Does annihilation always produce new particles?

  • Thread starter kdlsw
  • Start date
  • #1
16
0

Main Question or Discussion Point

I have some basic confusion on the annihilation, please help me to understand these:

1 Does antiparticles all have negative energy? And the energy we talking about here is the rest mass energy? If it is, does it means antiparticles have negative mass since E=mc^2 ?

My understanding on annihilation is simply two particles (one normal, one anti) collide, vanish and form new particles (photon or other bosons) to conserve momentum and energy.

2 If the answer to question 1 is yes and yes, then I assume the rest mass energy are cancelled, the new particles only have the kinetic energy of the old ones? And what if the kinetic energy of the old particles are not enough to form a new pair?

Please correct me if there is any mistake, thanks
 

Answers and Replies

  • #2
Nugatory
Mentor
12,834
5,463
No, antiparticles do not have negative energy and negative mass.
 
  • #3
Bill_K
Science Advisor
Insights Author
4,155
195
1 Does antiparticles all have negative energy? And the energy we talking about here is the rest mass energy? If it is, does it means antiparticles have negative mass since E=mc^2 ?
All particles, both "normal" and "anti", have positive energy. The masses of the particle and its antiparticle are always the same. (And before you ask, no, antiparticles do not travel backwards in time. :smile:)

Some particles, like the photon, are their own antiparticle. Others, like the gluon, are distinct from their antiparticle but you can't say which is normal and which is anti. (The antiparticle of a gluon is a gluon of a different color.)

My understanding on annihilation is simply two particles (one normal, one anti) collide, vanish and form new particles (photon or other bosons) to conserve momentum and energy.
The terminology is not always consistent. For example, the reaction e+ + e- → ν + ν-bar is also sometimes called annihilation. And W+ + W- → (whatever) is usually referred to as vector boson fusion.
 
  • #4
1,948
200
This is a very common misconception. Anti particles actually have masses identical to their particles (the mass of a positron is identical to the mass of an electron, for instance). In fact there is no particularly important reason to call a particle matter and the other one antimatter. It's just a convention and the reverse convention would be just as good.
 
  • #5
26
0
Antiparticles do, in fact, have a positive mass-energy. It's just their charge which is negative.

An annihilation is when a particle collides with its antiparticle. This collision turns the entire mass-energy of both the particles into energy. That is, all the rest mass, all the kinetic energy, everything, is converted into energy, which will then be released carried by a boson or bosons (we'll say photons).
These photons will have a total energy equal to the total energy of the particles and antiparticles (including the energy of its rest mass given by Einstein's formula of relativity, kinetic energy, and any other energy it possesses. I believe this would include the energy of the strong force between quarks if the annihilation was of a hadron).
Their total momentum will also be equal to the momentum of the particles which were annihilated.
 
Last edited:
  • #6
34,465
10,584
It's just their charge which is negative.
Inverted, not negative. And that is true for all sorts of charges, not just the electric one.
Electrons are counted as matter and have a negative (electric) charge, while positrons (their antiparticles) have a positive charge.

An annihilation is when a particle collides with its antiparticle. This collision turns the entire mass-energy of both the particles into energy. That is, all the rest mass, all the kinetic energy, everything, is converted into energy, which will then be released carried by a boson or bosons (we'll say photons).
Or other particles.

I believe this would include the energy of the strong force between quarks if the annihilation was of a hadron).
Sure.
Hadron annihilations usually produce a few pions and sometimes other particles.
 

Related Threads on Does annihilation always produce new particles?

Replies
2
Views
2K
Replies
23
Views
2K
Replies
7
Views
2K
  • Last Post
Replies
11
Views
4K
Replies
11
Views
5K
Replies
6
Views
1K
Replies
1
Views
4K
Replies
6
Views
4K
Replies
8
Views
5K
Top