High Rapidity Physics with the BRAHMS Experiment

We analyze the recent data from the BRAHMS Collaboration on the pseudorapidity dependence of nuclear modification factors in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV by using the full three dimensional hydrodynamic simulations for the density effects on parton energy loss. We first compute the transverse spectra at $\eta=0$ and 2.2, and next take a ratio $R_{\eta}=R_{AA}(\eta=2.2)/R_{AA}(\eta=0)$, where $R_{AA}$ is a nuclear modification factor. It is shown that hydrodyn...

The BRAHMS experiment at RHIC has measured the production of charged hadrons as a function of pseudorapidity and transverse momentum in Au+Au, d+Au and p+p collisions at a common energy of sqrt(s_NN)=200GeV, and from these spectra we construct the nuclear modification factors for both ``hot'' and ``cold'' nuclear matter. In this contribution I will show how these factors evolve with pseudorapidity and collision centrality. We see a Cronin-like enhancement in d+Au collisions a...

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 ${\rm p}+\bar{{\rm p}}$ 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...

We present spectra of charged pions and protons in 0-10% central Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV at mid-rapidity ($y=0$) and forward pseudorapidity ($\eta=2.2$) measured with the BRAHMS experiment at RHIC. The spectra are compared to spectra from p+p collisions at the same energy scaled by the number of binary collisions. The resulting nuclear modification factors for central Au+Au collisions at both $y=0$ and $\eta=2.2$ exhibit suppression for charged pions but n...

We report BRAHMS results from RHIC d+Au and p+p collisions at Sqrt(s_NN)=200GeV. A remarkable change in the nuclear modification factor RdAu is seen as the pseudorapidity of the detected charged hadrons changes from zero at mid-rapidity to 3.2 at the most forward angle studied during the 2003 run. For pseudorapidity eta>1 the suppression of the Rcp factor is more pronounced in the sample of central events in contrast to the behavior at mid-rapidity where the central events sh...

We present recent results obtained by the BRAHMS experiment at the Relativistic Heavy Ion Collider (RHIC) for the systems of Au + Au and Cu + Cu at \rootsnn{200} and at 62.4 GeV, and p + p at \rootsnn{200}. Nuclear modification factors for Au + Au and Cu + Cu collisions are presented. Analysis of anti-particle to particle ratios as a function of rapidity and collision energy reveal that particle populations at the chemical freeze-out stage for heavy-ion reactions at and above...

Recent results on high transverse momentum (pT) hadron production in p+p, d+Au and Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC) are reviewed. Comparison of the nuclear modification factors, $R_{dAu}(pT)$ and $R_{AA}(pT)$, demonstrates that the large suppression in central Au+Au collisions is due to strong final-state effects. Theoretical models which incorporate jet quenching via gluon Bremsstrahlung in the dense partonic medium that is expected in central A...

RHIC data on high-$p_T$ hadron production display strong suppression in a wide rapidity region, indicating strong induced energy loss for both transversally and longitudinally traveling partons. We investigate the interplay of energy loss and rapidity dependence in a perturbative QCD improved parton model, and estimate the opacity of the produced hot matter in $AuAu$ collisions at energies $\sqrt{s}=200$ $A$GeV and 63 $A$GeV at different rapidity values. Direction-dependent s...

The BRAHMS measurement of proton-to-pion ratios in Au+Au and p+p collisions at 62.4 and 200 GeV is presented as a function of transverse momentum and collision centrality within the pseudorapidity range 0 < eta < 3.2. The p/pi ratio measured for Au+Au system at 62.4 GeV, eta = 3.2 reaches astounding value of 8-10 at pT >= 1.5 GeV/c. For these energy and pseudorapidity interval no centrality dependency of p/pi ratio is observed. The baryon-to-meson ratio of nucleus-nucleus dat...

We present recent high transverse momentum measurements by the PHENIX experiment for Au+Au and p+p collisions at $\sqrt{s_{NN}} = 200$ GeV at the Relativistic Heavy Ion Collider (RHIC). We show particle spectra for neutral pions and charged hadrons, define and show the nuclear modification factor, and discuss particle composition. By means of the nuclear modification factor, we observe a suppression factor of 5-6 for neutral pions and 3-4 for charged hadrons in central collis...