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Particle Physics. Past and Future H.Arfaei IPM 26/2/86. Ancient view : Earth, Air, Fire, Wate r By 1900, nearly 100 elements By 1936, back to three particles: proton, neutron, electron. Ancient Principles Symmetry Geometrical pictures Theory for the four elements!
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Particle Physics Past and Future H.Arfaei IPM 26/2/86
Ancient view: • Earth, Air, Fire, Water • By 1900, nearly 100 elements • By 1936, back to three particles: proton, neutron, electron
Ancient Principles • Symmetry • Geometrical pictures • Theory for the four elements! • Platonic Polyhedra • Search for the fifth element! • Still Valid
Who ordered THAT ? • From the particle garden to the jungle : In 1937, Anderson discovered the muon μ. The μ proved to be some sort of heavier electron (lepton). The muon decays intothrough β decay: μ νμ + e- +¯νe I.I Rabi, Nobel 1944 In 1947, pions (mesons) were detected in cosmic rays. They were thought of as Yukawa’s mediator particle for the strong interaction. The Universe was in order again, except for the muon, which played no visible role. In December 1947, new mesons were found : the kaons. The place got crowded again… With the use of particle accelerators in the 50’s, many new particles were discovered. Some of them were « strange » because they were produced by the strong force but decayed through the weak force.
1932 : Chadwick discovers the neutron, which is not stable when isolated, and decays as follows : n p + e- (+ ¯νe). The proton, electron and neutron account for all the atoms of all the elements in the Universe. This was the “simplest” elementary particle set ever described. A small number of particles, a small number of interactions. LEPTON (leptos = light) : e- BARYONS (baryos = heavy) : p , n
2. Which particles were considered elementary throughout History? • Antiquity : Four elements. Unsuccessful attempt at an atomistic theory during the 5th century BC (Democritus). • 18th century : Lavoisier and Dalton verify experimentally the validity of the atomic structure. • 1868 : Mendeleev proposes his chart of elements, containing the 63 atoms known at the time. The “empty cases” he left were soon filed. By 1896, 77 atoms have been discovered, and are considered elementary. • 1897 : Discovery of the first subatomic particle by J.J Thompson : the electron. The search for its positive counterpart begins, until… • 1911 : Rutherford discovers the nucleus. Transmutation reactions showed that the hydrogen nucleus played a specific role (42He + 147N --> 189F --> 178O + 11p). Rutherford named it proton (protos = first)
Moreover, some rules seemed to be missing to predict if a decay could occur or not : • Why is π- + p+ K+ + Σ- possible , • When π- + p+ K0 + n is impossible ? • In 1953, Gell-Mann and Nishijima came with a simple and elegant idea. Each particle was to be assigned a «strangeness », and the overall strangeness had to be conserved during a collision (not through decay). • There were then THREE laws of conservations for reactions : • Charge • Baryonic number (proton like particles) • Strangeness
Ancient times People think that earth, air, fire, and water are the fundamental elements. 1802 Dalton’s Atomic theory began forming. 1897 J. J. Thompson discovered the electron. 1911 Rutherford discovered positive nucleus. 1930 Pauli invented the neutrino particle. 1932 James Chadwick discovered the neutron. 1937 The muon was discovered by J. C. Street and E. C. Stevenson. 1956 First discovery of the neutrino by an experiment: the electron neutrino. 1962 Discovery of an other type of neutrino: the muon neutrino. 1969 Friedman, Kendall, and Taylor found the first evidence of quarks. 1974 The charmed quark was observed. 1976 The tau lepton was discovered at SPEAR. 1977 Experimenters found proof of the bottom quark. 1983 Carlo Rubbia and Simon Van der Meer discovered the W and Z bosons. 1991 LEP experiments show that there are only three light neutrinos. 1995 The top quark was found at Fermilab. 1998 Neutrino oscillations may have been seen in LSND and Super-Kamiokande. 2000 The tau neutrino was observed at Fermilab. 2003 A Five-Quark State has been discovered. A short summary of events
S0 po L+ D- Do K- D+ W- p- p p+ D++ K0 K+
1. What makes a particle “elementary” ? • A particle is elementary if it has no inner structure (i.e not “made” of some even smaller entities).
3. New particles again, but some symmetry and order gained... • Quark dynamics was understood later, and brought 8 photon like mediator particles : gluons. • After a few years of quiet, the November Revolution (1974) brought a new quark (charm quark) through the discovery of the J/ψ meson (c ¯c). • In 1975, the Τ lepton was discovered. • In 1977, the Υ meson (b ¯b) was discovered, introducing the bottom quark. • In 1983, the mediators for the weak interaction were discovered at CERN : W+- and Z0 • The symmetry of six quarks and six leptons was completed with the top quark in 1995.
Unifying Principle • Symmetry, Gauge Invariance Generalization from EM and Breaking the symmetry!!! by Giving nonzero VEV to Higgs Field • Responsible for mass of the Quarks, Leptons and gauge Bosons
1. The Nobel Prize winners 1979 Nobel Prize-- GLASHOW, SALAM and WEINBERG the theory of the unified weak and electromagnetic interaction. 1984 Nobel Prize-- RUBBIA and VAN DER MEER the discovery of the field particles W and Z, communicators of weak interaction.
Present activitiesnews in 2006 and 2007 sky Dark matter accelerators CP violation, mixings WZ pair production Single top events Proton and strangeness Pentaquark Quark Gluon Plasma underground activities Neutrino vanishing ! Opera
What next? • Theory Supersymmetry, Extra dimensions, String Theory, Unification with gravity.. M-theory…… • Experiment LHC
3. Science needs advanced technology and vice versa Accelerator How to Obtain Particles
Modern Detectors Bubble Chamber
The large hadron collider • The large hadron collider (LHC) uses the same tunnel as LEP, at Cern in Geneva • The machine is a 14 TeV proton-proton collider, so each stored beam will have an energy of 7 TeV • It is being built now, and shall start operation sometime in 2007 • There are a number of experiments
What to look for? HIGGS SUSY Particles ( Candidate for Dark Matter?) Hierarchy problem Extra dimensions CP violation Quark gluon Plasma
What to look for? • Higgs • Top quark Physics • Susy particles (candidates for dark matter?) • Hierarchy problem • Extra dimensions • CP violation, Flavor Mixing • Quark gluon Plasma
HIGGS expected around 115 GEV Guides us to the origin of mass • Decays in to two Z bosons that decay into pair of Muons • If it is not seen up to 1TEV we have to find a way out, though life!
Susy particles • Candidate for Dark matter May be seen as missing mass
