Is the Proton's Half Life Really 10 to the Power of 32 Years?

[Terry Giblin]

Where did all the electrons disappear too?

If you separate electrons from protons, you have a box of electrons and a box of protons. You can't destroy electrons, nor can you create them.

- Warren

Warren,

Assuming you now have a box of electrons, and the walls of the box, act as a square-square potential well - quantum barrier which we can control, to release only one single electron at a 'time'.

Now we build two concentric circular walls around the box, the inner wall has two slits in it and the outter wall is painted white.

How did the electrons tunnel throught the wall?

Where do all the electrons disappear too?

Where did all the photons appear from and how?

I can only see a intereference wave pattern, but no electrons?

"You can't destroy electrons" - or matter or energy only change its form.

Regards

Terry Giblin

 

[ahrkron]

yes but in an acid, you don't get H+ ions but H30+ ions instead

How is that relevant?

In a chemical reaction, by definition the number of protons do not change. Actually, even the number of protons in each nucleus is not altered.

 

[garytse86]

How is that relevant?

In a chemical reaction, by definition the number of protons do not change. Actually, even the number of protons in each nucleus is not altered.

yes but the proton is not chemically stable otherwise it would not form an ion with H2O.

 

[chroot]

We're not talking about "chemical stability," gary, for the last time.

- Warren

 

[chroot]

I have split off MRP's discussion of whether or not chemistry includes nuclear effects to the Theory Development subforum.

- Warren

 

[IooqXpooI]

Isn't a proton just a combination of quarks?

It is stable, yet turns into a Neutron by means of Weak Force quickly...(in the atom)

 

[Nereid]

Isn't a proton just a combination of quarks?

Yes.

It is stable, yet turns into a Neutron by means of Weak Force quickly...(in the atom)

I think you mean 'in a nucleus', and only in certain cases, e.g. where it can capture an orbital electron, and where the resulting nucleus has lower energy than the starting one, ...

 

[Mr. Robin Parsons]

And in radio-active decay, it reverts back to a proton, from a neutron by decay emitance of either, an electron, or a positron. (and a neutrino too, I suspect, I recall)

 

[chroot]

Beta decay:

$$n \rightarrow p + e^- + \overline{\nu}_e$$

- Warren

 

[Haelfix]

Note the inverse process is not a 'decay', its a reaction... One with very small cross section too I might add.

So the point stands, the proton has nothing to decay into... In nuclear and particle physics, any situation like that is defined to be 'stable'. Note this is not the same meaning as a chemist would use, where typically you aren't dealing with extreme vacuums.

You have to go beyond the SDM* to find a mechanism for its decay. (*aside from one technicality which has vanishingly small contribution)

 

[Antonio Lao]

What I don't understand is why the sum of the mass of the quarks composing the proton is larger than the mass of the proton.

Experimentally it can be said that the formation of proton liberates mass in term of energy because it takes about the same energy to form the jets which have proven the existence of quarks. But individual quark cannot be isolated. How much more energy does it takes to isolate the quark?

 

[Mr. Robin Parsons]

Have protons been created experimentally? or are you simply referring to the math's prediction(s)?

 

[Antonio Lao]

Experimental verification of quarks by the formation of jets proving the compositeness of nucleons and mesons of all hadrons.

 

[chroot]

What I don't understand is why the sum of the mass of the quarks composing the proton is larger than the mass of the proton.

You have it backward. The proton has more mass than the sum of its constituent quarks, because the binding energy between them counts as additional mass via E=mc².

How much more energy does it takes to isolate the quark?

You can't isolate quarks, because the energy required to pull two apart is more than the energy required to create two more. In other words, you can pull a pair apart to a point and then *pop* you'll wind up with two pairs.

- Warren

 

[Mr. Robin Parsons]

Uhmmm, this was the question I had asked: "Have protons been created experimentally?" Lord knows what question you answered...

 

[Antonio Lao]

The natural decay of the "free" neutron does produce a proton as shown by trivial experiments requiring a lot less energy than all other modern accelerators.

 

[chroot]

I'd like to make sure that you understand, Robin, that these protons are not being created out of nothingness; that would violate many conservation rules. Instead, when you smash bits of matter together in particle accelerators, the kinetic energy of the particles can be manifested in the creation of various kinds of particles, some very exotic -- that's the fun part. In no situation does an experiment end up with more mass and energy than it started with, however.

