sci.physics.particle

The Master writes:
> I know that sub-atomic particles like protons and electrons are made
> up of three quarks each, as is a neutron. I no longer have my old
> college physics book, so I cannot look it up myself, and I have so far
> been unable to find a web reference to answer my question.

Protons and neutrons are composed of quarks, but not electrons;
electrons don't have any internal structure that we've observed.
So there's only three quarks in the initial and final states.

> That question is, when the three quarks of the electron and the three
> quarks of the proton combine, creating a neutron... What sub-atomic
> particle do the three "left over" quarks create? Is it a neutrino?

http://en.wikipedia.org/wiki/W_and_Z_bosons

has a neutron decay diagram; electron capture by a proton is the same
process turned sideways. The proton and electron exchange a W boson,
turning the electron into a neutrino and one of the u quarks in the
proton into a d quark, which changes the proton into a neutron.

> Have they actually been discovered? Last time I knew, they were
> theorized, but never actually "seen".

Neutrinos have been "seen". Since neutrinos interact very weakly
with normal matter, it takes a lot of mass to observe neutrino
interactions. One of my favorite neutrino observatories used
photomultiplier tubes embedded in the Antarctic ice cap:

http://www.amanda.uci.edu/public_info.html

Also see the follow-on experiment,

http://www.icecube.wisc.edu/info/

And for a list of recent neutrino detectors:

http://en.wikipedia.org/wiki/Neutrino_detector

-dan