On 4/30/2013 7:48 PM, Axil Axil wrote:
> “And remember that to turn a proton into a neutron you merely have to
replace one of its up quarks by a down quark (Figure 3); that
replacement is enough to make the neutron slightly heavier than a
proton, and shift its electric charge from +e to zero.”
Protons and neutrons exchanges pions. Pions are mesons. All mesons
consist of a quark and an anti-quark.
There are three types of pions:
1. (pi)+ consisting of an up and an anti-down (2/3 + -(-1/3) = 1)
2. (pi)0 consisting of an up and an anti-up (2/3 + -(-2/3) = 0) --
actually, a superposition of (up+anti-up) and (down+anti-down)
3. (pi)- consisting of a down and an anti-up (-1/3 + -(2/3) = -1)
So possible pion charges are -1, 0, and +1.
Pions are not "reused"... when a proton sends a (pi)+ to a neutron,
turning them into a neutron and a proton respectively, the pion is
absorbed by the neutron and that's it.
The history of pions is interesting. They were predicted (including
their mass) before they were observed. Then when muons were discovered,
folks initially thought they were the predicted pions, until they
realized that muons don't interact via the strong force. That's why they
can pass through a lot of steel without being absorbed. Finally pions
were discovered. It turns out that cosmic rays create pions in the upper
atmosphere when interstellar protons collide with atmospheric nuclei
(nitrogen or oxygen). But pions decay very quickly into muons. So it's
principally muons that we detect at sea level from cosmic rays.
Pions are bosons and are approximate force-carrying goldstone bosons for
the residual strong force. But the real strong force is carried by
gluons (also bosons, but massless indivisible particles, as opposed to
pions which are composite and have mass).
- Joe
