Quarks and Leptons

The Particle Zoo

·     

Baryons are always either 3 quarks or 3 anti-quarks

·      There is a further set of leptons called Tau particles that are not required for AS Physics

Table of Quarks

Name	Symbol	Charge	Strangeness
Up	u	+2/3	0
Anti-up		-2/3	0
Down	d	-1/3	0
Anti-down		+1/3	0
Strange	s	-1/3	-1
Anti-strange		+1/3	+1
Charm	c	+2/3	0
Anti-charm		-2/3	0
Bottom	b	-1/3	0
Anti-bottom		+1/3	0
Top	t	+2/3	0
Anti-top		-2/3	0

 

Conservation Rules

·     

You will be familiar with the concept of ‘conservation of energy’. This states that energy cannot be created or destroyed, just converted from one form to another. In a particle accelerator this would be used to calculate the rest energy of the new particles made: 

·      Other conserved quantities

-   Charge, Q

Particles charge is normally indicated in the symbol – anti-particles have the opposite to their corresponding particle.

Total charge before      =      Total charge after

 

-   Lepton Number, L

Leptons e.g. electrons have L= +1, anti-leptons e.g. positrons have L= -1

Lepton number before =      Lepton number after

 

-   Baryon Number, B

Baryons e.g. protons have B= +1, anti-baryons e.g. anti-protons have B= -1

Quarks have B = +1/3, anti-quarks have B = -1/3

Baryon number before        =          Baryon number after

 

-   Strangeness, S

Is not conserved in weak interaction – only strong (where quark flavor is changing)

Strange quarks have (or particles containing them) have S = -1, anti-stange quarks (and particles containing them) have S = +1

Strangeness before      =      Strangeness after

Examples:

Are the following particle interactions possible?

1.        

Q:

L:

B:

S:

 

2.        

Q:

L:

B:

S:

 

3.        

Q:

L:

B:

S:

 

4.        

Q:

L:

B:

S: