Re: [Phys-L] Particle physics

["Daniel V. Schroeder" <dschroeder@weber.edu>]

For a model in which the Higgs is not fundamental, look up "technicolor".

You're correct that "daughter" particles needn't be fundamental.  An especially interesting example is the decay of a tau lepton (a "fundamental" particle) into mesons--although if you zoom in to the fundamental level, the tau is really decaying first into a quark-antiquark pair, and these particles then "pull additional quark-antiquark pairs out of the vacuum" to become mesons.

I'm still unhappy with your "rearrangement" vs. "result of leftover energy" dichotomy.  Again, I think you might benefit from studying a pure QED process such as e+ e- --> mu+ mu-, in which the initial and final states contain no quarks.  Once you understand that reaction, change the muons to quarks, which pull more quarks out of the vacuum to materialize as jets of mesons.  This is called "e+ e- --> hadrons".

At the LHC, things seem complicated because the initial-state particles are composite (protons).  The vast majority of collisions at the LHC are rather uninteresting, tearing protons apart and creating lots of mesons without any two "fundamental particles" colliding close enough to "head-on" with very much energy exchange.  The interesting collisions are those in which a quark or gluon from inside each proton collide with sufficient energy/momentum exchange to produce something heavy like the Higgs.

The Higgs is (probably) its own anti-particle, like the photon.  Just as photons can be emitted one at a time by a charged particle that accelerates (interacts with something else), Higgs particles can be emitted one at a time by interacting massive particles.  Of course, since Higgs particles are rather heavy, you need much more energetic interactions to produce them.

Have you looked up the principal Feynman diagrams for Higgs production and decay at the LHC?  If not, I think you'll find them helpful.

And again, I highly recommend particleadventure.org.

Dan


On Jun 18, 2013, Paul Lulai <plulai@stanthony.k12.mn.us> wrote:
> Is the Higgs boson fundamental?  I thought it must be, but that is simply 
> because it felt like it must be if it is what the Higgs field uses to interact 
> with particles to give them mass.  Since I am going on feelings, I don't trust 
> them. 
> Dan addresses this to a certain extent.  My interpretation, 'The Higgs seems to 
> be as fundamental as anything else, however, we simply might not have the 
> resolution to see anything smaller just yet.'  So I feel somewhat at (perhaps 
> temporary) peace with this point.
>
> When talking about daughter particles, I chose my words poorly.  It may be 
> better asked, 'must daughter particles be fundamental?' I believe the answer to 
> that question is 'no.'  Must daughter particles be composed of multiple 
> fundamental particles? Again, I believe the answer is no.  As I read about 
> these particles, they are often stated as being the product of a decay process. 
>  I have read some information from a few sources, but they typically don't 
> address this question directly.  I've come to my conclusion by simply thinking 
> about what particles are produced from some decay processes.  They are not 
> always fundamental, nor are the always structures.  However, I asked the 
> question here, because I am not sure if how /I/ am using the term daughter 
> particle is correct.  I think this was answered yesterday.  I believe both 'no' 
> answers are correct.
>
> Another cleaning up of my language, discussing the creation of a particle, 
> energy, charge, momentum, lepton number (possibly baryon number) are conserved. 
>  If one runs a proton - proton collision, are all of the particles detected 
> just the rearrangement of the quarks and bosons present in the initial protons? 
>  Are some created as the result not of the reaarangement of particles, but as a 
> result of (really bad phrasing here) leftover energy?  I understand that some 
> of the energy would simply go to the kinetic energy of the particles.  
> I think this would likely not be simply the rearrangement of particles since 
> positron - electron collisions also produce particles.
>
> The above questions lead to what maybe should have been the only question I 
> asked, but the question I am trying to resolve.  I guess I am wondering if 
> within the accelerator & detector, is there something like pair production 
> happening?  If so, what would be the other half of the pair produced with the 
> Higgs Boson?  Quick answer would be the anti-Higgs, but that is so knee-jerk 
> that I feel I should put it back in my mouth and fingertips before I send the 
> note.  If there is not pair-production, then is everything either the 
> re-arrangement of existing particles (with some color changing of quarks 
> possible) along with some decay processes to more stable particles?