Particlezoo
This presentation is the property of its rightful owner.
Sponsored Links
1 / 29

ParticleZoo PowerPoint PPT Presentation


  • 61 Views
  • Uploaded on
  • Presentation posted in: General

ParticleZoo. The Zoo of Subatomic Particles. The Standard Model of Quarks and Leptons. e -. p. hadron jet. excited states of the proton. scatter probability. ground state of the proton. Bartel etal. PL28B, 148 (1968). energy of scattered electron. Nucleons Are Not Elementary Particles!.

Download Presentation

ParticleZoo

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Particlezoo

ParticleZoo

The Zoo of Subatomic Particles

The Standard Model of Quarks and Leptons


Nucleons are not elementary particles

e-

p

hadron jet

excited states of the proton

scatter probability

ground state of the proton

Bartel etal. PL28B, 148 (1968)

energy of scattered electron

Nucleons Are Not Elementary Particles!

e-

Scatter high-energy electrons off protons. If there is no internal structure of e- or p, then well-defined “elastic” e- energy for each angle. See structure!!

Each line in the energy spectrum of scattered electrons

corresponds to a different energy state of the proton.

elastic

x1/8.5


The quark model

The quark model represents a relatively simple picture of the internal structure of subatomic particles and makes predictions of their production and decay. It uses a minimum of adjusted quark parameters and has great predictive power, e.g., for the composite-particle masses, magnetic moments, and lifetimes.

There are no contradictions to this model known so far, (but many questions remain).

The Quark Model


Internal nucleonic structure

e-

e-

p

D

S=3/2

N

S=½

Internal Nucleonic Structure

The proton has internal structure, so-called quarks (u,u,d).

Quarks combine to nucleon states of different excitations.

Proton is the (u,u,d) ground state

1200 MeV

N: one doublet with a splitting of onlyDm = 1.3 MeV

D: one quadruplet with a splitting of only Dm = 8 MeV

938 MeV

p S=0 Mesons

135 MeV


The quark lepton model of matter

Nucleons (q,q,q)

Mesons (q, q-bar)

q-bar:anti-quark

The Quark-Lepton Model of Matter

Explains the consistency of the known particles in all of their states.

3

families of quarks (3 “colors” each) and associated leptons.

All are spin-1/2 particles, quarks have non-integer charges


Particle spectrum

Particle Spectrum

Mass (GeV/c2)

Leptons

Hadrons

Baryons

Mesons

Y'’

4

n, e

Y'

J/Y

3

t

2

W X*Y*

D

10

X

S

L

N

8

K*w

r

1

8

hK

p

m

0

Spin ½ ½ 3/2 0 1

Simplified scheme of stable or unstable subatomic particles.

Families have different interactions, Leptons: weak+elm, Hadrons: weak+elm+strong

Each particle also has an anti-particle, with inverse quantum numbers.

“strange”


Quark quantum numbers

Quark Quantum Numbers

All: spin=1/2, baryon number B=1/3

T,T3: isospin; S: strangeness; C: charm; B*: bottom qu.#, Top: top qu.#


Structure of composite particles

_u

_u

_u

_u

_u

_u

u

u

u

s

u

s

s

u

s

u

u

u

u

d

d

s

d

s

d

d

s

d

d

u

d

d

d

d

d

_s

_s

_s

_s

s

s

s

s

quarks antiquarks

_d

_d

T3

0

K+

p

n

K0

p0

S-

S0

S+

p-

L0

h

h’

_K0

K-

X-

X0

Structure of Composite Particles

There are only 3-quark (q,q,q)  Baryons and quark-antiquark

configurations. No free quarks or higher quark multiplicities.

s= 1/2

s= 0

Baryon Octet

Meson Nonet

p+

S


Particlezoo

D-

D0

D+

D++

T3

0

u

u

u

d

s

s

u

s

u

s

s

s

s

s

u

u

u

u

d

d

d

s

d

d

d

s

d

d

d

u

S*-

S*0

S*+

X*-

X*0

W-

S

Baryon Decuplet

s = 3/2


Meson wave functions

Meson Wave Functions

Examples to interpret the graphic shorthand in these figures:

Meson spins are integer, vector sum of half-integer quark and anti-quark spins, and their integer orbital angular momentum l. In ground state, mostly l =0.


Baryon wave functions

Baryon Wave Functions

Examples to interpret the graphic shorthand:

These Baryon and Meson wave functions are schematic, do not have proper (anti-)symmetry property required by Pauli Principle: The total particle wave function

must be antisymmetric under quark exchange (quarks are fermions)


Pauli principle and color coordinate

u

d

u

d

u

d

d

d

d

_d

_d

D-

_d

D++

s3,T3

s3,T3

d quarks anti-d quarks

Pauli Principle and Color Coordinate

Quarks are Fermions  no two same quarks can be in the same state

have both 3 identical fermions (same quarks) with same spins (S=3/2) and isospin (T3=+3/2) states

Violates Pauli Principle !?

Conclusion: There must be an additional quantum number (degree of freedom), “color”. Need 3 colors and their anti-colors

Color and complementary color (anti-color) add up to color-less (white)


Color wave function

d

d

d

_d

_d

_d

d quarks anti-d quarks

Color Wave Function

D++ : Flavor and spin configurations symmetric, spatial configuration symmetric (no orbital angular momentum, l=0)

color configuration must be antisymmetric. All colors are present with equal weights. All physical particles are “white.”

