PARTICLE SORTING

Classification of Particles and Patterns

So we've come across a bunch of particles and antiparticles that have varying properties, but they still seem to interact similarly. The table below shows the particles we've discussed previously - can you make any links?

Defining Hardons and Leptons

The trick is to lump the above into two categories, depending on whether or not said particle/ antiparticle interacts via the strong interaction. The two categories are hadrons and leptons.

• Hadrons interact through the strong interaction, e.g. protons, neutrons and mesons, and if charged via through the electromagnetic interaction. 
• Leptons do not interact through the strong force, e.g. electrons, muons and neutrinos, and if charged via through the electromagnetic interaction.

Remember: HEAVY HADRONS ARE STRONG! 

              LIGHT LEPTONS ARE WEAK!

"The picture [below] shows particle tracks from an electron-positron collision in the former Large Electron-Positron Collider (LEP) at CERN in Geneva. Here a Z0 particle is produced in the collision, which then decays into a quark-antiquark pair. The quark pair is seen as a pair of hadron jets in the detector." (Source: http://laganphysics.weebly.com/)

As has been mentioned endlessly, energy/ charge/ mass is conserved. Always. The sum of the rest mass energy of a particle/ antiparticle and their kinetic energy equates to the total energy of the particles/ antiparticles before the collision 

AND

the total energy of the particles/ antiparticles after the collision equates to the sum of their rest mass energy and their kinetic energy. Which is all a mumbo-jumbo way of saying that:

So if a K+ meson decayed into its π+, π+ and π counterparts, the maximum kinetic energy of the pi mesons would be calculated as follows (assuming the K meson is at rest before decay):

1. Rearrange the above equation to state that: the kinetic energy of the products equates to total energy before minus the rest energy of the products
2. Substitutue in the appropriate values (by making use of the particle-antiparticle table at the top of this page): kinetic energy = 494 - (140 + 140 + 140) 
3. End up with kinetic energy of the products equating to: 494 - 420
4. The answer is 74MeV. :-)

Baryons and Mesons

Baryons and mesons are classified under the category of hadrons, as they're created through the strong interaction. But they're pretty weird, as they can decay into protons as well as π mesons - this is weird because protons are never the decay products of a K meson. Freaky stuff. Okay, not really. 

SO ANY WAYS these splendid hadrons are divided into baryons and mesons, which - wait for it - are MADE UP OF YET MORE PARTICLES called quarks and antiquarks. But more of that later.

• Baryons are protons (and other hadrons, like neutrons) that decay into protons
• Mesons are hadrons (such as K mesons and π mesons) that do not include protons in their decay products

Energy Principles in Particle Collisions

If you haven't checked out the GLOSSARY then you should go ahead and do that. Good stuff. So you should have grasped the fact that these particles/ antiparticles are like your stereotypical characters in everyday life or games. They interact in very particular ways, and abstain from living life in any other way... Fun stuff.