# Graviton and other particle interections

1. ### Quarlep

257
We know that graviton spin is 2 so other lepton and quarks spin is 1/2 I am confused because If Graviton and a quark or maybe a lepton make an interaction than the last spin must be 3/2 or 5/2 but theres no particle exist in this spin quantity.It means theres no particle called graviton or I dont know I am confused

Thanks

2. ### Shyan

2,020
You only add spins if you have a particle which is the bound state of other particles. But not all kinds of interactions give bound states!

3. ### Quarlep

257
Whats bound state I googled but its hard to understand

2,020
5. ### Quarlep

257
I lookes there But I didnt undertsand I am 16 years old and I dont know QM. Its complicated and I dont know english very well.

6. ### Quarlep

257
Can you tell me more specific so you are trying to tell me theres a graviton but is not interact with other particles.
Or its interacts ?

7. ### Shyan

2,020
OK. The point is, in some situations, the interaction is somehow that the particles are going to remain close to each other. In these situations, we say that they formed a bound state, a composite particle. Like a proton which is formed from two up quarks and one down quark.
But for some other situations, the particles just attract or repel each other for some time and then leave each other alone. These are called scattering processes or sometimes collisions.

8. ### Quarlep

257
I ask it because I read a book about particle phyiscs and the author said that spin is conserved its true or not ?
And thanks for explanation Thanks I understand it

### Staff: Mentor

Total angular momentum is conserved. Spin is one part, but the motion of particles can contribute to the angular momentum as well.

We know that if it exists, its spin has to be 2.

Yes a (hypothetical) graviton would interact with other particles.

18,055
Staff Emeritus
Why? A spin-1 photon can interact with a spin-0 alpha particle and it will remain a spin-0 alpha particle?

11. ### ChrisVer

2,291
As for the photon-alpha particle interactions, in case the alpha particle absorbs a photon, it's going to get excited and so will get orbital momentum to conserve the angular momentum. Is giving composite particles for this case good?

12. ### Quarlep

257
I learned that total angular momentum is conserved as indicated above.But I am confused here because total angular momentum is equal spin angular momentum plus orbital angular momentum. In particle interactions like two electron collusions or proton proton collusion every collusions or decays there's no orbital angular momentum(my idea) so I guess total angular momentum must be equal spin angular momentum because theres no orbital momentum so If graviton interects with another particle total angular momentum must be conserved so I claimed that its equal spin angular momentum.Its the reason why I said that graviton and other particle interactions result of spin is 3/2 or 5/2.
Am I wrong.

18,055
Staff Emeritus
Let's not complicate things when we explain things. It doesn't have to absorb the photon.

14. ### ChrisVer

2,291
if it doesn't absorb the photon then the alpha+gamma will give alpha+gamma

18,055
Staff Emeritus
Chris, you are not helping. What I am trying to get across is the idea that you can have an interaction with no exchange of angular momentum. Quibbling does not help.

### Staff: Mentor

As soon as there is more than one particle, you can have "orbital" angular momentum (not really as orbit, but as displaced relative motion).
Collision with i.