29 Chapter 2: Motivation a measured 5 GeV pion has a boost factor of γ ∼ 36 which means that in the lab frame it is formed ∼ 50 fm away from where it was originally produced. This is well outside the medium and at a time much later than any QGP is reasonably expected to exist so it seems the use of vacuum fragmentation functions is quite safe for light mesons. We note that the same analysis for a 5 GeV detected proton yields a distance of just ∼ 1 fm, most likely well within the medium. As noted previously, recombination [117, 118] and quark coalescence [119, 120] are two proposed models of medium-modified hadronization; there are even indications that heavy quark mesonic states, whose large mass also precludes a necessary vacuum fragmentation, might also survive in the QGP phase [193, 194]. Changes to the hard cross section are also unlikely as for large momentum transfers asymptotic freedom must make the coupling small. While it seemed unlikely that binary scaling did not hold in Rhic colli- sions many believed the initial state PDFs were significantly altered due to, for instance, the color glass condensate (CGC) [195–203, 203–216]. The ef- fects of large nuclei on all the aforementioned possibilities were tested by the deuteron-gold, d + Au , so-called ‘control run.’ By smashing these together at the same energy per nucleon as the A + A run changes to binary scaling, hard cross sections, and nuclear distributions were minimized while removing the medium, and thus final state energy loss or any modifications of the fragmen- tation functions. Fig. 2.7 (a) shows that R$_{dA}$ ∼ 1 for high- p$_{T}$ hadrons (with a rather large Cronin enhancement at lower momenta [217]), thus falsifying the claims of CGC-type suppression and showing that the hard production in