Particles 1

Particlesenergy states

Particles decay, transform, change, behave like waves, emit energy and absorb energy as if they are energy states.

Particles include electrons, protons, neutrons, pions, kaons, J, D, Upsilon, sigma, rho, etc., some have strange names.

The study of particles is called particle physics or high-energy physics.

Particle studies proposed a standard model with a few fundamental components for all matter.

Particles interact with via a force, and each force has a carrier. Fynman diagrams neatly represent these interactions.

See particleadventure.org/particleadventure/other/othersites.html for more info

Particles 2

Particlesparticles and antiparticles

Antiparticles of electrons, positrons, have been introduced in the discussion of beta decay.

Theory about particles and antiparticles is simple and symmetric.Particles and antiparticles have the same mass, but opposite electric charge, and magnetic moment.

Some questions regarding particles:

Do all particles have corresponding antiparticles as do electrons?

Do neutral particles such as neutrons have antiparticles?

Particles 3

The Particle-antiparticle Concept

Dirac's energy equation from Einstein's equation

E = m c2 = m0 c2 (1 - (v/c)2)-1

E 2 = (m c2)2 = m0

2 c 4/(1-(v/c)2)From this, he has

(m c2)2 - m 2 v 2c 2 = m02 c 4

Thus, (p = m v)E 2 = p 2 c 2 + (m0 c 2)2

ThereforeE + = [p 2 c 2 + (m0 c 2)2]1/2

E - = -[p 2 c 2 + (m0 c 2)2 ]1/2

Ignore the formula box if you find the equations hard to follow.

Dirac combined theory of relativity with quantum mechanics to get a theory, that predicted a new state for an electron whose energy becomes more negative as the electron increases speed. He worked out the wave functions for such a positive electron, and called it antiparticle.

Particles 4

The Particle-antiparticle Concept (continue)

In a vacuum, all negative-energy states are occupied, and positive energy states are empty. Fully occupied or unoccupied states are unobservable

Singly occupied states are observableA pair of particle and antiparticle

Particles 5

Particle Antiparticle Annihilation

2hv

Unstable particle-antiparticle pair

Return of particle to negative-energy state

Particle-antiparticle annihilated

Particles 6

Discovery of AntiparticleIllustration of Electron and PositronTracks Observed by C. Anderson

e–

e+

Leadplate

C.D. Anderson observed tracks of positive electrons in his cloud chamber in 1932, and called them positrons, antiparticle suggested by Dirac.

Particles 7

Generalizing the Antiparticle ConceptIn particle physics, every particle has a corresponding antiparticle. A particle and its antiparticle have identical mass and spin.

A particle and its antiparticle have opposite signs for nearly all non-zero quantities such as: electric charge, (abstract) flavor, electron number, muon number, tau number, and baryon number.

We call commonly observed particles such as protons, neutrons, and electrons "matter" particles, and their antiparticles are “antimatter”

Matter: anything built from quarks, negatively charged leptons and left-hand neutrinos

Antimatter: anything built from antiquarks, positively charged leptons and right-handed neutrinos.

Particles 8

annihilation and pair production

At the ends of positron tracks, two tracks appeared due to gamma photons in annihilation.

A year later, electron-positron pair productions were observed at track ends of high-energy photons.

Annihilation and Pair Production

+ + – 2

+ + –

e–

e–

e+

Particles 9

Generalized annihilation and pair production

Whenever sufficient energy is available to provide the mass(energy), a particle and its antiparticle can be produced together, obeying the conservation laws in all processes.

When a particle collides with its antiparticle, they may annihilate – they disappear and combine into a boson (a carrier particle of interaction forces).

The boson may decay (change to) into other particles and antiparticles.

Particles 10

The discovery of protons and antiprotons

Star-like Tracks Produced by an AntiprotonAnnihilating a Proton in a Bubble Chamber

antiproton

The discovery was made by observing a bubble chamber photo of antiproton annihilation.

Antiproton: same mass as proton, 932 MeV.present in accelerators and cosmic raysannihilated with proton to give a set of starburst of particles (pions).

p + p 4 – + 4 +

Particles 11

The actual bubble chamber photograph of an antiproton (entering from the bottom of the picture) colliding with a proton at rest and annihilating.

Eight (8) pions were produced in this process.

One decayed into a + and a . The positive and negative pions curve different ways in the magnetic field.

Particles 12

The Discovery of Antineutrons

This bubble-chamber picture, taken in 1958, demonstrated the existence of the antineutron, n.

At the point marked by the arrow, an incoming antiproton beam particle undergoes the `charge exchange' reaction

p + p --> n + nThe kinetic energy of the interacting antiproton is estimated to be ~50 MeV.

The n formed in the process travels an actual distance of 9.5 cm before annihilating in a characteristic `annihilation star‘.

n + p --> 3 + + 2 -

The energy released is > 1500 MeV.

See L. E. Agnew et al, Phys. Rev., 110 (1958) 994

Particles 13

Particles and the standard model

Two types of fundamental particles are leptons and quarks. Charged particles interact via gauge bosons, and quarks via strong-force carriers called gluons.

Particles of the Standard modelFirst Generation Second Generation Third Generation

Leptons Electron, e–

Positron, e+

Neutrino, ve,Antineutrino, e.

Muon, –,Antimuon, +

Muon-neutrino,Anti-muon-neutrino, v,

Tau, –,Antitau, +,

Tauneutrino, Antitauneutrino, v

QuarksChargeMass(GeV)

Up, u; Down, d+2/3; –

1/30.3 0.3

Strange s; Charm, c –1/3; +

2/3 0.5 1.5

Bottom b; Top, t–1/3; +

2/3 4.8 176

Particles 14

The Standard ModelParticles are grouped into families – leptons and quarks.