- Warren

 

[Antonio Lao]

Robin Parsons,

As a novice in any experimental process, I know I don't how to create a proton. And I don't recall any experiment done by the experts. But in the early age of the universe, I think, it was naturally done by the first nucleosynthesis?.

 

[ZapperZ]

Just to make sure that there are NO misconceptions about our ability to create protons experimentally, we can do this the quick and dirty way (zap a hydrogen atom with enough energy and voila! We have a proton), or systematically to generate a high "quality", low emittance, high brightness proton beam as done routinely at Fermilab and many other accelerator/collider facilities.

http://www.fnal.gov/pub/inquiring/physics/accelerators/chainaccel.html

Zz.

 

[Antonio Lao]

I am thinking more in the line of creating proton from the component quarks than that of dissociation of hydrogen atoms.

 

[ZapperZ]

I am thinking more in the line of creating proton from the component quarks than that of dissociation of hydrogen atoms.

Yes, I was aware of that. I was merely addressing to the broader issue of "can we create protons experimentally", in case there are peole jumping in in the middle and see a discussion that might give them the impression that we do not know decisively that we have created protons.

As for your line of thinking, either beta decay (change of flavor by quarks) might answer your question, or you will have to wait till we make and verify the first gamma-gamma collider.

Zz.

 

[Antonio Lao]

Sorry for my being narrow and one trackly minded.

 

[taxman]

If the theroies are correct mass and energy are essentially the same thing just in a different form. It is not impossible for a decay of protons. Everything changes so over time it is not unlikely that the energy of the proton would decay into its principle parts. I just don't think that we know or understant all of the parts yet.

 

[chroot]

taxman,

According to the standard model, it is absolutely impossible for protons to decay. The argument "everything changes over time" is not a strong one at all.

- Warren

 

[Nereid]

If the theroies are correct mass and energy are essentially the same thing just in a different form. It is not impossible for a decay of protons. Everything changes so over time it is not unlikely that the energy of the proton would decay into its principle parts. I just don't think that we know or understant all of the parts yet.

Welcome to Physics Forums, taxman!

As chroot said, the proton is a stable particle in the Standard Model, so it will not decay (by itself; there are certainly situations under which it will 'decay' e.g. in certain proton-rich nuclides). Of course, one of the tests of the Standard Model is to look for decays of the proton. AFAIK, several research projects to find proton decays, by a wide variety of channels, have been undertaken. No confirmed proton decays have been observed, so we can conclude that the proton's 'half-life' is at least 10³⁸ years (though it may be somewhat less, in some hypothesised decay modes).

To put this into context, a proton half-life of 10³⁸ years would mean an expectation of just *one* decay in ~12,000 moles of ordinary hydrogen, in a period of time equal to the life of the universe to date!

 

[quantumdude]

taxman,

According to the standard model, it is absolutely impossible for protons to decay. The argument "everything changes over time" is not a strong one at all.

To that I would add only that "everything changes over time" does not imply "everything decays". The proton does constantly change--internally. There are gluons running around, virtual quark-antiquark pairs constantly popping into and out of existence, etc. Also, if struck with a sufficiently energetic particle, the proton will be exicted into a resonance, and then deexcite back down.

The inside of a proton is a hive of activity. It just so happens that it goes through all that change without changing its asymptotic identity (that is, it don't decay ).

 

[arivero]

As for the question of artifitial production of protons... Machines as the LEP get hadrons, ie mesons and barions, from the product of electron positron colisions. This should include protons, shouldn't it?

 

[bkfizz02]

The original question was about the stability of the proton. I agree that the proton does not decay, but I do not believe that we can "prove" this. One could imagine a scenario the the original post presented - proton --> positron + photon. Certainly this is allowed by energy considerations. But it is not allowed by conservation of lepton number. In fact, for every proton decay that you can imagine that does not violate conservation of energy (a physics axiom), a conservation law is broken.
I think that this fact is what makes the original question really important. If we could observe a proton decay, we would be observing the breaking of a conservation law. Since we believe in many conservation laws, the direct experimental contradiction of them would be crucial for retooling our thinking.

Another example of a process which "cannot" happen is neutrinoless beta decay. People look for this process, which would violate lepton number conservation. If they found it, the proton decay question would almost certainly need to be revisited.

 

[Terry Giblin]

More to the point...

Unless the laws of statistics have changed since I left school.

Has anyone simply calculated the probability that we have not seen a proton decay already, by now - what's the definition of a "half-life"?

Regards

Terry Giblin

 

[marlon]

The only way a proton would disintegrate is if it were to have a tremendously high speeds. Asymptotic freedom then states that the strong force becomes smaller so the fluxtube between the constituent quarks will "decay" into gluons and the quarks would move away from each other.

At least this is the picture of the dual abelian higgs model using the concept of dual superconductivity and the S-duality of coupling constants + charge quantization from Dirac.

Ahhh, and you also need magnetic monopoles, responsible for this quantization.

regards
marlon

 

[humanino]

I really don't get it Marlon. The proton is more likely to decay at higher speed !? Usually, at higher speed, decay is just lowered by lorentz contraction of time. Or : the fastest decay should occur in the rest frame !

I could concieve that there is a dynamical process occurring during the acceleration process.

for every proton decay that you can imagine that does not violate conservation of energy (a physics axiom), a conservation law is broken.

Barionic number conserved through other conservation laws !?
Oh, by the way : is barionic number conservation not much better experimentally tested than the other conservation laws (with regards to proton's lifetime. I have been checking PDG online, and I am not quite sure.) ?

 

[vanesch]

The original question was about the stability of the proton. I agree that the proton does not decay, but I do not believe that we can "prove" this. One could imagine a scenario the the original post presented - proton --> positron + photon. .

The idea of proton decay comes from GUT (Grand Unifying theories). In the standard model, we have the gauge group SU(3)xSU(2)xU(1), where SU(3) describes a (non-broken) gauge symmetry group between the colors of the quarks (and the relevant bosons are the gluons of the strong interaction), while SU(2)xU(1) describes the (broken) symmetry of the electroweak charges (essentially chirality, hypercharge and electrical charge) and the relevant bosons are W+, W-, Z0 and the photon.

As such, there is no interaction possible which turns a quark into a lepton and from this follows baryon conservation. In the standard model, the 3 lepton families, and the 3 quark families, have a priori not much to do with each other, but the very fact that there are 3 of each cries out for a deeper structure.
Indeed, if you make a large tuple of all the fermion fields in one family (the 2 quarks - righthand, the two quarks - lefthand, the electron and neutrino - lefthand, and the electron, righthand) this big tuple transforms under a composite representation of SU(3)xSU(2)xU(1) which is really put in there by hand. On the other hand, it fits into only 2 different representations of SU(5), which contains SU(3)xSU(2)xU(1), namely the so-called 5* and the 10 representation. But SU(5) is not equal to SU(3)xSU(2)xU(1), it contains in fac t 24 gauge bosons, so there are EXTRA INTERACTIONS, and some of these link quarks and leptons, which comes down to say that a quark could, through this interaction, change into a lepton. Of course one assumes that this symmetry is broken, and that the relevant bosons have a big mass (the "GUT" scale), which decreases this interaction rate. If one estimates this scale (that's where the 3 coupling constants of the standard model should unify) one arrives at something of 10^15 GeV. Using this value, the proton decay rate should be of the order of a life time of 10^31 years, which has been falsified by experiment. So that's where all the hassle came from.
But people have not given up: other groups than SU(5) are possible ; this was simply the "smallest" group that could contain the standard model. People have been working on SO(10), for example.

cheers,
Patrick.

 

[Nereid]

IIRC, the experimentally observed limit on the proton's half-life is ~10³⁵ years, at least for several (one?) of the more 'likely' decay modes.

 

[Terry Giblin]

What's the probability of not seeing one decay

the proton decay rate should be of the order of a life time of 10^31 years, which has been falsified by experiment.

Lets assume the half-life on an electron, as estimated is 10^31 years, based on our current on going testing for detection of the first ever observed proton decay.

Is it not time to start considering alternative ideas and models

Regards

Terry Giblin

 

[Nereid]

Lets assume the half-life on an electron, as estimated is 10^31 years, based on our current on going testing for detection of the first ever observed proton decay.

Why not simply do an experiment to measure the half-life of the electron? How do experimental results showing that the half-life of the proton is ~>10³⁵ years lead to an estimate of half-life of the electron?

Is it not time to start considering alternative ideas and models

Of course! It's been obvious for some time that the Standard Model is in need of replacement/extension/etc! I doubt that there are any researchers active in particle physics who feel that the Standard Model is the end.