Has the Higgs Boson Particle Been Discovered at Cern?

[Dickfore]

Sure, but standard deviations of what?

 

[DrDu]

In other words, it looks like a duck, and it's where we would expect to find a duck (according to the predictions of QAD = quantum aviodynamics), but we have to do further study to verify that it walks like a duck and quacks like a duck.

Maybe you read too much in Zee's book :-)

 

[Dadface]

From what little I know about this at present there is a Higgs field which is instrumental in giving particles mass and a Higgs boson which is instrumental in setting up the Higgs field.If this is right then what is instrumental in giving the Higgs boson its mass?

 

[Dead Boss]

scalar particle means it is not vectorial.. meaning no directions... does it mean it's non-local? is a higgs value say in a pluto identical to the one on earth?

Scalar particle means it has spin 0.

 

[haael]

scalar particle means it is not vectorial.. meaning no directions... does it mean it's non-local? is a higgs value say in a pluto identical to the one on earth?

No, it can vary in space, but it means that it has always the same value at a given point no matter at which angle we look at it.

This is not a case with a photon for example. We could construct an instrument for detecting photons that depend on an angle. I.e. a polarizer. We detect photons when a polarizer is set at some angle and do not detect them when it is rotated by 90 deg. It is impossible to obtain such a polarizer for scalar particles and this is the very definition of a "scalar".

 

[viraltux]

From what little I know about this at present there is a Higgs field which is instrumental in giving particles mass and a Higgs boson which is instrumental in setting up the Higgs field.If this is right then what is instrumental in giving the Higgs boson its mass?

That might be why they call it "The God's particle"

 

[Demystifier]

Sure, but standard deviations of what?

Any signal in any experiment could, in principle, be only a statistical fluctuation, an error. Nothing is absolutely certain. The number 99.99994% measures how certain they are that it is NOT an error.

 

[Dickfore]

Any signal in any experiment could, in principle, be only a statistical fluctuation, an error. Nothing is absolutely certain. The number 99.99994% measures how certain they are that it is NOT an error.

I also saw the following formulation:

CMS observes an excess of events at a mass of approximately 125 GeV^[2] with a statistical significance of five standard deviations (5 sigma)^[3] above background expectations. The probability of the background alone fluctuating up by this amount or more is about one in three million.

[2] The electron volt (eV) is a unit of energy. A GeV is 1,000,000,000 eV. In particle physics, where mass and energy are often interchanged, it is common to use eV/c² as a unit of mass (from E = mc², where c is the speed of light in vacuum). Even more common is to use a system of natural units with c set to 1 (hence, E = m), and use eV and GeV as units of mass.

[3] The standard deviation describes the spread of a set of measurements around the mean value. It can be used to quantify the level of disagreement of a set of data from a given hypothesis. Physicists express standard deviations in units called “sigma”. The higher the number of sigma, the more incompatible the data are with the hypothesis. Typically, the more unexpected a discovery is, the greater the number of sigma physicists will require to be convinced.

The BBC news article has the following descriptions:

• Particle physics has an accepted definition for a discovery: a "five-sigma" (or five standard-deviation) level of certainty
• The number of sigmas measures how unlikely it is to get a certain experimental result as a matter of chance rather than due to a real effect
• Similarly, tossing a coin and getting a number of heads in a row may just be chance, rather than a sign of a "loaded" coin
• A "three-sigma" level represents about the same likelihood as tossing eight heads in a row
• Five sigma, on the other hand, would correspond to tossing more than 20 in a row
  Independent confirmation by other experiments turns five-sigma findings into accepted discoveries

So, I guess, the sigma refers to fluctuation in the background number of events.

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?

 

[Raekwon]

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?

http://en.wikipedia.org/wiki/Standard_deviation#Rules_for_normally_distributed_data

 

[viraltux]

But, how did you come up with the number 99.99994% in relation to 5 sigma?!

That would be the probability from -5 to 5 in a standard normal distribution. $N(0,1)$

 

[Dickfore]

http://en.wikipedia.org/wiki/Standard_deviation#Rules_for_normally_distributed_data

That would be the probability from -5 to 5 in a standard normal distribution. $N(0,1)$

But, isn't the number of background events following a Poisson distribution?

