Re: [Phys-L] Particle physics

[John Denker <jsd@av8n.com>]

On 06/17/2013 05:43 PM, Paul Lulai wrote:
> Hi. I am working to create some materials for 20th century physics &
> particle physics. Before I do, I need to understand some of it.

OK.

> When
> particles collide inside cern / fermi / slac, and produce particles,
> do the particles form from the energy of the collision? 

> From the energy, among other things.  In particular, if the products
have more mass than the reactants, the extra mass must have come from
the kinetic energy of the reactants.  That's just conservation of
energy.
  Reference:  How to make antimatter:
    http://www.av8n.com/physics/spacetime-welcome.htm#sec-bevatron-vector

However, conservation of energy is not the only criterion.  There is
also conservation of momentum, conservation of charge, conservation of
lepton number, et cetera.

> Do the
> particles form because the quarks rearrange?

Sometimes.

OTOH sometimes you make new quarks from scratch.  Also, sometimes
quarks have got nothing to do with it, e.g. positron annihilation
(or, equivalently, photoproduction of positrons or muons or other
leptons).

>  When massive particles
> decay to daughter particles, are the daughter particles composed of
> fewer fundamental particles?

That's not the best way to phrase the question.  The interesting
question is, why is that not a good question?

The point is, you can't really count fundamental particles.  This
is a famous question that Richard Feynman's father pestered him 
about.  Suppose an atom in excited state emits a photon.  Where
did the photon come from?  The answer (or non-answer) is that
the photon didn't come from anywhere.  Photons aren't conserved.
If some /conserved/ quantity showed up, you would have every
right to ask where it came from ... but there are lots of
non-conserved things in this world, and number of particles 
certainly not conserved.

> Now, I believe a particle can be made from energy for to particle
> interaction (photon vs photon). So I thought an interaction in a
> detector would produce particles at least (!) partly due to the
> energy of the interaction, not just rearranging particles like
> quarks. I believe muons are fundamental, and decay (perhaps there is
> a better term) into particles. Would the particles a myob decays into
> be considered daughter particles?
>
> One more... Is the higgs boson fundamental?

First of all, there is no dichotomy between "matter" and "interactions",
despite the impression you might get by reading the cover of certain
textbooks.  The physics is what it is, and does what it does.  Sure,
*sometimes* you can think in terms of matter "interacting" with other
matter, by means of an "interaction" ... but there are also lots of
ways that the so-called interactions can interact with each other, and
you very quickly conclude that the supposed dichotomy is not worth
worrying about.  It doesn't tell you anything worth knowing.  It is
wrong more often than it is right.  For the gory details on this, see
  http://www.av8n.com/physics/matter-interactions.htm#sec-matter-interactions

To say the same thing in more constructive terms:  Basically it's all
fields.  The "particle" we call a photon, to the extent that it can be
considered a particle at all, is an excitation of a certain bosonic
field, the electromagnetic field.  Similarly, the "particle" we call
an electron, to the extent that it can be considered a particle at all,
is an excitation of a certain fermionic field.  Et cetera.

Here's something to think about:  The classical equation for EM waves
in a waveguide is /exactly/ the same as the massive scalar Klein-Gordon
equation in particle physics.  The cutoff frequency in the waveguide 
plays the role of the mass gap.

This gives you 1% of a hint as to what's going on with the Higgs, 
insofar as it shows you how a massless field can acquire mass, or
something that acts just like mass.

That's all for now.  Gotta run.