1 particle physics professor kay kinoshita university of cincinnati
TRANSCRIPT
2Particle Physics (also called High Energy Particle Physics (also called High Energy Physics) at UCPhysics) 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 materialsReference materials
History and description of Standard Model:
The Particle Adventure
CP Violation
http://www.particleadventure.org/
http://www.physics.uc.edu/~kayk/cpviol/CP.html
4
what is particle physics?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?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?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?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
Yscattering
X
anti-Xannihilation
X X’Y
Z
decay
8
what is a force?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?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?what is a force?
electromagnetic force
• binds electrons to nuclei
• field quantum: photon
• strength ~ 10–2
.
11
what is a force?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?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)
uupp
ddownown
ccharmharm
sstrangetrange
ttopop
bbottomottom
quarks
3 generations
ee––
ee
––
--
leptons(color = 0)
electric
charge
–e
0
+2e/3
–e/3
interesting patterns...
13what is different about the Weak what is different about the Weak Interaction?Interaction?
• universality of weak charge in quarks is not apparent for interactions involving W±
... unlike interactions involving Z0
• observe “CP violation” <-> complex “weak charge”
uupp
ddownown
ccharmharm
sstrangetrange
ttopop
bbottomottom
quarks(all
different)
ee––
ee
––
--
leptons(universal)
ZZ00 "neutral current" "neutral current"
suppressedsuppressed
seenseen
not seennot seen
14what is different about the Weak what is different about the Weak Interaction?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
uupp
d’d’ownown
ccharmharm
s’s’trangetrange
ttopop
b’b’ottomottom
complexpreserves metric
“ orthogonality
Cabibbo-Kobayashi-Maskawa (CKM) matrixd'd's’ =s’ =b'b'
ddssbb unitary
15
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
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)
16
Is there more?Is there more?
... 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
uupp
ddownown
ccharmharm
sstrangetrange
ttopop
bbottomottom
quarks
3 generations
ee––
ee
––
--
leptons(color = 0)
electric
charge
–e
0
+2e/3
–e/3
WHY?3 generations
2 leptons/2 quarkspattern of charges