Collective flow signals the quark-gluon plasma

摘要

A critical discussion of the present status of the CERN experiments on charm dynamics and hadron collective flow is given. We emphasize the importance of the flow excitation function from 1 to 50 A GeV: here the hydrodynamic model has predicted the collapse of the v(1) -flow and of the V-2-flow at similar to 10 A GeV; at 40 A GeV it has been recently observed by the NA49 Collaboration. Since hadronic rescattering models predict much larger flow than observed at this energy we interpret this observation as evidence for a first order phase transition at high baryon density (PB). A detailed discussion of the collective flow as a barometer for the equation of state (EoS) of hot dense matter at RHIC follows. Here, hadronic rescattering models can explain < 30% of the observed elliptic flow, v(2)), for PT > 2 GeV/c. This is interpreted as evidence for the production of superdense matter at RHIC with initial pressure far above hadronic pressure, p > 1 GeV/fm(3). We suggest that the fluctuations in the flow, v(1) and v(2), should be measured in future since ideal hydrodynamics predicts that they are larger than 50% due to initial state fluctuations. Furthermore, the QGP coefficient of viscosity may be determined experimentally from the fluctuations observed. The connection Of v2 to jet suppression is examined. It is proven experimentally that the collective flow is not faked by minijet fragmentation. Additionally, detailed transport studies show that the away-side jet suppression can only partially (< 50%) be due to hadronic rescattering. We, finally, propose upgrades and second generation experiments at RHIC which inspect the first order phase transition in the fragmentation region, i.e., at mu(B) approximate to 400 MeV (y approximate to 4-5), where the collapse of the proton flow should be seen in analogy to the 40 A GeV data. The study of Jet-Wake-riding potentials and Bow shocks-caused by jets in the QGP formed at RHIC-can give further information on the equation of state (EoS) and transport coefficients of the quark-gluon plasma (QGP). (c) 2005 Elsevier B.V. All rights reserved.