# Quark distribution Functions

describe and here

## Polarized

The inclusive double polarization asymmetries can be written in terms of polarized and unpolarized valence quark distributions,

I =
I =

The semi-inclusive pion electro-production asymmetries can be written in terms of the valence quark distributions
=

=

where

=
where is the measured difference of the yield from oppositely charged pions.
The semi - inclusive asymmetry can be expressed in the following way

-

where and

An asymmetry

The last equation can be expressed as