Also, the probability of getting k heads in a row follows the distribution:
$$P_k = \frac{1}{2^k}, \ k = 1, 2, \ldots$$

 

[mfb]

But, isn't the number of background events following a Poisson distribution?

Also, the probability of getting k heads in a row follows the distribution:
$$P_k = \frac{1}{2^k}, \ k = 1, 2, \ldots$$

As different situations have different distributions, "5 standard deviations" is a bit sloppy. The real meaning is "with background only [no higgs], observing so many events is equally unlikely than getting a value >=5 standard deviations away from the mean in a gaussian distribution".

ATLAS and CMS have a 99.9999% certainty that there they have found a new boson with a mass of 125 GeV- consistant with the Higgs.

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.

scalar particle means it is not vectorial.. meaning no directions... does it mean it's non-local? is a higgs value say in a pluto identical to the one on earth?

Particle properties are assumed to be the same everywhere (and up to now, no variation was found). This is independent of the spin.
A scalar field can depend on spacetime. As a simple example: Temperature is scalar, and it is different on pluto.

 

[jtbell]

Posts relating to decoherence have been moved to a new thread:

https://www.physicsforums.com/showthread.php?t=618463

 

[rodsika]

Particle properties are assumed to be the same everywhere (and up to now, no variation was found). This is independent of the spin.
A scalar field can depend on spacetime. As a simple example: Temperature is scalar, and it is different on pluto.

Okie. For a while there. I thought the higgs boson is the carrier of quantum non-locality or connected to it. But then, what's proof it is not connected...

 

[Dickfore]

Okie. For a while there. I thought the higgs boson is the carrier of quantum non-locality or connected to it. But then, what's proof it is not connected...

No. Since you claim something completely unfamiliar to the rest of us, it is up to you to prove that it is.

 

[atyy]

Echoing Dickfore's question: what do all the sigmas mean? For example, Cosmic Variance at one point says 4.9 for a SM Higgs. But if the particle is a non-SM Higgs, then surely this value must decrease?

BTW, are any papers out yet?

 

[mfb]

For example, Cosmic Variance at one point says 4.9 for a SM Higgs.

This is wrong. 4.9 sigma for "there is something". And measurements indicate that this "something" looks like a Higgs boson.
Concerning the meaning of the number, see the previous page (at 16 post per page*)

*interesting, the option to change this seems to be disabled in this board

 

[Dadface]

From what little I know about this at present there is a Higgs field which is instrumental in giving particles mass and a Higgs boson which is instrumental in setting up the Higgs field.If this is right then what is instrumental in giving the Higgs boson its mass?

That might be why they call it "The God's particle"

I think some have referred to it as the goddam particle.Anyway,does anyone know what gives the Higgs particle its mass? If it's not a silly question a reference where I could look it up would be nice.

 

[tom.stoer]

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

 

[scijeebus]

Higg's Discovered?

http://news.yahoo.com/scientists-unveil-milestone-higgs-boson-hunt-044513533.html

First off, how do you "observe" a higg's boson? They don't emit light, make sound or conduct any sort of electricity, it's impossible to observe them with any human senses in any way. Then, the article doesn't even explain "how", it just explains "oh yeah trust it's not something else, it's just w/e we said it is". Even if you have a pattern in a particle collision like a particle swirls around a point where we don't observe something, how do we know that point is the unknown particle predicted?
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?

 

[atyy]

This is wrong. 4.9 sigma for "there is something". And measurements indicate that this "something" looks like a Higgs boson.
Concerning the meaning of the number, see the previous page (at 16 post per page*)

*interesting, the option to change this seems to be disabled in this board

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

 

[Kevin_Axion]

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

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

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

 

[AdrianTheRock]

In the press conference they talk about determining whether the particle is spin 0 or spin 2, does anyone know why these two particular values for the spin are the discussed candidates? A spin 0 particle would give an isotropic decay guess, how would a spin 2 decay look like, will there be angular dependence (I guess it will) and in that case, how does it look like in detail?

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?

 

[atyy]

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

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

So that would mean the CMS 5 sigma from the combination of 2 channels is illegitimate, as is the 5 sigma from ATLAS, since that seems not to have used all the relevant channels?

 

[skydivephil]

Is there a video of the conference online ?

 

[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%