Introduction to Particle Physics Achim Geiser, DESY Hamburg DESY summer student program, 28.-29.7.21 Scope of this lecture: Introduction to particle physics for novices rather elementary more details -> specialized lectures particle physics in general thanks to B. Foster for some of the nicest slides/animations other sources: some emphasis on DESY-related topics www pages of DESY and CERN 28.-29.7.21 A. Geiser, Particle Physics 1 What is Particle Physics? 28.-29.7.21 A. Geiser, Particle Physics 2 What is “science”? Wikipedia.org: Science (from Latin scientia , meaning "knowledge") is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe. First large scale scientific experiment: proposal: Galilei 1632 historically^ recorded realisation: Pierre Gassendi 1640 Galileo Galilei French navy Galley with M. Risch international crew of ~100 people Physik in Unserer Zeit cannon (fraction of students not reported) 38 (5) (2007) 249 ball => 5 m/s ? 28.-29.7.21 A. Geiser, Particle Physics 3 What is a „particle“? Classical view: particles = discrete objects. Mass concentrated into finite space with definite boundaries. Particles exist at a specific location. -> Newtonian mechanics Isaac Newton Modern view: (Principia 1687) Emilie du Châtelet particles = objects with discrete (1759) Niels quantum numbers, e.g. charge, mass, ... Bohr not necessarily located at a specific position (Nobel 1922) (Heisenberg uncertainty principle), can also be represented by wave functions (quantum mechanics, particle/wave duality). Louis Werner Erwin de Broglie Heisenberg Schrödinger (Nobel 1933) (Nobel 1929) (Nobel 1932) 28.-29.7.21 A. Geiser, Particle Physics 4 What is „elementary“? Greek: atomos = smallest indivisible part John Dalton 1803 (atomic model) Dmitry Ivanowitsch Mendeleyev 1868 (elements) Ernest Rutherford 1911 (nucleus) (Nobel 1908) Murray Gell-Mann 1962 (quarks) (Nobel 1969) ? 28.-29.7.21 A. Geiser, Particle Physics 5 History of basic building blocks of matter 0 − − + οο ΚΣ∆Λ+∆π − ∆− + Ω motivation: ππ∆0 + find Κ+ pΚ smallest + possible Super- number symmetry 2030? AD 28.-29.7.21 A. Geiser, Particle Physics 6 Which “interactions”? at ~ 1 GeV -2 28.-29.7.21 A. Geiser, Particle Physics 7 What we know today u c t g up charm top gluonγ Quarks s downd strange bottomb photon ν ν ν e µ τ τ W e-neutrino µ-neutrino -neutrino W boson e µ τ Z Leptons electron muon tau Z boson Higgs Boson 28.-29.7.21 A. Geiser, Particle Physics 8 The Power of Conservation Laws e.g. radioactive neutron decay: - ν not visible n p + e + e Pauli 1930: Wolfgang Emmy Noether Pauli 1919: (Nobel 1945) E,p,L conservation related to homogeneity of time+space and isotropy of space 28.-29.7.21 A. Geiser, Particle Physics 9 confirmation: neutrino detection e.g. reversed reaction: ν e+ n p + e extremely rare! Frederick Reines (absorption length ~ 3 light years Pb) (Nobel 1995) first detection: 1956 Reines and Cowan , neutrinos from nuclear reactor 28.-29.7.21 A. Geiser, Particle Physics 10 The power of symmetries: Parity Will physical processes look the same when viewed through a mirror? In everyday life: violation of parity symmetry is common „natural“: our heart is on the left „spontaneous“: cars drive on the right Eugene (on the continent) Wigner What about basic interactions? (Nobel 1963) Electromagnetic and strong interactions conserve parity! 28.-29.7.21 A. Geiser, Particle Physics 11 The power of symmetries: Parity Lee & Yang 1956 : weak interactions violate Parity experimentally verified by Wu et al. 1957: Chen Ning Yang (Nobel 1957) spin Tsung -Dao consequence: Lee neutrinos are always Chieng Shiung lefthanded ! Wu (antineutrinos righthanded) 28.-29.7.21 A. Geiser, Particle Physics 12 The Power of Quantum Numbers 1948: discovery of muon Who ordered THAT ? same quantum numbers as electron, except mass (Nobel 1988) I.I. Rabi (Nobel 1944) µ- ν - ν muon decay: -> µ e e conservation of Leon M. Melvin Jack Ledermann Schwartz Steinberger electric charge -1 0 -1 0 lepton number: 1 1 1 -1 ν = ν (1955) ν ν „muon number“: 1 1 0 0 µ = e (1962) There is a distinct neutrino for each charged lepton 28.-29.7.21 A. Geiser, Particle Physics 13 The Power of Precision Precision measurements of shape and height of Z 0 resonance at LEP I (CERN 1990’s) ν number of ν ν (light) neutrino flavours = 3 Gerardus Martinus t’Hooft Veltman (Nobel 1999) e+e- -> Z 0 28.-29.7.21 A. Geiser, Particle Physics 14 Can we “see” particles? Luis Walter Alvarez (Nobel 1968) we can! bubble chamber photo Donald Arthur Glaser (Nobel 1960) 28.-29.7.21 A. Geiser, Particle Physics 15 A typical particle physics detector see e.g. ARGUS near DESY entrance more details: lecture I. Gregor 28.