the subatomic zoo
DESCRIPTION
The Subatomic Zoo. Atomic Physics. 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 -8 m) which is the size of a nucleus - PowerPoint PPT PresentationTRANSCRIPT
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.