u, d, anti-u Quarks

Weighted cross sections are shown for neutral current (NC) and charged current (CC) scattering in positron-proton collisions: 

• s(CC) ~ (d+s) (1-y)^2 + (anti-u + anti-c) 
• s(NC) ~ 4/9(u+anti-u)|multiply with (1-y)^2

They are shown as a function of the 

• x = parton fractional momentum relative to the proton, and 
• Q^2 = negative squared momentum transfer.

At high x, the comparison of s(CC) and (1-y)^2 s(NC) allows for the direct comparison of the u and d quark densities.

• At high x, the d valence quark density is about 1/2 of the u quark density. 
• The contribution of the anti-u quark is clearly visible at x=0.1. 
• At x=0.2 the valence quark densities decrease with increasing resolution Q^2

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