-29.7.21 A. Geiser, Particle Physics 16 Why do we need colliders? early discoveries in cosmic rays, but need controlled Mont Blanc conditions E V.F. Hess m = (Nobel 1936) c2 Albert Einstein CERN (Nobel 1921) need high energy to discover new heavy particles LEP/LHC colliders = microscopes (later) more details: lecture P. Castro 28.-29.7.21 A. Geiser, Particle Physics 17 The HERA ep Collider and Experiments Data taking stopped summer 2007. Data analysis continues even now at small rate. 28.-29.7.21 A. Geiser, Particle Physics 18 Particle Physics = People 28.-29.7.21 A. Geiser, Particle Physics 19 Strong Interactions: Quarks and Colour strong force in nuclear interactions = „exchange of massive pions“ between nucleons = residual Van der Waals-like interaction Hideki Yukawa (Nobel 1949) n modern view: π (Quantum Chromo-Dynamics, QCD) exchange of massless gluons p between quark constituents „similar“ to electromagnetism (Quantum Electro-Dynamics, QED) 28.-29.7.21 A. Geiser, Particle Physics 20 The Quark Model (1964) arrange quarks (known at that time) into flavour-triplet => SU(3) flavour symmetry Q=-1/3 Q=2/3 almost d v u treat all known hadrons S=0 (protons, neutrons, pions, ...) as objects composed of two or three such quarks (antiquarks) Murray S=-1 Gell-Mann s (Nobel 1969) 28.-29.7.21 A. Geiser, Particle Physics 21 The Quark Model baryons = qqq mesons = qq 28.-29.7.21 A. Geiser, Particle Physics 22 Colour Quark model very successful, but seems to violate ++ quantum numbers (Fermi statistics), e.g. ∆ =uuu ↑↑↑ => introduce new degree of freedom: q g g q q ggg g q q g g q 3 coulours -> SU(3) colour qqq = qq = white! (exact symmetry) 28.-29.7.21 A. Geiser, Particle Physics 23 Screening of Electric Charge electric charge polarises vacuum -> virtual electron positron pairs positrons partially screen electron charge effective charge/force (Nobel 1965) decreases at large distances/low energy (screening) increases at small distance/large energy 28.-29.7.21Sin-Itoro Julian Richard P. A. Geiser, Particle Physics 24 Tomonaga Schwinger Feynman Anti-Screening of Coulour Charge! quark-antiquark pairs -> screening gluons carry colour -> gg pairs -> anti-screening ! (Nobel 2004) asymptotic confinement freedom 1/r 2~E 2, 28.-29.7.21 A. Geiser, Particle Physics 25 Comparison QED / QCD electromagnetism strong interactions QED QCD 1 kind of charge (q) 3 kinds of charge ( r,g,b) force mediated by photons force mediated by gluons photons are neutral gluons are charged (eg. rg, bb, gb) α α is nearly constant s strongly depends on distance confinement limit: The underlying theories are formally almost identical! 28.-29.7.21 A. Geiser, Particle Physics 26 The effective potential for qq interactions confinement lattice asymptotic freedom gauge calculation 28.-29.7.21 A. Geiser, Particle Physics 27 Burton Heavy Quark Spectroscopy Richter Charmonium = bound system (Nobel 1976) + - of cc quark pair Positronium = bound e e system Samuel C.C. Ting 1974 28.-29.7.21 A. Geiser, Particle Physics 28 calculation of proton mass in QCD from lattice gauge theory: p spontaneous breakdown of “chiral symmetry” Yoichiro (left-right-symmetry) yields Nambu QCD “vacuum” expectation value (Nobel 2008) proton mass (~= neutron mass) , mass of the visible part of the universe ! 28.-29.7.21 A. Geiser, Particle Physics 29 How to detect Quarks and Gluons? Jets! hadrons Example of the hadron + - q production in e e e+ e- annihilation in the JADE ~1979 q detector at the PETRA e+e- collider at DESY, hadrons Germany. Georges √s energy 30 GeV. Charpak Lines of crosses - reconstructed trajectories in drift chambers (gas ionisation detectors). (Nobel 1992) Photons - dotted lines - detected by lead-glass Cerenkov counters. Two opposite jets. 28.-29.7.21 A. Geiser, Particle Physics 30 Discovery of the Gluon (1979) PETRA at DESY: look for α s Björn Wiik Paul Söding TASSO event picture Günter Wolf Sau Lan Wu (EPS prize 1995) 28.-29.7.21 A. Geiser, Particle Physics 31 Jets in ep and pp interactions LHC HERA more details: lecture H. Jung 28.-29.7.21 A. Geiser, Particle Physics 32 α Running strong coupling „constant“ s e.g. from jet production at e +e-, ep, and pp at DESY, Fermilab and CERN (HERA) (LEP, PETRA) courtesy T. Dorigo 28.-29.7.21 A. Geiser, Particle Physics 33 How to determine the „size“ of a particle? microscope: resolution ~ 10 -18 m = 1/1000 of size of a proton low resolution -> small instrument high resolution -> large instrument 28.-29.7.21 A. Geiser, Particle Physics 34 How to resolve the structure of an object? e.g. X-rays scattering image probe (Hasylab, FLASH, accelerator PETRA III, XFEL) E~ keV -> structure of a biomolecule Ada Yonath (Nobel 2009) 28.-29.7.21 A. Geiser, Particle Physics 35 Resolve the structure of the proton E ~ MeV resolve whole proton static quark model, Jerome I.