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Outline Relativistic Kinematics (4-momentum)2 invariance, invariant mass Hypothesis testing, production thresholds Cross-sections, flux and luminosity, accelerators Particle lifetime, decay length, width Classification of particles Fermions and bosons; Leptons, hadrons, quarks Mesons, baryons Quark Model Meson and baryon multiplets Isospin, strangeness, c, b, t quarks Particle Interactions Colour charge, QCD, gluons, fragmentation, running couplings Strong and weak decays, conservation rules Virtual particles and range of forces Previous lecture Parity, charge conjugation, CP Weak decays of quarks Charmonium and upsilon systems Electroweak Interactions Charged and neutral currents W, Z, LEP experiments Higgs and the future Higgs phenomenology - new in 2015 Dark Matter phenomenology (and searches) – new in 2015 LHC Experiments’ Results [Introduction to accelerator physics??] Today Synchrotron Radiation SR loss for e- 4 e 2 2 4 E / turn 3 r 4 re (m) E 4 (GeV ) E (GeV ) / turn 3 me3 (GeV ) r (m) Lower version more useful r=bending radius re is classical e- radius (2.8x10-15m) and is proportional to 1/me me is electron mass (in energy units) Great if you want SR for experiments (“light sources”, e.g. LCLS, Diamond, etc. Disaster if you want high energy e+ecollisions e.g. 200 GeV e- collider of radius 4.3km (~LEP2) radiates ~32 GeV (/e-/turn). Decay Length <xlab> Time t in decay e-t/t A is proper time (measured in A’s rest frame) Time dilation (as seen in lab. frame) Particles moving at >1 live longer (to us) tlab= t <xlab> = c t Particle mass m, energy E, momentum p E/m p/E p/m Examples… asymmetric colliders PEPII, KEKB B C Decay length example: BaBar Makes decay vertex easier to measure because of time dilation Example lifetime measurement LHCb collaboration: R. Aaij et. al, Measurement of the B¯0s→D−sD+s and B¯0s→D−D+s effective lifetimes, arXiv:1312.1217 (4 Dec. 2013), to appear in Phys. Rev. Lett. 3. Classification of Particles Historical names, but need to be familiar with definitions amd symmetries Fermions Bosons Leptons Hadrons Quarks Flavours Mesons Baryons Has impact on the allowed baryon and meson states in particular 3.1 Identical Particles If particles A and B identical yAB(x1,x2) A x1 yAB(x2,x1) B x1 B x2 A x2 Then 2-particle system is indistinguishable under exchange A B | yAB |2 | yBA |2 Therefore, yAB yAB yBA (symmetric). Case if identical bosons - yBA (antisymmetric). Case if identical fermions 3.2 Fermions Particles of half-(odd) integer spin, 1/2,3/2 QM wavefunction for pair of identical fermions, A, B, is antisymmetric under particle interchange yAB(x1,x2) ≡ yA(x1) yB(x2) - yB (x1) yA (x2) Fermi-Dirac Statistics Pauli Exclusion Principle: 2 identical fermions cannot occupy same quantum state Implication: atoms and nuclei stable “Fermion number” conserved in all reactions 3.3 Bosons Particles of integer spin, 0, 1, 2, … QM wavefunction for pair of identical bosons, A, B, is symmetric under particle interchange yAB(x1,x2) ≡ yA(x1) yB(x2) + yB (x1) yA (x2) Bose-Einstein Statistics 2 or more identical bosons can occupy same quantum state Examples? “Boson number” not conserved (so not useful concept)