We review the main results obtained by the BRAHMS collaboration on the properties of hot and dense hadronic and partonic matter produced in ultrarelativistic heavy ion collisions at RHIC. A particular focus of this paper is to discuss to what extent the results collected so far by BRAHMS, and by the other three experiments at RHIC, can be taken as evidence for the formation of a state of deconfined partonic matter, the so called quark-gluon-plasma (QGP). We also discuss evidence for a possible precursor state to the QGP, i.e. the proposed Color Glass Condensate.

We report on a study of the transverse momentum dependence of nuclear modification factors R dAu for charged hadrons produced in deuteron + gold collisions at √ sNN = 200 GeV, as a function of collision centrality and of the pseudorapidity (η = 0, 1, 2.2, 3.2) of the produced hadrons. We find a significant and systematic decrease of R dAu with increasing rapidity. The mid-rapidity enhancement and the forward rapidity suppression are more pronounced in central collisions relative to peripheral collisions. These results are relevant to the study of the possible onset of gluon saturation at energies reached at BNL RHIC.

We present spectra of charged hadrons from Au+Au and d+Au collisions at sqrt[s(NN)]=200 GeV measured with the BRAHMS experiment at RHIC. The spectra for different collision centralities are compared to spectra from p+(-)p collisions at the same energy scaled by the number of binary collisions. The resulting ratios (nuclear modification factors) for central Au+Au collisions at eta=0 and eta=2.2 evidence a strong suppression in the high p(T) region (>2 GeV/c). In contrast, the d+Au nuclear modification factor (at eta=0) exhibits an enhancement of the high p(T) yields. These measurements indicate a high energy loss of the high p(T) particles in the medium created in the central Au+Au collisions. The lack of suppression in d+Au collisions makes it unlikely that initial state effects can explain the suppression in the central Au+Au collisions.

A delayed fission activity with a half-life of (55 _+ 7)s and a production cross section of (5_+ 1)nb has been observed in the irradiation of 237Np with 104 MeV a particles. It is tentatively assigned to the electron capture decay of 232Am followed by fission of 232pu with a probability of (1 3 +4 ] 10_2 . A barrier height of (5.3 +0.4) MeV is extracted for " -0.8/ 232pu exceeding theoretical barrier heights by about 2MeV. Systematic deviations between experimental and theoretical barrier heights previously observed in particular for U and Th isotopes are now also established for neutron deficient Pu isotopes indicating severe defects in the procedure of calculating static fission barriers.The heights of double humped fission barriers [1] in actinide nuclei have generally been determined by measuring fission probabilities as a function of excitation energy [2]. If resonance structures due to the potential well between the barrier peaks occur the analysis of such data yields information on both barriers. Additional information on the outer barrier has been derived from fission isomeric lifetimes. The heights of the inner barriers E A show a systematic deviation from calculated values [3], particularly evident for Th isotopes. The limited number of available targets has, however, restricted this comparison to nuclei along the stability line. In this paper a new method is proposed to derive fission barriers of nuclei far off the stability line by simple cross section measurements exploiting fidelayed fission [4,5]. Using this technique barrier heights of neutron deficient Pu nuclei have been found to be about 2MeV higher than expected theoretically, thus providing further evidence for severe deviations between calculated and experimental barrier heights, hitherto called "Th-anomaly". The probability for fission following fi or electron capture decay of a precursor nucleus Qa ~f(Q~ -E) S~(E) _ FI_ (E)dEJ;+~z g,,=~pz =o e~(1)is a sensitive function of the fission barrier parameters. Here, the product of the integrated Fermi function f and the fl-strength function S~ accounts for the population of excited states in the daughter nucleus, and the ratio FI describes the competition between fission and 7-cascades leading to the ground state. The main energy dependence of the integrand in (1) is essentially determined by the barrier parameters (heights EA, E B and curvature energies hCOa, hOB) and the Q~-value for the electron capture decay which is rather reliably predicted by mass formulae.