Question

Why are there both scalar and vector mesons?

Answer 1

Hello!!..
SCALAR: Which has only magnitude and it is dependent...
VECTOR:Which as both magnitude and direction and it is independent...

Answer 2

You could say that one of the quarks in the meson can 'flip' it's spin when it reacts with some other particle, causing the vector meson to become a scalar meson. It is also possible for the ρ meson to decay into two pions, since the ρ mesons are charged and this charge has to be conserved, decays like ρ±→π±+π0 or ρ0→π++π− are possible.

HOPE this helps ☺️