# How can a photon have hadronic components?

1. May 4, 2013

### Pseudo Epsilon

the wiki article on vector meson dominance says "hadronic components of the physical photons". How can a photon have hadronic photon components? Could someone please enlighten me?

2. May 4, 2013

### Bill_K

See another reference which gives a more complete description, such as this one. The basic idea is that a virtual photon turns into a quark-antiquark pair, which then turns into one of the vector mesons, and that furthermore all interactions of photons with hadrons take place predominantly via this process.

3. May 4, 2013

### Pseudo Epsilon

what is a vector meson?

4. May 4, 2013

### Bill_K

A meson is a bound state consisting of a quark and an antiquark. Since each quark has spin 1/2, a meson can have either spin 0 or spin 1. The vector mesons are the ones that have spin 1.

If you use just the three lightest quarks, (up, down, strange) you can make 3 x 3 = 9 vector mesons. The ones being discussed in connection with photon-hadron interactions are the ones that have charge 0, namely ρ0 (rest mass 770MeV), ω (780 MeV) and φ (1020 MeV). You can find much more about these particles, and also other mesons, on Wikipedia.

5. May 4, 2013

### Pseudo Epsilon

thanks bill_k