Understanding Hadrons: A Beginner's Guide to the Proton and Quarks

[KylBlz]

Hi,

Im not going to lie, I am new to particle physics. Right now I am writing my Junior Research Paper on the LHC which brings up the Hadron. Wikipedia has a very confusing article about hadrons

it states that protons "composed of two up quarks (each with electric charge +2/3) and one down quark (with electric charge -1/3). Adding these together yields the proton charge of +1"

i also know that protons have a charge of +1. So to me they sound like the same particle. Also, i remember reading that a proton is in a group of quark comprized particles called hadrons.

please help me distinguish these particles :)

 

[hamster143]

There are 6 different types of quarks. Excluding the top (which is too unstable), you have 5. Each quark has a corresponding anti-quark.

"Hadron" is a generic term that denotes a composite particle that is consists of quarks and antiquarks.

There are two known families of hadrons: baryons and mesons. Any 3 quarks can combine to form a composite particle. The family of such 3-quark composite particles is called baryons. In addition, any quark can combine with any anti-quark, and these composite particles are called mesons.

Proton is the only stable member of the family of hadrons. (There are theories that protons might decay, but so far there's no evidence of that) Neutron is "almost" stable (free neutron has a half-life of around 15 minutes). All other hadrons decay in fractions of a second.

 

[KylBlz]

Thank you for the information. That was a very clear explination

There should be a karma system or something simmelar after the forums move to another server. +1 for you.

 

[bomanfishwow]

Proton is the only stable member of the family of hadrons.

Being pedantic, we don't know it's stable, we just know it at least has a massive lifetime, PDG tells me it's greater than 1.6 x 10²⁵ years in a mode dependent measure, or greater than 10³¹ to 10³³ years depending on mode. It is dangerous to make explicit statements on these things ;)

 

[hamster143]

Being pedantic, we don't know it's stable, we just know it at least has a massive lifetime

It's impossible to prove unequivocally that something is stable. This same argument can be applied to any other particle. E.g. we don't know that electron is stable, but we don't have any evidence that it decays. If we want to apply the term "stable" to any particles at all, we have to invoke the principle of presumption of stability: X is stable unless proven to decay.

 

[humanino]

This same argument can be applied to any other particle.

True, and the same argument can be applied quite generally to any scientific "truth". We don't know that the Sun will rise tomorrow actually...

 

[Tac-Tics]

True, and the same argument can be applied quite generally to any scientific "truth". We don't know that the Sun will rise tomorrow actually...

Yes, but it's more interesting to bring attention to the half-crackpot theories which predict the destruction of everything and everyone you've ever known.

 

[humanino]

Yes, but it's more interesting to bring attention to the half-crackpot theories which predict the destruction of everything and everyone you've ever known.

Except that the theories bomanfishwow is referring to are far from "crackpot" theories.