Transverse and longitudinal dynamics at RHIC

Abstract

We review results obtained by the BRAHMS experiment at the Relativistic Heavy Ion Collider (RHIC) for the systems of Au+Au and p+p colliding at and at . Rapidity-dependent and K±/π± ratios within 0 < y < 3 for Au+Au at are found to be enhanced in nucleus–nucleus collisions as compared to p+p collisions. The particle ratios are discussed in terms of their system size and rapidity dependence. From comparison of RAA for different systems and energies it is found that RAA increases with decreasing collision energy, decreasing system size and when going toward more peripheral collisions. However, RAA shows only a very weak dependence on rapidity (for 0 < y < 3.2), both for pions and protons. The ratio for p+p collisions at is below 0.1 at high pT (≈4 GeV/c) and y ≈ 3. Such a strong asymmetry in p and production cannot be described within next-to-leading order perturbative QCD utilizing any known sets of FFs. At the same rapidity but lower energy the charge asymmetry is stronger by an order of magnitude for both protons and kaons.