Interplay of soft and hard processes and hadron p(T) spectra in pA and AA collisions - art. no. 034901

Motivated by a schematic model of multiple parton scattering within the Gla uber formalism, the transverse momentum spectra in pA and AA collisions are analyzed in terms of a nuclear modification factor with respect to pp coll isions. The existing data at the CERN Super Proton Synchrotron energies are shown to be consistent with the picture of Glauber multiple scattering in which the interplay between soft and hard processes and the effect of absor ptive processes lead to nontrivial nuclear modification of the particle spe ctra. Relative to the additive model of incoherent hard scattering, the spe ctra are enhanced at large p(T) (hard) by multiple scattering while suppres sed at low p(T) (soft) by absorptive correction with the transition occurri ng at around a scale p(0) similar to 1 - 2 GeV/c that separates soft and ha rd processes. Around the same scale, the p(T) spectra in pp collisions also change from an exponential form at low p(T) to a power-law behavior at hig h p(T). At very large p(T)>>p(0), the nuclear enhancement is shown to decre ase as 1/p(T)(2). Implications of these nuclear effects on the study of jet quenching, parton thermalization, and collective radial flow in high-energ y AA collisions are discussed.