4 QCD: The Theory of Strong Interactions
121
Fig. 4.16 Single photon
production in p ¯
p colliders as
function of p T [9]
Fig. 4.17 The t production
cross-section at the Tevatron
p ¯
p collider [44]
Drell-Yan processes, including lepton pair production via virtual γ , W or Z
exchange, offer a particularly good opportunity to test QCD. The process is
quadratic in parton densities, and the final state is totally inclusive, while the large
scale is specified and measured by the invariant mass squared Q 2 of the lepton pair
which itself is not strongly interacting (so there no dangerous hadronisation effects).
The QCD improved parton model leads directly to a prediction for the total rate as
a function of Q 2 . The value of the LO cross-section is inversely proportional to the
number of colours N C because a quark of given colour can only annihilate with an
121
Fig. 4.16 Single photon
production in p ¯
p colliders as
function of p T [9]
Fig. 4.17 The t production
cross-section at the Tevatron
p ¯
p collider [44]
Drell-Yan processes, including lepton pair production via virtual γ , W or Z
exchange, offer a particularly good opportunity to test QCD. The process is
quadratic in parton densities, and the final state is totally inclusive, while the large
scale is specified and measured by the invariant mass squared Q 2 of the lepton pair
which itself is not strongly interacting (so there no dangerous hadronisation effects).
The QCD improved parton model leads directly to a prediction for the total rate as
a function of Q 2 . The value of the LO cross-section is inversely proportional to the
number of colours N C because a quark of given colour can only annihilate with an