particle physics comments

Greetings!

I'm very new to TML and hadn't intended to post anything yet until I had
more of a "feel" for the flow of discussion on this group.  But, when I
saw the comments below, I just had to respond!  Byt the way, my
background is in physics and I design/build particle detectors for a
living.  Thus I keep current on high energy physics and, to a lessor
degree, nuclear physics.  If y'all have any questions in this area I'll
be glad to try to answer them.

[email removed] (Jack Dietz) writes:

>As far as I can remember, current theories call for a charge carrier
>particle for all four forces.  The carriers of electromagnetism (the
>photon), the strong nuclear force (the pion) and the weak nuclear
>force (the intermediate weak boson) have been found.  All have zero
>rest mass and all have a set velocity of c, 2.998x10^8 m/s.  The
>reason that they are affected by gravity is that they have a mass
>due to their speed -- zero mass and infinite (relativistic) speed
>yields any number for relativistic mass you want... ^_^  Since they
>have mass, black holes can haul them back, and they end up orbiting
>inside the event horizon if they enter it.

This description is out of date in some ways and wrong in others.
Current thinking goes like this.  Electromagnetism (the unification of
the 1800's) and the weak nuclear force have been unified by Glashow,
Weinberg, and Salam into the Standard Model of the Electroweak
Interaction, or for short, the Standard Model.  These fellows won a
Nobel Prize for this a few years ago.  This model describes the
common things from electromagnetism and reactions covered by the weak
force, such as beta decay of nuclei or neutrino interactions.  The
"carriers" of electroweak are the photon, W, and Z bosons.  Some properties
are:

    mediator   charge   rest mass         possible velocities
    ----------------------------------------------------------------
    photon     none     none              only at the speed of light (c)
    W          + or -   80.22 GeV/c**2    anything < c
    Z          none     91.17 GeV/c**2    anything < c

Note that the electroweak interaction affects both hadrons (mesons and
baryons) and leptons (electron, muon, tau, and their neutrinos).

Now the strong interaction.  This covers the interactions between quarks
but does not have anything to do with leptons.  It is mediated by the
gluon, which carries the **color** charge and has zero rest mass.  Color
charge comes in three varieties, red, green, and blue.  Hadrons must be
color neutral or "white".  Thus mesons are color-anticolor doublets of
quarks and baryons are RGB triplets of quarks.  By the way, remember
this is NOT color in the visual sense.  The mathematics describing this
(Quantum Chromodynamics or QCD) works out in a certain way having nothing
to do with visual color.  The use of the word "color" for the strong charge
and that the color charge is red, green, or blue is just a convenient
analogy.

A little bit about the pion.  It is made up of a quark doublet (actually a
superposition of doublet states) and hence is classified as a meson.  It
comes in both electrically charged and neutral forms and has a rest mass.
The mass of the neutral pion is 134.97 MeV/c**2 and the charged pion mass
is 139.57 MeV/c**2.  It can move at any velocity below the speed of light.
In nuclear physics pion exchange between nucleons was given as the
mechanism for some reactions, but this is not a fundamental interaction.

As to the graviton, I don't have any information off the top of my head.
If anyone is interested, I can pursue this with my theory colleagues
down the hall and then post an overview of the situation.

Regards,
Richard

P.S.  Is anyone else as completely disgusted with the description of how
meson weapons work as I am?

******************************************************************************
*  Richard Fernholz               Internet:  [email removed]                 *
*  Dept. of Physics               HEPnet:  muhep::fernholz (19191::fernholz) *
*  McGill University                                                         *
[address removed]                 voice:  [phone removed]                       *
*  Canada                                                                    *
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