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## Appendix B Power Law R$_{AA}$ 

## B.1 Fragmentation Functions 

The fragmentation function D h $_{q}$( z ), where z = 2 E$_{h}$/Q , gives the probability of producing hadron h of energy E$_{h}$ from parton q in a process of total energy Q . If we take the problem as the production of a quark and an antiquark and ignore all masses then, in the center of mass frame, each parton carries half the total energy, 

Therefore 

Conservation of energy then demands 

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