Date: Sun, 04 Oct 1998 13:58:53 CST6CDT5,M4.1.0,M10.5.0
Brian writes:
Suzanne here describes force ratios between em and strong force.
I read that there are particles insensitive to the strong force -
to these, I suppose the strong force would be no force: this is
the group of leptons which includes the electron, muon, tau, their
neutrinos and all of their antiparticles (12 in all)
--
Yes, exactly. The charged leptons (e, mu tau) interact
electromagnetically, but the neutrinos interact only weakly; this
is why they are so hard to observe, and so penetrating (they
emerge unscathed from the solar interior, for example, except
possibly for oscillating into a different sort of neutrino - this
is not relevant to the strength of the interaction, though).
Then Brian writes:
It is Yukawa's proposition that we can explain the range of force
carriers by means of their energy or mass.
I take it that this is an implication of the idea that mass or energy,
and range or velocity or lifetime are connected for hypothetical
particles like these force carriers.
--
It's the uncertainty principle - the creation of the intermediate
particle violates the conservation of energy (unless it's massless)
so it can only exist for a short amount of time (delta t times
delta E being of the order of h bar).
Brian again (sorry, I am dealing with a combination of editor and
ISP that don't get along too well here!):
The exchange carrier of em, the
photon is 'massless' and so has infinite range.
The moderately heavy meson limits the range of the strong nuclear force.
The exchange carrier of the weak force is described as the intermediate
(or mediating) vector (or unit) boson, a creation of Yukawa's.
The weak nuclear force has an even shorter range than the others, so its
carrier, or intermediate vector boson (of three kinds, W+, W-, and Zero)
is a heavier particle type.
--
Right, the W and Z have masses roughly 100 times that of the
proton, so the range is very short (and the probability of
creating them in the first place low). The oddball is the strong
force between quarks, which is described as the exchange of
massless gluons; the range is still limited, but now we have to
ascribe it to color confinement (single quarks and gluons are
colored, and don't exist as free particles; this makes the
interaction strength increase with separation so it is short
range even though the carriers are massless.)
Sue Willis
Suzanne Willis, Professor, Physics Department
Northern Illinois University, DeKalb, IL 60115 USA http://niuhep.physics.niu.edu/~willis/ swillis@niu.edu
phone: 815-753-0667 fax: 815-753-8565