Has the Higgs Boson Particle Been Discovered at Cern?

[mfb]

Since ATLAS has not looked at all its channels, could the joint significance of the CMS and ATLAS data be less than 5 sigma in the final analysis?

I doubt this. The significance will be driven by the most sensitive channels (2 gamma and ZZ->4 leptons), and they both see a significant deviation. Assuming no significant correlated systematic uncertainty, the combined significance should be about 5*sqrt(2)=7 standard deviations. However, I do not think a combination will give anything interesting new. There is no need to combine the data - the result ("hey we found the Higgs") is clear anyway.
In addition, it is expected that they can double the size of the datasets within the next 2-3 months (they already collected 0,15/pb today, for example, ~1/30 of the 2012 dataset), therefore both can get this significance individually.

The CMS team reported a Higgs mass of 125.3 +- 0.6 GeV, and the ATLAS team 126.5 GeV. But from the quoted uncertainty, that's only 1.4 stdevs, if the ATLAS result also has that uncertainty. So is it fair to say that that's not a big discrepancy?

Yes. In addition, the 0.6 GeV might be the statistical uncertainty only. The systematic uncertainty from the energy scale calibration is a bit harder to get, and can contribute to the total uncertainty.


@geordief: To our current knowledge, all particles are point-like.

If the Higgs field is everywhere, why are Higgs bosons so fragile that they decay before they reach the detectors?

Hmm... imagine a surface of thin honey. It is everywhere. Now try to "excite" this, e.g. create waves in the honey. They will vanish very quickly, even with the honey being everywhere. This example does not resemble the actual decay of the Higgs into other particles, but it should give you some idea.

 

[cumfy]

Where is the technical paper for the Higgs discovery ?

Could someone provide a link to the paper/analysis which accompanies the announcement ?

Can't find anything obvious at public.web.cern.ch
Thanks

 

[ZapperZ]

Could someone provide a link to the paper/analysis which accompanies the announcement ?

Can't find anything obvious at public.web.cern.ch
Thanks

Please read the http://press.web.cern.ch/press/PressReleases/Releases2012/PR17.12E.html. In particular, this paragraph:

The results presented today are labelled preliminary. They are based on data collected in 2011 and 2012, with the 2012 data still under analysis. Publication of the analyses shown today is expected around the end of July. A more complete picture of today’s observations will emerge later this year after the LHC provides the experiments with more data.

Zz.

 

[cumfy]

Technical presentation of Higgs results

OK. there is 177 slide tech pres at:

 

[Marioqwe]

https://twiki.cern.ch/twiki/bin/view/AtlasPublic

 

[cuallito]

Do any other particles decay into two photons?

 

[atyy]

Do any other particles decay into two photons?

Lubos Motl gives the answer in one of these comments. A particle that decays into only 2 photons with significant probability must have spin 0 or spin 2. The only spin 2 particle in current theory is the graviton, while no previous spin 0 particles are known. The CERN announcement seems to say that their data is consistent with a particle involved in the Higgs mechanism. They don't rule out that the mechanism might involve more than one Higgs-like particle.

 

[PAllen]

Lubos Motl gives the answer in one of these comments. A particle that decays into only 2 photons with significant probability must have spin 0 or spin 2. The only spin 2 particle in current theory is the graviton, while no previous spin 0 particles are known. The CERN announcement seems to say that their data is consistent with a particle involved in the Higgs mechanism. They don't rule out that the mechanism might involve more than one Higgs-like particle.

A small clarification: no prior spin zero fundamental particles. Composite spin zero particles (pion) are known, and pion di-photon decays are common.

 

[Dead Boss]

Do any other particles decay into two photons?

Yes, for example eta meson.

 

[tom.stoer]

Mesons have the wrong parity

 

[PAllen]

Mesons have the wrong parity

I wasn't implying a meson could be confused with the current LHC data: only that there are non-fundamental particles with spin zero that decay into two photons.

 

[Dead Boss]

Mesons have the wrong parity

I was just answering the question as stated and eta meson most certainly can decay into two photons.

 

[tom.stoer]

OK, OK, you are right. Sorry!

 

[ranrod]

The 4.9 sigma refers to the data not being an error, but what are the odds that what was found is not a higgs boson? Didn't they say the spin is either 0 or 2? Does that mean a 50-50 chance it's NOT a higgs boson?

 

[Syrinx]

Here's the link to the presentations (introduction, CMS, and ATLAS) and also the slides:

http://indico.cern.ch/conferenceDisplay.py?confId=197461

The slides are quite large. Be patient when downloading.

 

[cuallito]

What fundamental force does the Higgs field/particle belong to?

 

[PAllen]

A co-worker of mine who is a former Cern physicist tells me the the data and results announced so far provide no evidence of the parity of the boson yet. I looked over the slides of the presentations and saw nothing that indicated to me anything about parity. My co-worker claimed much more data and difficult analysis would be needed to establish the parity of the new particle.

Comments?

 

[Dead Boss]

What fundamental force does the Higgs field/particle belong to?

None as far as I know.

 

[zonde]

As I understand physicists are rather certain that Higgs boson (field) gives mass for W and Z bosons (they are linked with certain symmetry considerations).
But how "strong" is the idea that the same Higgs boson that gives mass for W and Z also gives mass for other particles?

 

[tom.stoer]

I don't think so. They said 4.9 sigma, they said that there is a new particle (again - 4.9 sigma) and that it could be the SM Higgs, but that they have to get more data and analysis to be sure about that; they said that there are decay channels looking like thew SM Higgs, but that there are others still to be investigated; so I think they were rather careful.

And what do you mean by "a lot of proof"? What do you expect?

 

[Neandethal00]

I myself am a little disappointed to see
six sigma is being used to prove a Physics Theory.

Has it been a normal practice in science this days?

 

[AnTiFreeze3]

I myself am a little disappointed to see
six sigma is being used to prove a Physics Theory.

Has it been a normal practice in science this days?

What do you think they've proven? Like it has been stated countless times in this thread before, the data that they have recorded at CERN appears to match what the Higgs boson should be. Nobody claimed that they have definitive proof that they found the Higgs boson with complete certainty.

Besides, it's 4.9 sigma, anyways. Not six.

 

[tom.stoer]

Statistical significance like 'x sigma' never proves a (physical) theory, it is to be seen as a significance of (the interpretation of) the results, i.e. that it's 'unlike to have occurred by chance'; it therefore provides some evidence (depending on x) to either ascept the hypotheses ('there is a particle') or to reject it ('there is something else, noise, ...').

You can never prove a physical theory! You can only try to disprove it and you will trust in the theory if it agrees with 'most' observations 'enough' attempts to disprove it have failed.

In particle physics they use 5 sigma, but of course they will collect more data and try to improve their analysis, so they will (hopefully ;-) report > 5 sigma in the next month or years

 

[geordief]

another question

Would I be right to suppose that the Higgs Boson is believed to exist everywhere in the universe and with an even distribution?

In between galaxies as much as in the centre or at the surface of the earth?

Has anyone a link towards any theories ( in layman's language where possible) about the putative behaviour of this particle?

Is there any connection between the Higgs Boson and the graviton I sometimes hear tell of?

 

[Drakkith]

Would I be right to suppose that the Higgs Boson is believed to exist everywhere in the universe and with an even distribution?

In between galaxies as much as in the centre or at the surface of the earth?

Has anyone a link towards any theories ( in layman's language where possible) about the putative behaviour of this particle?

Is there any connection between the Higgs Boson and the graviton I sometimes hear tell of?

No, the higgs field exists everywhere, there are not actual higgs bosons everywhere in the universe.

 

[geordief]

No, the higgs field exists everywhere, there are not actual higgs bosons everywhere in the universe.

Thanks .Well would this field be evenly distributed then in the same way as I was wondering about the particle- or might it be stronger in different regions of the universe than in others?

Or can the field be dynamic? Can it feed off interreacting particles and become stronger?

 

[TrickyDicky]

A co-worker of mine who is a former Cern physicist tells me the the data and results announced so far provide no evidence of the parity of the boson yet. I looked over the slides of the presentations and saw nothing that indicated to me anything about parity. My co-worker claimed much more data and difficult analysis would be needed to establish the parity of the new particle.

Comments?

So then if we haven't the parity yet, nor the exact spin (other than it must be integer), objectively what we have so far is a very high chance to have found a new particle, not necessarily the SM Higgs, right? Maybe here is where all the media (and some scientists) hype might confuse the laymen.
So, basically everyone in the know expects this new particle to be the Higgs (or some Higgs), but just in case, what other SM (already observed or hypothesized) particles are compatible with what has been observed so far?
Meson?, Z-prime? graviton?...

 

[Drakkith]

Thanks .Well would this field be evenly distributed then in the same way as I was wondering about the particle- or might it be stronger in different regions of the universe than in others?

Or can the field be dynamic? Can it feed off interreacting particles and become stronger?

Not sure. Try searching the forum or google for the Higgs field. That may help you. Unless someone explains it before then of course.

 

[atyy]

So if the tau decays remain low, could the significance using the same analysis fall, even if more data is collected?

Presumably though, since statistics are a matter of taste, common sense would say to use another analysis using only the relevant channels?

 

[mfb]

The 4.9 sigma refers to the data not being an error, but what are the odds that what was found is not a higgs boson? Didn't they say the spin is either 0 or 2? Does that mean a 50-50 chance it's NOT a higgs boson?

I am either president of the US or not. This does not imply a 50%-probability for both.@scijeebus: There is a new particle - this is nearly certain. While the 4-lepton-channel is a bit tricky, you do not get the 2-photon peak via (reasonable) measurement errors. The talks contained really strong evidence for the new particle. And it looks similar to the SM higgs boson.

Imagine someone tells you "I have the biggest diamond in the world"

... and you give this object to multiple independent experts (chosen by you and not revealed to him) to investigate it with several different methods. And all agree that it is a diamond and report its size. Sure, there is the possibility that all are wrong, but how likely is that?

You may be right, the audience still does not understand what they are doing and they could invest more time in explanations.

Depends on the audience.

Well would this field be evenly distributed then in the same way as I was wondering about the particle- or might it be stronger in different regions of the universe than in others?

Or can the field be dynamic? Can it feed off interreacting particles and become stronger?

These questions do not make sense.

objectively what we have so far is a very high chance to have found a new particle, not necessarily the SM Higgs, right?

Right.
There are no other SM particles which could give this observation. There are some extensions to the SM which can have bosons in the mass range, usually somehow connected to the Higgs boson(s). But I do not know details here, I do not think any of them is realized in nature anyway :p.