ago and if I remember correctly the conclusion was that while the available parameter space for MSSM is rapidly shrinking with new LHC data, it is still possible to have a 125 GeV Higgs as the lightest SUSY Higgs. But this presentation did not include the latest 5/fb of data taken in 2012 of course, so maybe the MSSM is not compatible with the 125 GeV Higgs. An interesting question however.

And as far as I understand the sparticle limits from the LHC is still quite model-dependent. Maybe someone with more expertise on the subject could confirm or deny this?

 

[TrickyDicky]

So how do we know that the new particle is not a combination of a very heavy newly encountered quark and its anti-partner?

- It would have a mass of ~63 GeV, and therefore have been within the range of LEP (as the process e- e+ -> q anti-quark is quite likely, if the energy allows it) and Tevatron.

Reason two: A 65 GeV quark would completely screw up precision electroweak measurements and would have been discovered indirectly years ago.

I don't really understand these answers given to Applepion.
Why would the quarks in that putative new boson particle have to be that heavy and therefore not any of the six SM ones? As I understand it the fact that the mass of the new particle is around 125 GeV doesn't imply that in case it was a composite boson its individual quarks have to add up to 125 GeV, just like in a proton its three quarks individual mass terms don't add up close to 1 GeV, only around a 1% of that. One thing is the effective or constituent mass and other the algebraic mass of the quark. Please correct if I got this wrong.In view of all this I'd like to reiterate my question, does the SM Higgs boson have to be an elementary particle or it could be a composite boson and still be an SM Higgs?
Matt Strassler' Higgs FAQ: "we don’t know whether the Higgs is an elementary field, as is the electron field, or a composite of more elementary fields, as is the proton field."

 

[ApplePion]

mfb: "Or the 7th quark with up, down, strange and (rare) charm and bottom. None of these combinations was observed"

Have those mass ranges been examined thoroughly?

 

[tom.stoer]

In view of all this I'd like to reiterate my question, does the SM Higgs boson have to be an elementary particle or it could be a composite boson and still be an SM Higgs?

Interesting question. In condensed matter physics these quasi-particles are never elementary, so I guess simply for the mass generetion there's no need for the Higgs to be elementary.

 

[ApplePion]

Vanadium: "if this is a 1S0 state of a new quarkonium state (bound state of a quark-antiquark pair), there will also be a 3S1 state that will decay to e+e- and mu+mu- pairs, at a rate where there should be a hundred thousand or more events by now. Such a thing would have been discovered long ago - probably at the Tevatron or HERA, but certainly by the LHC last year"

The 3S1 decays you refer to are weak force decays, right? The two-photon decay of the putative 1S0 state is an electromagnetic force decay, right? So wouldn't the weak force decay be very *rare* compared to the electromagnetic force decay? How many of the electromagnetic force two-photon decays have been observed?

 

[TrickyDicky]

Interesting question. In condensed matter physics these quasi-particles are never elementary, so I guess simply for the mass generetion there's no need for the Higgs to be elementary.

Right, and the analogy is quite justified since the Higgs mechanism was actually an analogy about superconductivity and condensates since the initial idea by Higgs, Englert, Brout and Kibble but applied to the vacuum instead of condensed matter.

 

[mfb]

I think we have to clarify "Standard Model" (SM):

In the way I use it - and in the way I usually see it in talks and publications - it contains the known 6 quarks, leptons and neutrinos, with the strong and electroweak interaction and the Higgs mechanism with a single Higgs boson. It may or may not contain neutrino masses and mixing, I saw both definitions.
Anything beyond that is "beyond the SM". While a 4th quark generation could somehow fit in the same framework, it is not part of the current model (SM). Similarly, all other ways of electroweak symmetry breaking are beyond the SM.

If you use a different definition, please post what exactly you mean with SM.

Why would the quarks in that putative new boson particle have to be that heavy and therefore not any of the six SM ones? As I understand it the fact that the mass of the new particle is around 125 GeV doesn't imply that in case it was a composite boson its individual quarks have to add up to 125 GeV, just like in a proton its three quarks individual mass terms don't add up close to 1 GeV, only around a 1% of that.

