The Subatomic ZooAtomic Physics

4 Fundamental Forces

Range Relative Strength for Protons in a Nucleus

Mediating Particle

Electromag-netic

Infinite 10-2 Photon

Weak Nuclear

< 0.003 fm (x10-15)

10-6 W+,W-, Z0

Strong Nuclear

<1 fm 1 Gluons ?

Gravitational Infinite 10-39 Gravitron ?

Physicists believe (hope?) they will eventually show that these are all different manifestations of single fundamental force (aka Grand Unified Theory or GUT).

•strong nuclear force is very large over a short distance (x10-8m) which is the size of a nucleus

- to separate the parts of the nucleus, scientists need very large energies

•cosmic rays – energies of 102 – 1014 MeV - are EM photons protons,

- antiprotons, electrons

positrons, alpha particles

•Muons – unstable particles having similar properties to electrons but 207 x the mass

•Discovered in cosmic rays observed in cloud chambers

•Pion – unstable particle – 270 x mass of the electron

Subatomic Particles ( > 300)

•The Large Hadron Collider at CERN can accelerate protons to an energy of about 7 TeV (7 x 1012 eV) each, or lead nuclei to about 574 TeV per nucleus.

•Beams of protons, moving in opposite directions, will be collided (each beam moving very close to c).

http://www.youtube.com/watch?v=j50ZssEojtM

•CERN on Wikipedia

CERN and the movies•In the movie Angles and Demons, a

container with ½ g of antimatter is stolen from CERN, to be used as a bomb which would produce a sizable boom.

•CERN does produce antimatter, but much less than ½ g. (x 10-14g)

•Leptons – subatomic particles that do not interact by means of the strong nuclear force

•eg) electrons, neutrinos, muons

•Hadrons – subatomic particles that do interact by means of the strong nuclear force

•eg) protons and neutrons

Two Separate Families

, , ,e e v v

1. Mesons – hadron with an integer spin eg(0, 1, or 2) eg) pion

2. Baryons- hadron with a half integer spin eg (1/2, 3/2) eg) proton or neutron

Hadrons are divided into 2 groups based upon spin

Text: p. 842 – 843 tables

•*Fermions – a particle with a half integer spin – all leptons and baryons

•Bosons – a particle with an integer spin

Mass of Subatomic Particles•Too small to be measured in kg •Measured in energy/speed squared•Based upon:

2

2

E mcEmc

Reminder: Converting units•1. Mass into u (atomic mass units-amu)

27Divide mass by 1.66 10

2. Atomic mass units into Energy2 27 Multiply u by1.66 10 and then by speed of light squaredE mc

3. Energy into eV.19Divide by 1.60 10

•Eg) electron

Masses of subatomic particles are expressed in MeV/c2

2

2 2

2 2 2 2 2 2 2 2

362

// / /

1 1.7827 10

E mc

E J Nm kgm s eVm kgc m s m s m s c

eV kgc

31 4 29.11 10 5.4858 10 0.5110 /m kg u MeV c

27 21.6726 10 1.0073 938.23 /m kg u MeV c

• Eg) proton

Divide mass by 1 u

Divide mass in kg by 1.78x10-36

Divide charge by speed of light squared

Quark•any group of fermions or

fundamental particles in hadrons

Quarks for real•Hadrons(protons and neutrons) are

believed to be composed of 3 smaller particles

•All known hadrons were first believed to be composed of these particles and their antiparticles

up quark +2/3 e down quark -1/3estrange quark

Charge on Quarks•Quarks have fractional charges of 1/3 or

2/3 the charge of an electron or proton•Scattered electrons suggested the mass

and charge of a proton were concentrated in 3 centers

•Only protons and neutrons contain up and down quarks

Composition of a Proton and Neutron

• The proton and neutron are both made up of three quarks.

Proton: up up down (uud)     charge = +2/3 +2/3 -1/3 = +1 Neutron: down down up  (udd)    charge = -1/3 -1/3 +2/3 =

0

Example•A hypothetical hadron has a charge of +2.

Determine the up and down quarks that make up this hadron.

Up: +⅔ eDown = -⅓ e•+⅔ e + +⅔ e ++⅔ e = +2•particle composition: uuu

Some other examples•Pion : (πo): uu•Pion (π+ ) : ud•sigma-plus (Σ+ ) : uus•sigma-minus (Σ− ) : dds•anti-proton (p− ) : uud

•See page 847

Beta Decay Using Quarks and Leptons•Beta decay emits a high energy electron

or positron•β- decay – neutron transforms into a

proton and an electron and antineutrino ( ) are emitted

•Change is:0 1 10 0

udd uud e ve e

v

The decay is actually described as

udd uud W

ee v Virtual mediating particle that decays into an electron and a antineutrino

β+ Decay• β+ decay – proton transforms into a neutron

and a positron and a neutrino are emitted

• Change is:

1 0 11 1

euud udd e ve ee e

W

Diagrams to describe Beta Decay

Quark version: •In beta plus decay an up quark changes

into down quark while in beta minus decay an down quark changes into a up quark.

NOTE:The "mass" of the up and down quarks is 360 MeV. Three of them in a proton gives a mass of 1080 MeV. The mass of the proton is around 930 MeV giving a sort of binding energy of 150 MeV.