PARTICLE PHYSICS Particles and Interactions

Classifying Particles Most particles fall broadly into two types which can then be broken down further The HADRONS (Greek for the HEAVY ones) These are particles with mass and interact/ feel the strong nuclear force The LEPTONS (Greek for the LIGHT ones) These are particles with little or no mass and do not feel the strong nuclear force

Antiparticles Paul Dirac 1931 “Every particle has an opposing antipartlcle with equal but opposite charge” They also have equal and opposite QUANTUM NUMBERS

The Hadrons These break down to the BARYONS and the MESONS BARYONS are made up of three quarks (ANTIBARYONS are made of three ANTIQUARKS) MESONS are made of a quark anti-quark pairing Depending on their quark composition, Baryons and mesons can have a large variety of charges, strangeness, colour and spin These quantities are called QUANTUM NUMBERS

The Leptons These break down into three families or branches Electron branch Muon branch Tau Branch

The Quarks Quarks are the building blocks of all HADRONS. There are 6 flavours of quark.

Determining a particle’s quark composition Use the quark composition table to determine the quark composition of the following particles Proton (Q=1, B=1, S=0) Neutron (Q=0, B=1, S=0) Ω - (Omega minus) (Q=-1, B=1, S=-3) Σ + (Sigma Plus) (Q=1, B=1, S=-1) κ 0 (Kaon Zero) (Q=0, B=0, S=1) κ + (Kaon Plus) (Q=1, B=0, S=1) π + (Pion plus) (Q=1, B=0, S=0)

Determining whether a quantum interaction will be seen QUANTUM NUMBERS must be conserved for a theoretical process to be actually seen in a real life situation. Key Quantum Numbers Baryon Number Lepton Number Charge Strangeness Spin Colour (Truth and Beauty)

What is Strangeness?? Strangeness is a quantity used to describe when a particle does not interact as predicted It interacts in a STRANGE way. This led to a new quantum number – STRANGENESS Non- strange particles get a S value equal to 0. The strange quark has S=-1 and the anti-strange quark S=+1

Strangeness is not always conserved Importantly before looking at some particle events we need to understand that strangeness is one quantum number not always conserved. It is always conserved in STRONG or ELECTROMAGNETIC interactions BUT… It won’t be conserved in WEAK INTERACTIONS

Determining whether a quantum interaction will be seen Look at the following particle interactions and decide whether they are possible. If they are not possible, explain which conservation law has been broken.