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afterburner
2006-Jul-26, 04:51 PM
When we look at neutron decay, we get a proton, an electron and an antineutrino. This process happens so fast, that is it apparently not observable. Although this is appears to be true, something does indeed happen in that billionth of a billionth of a billionth of a second.

When a neutron decays, does it ALWAYS decay into a proton, electron and an antineutrino…without any variation?

Is it possible/does it ever happen that instead of say an antineutrino, we get a burst of high-energy photons to make up for the “not formed” antineutrino (so that conservation of energy still holds?)

When the down quark changes to an up quark, we say it releases a W- boson, which is virtual. If it later “transforms” into an electron and an antineutrino, how/why exactly is it virtual between the time of “release” and “transformation”? Is it just a blob of energy that is nothing, until it “shapes” into an electron and antineutrino, or is it something completely different?

Why I’m asking is because of the following though experiment.
If we have a large amount of gas (enough to form a solar system), given some billion years it will form a star and perhaps a few planets. If we run this experiment a total of 10,000 times (with exactly the same amount of gas), each time we will get a star and some planets. However, the mass of the stars may be different each time, much like the number of planets, and their masses. Over 10,000 trials, we will get a most probable outcome. Is the subatomic world similar to this, but happens over a much shorter period of time? Just to make it clear, I’m not equating the physical properties of a solar system to the subatomic particles, just the idea of transformation (with gas representing whatever energy is…)

There are electrons and positrons (antielectrons). These are the same, but have different charges. So my question is…what are charges and what determines them. (I am not satisfied with - one is –1 and the other is +1) That is to say…if I were to have a “bunch” of energy…and for example I would like to make a variety of particles (electrons/positrons)…what would I have to do differently, so that one electron has a negative charge, and the other one has a positive charge? IOW, how would I have to “redistribute” the energy to make the same particle BUT with different charge.

For the above question (in terms of fields)…would the carrier particles (virtual photons?) for the charge be different or the same in electrons and positrons?

I know I asked this before, but I still don’t get it…. What is spin?
How is spin of real photons different from proton spin, or electron spin etc.?

Thats it for now. Thakns in advance.:think:

Celestial Mechanic
2006-Jul-26, 05:51 PM
[Snip!] When a neutron decays, does it ALWAYS decay into a proton, electron and an antineutrino…without any variation? [Snip!]
As long as electric charge, angular momentum, baryon number, and electron lepton number are conserved there is only one likely channel for neutron decay. Because baryon number is conserved, a baryon must be among the decay products and the only baryon less mass than the neutron is the proton. Because charge is conserved, there must also be a negatively-charged particle, and the only one with a mass less than mn-mp is the electron. Since electron lepton number is conserved, there must be a particle with mass less than the electron and no electric charge that carries a negative electron lepton number, and that's the antineutrino. Angular momentum conservation implies that since the original number of fermions was odd, the final number of fermions is odd, which is satisfied by the proton + electron + electron anti-neutrino.

There could be additional decay channels, but conservation of angular momentum requires additional bosons and/or fermion/anti-fermion pairs. In other words, maybe we could have a photon in addition to the usual decay products, or maybe a neutrino/anti-neutrino pair in addition. But the probability of these exotic decays is very small and I don't think they've been seen. (I will have to check the Particle Data Group's booklet!)

Conservation of electric charge and angular momentum are both pretty much non-negotiable. But if there are processes that violate baryon conservation then the neutron could decay in a manner similar to that of the proton, that is, into a pion and an anti-lepton (plus others). However, since proton decay is EXTREMELY rare, neutron decay via that channel is rare also. The neutron will have most likely decayed via the weak interaction.

Likewise, if electron lepton number is not conserved, there may be some exotic channels available for neutron decay, but again they will be quite rare.

In conclusion, the decay channel available to the neutron is so overwhelmingly probable compared to the possible exotic decay channels that we rarely if ever see these exotic channels.

Grey
2006-Jul-26, 07:14 PM
However, since proton decay is EXTREMELY rare...In fact, it's so rare that it's still an unobserved theoretical prediction of some theories. ;) The theoretical lower limit for the half-life of a free proton is something like 1035 years, but they may also be stable.

afterburner
2006-Jul-26, 07:19 PM
Thank you Celestial Mechanic and Grey for your answers. Does anyone know the answer to the charge and spin questions at the end of my post?

korjik
2006-Jul-26, 07:44 PM
Charge is still a bit unknown. If there is a magnetic monopole somewhere in the universe QM give a reason why charge is quantized, but other than that I dont think there is a good reason why charge is quantized.

Spin might come from conservation of angular momentum and QM. I dont know for sure tho.

basically, the actual values of charge and spin are basic values of properties of the universe like G or pi. Cant really say why they are what they are

Grey
2006-Jul-26, 08:09 PM
Thank you Celestial Mechanic and Grey for your answers. Does anyone know the answer to the charge and spin questions at the end of my post?It's hard to give a precise definition of what charge actually is. The best I can do is that it's a fundamental property that particles have, and determines how (and whether) the particle is coupled with the electromagnetic field. You probably could say that charge is just the ability to create and interact with virtual photons. And yes, the carrier particles for the elecromagnetic force are the same virtual photons, regardless of the charge of the interacting objects.

