Buxton & District U3A Science Discussion Group Subatomic Particles & Antimatter

1. Buxton & District U3A Science Discussion GroupSubatomic Particles & Antimatter John Estruch20 December 2013

2. What is antimatter?

4. What does Wikipedia say?(that’s always the right answer!) • antimatter is material composed of antiparticles • antiparticles have the same mass as particles of ordinary matter but have opposite charge and other particle properties • subatomic particles are particles smaller than atoms. (although some subatomic particles have mass greater than some atoms). Is that all clear now?

5. What does all of that mean? I’m going to work up to the answer in reverse order: • Subatomic particles • Antiparticles • Antimatter

6. Atoms & subatomic particles (all my talks seem to start here!): Electron In everyday physics and chemistry we see: Atoms made up of protons, neutrons and electrons So we call these protons, neutrons and electrons “subatomic particles” Proton Neutron Nucleus

7. Are there any other subatomic particles? Yes! • Only lightest of each type of particle exists in a “low energy” environment (i.e. electron, proton, neutron) • If a heavier particle exists it quickly tends to a lower energy state (i.e. decays to a lighter particle) • Heavier particles can exist in high energy environments (e.g. Shortly after Big Bang) • If we accelerate particles to high energy & collide them we can briefly bring heavier particles into existence E=mc2 Energy can manifest itself as mass Greater energy can be heavier mass

8. Linear accelerator (LINAC) Alternating current means next tube has right polarity to attract the particle as it approaches Getting to very high energies LINAC has to be very long and the amount of heat generated in the tubes becomes impractical

9. Synchrotron • Particles forced to move in curved path give off radiation • The tighter the bend the more energy is lost through this “synchrotron radiation” • To get to high energies need a large radius to minimise energy loss

10. LHC – The largest synchrotron • Largest accelerator to date • 27km circumference tunnel • 2 beams of protons circulate in opposite directions at 11,000 revs per second • Beams cross at 4 points – protons can collide here • Energy enough to create particles 7,000 times heavier than proton • Operates at -271.3°C (1.9 K) – colder than space • Vacuum of 10-13Atm – less gas than the moon • Consumes 120MW of electric power (6 x Buxton) • Cost about £2.6bn

11. Can we see these subatomic particles? • Not directly • But we can see evidence of their presence ……..

13. How do we find out about subatomic particles? • Charged particle moving in magnetic field is constantly pushed sideways. • Path is a circle • The faster the particle the straighter the track • The slower the particle the more curved Magnetic field Charged particle

14. Tracks of charged particles Negatively charged particles move anticlockwise. This picture is taken in a bubble chamber (more sophisticated version of cloud chamber). Magnetic field is applied to expose properties of charged particles Fast particles move in almost straight line Slow particles move in tight curve Positively charged particles move clockwise.

15. Modern Detectors • Large modern detectors use radial magnetic field, combination of electronic equipment and complex computer models to calculate: • Particle track • Measure momentum • Measure velocity • Calculate mass • Atlas at LHC • 45m long, 25m high, 7,000 tons • 3,000 physicists, 174 universities, 38 countries • 3,200 terabytes of data per year

16. Q. What was found? A. Loads of particles “Hadrons” “Baryons” Proton p Neutron n Lambda Λ0 Charmed Lambda Λ+c Bottom Lambda Λ0b Top Lambda Λ+t Sigma Σ+, Σ0, Σ− Charmed SigmaΣ++c, Σ+c, Σ0c Etc. etc. etc. “Mesons” Pion π+, π 0, π - Kaon K+, K0, K- Etc. etc. etc. “Leptons” Electron e – Electron Neutrinoνe Muonμ – MuonNeutrinoνμ Tau τ– Tau Neutrinoντ 2 Quarks 3 Quarks

17. What does all of that mean? I’m going to work up to the answer in reverse order: • Subatomic particles • Antiparticles • Antimatter

18. Conservation rules • There are clear patterns in the interactions that produce new subatomic particles • Only certain combinations can be produced together • This is expressed as a number of conservation rules which each have an associated property For example conservation of electric charge: “The total charge of the particles going into an interaction must be equal to the total charge of particles produced “ neut neut +ve +ve +ve +ve -ve +ve +ve +ve +ve +ve +ve

19. Other conserved properties Based on which interactions do / do not occur other conserved properties were identified: • Quark (or hadron) “Flavours” • Strangeness • Charm • Topness • Bottomness • Lepton numbers: • Electronic number • Muonic number • Taonic number Baryon Number

20. Antiparticles For each particle there is an equivalent anti-particle with: • Same mass • Opposite electric charge • Opposite of any other conserved properties

21. Particle-antiparticle examples

22. Particle-antiparticle annihilation A particle and its antiparticle can interact with each other through a process called annihilation. • Annihilation must produce a result which has zero electric charge (as well as zero for all the other properties) • Annihilation produces “photons” which are massless particles with zero charge and zero values of the other conserved properties • When a particle & antiparticle annihilate their entire mass is converted into the energy of the resulting photons

23. What does all of that mean? I’m going to work up to the answer in reverse order: • Subatomic particles • Antiparticles • Antimatter

24. Antimatter atoms Hydrogen atom “Antihydrogen” Electron Positron Proton Antiproton The chemical properties of an antimatter atom is the same as a “normal” matter atom.

25. Can we make antimatter atoms?(other than in Dan Brown fiction) • 1955 - Antiprotons first confirmed experimentally • 2002 - first “cold” antihydrogen atoms made • 2011 - ALPHA experiment at CERN had trapped 309 antihydrogen atoms, for up to 1,000 seconds (about 17 minutes). • 1970s – antihelium-3 nucleus (2 antiprotons plus 1 antineutron) observed • 2011 – antihelium-4 nucleus (2 antiprotons plus 2 antineutrons) observed • CERN can produce 10 million antiprotons per minute - If all could be turned into antihydrogen it would take 100 billion years to produce 1 gram (Sorry Dan!)

26. Does antimatter exist in nature? • Natural  radioactive decay produces either: • Electron and antineutrino • Positron (antielectron) and neutrino. • Positrons have been detected above thunderstorms • Antiparticles are created in stars and other high-energy astronomical objects and appear in cosmic rays • The Van Allen Belts around the earth contain antiprotons. But none of these last for very long because they eventually interact with normal matter and annihilate.

27. Why isn’t there more antimatter in the universe? • Everywhere we look around from earth seems to be made of matter. • If all matter was created in the big bang why isn’t there an equal amount of antimatter?

28. Why isn’t there more antimatter in the universe? • Option 1 “Baryon asymmetry ” • In the very high energy conditions of the big bang the conservation rules didn’t quite apply for some reason • Slightly more matter particles than antimatter was produced • Matter & antimatter annihilated leaving only the excess matter and a lot of energy • Modern theories recognise the violation of conservation rules but mechaism not understood • Option 2 “Heterogeneous distribution” • Following the big bang particles were not evenly distributed (hence structures such as stars and galaxies) • Some regions may have had slightly more antimatter and so eventually led to antimatter galaxies • If this is the case there would be large scale annihilation at the boundaries between matter & antimatter regions

29. Questions?