Has the Higgs Boson Particle Been Discovered at Cern?

[profgemelli]

In any case I am very surprised that LHC thus seems to confirm the standard model, somehow. It seems to me such a complicated and anti-easthetic thing, with too many free parameters... that I have never seen it as a model that could be definitely confirmed or disproven. The discovery of the Higgs boson, does it really prove the standard model? Is this possible? If the answer is yes, then no problem: I was wrong, simply that. But the answer IS "yes"? Is it?

 

[mfb]

So why does it go up above 5 sigma for some combination of channels and then down to 4.9 for some other combination?

The other combination included a channel where they observed less events than expected with background only. In terms of a combination, the signal strength gets smaller if you include this.
@Vorde: My example was not as hypothetical as it might look like. The higgs-search alone is similar to ~50 independent searches (with different masses), and if you include all the searches for SUSY, extra dimensions and whatever, you could end up with 1000 independent measurements. The probability that one of them gives a 3-sigma discovery is large, and the probability that one gives a 5-sigma observation is still significant.
You can say with confidence "I think this is the higgs" - but only if you follow Bayesian statistics and assign some prior probability to have a Standard Model Higgs. But even in this case, I would assign some probability to measurement errors - probably not large (and $H \to \gamma \gamma$ is quite easy to interpret), but larger than 1-0.999999 = 10^-6.
Concerning the Nobel Prize: As far as I heard (and I heard this from several sides), the general opinion in the community is something like this: It would be unfair to give the prize to single persons of the experiments - the Higgs discovery is the collaborative work of hundreds. At the same time, the discovery is surely worth the prize. While the current rules do not allow this, the Nobel Committee might find a way to give the prize to the collaborations as a whole. <-- Edit: This turned out to be wrong. Prizes to collaborations are possible, it just has never been done (apart from the Peace Prize). And the prize went to theoreticians.

 

[iced199]

I just find it interesting that this was found on independence day. Go figure. :D

 

[Borek]

I just find it interesting that this was found on independence day. Go figure. :D

It wasn't found, it was announced on July 4th.

 

[atyy]

The other combination included a channel where they observed less events than expected with background only. In terms of a combination, the signal strength gets smaller if you include this.

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?

Concerning the Nobel Prize: As far as I heard (and I heard this from several sides), the general opinion in the community is something like this: It would be unfair to give the prize to single persons of the experiments - the Higgs discovery is the collaborative work of hundreds. At the same time, the discovery is surely worth the prize. While the current rules do not allow this, the Nobel Committee might find a way to give the prize to the collaborations as a whole.

I think the accelerating expansion is another one of those prizes that is already thought to be teamwork, but they weren't able to get round the rules already. OTOH, the peace prize did go to Doctors without Borders, so I wonder if the rules are different for that prize, or there's always been some way to get round the rules.

 

[Vorde]

I just find it interesting that this was found on independence day. Go figure. :D

Also CERN isn't american.

 

[lpetrich]

Some issues.

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?

I will now attempt to combine the CMS and ATLAS peak-height results, though I will use a rather crude algorithm: sqrt(sum of squares of individual heights). Their individual heights are 4.9 and 5.0 stdevs, giving a total height of 7.0 stdevs. Going from local to global here involves multiplying by some factor that's 0.75 to 0.8. That means a combined height of 5.2 to 5.6 stdevs.

Fabiola Gianotti of the ATLAS team stated that the LHC had made 1/3 of the collisions that it's expected to make this year. I had expected 1/2. Using those figures, the peak heights should go up by a factor of 1.2 to 1.4 by the end of this year. That will be enough to push come of the individual decay channels close to 5, and it's likely good enough to get directional info for finding this particle's spin.

At the end of this year, the LHC is to be shut down for upgrading to its full design energy of 14 TeV. It's now at 8 TeV, and it was at 7 TeV last year. It should restart in 2015.

 

[Vorde]

Some issues.

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?

I will now attempt to combine the CMS and ATLAS peak-height results, though I will use a rather crude algorithm: sqrt(sum of squares of individual heights). Their individual heights are 4.9 and 5.0 stdevs, giving a total height of 7.0 stdevs. Going from local to global here involves multiplying by some factor that's 0.75 to 0.8. That means a combined height of 5.2 to 5.6 stdevs.

Fabiola Gianotti of the ATLAS team stated that the LHC had made 1/3 of the collisions that it's expected to make this year. I had expected 1/2. Using those figures, the peak heights should go up by a factor of 1.2 to 1.4 by the end of this year. That will be enough to push come of the individual decay channels close to 5, and it's likely good enough to get directional info for finding this particle's spin.

At the end of this year, the LHC is to be shut down for upgrading to its full design energy of 14 TeV. It's now at 8 TeV, and it was at 7 TeV last year. It should restart in 2015.

In the press conference they said that with the various uncertainties the two detector's estimates for the Higgs' mass were definitely compatible.

Also they said that they are planning to extend this year's science run by two or three months in order to facilitate more data gathering, which might hopefully mean that upon intense review of the data they could really discover some cool stuff even before the LHC resumes operation in a couple years.

 

[pgardn]

The mass of the Higgs particle is 'created' by two parameters in the Lagrangian

Follow up on Dadfaces question:
So is it wrong to say at this time that the Higgs field is a manifestation of the Higgs boson and vice versa?

After reading all the press releases:
I have been having a very difficult time with the word particle. To me it has a connotation, oh heck, I am not sure what a particle is any more... What is a particle? Anything that is not a field?

Never mind. I read the particle article and am now able to rhyme. I did not read far enough. Force particles... gravitron. Caused me confusion based on what I understood a particle to be defined as.

 

[geordief]

I have some questions

Is the postulated higgs particle substantially larger than most other particles?
Is it larger than the electron?Larger than the proton? Larger than the atom?
I had assumed it was difficult to find because it was infinitesimally tiny -far far smaller than the particles hitherto discovered but it seems the opposite may be the case.

If it exists and operates as thought is that an indication of a primacy of energy over matter -or is that a ridiculous question?

 

[Vorde]

Is the postulated higgs particle substantially larger than most other particles?
Is it larger than the electron?Larger than the proton? Larger than the atom?
I had assumed it was difficult to find because it was infinitesimally tiny -far far smaller than the particles hitherto discovered but it seems the opposite may be the case.

If it exists and operates as thought is that an indication of a primacy of energy over matter -or is that a ridiculous question?

This particle they've just announced is heavier than all fundamental particles apart from the Top Quark, which is about 35 GeV heavier. Both are far heavier than the proton, which is far heavier than the electron.

The reason heavier particles are tougher to find is that the way they 'discover' these particles is by taking two light (in weight, not photons) particles and injecting lots of energy into them (by speeding them up, the added energy increases their mass because of e=mc²). Then they collide two of these particles. All the energy that you put in them has to go somewhere, so it goes into the creation of new particles. The heavier a particle is, the more energy you need to create it (its more complicated than this, but this is the general gist).

As to the last question, mass and energy are one and the same (e=mc²), so it's a silly question.

 

[lpetrich]

Follow up on Dadfaces question:
So is it wrong to say at this time that the Higgs field is a manifestation of the Higgs boson and vice versa?

I think that it's legitimate to say that.

After reading all the press releases:
I have been having a very difficult time with the word particle. To me it has a connotation, oh heck, I am not sure what a particle is any more... What is a particle? Anything that is not a field?

Welcome to the wonderful world of wave-particle duality.

Elementary-particle theories are constructed within a paradigm, quantum field theory. It states that elementary "particles" are quantized fields, with an individual "particle" being a localized excitation.

Is the postulated higgs particle substantially larger than most other particles?
Is it larger than the electron?Larger than the proton? Larger than the atom?
I had assumed it was difficult to find because it was infinitesimally tiny -far far smaller than the particles hitherto discovered but it seems the opposite may be the case.

"Size" is not very meaningful for non-composite elementary particles. The closest thing to a size for such particles is its Compton Length, 1/(mass) in quantum-mechanical units.

 

[Neandethal00]

Has anyone else noticed in their press releases, interviews?
I have never seen a Physicist talks like a Politician!

You don't deny it but you don't totally agree with it either.

 

[Jakeness]

Has anyone else noticed in their press releases, interviews?
I have never seen a Physicist talks like a Politician!

You don't deny it but you don't totally agree with it either.

I believe the information they supplied is sufficient, given the uncertainty still surrounding the topic. In the press conference, they've stated that the results from the two experiments will be combined in 4 weeks or so, but it won't be until the end of the year until they can determine what "type" of Higgs particle was detected, if I can recall correctly. So you'll have to wait until then.

 

[TrickyDicky]

When it is expected that enough data from the new particle will have been gathered to be certain about its spin?

 

[calgarian]

I have a question which is probably pretty basic. If the Higgs field is everywhere, why are Higgs bosons so fragile that they decay before they reach the detectors?

 

[Vorde]

When it is expected that enough data from the new particle will have been gathered to be certain about its spin?

They said that best case scenario it would be by the end of the year.

 

[calgarian]

Is there a video of the conference online ?

2 hour "technical" seminar

1 hour "layman" press conference

 

[TrickyDicky]

They said that best case scenario it would be by the end of the year.

Thanks (I missed this was already answered in #77 and #78).
I know there is enough data to say it is an integer spin (boson), and that it is expected that it is 0 (scalar). How would it alter the state of things if it was found out its spin is 1 instead? Could it be the Higgs in that case?

 

[lpetrich]

I have a question which is probably pretty basic. If the Higgs field is everywhere, why are Higgs bosons so fragile that they decay before they reach the detectors?

The Higgs-particle ground state has a nonzero field value, but the Higgs particles that one makes are essentially field excitations, like every other elementary particle.

Has anyone created a FAQ file explaining quantum field theory and how wave-particle duality works in it?

 

[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.