1. Particle Physics
Professor Kay Kinoshita
University of Cincinnati

2. 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

3. Reference materials http://www.particleadventure.org/
History and description of Standard Model: The Particle Adventure CP Violation

4. 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

5. 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

6. 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” .

7. 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

8. 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 .

9. 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) .

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

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

12. 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

13. 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)

14. 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

15. • 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)] ( )
• CP asymmetry observed in diverse processes in B decay
-> many measurements, (over)constrain CKM, confirm unitarity

16. 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