Necessity of color rules out combinations such as

There are no free quarks  Confinement


Gluons

Gluons

Gluons carry color and the corresponding anticolor.

Color can be transferred but particle remains colorless.

Bound quark systems (physical particles) by q-q interactions.

Field quanta: 8 Gluons (not actually pions!)

Spin and parity 1- like a photon.

_q

qc’

q

qc

gluon emission q-qbar creation self coupling changes color of the color charges

Usual conservation laws apply to reactions between quarks.


Gluon exchange

_b

_ b,g

_ b,g

b

b

g

r

_g

_ r,g

g

_ b,g

g

_b

_ b,g

g

b

_ r,b

b

_r

r

g

b

r

_d

u

u

u

d

p

p+

Gluon Exchange

time

Gluons are exchanged back and forth between q-q,

changing q colors and momenta dynamically

r, g, and b are visited with equal probability


Baryon production with strong interactions

u

u

u

d

s

_d

_s

u

u

Baryon Production with Strong Interactions

Typically: Energetic projectile hits nucleon/nucleus, new particles are produced.

  • Rules for strong interactions:

  • Energy, momentum, s, charge, baryon numbers, etc., conserved

  • q existing in system are rearranged, no flavor is changed

  • q-q-bar pairs can be produced

time 

u

S+

p

K+

p+

annihilation creation d, d-bar s, s-bar


Baryon resonances

p

p+

time 

_ d u

_ d u

u u d

u u d

p

p+

Baryon Resonances

Typically: Energetic projectile hits nucleon/nucleus, intermediate particle is produced and decays into other particles.

D++ produced as short-lived intermediate state, t = 0.5·10-23s

corresp. width of state: G = ħ/t = 120 MeV

This happens with high probability when a nucleon of 300 MeV/c, or a relative energy of 1232 MeV penetrates into the medium of a nucleus.  Resonance

u u u D++


Confinement and strings

Why are there no free quarks? Earlier: symmetry arguments.

Property of gluon interaction between color charges (“string-like character).

Q: Can one dissociate a qq pair?

Confinement and Strings

energy in strings proportional to length 0.9GeV/fm

field lines: color strings

successive q/q-bar creation, always in pairs!


Leptons

Leptons

Leptons have their own quantum number, L, which is conserved.

It seems likely, but is not yet known, whether electronic, muonic and tau lepton numbers are independently conserved in reactions and decays.


Conservation laws

Conservation Laws

Quantum numbers are additive.

Anti-quarks have all signs of quark quantum numbers reversed, except spin and isospin.

Derived quantities:

  • In a reaction/transmutation, decay, the following quantities are conserved (before=after):

  • The total energy, momentum, angular momentum (spin),

  • The total charge, baryon number, lepton number


Conservation laws in decays

Conservation Laws in Decays

Decay

A  B + C

possible, if

mAc2 ≥ mBc2 + mCc2

Otherwise, balance must be supplied as kinetic energy.

Example: Conservation of charge, baryon number, lepton number in neutron decay.


Weak interactions

Weak Interactions

10-5 weaker than strong interaction, small probabilities for reaction/decays. Mediated by heavy (mass ~100GeV) intermediate bosons W± ,Z0.

Weak bosons can change quark flavor

d

u

u

Z0

W+

W-

u

u

s

up-downstrange-non-strange no flavor change conversion conversion carries +e carries –e carries no charge


Decays of w and z 0 bosons

Decays of W± and Z0 Bosons

Hadronic decays to quark pair are dominant (>90%), leptonic decays are weak. All possible couplings:


Examples of weak decays

Can you predict, which (if any) weak boson effects the change?

Examples of Weak Decays

_ne

p

ne

p

n

m-

e-

?

?

?

time

n

n

nm

p

e-

n-decay? neutrino scattering neutrino-induced

off protons? reaction off e-?


Examples of weak decays1

Answer: Yes, all processes are possible. These are the bosons,

Examples of Weak Decays

_ne

p

ne

p

e-

n

m-

W+

Z0

W-

time

n

n

nm

p

e-

n-decay neutrino scattering neutrino-induced

off protons reaction off e-

  • Method:

  • Balance conserved quantities at the vortex, where boson originates. Remember W±carries away charge ±|e|.

  • Balance conserved quantities at lepton vortex.


Particle production

Particle Production

In electron-positron collisions, particle-anti-particle pairs can be created out of collision energy, either via electromagnetic or weak interaction.

probability

 collision energy (GeV)

anti-fermion

fermion

m+

m-

m+

m-

Z0

g

Z0

e-

e-

e+

e+

e-

e+

electromagnetic weak example


The standard model

The Standard Model

Interactions

Weak interactions violate certain symmetries (parity, helicity) see later

The body of currently accepted views of structure and interactions of subatomic particles.

Particles


The standard model ct d

Combine weak and elm interactions “electro-weak”

Type of isospin-symmetry: same particles carry weak and elm charge.

Vqq

0

r

1 fm

The Standard Model ct’d

Force range

Electromagnetic: ∞

Weak: 10-3fm

Strong qq force increases with distance

2mqc2

There are no free quarks. All free physical particles are colorless.


The end

The End


  • Login