Particle Physics Professor Kay Kinoshita University of Cincinnati

Particle Physics (also called High Energy Physics) at UC Faculty Theory Experiment Philip Argyres Randy Johnson Bernard Goodman* Kay Kinoshita Alex Kagan Brian Meadows Joe Scanio Alan Schwartz Peter Suranyi* Mike Sokoloff Rohana Wijewardhana Louis Witten* *emeritus

Reference materials http://www.particleadventure.org/ History and description of Standard Model: The Particle Adventure CP Violation http://www.particleadventure.org/ http://www.physics.uc.edu/~kayk/cpviol/CP.html

what is particle physics? • matter and energy: the study of elementary particles and forces between them “elementary” = not made up of other, “smaller,” particles • matter “everyday” matter is made of atoms each atom consists of a nucleus & electrons each nucleus is made up of protons & neutrons each proton/neutron contains even smaller particles, called quarks quarks and electrons are believed to be elementary • forces (interactions) in classical physics hold matter together push matter apart

what is a force? Classical forces gravitational exists between two objects with mass electromagnetic exists between two objects with electric charge • Matter experiences a force if it carries a property (“charge”) that couples to that force

what is a force? • In addition to gravitation and electromagnetism, particles are known to be influenced by two other forces, strong and weak, which cannot be described within classical physics – need relativistic quantum mechanics: strong exists between particles with “strong charge”, or “color” weak exists between particles with “weak charge” .

what is a force? In relativistic quantum mechanics • interactions are depicted as exchanges of particles (field quanta) associated with force • matter can be turned into energy and vice versa: E=mc2 • anti particle is equivalent to particle traveling backward in time • elementary particles may turn into other elementary particles X Y scattering X anti-X annihilation X X’ Y Z decay

what is a force? strong force • holds protons and neutrons together in nuclei • 3 types of “charge” = 3 colors combination of 3 is neutral, “singlet” => 3 quarks in proton, neutron • field quantum: gluon (8 types) • strength: weak at very short distances, strong at (~1) > nuclear dimensions (few x 10–15 m) => quarks can only exist in bound “color singlet” states .

what is a force? weak force • responsible for beta decay • the only force that allows particles to change into others •symmetry-violating (P, CP) couplings • 3 field quanta: Z0, W+,W– • strength: too weak to bind matter (~10–5) .

what is a force? electromagnetic force • binds electrons to nuclei • field quantum: photon • strength ~ 10–2 .

what is a force? gravitational force • apples, solar systems, galaxies, ... • field quantum: graviton (not yet seen) • strength: ~ 10–38 .

what is the Standard Model? • explains everything (so far) in terms of 12 elementary particles: 6 quarks, 6 leptons Strong, Electromagnetic, and Weak forces (gravitation not yet included effectively in the theory) electric charge –e +2e/3 –e/3 3 generations e– e –  -  leptons (color = 0) interesting patterns... up down charm strange top bottom quarks

what is different about the Weak Interaction? • universality of weak charge in quarks is not apparent for interactions involving W± ... unlike interactions involving Z0 • observe “CP violation” <-> complex “weak charge” e– e –  -  leptons (universal) seen Z0 "neutral current" not seen up down charm strange top bottom suppressed quarks (all different)

what is different about the Weak Interaction? • universality of weak charge seen by modifying picture: weak force sees {d,s,b} as mixed quantum mechanical states => weak charge is universal, but in a “rotated” perspective Cabibbo-Kobayashi-Maskawa (CKM) matrix d' s’ = b' d s b complex preserves metric “ orthogonality  unitary up d’own charm s’trange top b’ottom

• proposed 3rd generation of particles Kobayashi & Maskawa (1973) •  proposed 3rd generation of particles • could explain CP violation in K (& predict for B) due to complex nature of 3-generation matrix (vs. 2) B-Factory experiments [SLAC (Stanford), KEK(Japan)] (1999-2009) • CP asymmetry observed in diverse processes in B decay -> many measurements, (over)constrain CKM, confirm unitarity

Is there more? e– e –  -  up down charm strange top bottom ... yes (out of time) Is there more to be understood? Undoubtedly! • gravity is not included in the Standard Model • astrophysical evidence for “dark matter”, “dark energy” (???) • history tells us that patterns hint at new laws • new accelerators – LHC, super B-factory – the next microscopes electric charge –e +2e/3 –e/3 3 generations e– e –  -  leptons (color = 0) WHY? 3 generations 2 leptons/2 quarks pattern of charges \sin 2\phi_1:\ \ b\to c\bar c s,\ s\bar s s |V_{ub}|:\ \ b\to u\ell^-\bar\nu,\ B^-\to \tau^-\bar\nu :\ \ {B^-\to \tau^-\bar\nu\over B^-\to \mu^-\bar\nu}, \ {B^-\to D^{(*)} \tau^-\bar\nu\over B^-\to D^{(*)} \mu^-\bar\nu}, \ up down charm strange top bottom quarks