particle physics?

Question

please explain to me the relationship between these terms/theories:

QED(quantum electrodynamics)
QCD(quantum chromodynamis)
weak force
strong force
massive bossons
fermions
Higgs particles (do these give mass to others???? !)
and this leads to sayin that a photon has mass???

Answer 1

Well, this question is asking for alot of information. People have written books covering the above topics. So here I can really only highlight what they are.

QED - this is currently our relativistic quantum field theory of electromagnetism. QED describes all phenomena involving electrically charged particles interacting by means of exchange of photons.

QCD - the quantum field theory of the strong force. QCD describes all interactions involving quarks and gluons found in hadrons (such as the proton, neutron or pion).

So basically, the two theories each describes behavior of a certain type of fundamental force in nature and their corresponding particles.

The Weak Force or sometimes the Weak Nuclear Force happens to be another fundamental force, just like electromangetic force, the strong force, and gravity. The Weak Force involves the exchange of the heavy W and Z bosons. Its most familiar effect is beta decay (of neutrons in atomic nuclei) and the associated radioactivity. The word "weak" derives from the fact that the field strength is some 10^13 times less than that of the strong force.

All elementary particles and composite particles are either bosons or fermions. Bosons are particles having integer spin. So the term massive bosons refers to boson particles with mass. Other examples of bosons:

1. Photons, which mediate the electromagnetic force
2. W and Z bosons, which mediate the weak nuclear force
3. Gluons
4. Higgs bosons
5. Phonons
6. Cooper pairs

Fermions are particles with with half-integer spin. Fermions obey Fermi-Dirac statistics, whose consequence is the Pauli exclusion principle—no two fermions can occupy the same quantum mechanical state at the same time. This results in "rigidness" or "stiffness" of fermions and of fermionic matter (atoms, molecules, atomic nuclei, etc). This is why the world around us feels "solid".

Higgs Boson (http://en.wikipedia.org/wiki/Higgs_boson) - is a hypothetical elementary particle predicted to exist by the Standard Model of particle physics. It is the only Standard Model particle not yet observed, but plays a key role in explaining the origins of the mass of other elementary particles, in particular the difference between the massless photon and the very heavy W and Z bosons.

Now, I am not going to give you a very detail explanation about the Higgs particle, because it requires that you have a deeper understanding of gauge theory and the mathematics involved. But suffice to say, the Higgs particle is now the Holy Grail of modern particle physics. Everyone is looking for it, and it is expected that we will find it after LHC comes online later this year.

Why is it so important? Because without it, our entire theoritical development of the Standard Model of particle physics (this includes QED, QCD, etc.) would be WRONG! This would be a terrible situation to say the least.

I understand that from what you've heard, the Higgs particle gives mass to other elementary particles, and this sounds so absurd. However, mass, charge, etc. are all characteristics of elementary particles that needs to be explained. These characteristics are NOT consider intrinsic, meaning they are not basic features but are derived from other even MORE fundamental features.

So the Higgs particle is the interacting particle of another fundamental field in nature, called the Higgs Field. This field perveates all space, and is a feature of the the vacuum. This field has a non-zero energy value in empty space. It is the interaction of other particles with this Higgs field (or in other words, interactions with the Higgs particle), that gives the appearance of mass (or inertia).

Think of it like a pool of molasses which you are trying to wade through. It takes alot of effort to move through it. So it is the same for particles in empty space. If a moving particle interacts with the Higgs field, then it will be slowed down by the field. This slowing down also shows up as the characteristic of mass. If a moving particle does NOT interact with the Higgs field (like photons), then the particle appears to be massless and travels at the speed of light.

Answer 2

Read the Wikipedia articles on these. Read any of the many popular general science books on physics. Go to a library and browse some general physics texts.