CERN-THESIS-2012-153 26/07/2012 - CERN Document Server

ut instead fragment to color neutral hadrons [76].
Hard Processes
There are many different possible hard processes. They can be classified according to the number of final-
state objects. The more particles in the final-state, the more complicated phase space. Similarly, they can
be classified according to the physics scenario:
• Hard QCD processes (e.g. qg → qg).
• Soft QCD processes (e.g. diffractive and elastic scattering).
• Heavy flavor production (e.g. gg → t¯t).
• Prompt-photon production (e.g. qg → qγ) and photon-induced processes (e.g. γg → q¯q).
• Vector boson production (e.g. q¯q → W + W − ).
• SM Higgs production (if Higgs is reasonably light and narrow, it can still be considered a resonance).
• Some BSM scenarios (e.g. SUSY, production of new gauge bosons, non standard Higgs production,
leptonquark production).
The list above is not exhaustive.
Parton Distributions
The cross section for a processes ij → k is given by:
σij→k = dx1
Here ˆσij→k is the cross section for the hard partonic process. f a i
dx2f 1 i (x1)f 2 j (x2)ˆσij→k. (4.1)
(x) are the parton-distribution functions
(PDF), which describe the probability to find a parton i inside beam particle a, with parton i carrying
a fraction x of the total a momentum. Parton distributions also depend on some momentum scale, q 2 ,
that characterizes the hard process. Since a derivation of hadron PDFs from first principles does not yet
exist, it is necessary to rely on parameterizations, where experimental data are used in conjunction with the
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