Particle Physics: Basics, Forces, and the Discovery of the Higgs Boson

1. Large Hadron Collider (LHC) Point 1 activities and perspectives Marzio Nessi ATLAS plenary 2nd October 2004

4. Basic constituents • Leptons • Electron , muon and tau – all negatively charged • Radioactive  decay produces a different particle – neutrino () . There are three types of neutrino! • Quarks • have fractional electric charges and are never seen alone!(qqq or q+antiquark make up hadrons like proton,pion …) • Each quark also is found with three different colour charges • Proton mass ~ 1 GeV, top quark mass ~175 GeV • Both • Three ‘generations’ of quarks and leptons • All quarks and leptons have antiparticles • Quarks and Leptons are all spin ½ particles

5. Quarks and Leptons Leptons Electric Charge Tau Tau -1 0 Neutrino Muon Muon -1 0 Neutrino Electron Electron -1 0 Neutrino Quarks Electric Charge Bottom Top -1/3 2/3 Strange Charm -1/3 2/3 Down Up -1/3 2/3 each quark: R , B , G 3 colors (Antimatter -Each one has antiparticle)

9. Basic Forces • Gravitational – by far the weakest force • Electromagnetic – vital for atomic structure • Strong – holds quarks inside the proton • Weak – responsible for radioactive decay and nuclear reactions in sun and stars

10. Force Carriers • Gravitational – • Electromagnetic – • Strong – • Weak – ? photon gluon W+ W- Zo All quarks and leptons are fermions (spin ½) All force carriers are bosons (spin 1)

11. The discovery of the W and Z dramatically confirmed the electroweak theory. Its unification of the seemingly unrelated phenomena of nuclear beta decay and electromagnetism is one of the major achievements of twentieth century physics. Robert N. Cahn and Gerson Goldhaber “The Experimental Foundations of Particle Physics” Cambridge University Press

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13. Matter and Forces “The standard model”

15. Higgs Boson – Current limit

20. Gravity – solar system, galaxies … Electromagnetic – atoms, electricity ….. Weak – beta decay, how stars generate energy Weak force Strong – binds quarks inside proton The Forces ForceRangeForce Carrier Strength Gravitational long 1 Electromagnetic long photon (massless) 1035 Weak short W, Z bosons (heavy) 1033 Strong short gluons (massless) 1038

21. Some of the big questions Where do the particles get their mass from? Where has all the anti-matter gone? What is dark matter made of? What else is out there?

22. What is Mass? In the mid 1960s, British physicist Peter Higgs came up with a theory on why some particles have mass. He proposed a new heavy particle, now called the Higgs boson, which generates a Higgs field. Particles who ‘feel’ this field gain mass. Light particles don’t feel this field strongly, heavy particles do.

23. What is Dark Matter? Normal: Made from atoms Includes stars, planets, people… Dark matter: Unknown substance (not atoms) May be a “fat cousin” of light (SUSY) Hope to make & study it at the LHC Dark energy: Even weirder!

24. A basic “Tracker” Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Multiple thin layers of, for example, silicon sensors

25. A basic calorimeter Basics The past Challenges Where to start? Detector Design Tracker Calorimetry Particle ID LHC detectors “Events” Final thoughts Total # of particles is proportional to energy of incoming particle Active detector slices produce a signal proportional to the number of charged particles traversing

26. E2 = p2c2+ m2c4