Higgs particle is 'found': Scientists at CERN expected to announce on Wednesday

QuarkCharmer

Quote by Dickfore

I don't mean to derail, but what exactly does it mean to have significance level 5 sigma?

It's just statistical speak for how accurate the date is more or less. The number of sigma represent the number of standard deviations.

*Dickfore*

Sure, but standard deviations of what?

DrDu

Quote by jtbell

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

Quote by rodsika

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

Quote by rodsika

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

Quote by 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"

Demystifier

Quote by Dickfore

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*

Quote by Demystifier

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

Quote by Dickfore

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/Standar...stributed_data

viraltux

Quote by Dickfore

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. [itex]N(0,1)[/itex]

*Dickfore*

Quote by Raekwon

http://en.wikipedia.org/wiki/Standar...stributed_data

Quote by viraltux

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

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:
[tex]
P_k = \frac{1}{2^k}, \ k = 1, 2, \ldots
[/tex]

mfb

Quote by Dickfore

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:
[tex]
P_k = \frac{1}{2^k}, \ k = 1, 2, \ldots
[/tex]

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".

Quote by Vorde

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.

Quote by rodsika

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:

http://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*

Quote by rodsika

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?

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Dadface Recognitions: Gold Member	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?

jtbell Mentor	Posts relating to decoherence have been moved to a new thread: http://www.physicsforums.com/showthread.php?t=618463

atyy Recognitions: Science Advisor	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?