Particle Physics

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Particle PhysicsParticle Physics

Professor Kay KinoshitaUniversity of Cincinnati

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

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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

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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

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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

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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”

.

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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

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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

.

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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)

.

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what is a force?what is a force?

electromagnetic force

• binds electrons to nuclei

• field quantum: photon

• strength ~ 10–2

.

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what is a force?what is a force?

gravitational force

• apples, solar systems, galaxies, ...

• field quantum: graviton (not yet seen)

• strength: ~ 10–38

.

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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)

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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”

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sstrangetrange

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quarks(all

different)

ee––

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––

--

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

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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

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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)

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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