Particle Physics

Particle Physics

1. Basics

   • Icetops: Same proton number, different mass
   • f =KQ1Q2/r^2
     • Radius of a nuclei (r) = r0 (basic radius) A (mass number)
   • Aprox size of: nucleus ~ x10-5m, atom ~ x10-10m

2. Particle accelerators and detectors

   • Thermionic emissions, using heat to get electrons
   • Particles can be sped up through use of an electric field, but not a magnetic field as as the force is centripetal so it will only bend and focus the beam
   • QV(P.d) = 1/2mv^2(velocity)
   • Linear accelerators
     • • Acceleration occurs in the gaps between the drift tubes
       • The tubes get longer as the particles speed up, it spends the same amount of time in each drift tube, during this time the a.c. p.d. reverses to allow further acceleration
       • The momentum of a linac ~ 3km due to the curvature of the earth
       • The tubes are excavated to avoid interactions of the particle beam and air molecules
       • A high voltage, high frequency a.c supply is used, alternate drift tubes connect to the same side of the a.c
       • Limitation, its a fixed target experiment
   • flemings LHR works for positive charges only, use RHR for negative, but say LHR
   • Cyclotron
     • In the dees the particles move at constant speed
       • Frequency = Bq/2πm
   • As particles approach the speed of light they gain mass

3. Electric and magnetic fields in accelerators

   • Electric fields are used to accelerate charged particles across the gap (linac) or between the dees (cyclotron)
   • Magnetic fields are used in cyclotrons to produce a centripetal force
   • Electric fields can be used in detectors to determine the charge on a particle by seeing which plate the particle is attracted to
   • Magnetic fields can also be used to determine the charge on a particle using FLHR
   • Beams, having two beams collide is useful as the particles have 0 momentum before
   • Detectors, The charged particles these collisions produce will ionise into a liquid or gas

4. Rules for bubble chambers

   • The radius is proportional to the movement, faster/move momentum less curvature
   • The more ionising, the thicker the trail
   • Neutral particles leave no track (little or no ionisation) and they are not effected by the magnetic field
   • Opposite charged particles are deflected in opposite directions by the magnetic field, use LHR to determine charge

5. Standard model

   • Hadrons, particles that feel strong nuclear force; not fundemental particles, made of quarks
     • Two types of hadrons, brayons and mesons
       • Baryons are made from three quarks, the baryon number is the number of baryons in an atom
         • Protons and neutrons have a baryon number of B = +1, the total baryon number in a particle never changes
       • Mesons are unstable and have a baryon number of 0, mesons are made up of 2 quarks, a quark and an anti-quark
         • Pions (π mesons) are up +/ down quarks
         • Kaons (K mesons) are u/d + strange quarks
       • Mesons interact with baryons via the strong interaction
   • Antiparticles have the same mass, but an opposite charge, a line is put above the symbol
   • Leptons are fundemental particles, they do not feel the strong interaction
     • there are three types of leptons, electrons, muons and taus (all negative) each lepton has a neutrino which have 0 mass and 0 electric charge
     • Each lepton has a lepton number of 1, but the different types must be counted seperatly
   • In any particle reaction the charge, baryon number and momentum must be conserved aswell as each type of lepton

6. Binding energy

   • The mass of a nucleus is less that the sum of the masses of its parts as some mass is lost in energy
   • to seperate particles they must be pulled apart against the attractive strong force, they have potential energy when they are seperated
   • When the particles come together to form a nucleus their potential energy decreases so the energy is known as the binding energy as it is the energy needed to break bonds
   • Binding energy = mass defect x c^2
     • E = mc2