Has the Higgs Boson Particle Been Discovered at Cern?

[yuiop]

As i understand it, they don't directly observe the Higg's boson because it decays almost immediately and it has no electric or colour charge and no spin. What they can observe using instruments is the decay particles which tell the scientists something about the momentum, energy, colour, charge and spin of the original particle, using conservation principles.

And then on top of ALL of that, what about Einsteins theories? How does it explain frame-dragging? What about space-time curvature? What about conversion of mass to energy?

Despite sometimes being called the "God particle", the Higg's boson does not provide the answer to everything. The author that coined that term actually wanted to call the Goddamn particle, in reference to the extraordinary effort and cost involved in confirming its existence.

 

[Vorde]

No, and this contains a very fundamental error.
You can never measure "the probabilty that you found a particle". You can just give the probability that the measured signal occurs as a random fluctuation (and the probability that this signal occurs if there is a particle).
Simple example: Look for new particles at 1000 different places. Just by chance, you will expect at least one 3sigma-discovery, even if no particle is there at all. Are you 99,7% sure that you discovered a new particle? I hope not.

So in actuality I agree that you are totally correct, I would have worded it better were I thinking about more. But I still think that at a layman's level what I said is fine.

They have found a signal indicative of a new particle. And the likelihood of this signal being caused by the background noise is in the 5-sigma range (so .0001% I think). While my original vocabulary was quite sloppy, why can one not say that the research teams were 99.9999% sure they have detected a new particle?

 

[scijeebus]

As i understand it, they don't directly observe the Higg's boson because it decays almost immediately and it has no electric or colour charge and no spin. What they can observe using instruments is the decay particles which tell the scientists something about the momentum, energy, colour, charge and spin of the original particle, using conservation principles.

Ok, so what does it decay into and how do we in any way directly observe that?
And then still, how do we know those properties of spin and mass and colour are of the particle we are searching for?

 

[kloptok]

I would assume this is because of the decays into γγ or ZZ - these are spin 1 particles so I think the total spin can be either 0 or 2.

Something I certainly don't understand is the ZZ decay mode, as 2 x M_Z > 126GeV. I noticed the slides actually describe the mode as ZZ^* - what does that actually mean?

Yeah, that's true. At the same time one of the diphoton channel diagrams involves an intermediate quark loop, which requires a spin of 0 or 1. If this particular decay wasn't active I would expect a decrease in the number of detected diphoton events compared to expected, while the experiments have rather seen an excess compared to expected. Ahh well, I guess we will just have to wait and see what the data tells us.

The star superscript denotes that one of the Z's is virtual, which is why it can be produced at a lower energy than 2*m_Z.

Maybe because of look-elsewhere effects, is the parameter space of the data different?

http://en.wikipedia.org/wiki/Look-elsewhere_effect

The 5.0 sigma is local and does not include the Look-elsewhere effect, this was stated in the talk. Doing this makes the significance drop significantly ( ), down to around 3.5-4 sigma (I don't remember the numbers exactly, but it was not around 5 sigma).

However both experiments have a (local) significance of 5 sigma independently.

 

[TrickyDicky]

Is it accurate to say that the Higgs boson was theoretically linked to the massive W and Z bosons and that having found those, it was only logical to eventually find it?

 

[eXorikos]

As a Belgian I'm wondering if this is now really Nobel prize material for Englert and Higgs? It would be a massive boost for physics in Belgium to finally have a Nobel laureate.

 

[kloptok]

Remember though that the Nobel prize goes to a maximum of three persons. Two of those should most likely be reserved for people from the experiments, as there are two experiments. This leaves only one spot for the theorists. But who knows what the Nobel committee will do, maybe they will divide the prize over more than one year? I've never heard of that happening before though and maybe it is in contrast with the rules for the prize, but this is just speculation on my side.

Is it accurate to say that the Higgs boson was theoretically linked to the massive W and Z bosons and that having found those, it was only logical to eventually find it?

The standard version of the Higgs mechanism which predicts a Higgs boson is indeed a way to provide mass to the W and the Z, but there are also alternatives for giving mass to them. Just that the W and the Z are massive does not require a Higgs boson. Although it should be noted that most of the alternatives have become more and more unlikely with more experimental data (e.g. Technicolor).

 

[eXorikos]

Do the experimentalists really need a Nobel prize? It wouldn't be fair to pick only one of every collaboration, since the collaborations are so huge.

 

[kloptok]

You are definitely right in that the size of the collaborations is a BIG (pun intended!) problem! Who to give the prize to? But it would be strange not to award the prize to the experimental side as the discovery would never have happened without the machine. It would be a big insult to all the experimentalists. The prize is supposed to go to, quoting Nobel's testament, "the person who shall have made the most important discovery or invention within the field of physics". To be honest I have no clue how the committee will do it, and whatever they do it will probably be criticized by at least someone. They are in a tricky spot this time.

 

[snt]

But, how did you come up with the number 99.99994% in relation to 5 sigma?! Also, how did the BBC come up with their numbers of 8 heads in a row for 3 sigma, and 20 heads in a row for a 5 sigma?

99.99994% comes from 1-erf[n/sqrt(2)] for 5σ, this works out to a two-sided confidence level of 100-5.733x10^(-5)% which is about equal to 99.99994267%.

As for the coin toss, the probability of tossing a "heads" is 50%, or (.5). Two heads in a row has a probability of (.5)^2, or 25%. Conversely, this can be seen as the probability of not getting heads twice in a row is 1-.25, or 75%

The numbers used by the BBC are close enough to illustrate the point. The probability of not getting 20 heads in a row is 1-(.5)^20 or about 99.999904%. 3σ is 99.73% and 1-(.5)^8 is about 99.61%

 

[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?