The binding energy is related to the QCD energy scale, which is ~250MeV. Pions have less, light baryons have more, but it does not increase with the quark masses. For heavy hadrons, the mass is basically the mass of the quarks, excited states may have some hundred MeV more.

mfb: "Or the 7th quark with up, down, strange and (rare) charm and bottom. None of these combinations was observed"

Have those mass ranges been examined thoroughly?

I am sure LEP looked at it and Tevatron checked it. I know that both ATLAS and CMS are searching for a 4th generation in the full observable mass range, and the lower limits are at least some hundred GeV (probably more than 1 TeV now).

The 3S1 decays you refer to are weak force decays, right? The two-photon decay of the putative 1S0 state is an electromagnetic force decay, right?

It is the other way round: The decay of spin1-particles (here: 3S1) to e- e+ or mu+ mu- can occur via the electromagnetic interaction (q anti-q -> photon -> lepton antilepton).

 

[ApplePion]

"In the way I use it - and in the way I usually see it in talks and publications - it contains the known 6 quarks, leptons and neutrinos, with the strong and electroweak interaction and the Higgs mechanism with a single Higgs boson. It may or may not contain neutrino masses and mixing, I saw both definitions.
Anything beyond that is "beyond the SM". While a 4th quark generation could somehow fit in the same framework, it is not part of the current model (SM). "

Would it actually cause some sort of problem to go to a 4th generation? If there is no intrinsic problem, then why would anyone care whether it is 3 or 4 generations?

I realize that if there are too many types of quarks the derivation of asymptotic freedom fails--that would be something I would expect people would be concerned about, but that would take more than 4 generations. Is there anything like that if we go to a 4th generation?

 

[Vorde]

Well generation matters, there are certain interactions which only work within a given generation of matter (I should know which, but I don't- I think the weak nuclear force). And there 'wouldn't be a problem' (at least not as far as I know), but any sort of 4th generation isn't included in the standard model.

 

[tom.stoer]

There are constraints regarding the number of generations resulting from higher order processes. Very heavy fermions wouldn't be produced directly at LHC (and other collidiers) b/c they are outside the experimental accessable energy range. However they contribute indirectly via higher order terms (starting at one loop) to physical matrix elements. These contributions can be calculated and constraints regarding their masses etc. can be determined.

I guess there data should be available in the Particle Data Group files.

 

[Parlyne]

It's worth noting that if there is a fourth generation, its neutrinos cannot be light. Measurements of the width of the Z make it quite clear that there's only room for 3 light neutral fermion states in Z decays. This means that any new generation of fermions must have neutrinos heavier than ~45 GeV.

 

[PAllen]

It's worth noting that if there is a fourth generation, its neutrinos cannot be light. Measurements of the width of the Z make it quite clear that there's only room for 3 light neutral fermion states in Z decays. This means that any new generation of fermions must have neutrinos heavier than ~45 GeV.

Now that's a big neutrino!

I have also come across papers arguing that cosmological evidence precludes a 4th generation.

 

[eXorikos]

Unitarity of the CKM matrix also indicates a maximum of 3 generations.

 

[Vanadium 50]

Unitarity of the CKM matrix also indicates a maximum of 3 generations.

It doesn't, and indeed, it cannot. Non-unitarity of the 3x3 CKM can require a 4th generation, but unitarity cannot forbid one.

 

[jcsd]

What do people make of this?: [new paper on possible Higgs imposters]

http://arxiv.org/abs/1207.1093

 

[jcsd]

One question I have about the Higgs mechanism is, would the Goldstone bosons, the hypercharge gauge boson, etc be observable as individual particles in suitbaly high energy regimes?

 

[tom.stoer]

For a global symmetry: at high energies the broken symmetry is restored and therefore no Goldstone boson does exist.

For a gauge theory: there is no Goldstone boson at all b/c it's an unphysical d.o.f. The excitation which would be represented by the so-called "would-be" Goldstone is "pure gauge", i.e. can be absorbed in a local gauge transformation.

 

[eXorikos]

It doesn't, and indeed, it cannot. Non-unitarity of the 3x3 CKM can require a 4th generation, but unitarity cannot forbid one.

Can you explain me why?

 

[tom.stoer]

If the 3*3 matrix U is non-unitary, this means that a forth generation is missing which fixes the non-unitarity; i.e. a 4*4 matrix U' which contains U may be unitary again.