# Particle Physics, perhaps a classification problem

[SOLVED] Particle Physics, perhaps a classification problem

## Homework Statement

How are the classes of particles classified?

## The Attempt at a Solution

Classes of particles should be bosons, leptons, hadrons and baryons.
First, I had the idea that the particles are classified according to interactions to them i.e. gravity, weak, electromagnetic and strong nuclear interactions, respectively for from boson to baryon.
However, problems have raised when questions have become about exchange particles (force carriers). For example, for gravity interaction = graviton, weak = bosons, electromagnetic = photon, and baryon = gluons. I have had the idea some of these particles belong also to a group of particles such as photon to gravity.
I attached a table to illustrate my point. In this table, I have colour-coded the groups and particles of which I am unsure, such as groups of particles and classes of particles (Is groups of particles = classes of particles?).

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Gravity acts on all particles, and so I dont understand why "bosons" is in the classes of particles column here.

The weak interaction acts between both leptons and hadrons. Hadrons can be subdivided into baryons (3 quarks eg. proton, neutron and thir antiparticles) and mesons (2 quarks, one quark and one antiquark).

The electromagentic force acts between all charged particles.

The strong interaction acts between all particles with quarks ie. hadrons and not leptons.

I am assuming, that like me, you are an A-level student. Bosons are best considered as just exchange particles of the fundamental forces - so photons, gluons and intermediate vector bosons are bosons. Intermediate vector bosons (W and Z) mediate the weak interaction.

Hope that helps.

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You may need to rethink that table using the comments suggested by nokia.

Gravity acts on all particles, and so I dont understand why "bosons" is in the classes of particles column here.

The weak interaction acts between both leptons and hadrons. Hadrons can be subdivided into baryons (3 quarks eg. proton, neutron and thir antiparticles) and mesons (2 quarks, one quark and one antiquark).

The electromagentic force acts between all charged particles.

The strong interaction acts between all particles with quarks ie. hadrons and not leptons.

I am assuming, that like me, you are an A-level student. Bosons are best considered as just exchange particles of the fundamental forces - so photons, gluons and intermediate vector bosons are bosons. Intermediate vector bosons (W and Z) mediate the weak interaction.

Hope that helps.
I attached figure that indicates now what I think about EX particles and forces.
I put electron, proton, neutrons and mesons to hadrons - is that right?
I think so that neutrinos should also belong to lepton but this is missing in the figure.

Please, comment if there are any mistakes in the figure.

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There are still many mistakes. The electromagnetic section is correct.

The strong interaction is experienced by all particles with quarks; this is baryons (eg. protons, neutrons) and mesons (eg. pion, kaon). Leptons (which is positrons, electrons, neutrinos etc.) do NOT experience the strong interaction. Exchange particle = gluon.

Gravity is experineced by ALL particles. Exchange particle = graviton.

The weak interaction is experienced by both hadrons AND leptons. The exchange particle = Z, W+ and W- bosons.

Bosons is a term used to describe the exchange particles for ALL fundamental forces. So, the following are bosons:

Photons, which mediate the electromagnetic force
W and Z bosons, which mediate the weak nuclear force
Gluons, which mediate the strong nuclear force

I suggest that you need to buy/rent a physics textbook out specific to your sylabus out, and read it through several times, as this topic is exteremly confusing unless you look over it in a good textbook.

The weak interaction is experienced by both hadrons AND leptons. The exchange particle = Z, W+ and W- bosons.

Bosons is a term used to describe the exchange particles for ALL fundamental forces. So, the following are bosons:

Photons, which mediate the electromagnetic force
W and Z bosons, which mediate the weak nuclear force
Gluons, which mediate the strong nuclear force
Thank you!
Your comments really put me on the right track, particularly with my Giangoli Physics textbook and with this particle Physics: boson as a name happens to occur many times, and it is not only related to a force carrier of weak nuclear interaction.

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Almost.. dont forget that the weak interaction acts between both hadrons and leptons. Which board are you doing by the way?

cristo
Staff Emeritus
I may be misinterpreting your diagram, but I'm confused. What do the particles in the circles mean? Does it mean that they are affected by the respective force? If so, then you should have all charged particles inside the EM force circle, shouldn't you?

Also, if this is A level, I can't imagine a graviton being there, since it is hypothetical.

I think the "+/-" means all charged particles. Gravitons are on my A-level sylabus. We only have to know that they mediate the force though.

cristo
Staff Emeritus
I think the "+/-" means all charged particles.
Oh, ok. To the OP: are you actually required to draw a diagram like that? It's a little confusing to me!
Gravitons are on my A-level sylabus. We only have to know that they mediate the force though.
Really, well I stand corrected (it's a few years since my A levels). Sorry for the mis-information.

hmm, the sylabuses are always changing. I think the poster has done the diagram for revision purposes, its fairly confusing to me too! A table would have been better in my opinion.

cristo
Staff Emeritus
A table would have been better in my opinion.
I agree. There are important things missing from that diagram, like which of the particles are fundamental particles, and which are composite particles, etc..

Also, it is significant that in all interactions, baryon number, lepton number and charge are conserved. Also, strangeness is conserved, except is not conserved in the weak interaction. Check if your syalabus needs you to draw Feynman diagrams.

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Almost.. dont forget that the weak interaction acts between both hadrons and leptons. Which board are you doing by the way?
I agree with you - I have tried to indicate by the red circle that weak interaction act also between handrons and leptons. Currently, I am finishing my last 3 days of IB final exams, and after that I will move on to St Andrews university.

cristo said:
There are important things missing from that diagram, like which of the particles are fundamental particles, and which are composite particles, etc..
I completely agree with you. I have tried to make a revision diagram. I have omitted details such as about fundamental particles: exchange bosons, leptons and quarks or about observed particles: leptons, hadrons and exchange bosons, by purpose not to make the diagram too complicated.