As for how you'd "redistribute" energy to make a particle with a different charge, it doesn't work that way. If you have energy available to make particles, you'll always create them in pairs such that the total charge balances out. There's some tantalizing experimental evidence that there's some assymetry, but nobody has ever seen the total charge in a closed system change.

Spin is pretty weird, too. It behaves something like the angular momentum of a tiny particle spinning on an axis (hence the name), but there are important differences, too. It is, like charge, a fundamental property that any particle has. A photon always has a spin of one (measured in Planck units). A proton or electron has a spin of one-half. For reasons that are perhaps not entirely clear, all the force carriers (photon, graviton, gluon, etc.) have integer spin and obey Bose-Einstein statistics (any number of particles can be in the same energy state). On the other hand, all the particles that we think of as "matter" (quarks, electrons, neutrinos, etc.) have half-integer spin, and obey Fermi-Dirac statistics (the Pauli exclusion principle applies - no two particles can be in the same state). Wikipedia has pretty good introductory articles on charge and spin.

afterburner
2006-Jul-26, 11:07 PM
It's hard to give a precise definition of what charge actually is. The best I can do is that it's a fundamental property that particles have, and determines how (and whether) the particle is coupled with the electromagnetic field. You probably could say that charge is just the ability to create and interact with virtual photons. And yes, the carrier particles for the elecromagnetic force are the same virtual photons, regardless of the charge of the interacting objects.

If the virtual photons are exactly the same, then how is it that in some cases they make objects attract, and in other cases repel? I understand that the object creating these virtual photons is different (in terms of charge), however, if it is the photons that are the mechanism by which things attract electromagnetically, it makes no sence that they are exactly the same.

If without virtual photons, there would be no electromagnetic interactoin, and if both electrons and positrons produce identical photons, I dont see how the effects of these identical photons would produce different results when interacting with objects of different charge.

Would the photons of the charged particles be charged themselves? Im still confused.


As for how you'd "redistribute" energy to make a particle with a different charge, it doesn't work that way. If you have energy available to make particles, you'll always create them in pairs such that the total charge balances out. There's some tantalizing experimental evidence that there's some assymetry, but nobody has ever seen the total charge in a closed system change.

Assuming the conversion of energy into matter is easy...

When we want make matter, is it only posible to make electron/prositron and proton/antiproton pairs...or is it possible to make an electron and a proton right away?

Also, creating neutrons should be no problem then, right?

Why is it that creating electron/positron pairs is possible at all? If they come from the same point (do they?) then why is it that they dont cancel each other out right away (before they take a first breath so to speak)?

During creation of electron/positron or proton/antiproton pairs out of photons, it says everywhere that these pairs are created spontaneously...does that mean that we just dont know how the process occurs, or that the two up and one down quark (in the case of protons) are actually created spontaneously? (this reminded me of spontaneous generation of germs theory during Louis Pasteurs time)


Spin is pretty weird, too. It behaves something like the angular momentum of a tiny particle spinning on an axis (hence the name), but there are important differences, too. It is, like charge, a fundamental property that any particle has. A photon always has a spin of one (measured in Planck units). A proton or electron has a spin of one-half. For reasons that are perhaps not entirely clear, all the force carriers (photon, graviton, gluon, etc.) have integer spin and obey Bose-Einstein statistics (any number of particles can be in the same energy state). On the other hand, all the particles that we think of as "matter" (quarks, electrons, neutrinos, etc.) have half-integer spin, and obey Fermi-Dirac statistics (the Pauli exclusion principle applies - no two particles can be in the same state). Wikipedia has pretty good introductory articles on charge and spin.

In terms of why the particles are different, besides amount of energy, how are particles with 1/2, 1, and 2 spin different? Just the fact that ones with 1/2 integer spin are not allowed to be in the same state, and ones with integer spin are?

when two high-energy photons make an electron/positon pair, how is it that the two photons have spin 1 (and are able to ocupy the same space), yet the two created particles both have 1/2 spins (and are not able to occupy the same space)? this is not even mentioning the fact that during pair production a new property called charge appears spontaneously(virtual photons) :think:

Similarly, when an electron and positron annihilate, how is it that the two new particles have completely diferent properties?

Celestial Mechanic
2006-Jul-27, 04:29 AM
I just checked the Particle Data Group's website. Under baryon-number violating proton decays they also list some decay modes for neutrons, but they all have partial lives greater than 1030 years.

Among baryon-number conserving decay modes for the neutron the only alternative that they list is:

neutron -> proton + electron + electron anti-neutrino + photon,

and they give the fraction as < 6.9x10-3.

Reference: http://pdg.lbl.gov/2006/tables/bxxx.pdf (PDF file)