Electrone-neutrino

muon neutrino

tau neutrino

UpDown

CharmStrange

Top Bottom

Leptons Quarks

These are found inside 3rd generation matters

The Standard Model (a theory?) is the name given to the current theory of fundamental particles and how they interact.

Particles 15

Crossing Symmetry in Particle InteractionsIn a particle interaction

A + B C + Denergy (and mass), momentum, baryon number, lepton number, and charge are conserved.

The crossing symmetry suggests that any of the particles can be replaced by its antiparticle on the other side of the interaction.

A B + C + D (X is antiparticle of X)A + C B + D C D + A + B C + D A + B

The crossing symmetry allows us to see different phenomena as the same interaction.

Particles 16

quarks as fundamental particles

The study of particles, their relationships and classification led to the idea that some fundamental particles smaller than protons and neutron exist.

A mathematical theories support their existence.

The fundamental particles are called quarks.

Light Mesons with JP = 0–

S

ds usK0 K+

uu or dddu – 0 + ud

K– K0

su sd

I3

Particles 17

mesons and baryonsLight Mesons with JP = 0–

S

ds usK0 K+

uu or dddu – 0 + ud

K– K0

su sd

I3

Eight JP = ½+ Baryons

udd uudn p

dds uds uus– 0 +

– 0

dss uss

Mesons and baryons are collectively called hadrons.

Mesons consist of a quark and antiquark.

Baryons consist of three quarks.

Relations of some mesons and baryons are shown here.

Particles 18

properties of mesons

Light Mesons with JP = 0–

S

ds usK0 K+

uu or dddu – 0 + ud

K– K0

su sd

I3

Name Symbol Mass* Lifetime (s)

Pi-zero 0 135 0.8e-16 Pi-plus + 140 2.6e-8Pi-plus - 140 2.6e-8

K-zero K0 498 1e-8 to 1e-10K-plus K+ 494 1.2e-8K-zero K- 494 1.2e-8

J/psi J/ 3100 1e-20 cc#

D-zero D0 1870 1e-12 cuD-plus D+ 1870 4e-15 cdUpsilon Y 9460 4e-20 bb

* mass in MeV#quarks

Discovery in 1974 of J confirmed the charm (c) quark. D’s were discovered in 1976, and upsilon in 1977, conformed the bottom (b) quark.

Particles 19

discovery of mesonskaons and pionsBubble Tracks from Decay of K–

Interpreted for the Presence of 0

K–

–

0

e–e+

K– 0 + –

0

e+ + e–

Lead plate

Dark Lines Imitating Kaon TracksObserved in 1947

Lead Plate Lead Plate

+

K0

K+

Particles 20

decays of kaons

K0 2 or + + –

K+ + + v or + + 0

or + + ++ –

or 0 + e+ + ve

K– – + or – +0 or – + ++ –

or 0 + e– + ve

Feynmam Diagrams for Kaon Decays

e–

e+

K–

K+

o + + e+ + e – e– + e

Particles 21

four forces and force carriers

Particles interact with each other via a force. Particles responsible for the delivery of force are force carriers.

Feynman invented a method to represent the interaction.

Gravity, electromagnetic (e & m), weak, and strong are the 4 forces, each has its type of carriers.

Feynman Diagram for Electron Scattering

e

e’

time

space

Feynman Diagram for Beta Decay

e–ve

udd uud+

W–

Particles 22

four types of force carriers

Gravity e & m weak strong

Carrier graviton photon W+, W-, Z0 8 gluons (g)

Mass 83-91 MeV ~0

Charge +1, -1, 0 0

Spin unknown 1 1 1

strength 1e-39 1/137 1e-10 1.0

Decay of weak force carriers half-life 1e-25 s

W e,

Z e+,e;

Particles 23

Feynman diagrams

Feynman Diagram for the StableHydrogen Atom

proton

electron

Feynman Diagram for Beta Decay

e–ve

udd uud+

W–The Feynman Diagram of

a Weak Interaction

sud d

ud

W–

u

u

Particles 24

Particles 25

The Standard Model of

Fundamental Particles and Interactions

Chart

copyright 1999 by the Contemporary Physics Education Project. We grant permission for teachers and students to print these copyrighted images for their personal or classroom use.

Particles 26

Particles 27

Particles 28

Particles 29

Neutron Beta Decay

Feynman Diagram for Beta Decay

e–ve

udd uud+

W–

Particles 30

Particles 31

skills acquired for particles

describe the concept of particles and antiparticlesexplain energy aspects of particles and antiparticlesexplain how positron was discoveredspecify properties of antiparticles - particularly positronsexplain annihilation reactionsdescribe the standard model in terms of fundamental particlesshow organization and components of mesonsforces and force carriersdraw Fynman diagrams

Particles 32

Particles – energy states

Particles decay, transform, change, behave like waves, emit energy and absorb energy as if they are energy states.

Particles include electrons, protons, neutrons, pions, kaons, J, D, Upsilon, sigma, rho, etc., some have strange names.

The study of particles is called particle physics or high-energy physics.

Particle studies reveal a standard model with few fundamental components for all matter.

Particles interact with via a force, and each force has a carrier. Fynman diagrams neatly represent these interactions.

Particles 33

Ingredients for a Midnight Snack

Particles 34

SCI270 Midterm Examination Room Assignment for Feb. 11, 2004

Room ID number start with

P-150 (50) 0000xxxx – 2006xxxx

P-313 (50) 2007xxxx – 2011xxxx

P-145 (100) 2012xxxx – 9999xxxx