# Elementary particle physics Definition and 13 Discussions

Particle physics (also known as high energy physics) is a branch of physics that studies the nature of the particles that constitute matter and radiation. Although the word particle can refer to various types of very small objects (e.g. protons, gas particles, or even household dust), particle physics usually investigates the irreducibly smallest detectable particles and the fundamental interactions necessary to explain their behaviour.
In current understanding, these elementary particles are excitations of the quantum fields that also govern their interactions. The currently dominant theory explaining these fundamental particles and fields, along with their dynamics, is called the Standard Model. Thus, modern particle physics generally investigates the Standard Model and its various possible extensions, e.g. to the newest "known" particle, the Higgs boson, or even to the oldest known force field, gravity.

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1. ### Is my Feynman diagram for production of ##W^-## boson correct?

I think ##X## appears to be ##\pi^{+}## because it is light and energetically more favourable. Pion should be positive to ensure charge conservation. I am stuck at drawing a Feynman diagram for $$p+\bar{p} \to W^- + \pi^+$$. Is this correct? Is this the leading order diagram or is there a...
2. ### A What are the difficulties of the rishon model?

The risbon model model was inveted by Harari in 1981. It is a theory that lies beyond the standard model and explains the existence of quarks and leptons on the basis of jusr 2 elementary particles, the T- and V-rishon (heuristically that is, like the quark model did once for the plethora of...
3. ### B Electrons, quarks and gluons made from something or nothing?

Most articles said electrons, quarks and gluons are indivisible thus have no compositions unlike the other particles. So, does that means electrons, quarks and gluons are composed of nothing and these elementary particles are indeed 100% void?
4. ### Why does a symmetric wavefunction imply the angular momentum is even?

I looked in the instructor solutions, which are given by: But I don't quite understand the solution, so I hope you can help me understand it. First. Why do we even know we are working with wavefunctions with the quantum numbers n,l,m? Don't we only get these quantum numbers if the particles...
5. ### I Color state of quarks in quark-gluon plasma

Hi, I have been taught that quarks don't exist individually on their own, as they has with be with at least another antiquark to form a colorless state. But in the quark-gluon plasma, do we have individual quarks in a color state or do they still, somehow, are in a color-neutral state? Thanks!
6. ### "Since the energy is far less than the rest mass of the ion, we can use nonrelativistic kinematics to find [velocity] υ". Why?

Clarification: The statement in the title is actually from the solution to the homework question, as given by the textbook (you can see the whole thing below under "Textbook solution"). The solution doesn't explain everything, which is where my confusion comes from. Usually in my classes we...
7. ### Allowed or forbidden reactions

Hello everybody! I have a doubt about a reaction. $$p + n \rightarrow \Lambda + \Sigma^+$$ I have to establish if it is allowed or not. Charge is conserved (1 -> 1) Baryon number is conserved (2 -> 2) Strangeness is not conserved (0 -> -2) Third component of the isospin is not conserved (0...
8. ### I What exactly is the amplitude of an interaction?

I've been reading Griffths' intro to elementary particles and I encountered this symbol that looks similar to "M" called amplitude, which can be calculated by analyzing the Feynman diagram of an interaction. What exactly is it? When I hear amplitude I imagine waves, but not sure what this one's...
9. ### Initial states ppbar can proceed to npi^0 with parity conserved

I'm working on some stuff for particle physics and I had a few questions I wanted to ask . Heres the outline of the problem : Establish which initial states of the ppbar system amongst 1^S_0, 3^S_1, 1^P_1, 3^P_0, 3^P_1, 3^P_2, 1^D_2, 3^D_1, 3^D_2, 3^D_3 the reaction ppbar->npi^0 can...
10. ### How to determine particle energies in center of momentum frame?

That said, my approach was to determine the energies and 3-momenta at the center of momentum reference frame for each particle, with a fixed s, and check it corresponds to each one of the above, but I'm having some trouble proving that, for example, E_A=\frac{s+m^2_A-m^2_B}{2\sqrt{s}}. I've...
11. ### Peskin and Schroeder eq. 18.84

Homework Statement So I am self-studying the book of Peskin&Schroeder, and there is something I don't understand on page 616. In eq. 18.80, there is a numerical factor of ½ and going from e2 to α will introduce a factor 4π when proceeding to eq. 18.84. But then there should be a numerical...
12. ### He-3 Neutron absorption

I'm curious, why does Helium-3 fission into H-3 and H upon neutron absorption? Surely the He-4 nucleus configuration is more stable? I get that the energy release may be what splits the nucleus, because it releases quite a lot of energy if it were to simply absorb the neutron.
13. ### Who is this Jess Brewer?

Hi, I'm a retired (since 2011) Physics prof from the University of British Columbia. I originally set out to get a PhD in Physics to increase my credibility as a science fiction writer, but I discovered a field* that was so cool it was like being a character in my own SF novel. In short, I got...