In particular the hadronic components of the physical photon consist of the lightest vector mesons and .

In the range of higher masses, vector mesons include also charm and bottom quarks in their structure.

In 1963, Salam published his theoretical work on the vector meson.

Compare to a vector meson, which has a total spin 1 and odd parity.

There also exist composite particles that are vector bosons, such as the vector mesons, made of a quark and antiquark.

The two photons interact to produce either a vector meson or hadron-antihadron pairs.

Single resolved: The quark pair of the target photon form a vector meson.

Double resolved: Both target and probe photon have formed a vector meson.

At higher masses, the vector mesons include charm and bottom quarks in their structure.

Some vector mesons can, compared to other mesons, be measured to a very high precision.