Has the Higgs Boson Particle Been Discovered at Cern?

[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.

 

[eXorikos]

That I know, but why does unitarity not prove the impossibility of a fourth generation?

If the CKM matrix is unitary, how can there be a fourth generation that mixes with the three known generations?

 

[mfb]

You always have measurement uncertainties - while the measurements can be consistent with (3x3) unitarity, they cannot prove it. The other option would be no mixing with the 4th generation at all, but that looks odd.

If mixing with a 4th generation exists, it has to be small, otherwise it would have been detected in loops (similar to the top-quark). And the high required neutrino mass is extremely odd, given that the known three neutrinos have a mass of at most 1-2 eV (using the upper limit for the electron neutrino and the mixing measurements).

 

[PAllen]

References to the following paper are beginning to make the rounds, so thought I'd post here (though all differences from SM in the recent LHC data are 2 sigma or less, of course people will jump on the hints):

http://arxiv.org/abs/1207.1445

 

[tom.stoer]

... but why does unitarity not prove the impossibility of a fourth generation?

If the CKM matrix is unitary, how can there be a fourth generation that mixes with the three known generations?

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

If the 3*3 CKM matrix is not unitary this may (or must?) be fixed by adding a forth generation. If the 3*3 CKM matrix is unitary there may be a forth generation w/o CKM mixing. I am not even sure whether a 'putative unitary' 3*3 CKM matrix with experimental uncertainties taken into account does rule out a small 4*4 mixing.

EDIT: just saw mfb's reply ...

 

[PhysicsPimpin]

Super-symmetry Credence By This?

Hey, if the mass magnitude of the Higgs is reveal able at the Cern accelerator energies, does that not give some hope as to giving String Theories main hypothesis of Super symmetric partner predictions a possible testing scenario for 11-Dimensional Prerequisite String Theory Modeling using scientific methods for verification?

I would love to see the quantum gravitational solution to Einsteins life work and the Standard Model.

I think that may be the (what kind of box you ain't supposed to open?) key yo.

 

[mfb]

Searches for SUSY (=supersymmetry) particles are a big part of the physics analyses done with the ATLAS and CMS detectors.
So far, none were found. We'll see what happens in 2015 with the increased energy.

 

[Shin204]

We hear people talking about the "party model" of the Higgs boson, but what made that particle so popular in the first place? In a technical question:What makes matter interact with the higgs in the first place?

 

[mfb]

We hear people talking about the "party model" of the Higgs boson, but what made that particle so popular in the first place?

According to Boston Globe:

The celebrity analogy, for instance, was first concocted in 1993 by David Miller, a physicist at University College London. Miller submitted it as one of the winning entries to a challenge posed by UK Science Minister William Waldegrave: On one sheet of paper, explain what the Higgs boson is and why it’s important to find it.

In a technical question:What makes matter interact with the higgs in the first place?

There is no known deeper reason why things interact. We just observe those interactione and can describe them with formulas.

 

[ChrisVer]

Additionally to mfb's P#183 and why the matter interacts with Higgs:
They interact because they are allowed by the current symmetries... If some interaction terms are allowed by your theory's symmetries, then you have to take them into account. If these interactions happen not to exist, one can postulate additional symmetries to set the coupling constants to zero (so that you won't have naturalness problems - coupling constants extremely small). And although the general symmetry allows those terms, the extra one is going to kill them.

 

[euclideanspace]

Higgs may still be controversial..

http://www.dailymail.co.uk/sciencetech/article-2171611/Is-God-particle-impostor-Scientists-claim-signal-Large-Hadron-Collider-Higgs-all.html

 

[ChrisVer]

http://cms.web.cern.ch/sites/cms.we...public/field/image/image1_1.png?itok=fibts9L4

http://www.atlas.ch/news/images/stories/1-plot.jpg

Here are the graphs which showed the Higgs discovery from CMS and ATLAS. It's the graphs which made those two organizations to publish the papers in which they claimed to have found a new particle. From an experimental point of view, these results only need better statistical corrections which will be available by the time LHC starts operating again. It is a common knowledge however, and after further studies, that the new particle is indeed the Higgs and we only need time to pile up more data to get better sigmas.

 

[mfb]

Higgs may still be controversial..

http://www.dailymail.co.uk/sciencetech/article-2171611/Is-God-particle-impostor-Scientists-claim-signal-Large-Hadron-Collider-Higgs-all.html

This article is from 2012, one week after the discovery of the particle got announced. It is completely outdated.

It is uncontroversial that ATLAS and CMS found "a" Higgs boson. There might be more (but nothing else has been found so far), but the new particle is clearly a Higgs boson.

New results indicate that new particle is a Higgs boson (March 2013)
The birth of a Higgs boson (May 2013 - it is simply called "Higgs boson" since then).

 

[ChrisVer]

additionally again, it's a Standard Model Higgs (un)fortunately...without making clear whether there is any more extra physics beyond it or not... leaving us only with the chance of finding a 2nd one or not to make sure. Am I the only one who finds this irritating? Out of so much free region, for it to go and "stand" right between the MSSM and SM limits...
http://indico.cern.ch/event/186656/session/0/contribution/4/material/slides/0.pdf

 

[Superposed_Cat]

There is a thread like this every week, just see one of the other 100 duplicates, damn. seriously someone give me a week we went without a "higgs particle found?" In the high energy and nuclear physics section. Not a rhetorical question.

 

[mfb]

The last post in this thread was in July 2014.

 

[Superposed_Cat]

was in front page, many apologies. Must have been made a sticky for that reason.

 

[mfb]

It is sticky for exactly that reason.