1. BRAHMS Heavy Ion Results and Perspectives Erik Bjorn Johnson RHIC & AGS Users Meeting June 8, 2006

2. RHIC & AGS Users Meeting2 Who is BRAHMS? I.Arsene, I.G. Bearden 7, D. Beavis 1, S.Bekele 11, C. Besliu 10, B. Budick 6, H. Bøggild 7, C. Chasman 1, C. H. Christensen 7, P. Christiansen 7, R.Clarke 10, R. Debbe 1,J. J. Gaardhøje, K. Hagel 8, H. Ito 1, A. Jipa 10, J. I. Jordre 10, F. Jundt 2, E.B.Johnson 11, J.I.Jordre 9, C.Jørgensen 7, R. Karabowicz 3, E. J. Kim 11, T.M. Larsen 7, J. H. Lee 1, Y. K.Lee 5, S.Lindal 12, G. Løvhøjden 2, Z. Majka 3, M. Murray 11, J. Natowitz 8, B.S.Nielsen 7, D.Ouerdane 7, R.Planeta 4, F. Rami 2, C.Ristea 7, O.Ristea 10, D. Röhrich 9, B. H. Samset 12, S. J. Sanders 11, R.A.Sheetz 1, P. Staszel 3, T.S. Tveter 12, F.Videbæk 1, R. Wada 8, H.Yang 9, Z. Yin 9, and I. S. Zgura 10 1 Brookhaven National Laboratory, USA, 2 IReS and Université Louis Pasteur, Strasbourg, France 3 Jagiellonian University, Cracow, Poland, 4 Institute of Nuclear Physics, Cracow, Poland, 5 Johns Hopkins University, Baltimore, USA, 6 New York University, USA, 7 Niels Bohr Institute, University of Copenhagen, Denmark, 8 Texas A&M University, College Station. USA, 9 University of Bergen, Norway, 10 University of Bucharest, Romania, 11 University of Kansas, Lawrence,USA, 12 University of Oslo Norway

3. June 8, 2006RHIC & AGS Users Meeting3 What is BRAHMS? Mid-Rapidity Spectrometer Forward Spectrometer Multiplicity Array Beam Line Beam-Beam Counter

4. June 8, 2006RHIC & AGS Users Meeting4 BRAHMS Unique Perspective The RHIC experiments have provided volumes of results on the properties of the collision medium around mid-rapidity. The RHIC experiments have provided volumes of results on the properties of the collision medium around mid-rapidity. BRAHMS can explore the dynamics at the forward rapidities. BRAHMS can explore the dynamics at the forward rapidities. How does the QGP expand longitudinally? How does the QGP expand longitudinally? How does the fragmentation affect the particle production at large y? How does the fragmentation affect the particle production at large y? Is suppression at large y an initial state or energy loss effect? Is suppression at large y an initial state or energy loss effect? BRAHMS is working on decoupling these effects to give a more complete picture of the forward physics. BRAHMS is working on decoupling these effects to give a more complete picture of the forward physics. z x

5. June 8, 2006RHIC & AGS Users Meeting5 Suppression at Forward Rapidities at 200 GeV  = 0  = 3.2 R dAu dAu R AuAu AuAu Charged Hadrons

6. June 8, 2006RHIC & AGS Users Meeting6 Energy Loss at Forward Rapidity? From y = 0 to y = 3.2, the multiplicity is a factor of ~2 smaller. From y = 0 to y = 3.2, the multiplicity is a factor of ~2 smaller. The multiplicity is correlated to the energy density. The multiplicity is correlated to the energy density. Energy loss of jets in a QGP is correlated to the energy density. Energy loss of jets in a QGP is correlated to the energy density. The lack of rapidity dependence on the high p T suppression raises a lot of questions about the forward region. The lack of rapidity dependence on the high p T suppression raises a lot of questions about the forward region.  K

7. June 8, 2006RHIC & AGS Users Meeting7 NMF Dependence on Centrality The higher energy system begins to look more like pp collisions for less central events. The higher energy system begins to look more like pp collisions for less central events. The lower energy system shows Cronin enhancement similar to what is seen at SPS energies. The lower energy system shows Cronin enhancement similar to what is seen at SPS energies. 200 GEV 62.4 GEV R AuAu

8. June 8, 2006RHIC & AGS Users Meeting8 Identified Particle Nuclear Modification Factors 200 GeV AuAu pp

9. June 8, 2006RHIC & AGS Users Meeting9 Particle NFM Dependencies at 200 GeV There is a stronger dependence of suppression on centrality for the forward pions than the mid-rapidity pions. There also seems to be an indication that the suppression is saturating. PionsProtons y = 0: Phenix y ~ 3.2: BRAHMS Preliminary y = 0: Phenix y ~ 3.2: BRAHMS Preliminary y = 0: Phenix Pions

10. June 8, 2006RHIC & AGS Users Meeting10 Comparison over Different Species at 200 GeV Centrality N part AuAu33-43%96.3 CuCu0-10%96.8 AuAu59-79%15.7 CuCu40-60%17.2 AuAu CuCu Forward central CuCu looks like forward peripheral AuAu. R cp  = 3.2

11. June 8, 2006RHIC & AGS Users Meeting11 Comparison AuAu and CuCu at 62.4 GeV For both systems, the Cronin behavior increases from central to peripheral collisions. For both systems, the Cronin behavior increases from central to peripheral collisions. R AA and R CP can both be used to help understand suppression. R AA and R CP can both be used to help understand suppression.

12. June 8, 2006RHIC & AGS Users Meeting12 Baryon to Meson Production over y An important piece of the puzzle is the relative abundance of baryons to mesons. An important piece of the puzzle is the relative abundance of baryons to mesons. The p-bar to  - ratio decreases as a function of y, but it never looks like a system of multiple pp collisions. The p-bar to  - ratio decreases as a function of y, but it never looks like a system of multiple pp collisions. There is clearly large system nuclear effects at play across all rapidities. There is clearly large system nuclear effects at play across all rapidities.

13. June 8, 2006RHIC & AGS Users Meeting13 Particle ratios The proton to  ratio is large over all rapidities for both AuAu and CuCu collisions. When two systems collide with the same Npart, the ratio is similar even though the geometry of the system vary greatly.

14. June 8, 2006RHIC & AGS Users Meeting14 Dependence on y for AuAu at 200 GeV Particle production,, and p-bar/  - ratio have a dependence on y. Particle production,, and p-bar/  - ratio have a dependence on y. High p T suppression has a weak dependence on y. High p T suppression has a weak dependence on y. These effects will influence the flow in the forward region. These effects will influence the flow in the forward region.

15. June 8, 2006RHIC & AGS Users Meeting15 Elliptic Flow AuAu 200 GeV With the use of the BRAHMS multiplicity array and BB counters, a reaction plane can be determined. With the use of the BRAHMS multiplicity array and BB counters, a reaction plane can be determined. These elements were used to study the elliptic flow for charged hadrons over rapidity and centrality. These elements were used to study the elliptic flow for charged hadrons over rapidity and centrality.

16. June 8, 2006RHIC & AGS Users Meeting16 AuAu 200 GeV v 2 vs. y 10-30% Central PIONS CHARGED HADRONS With a weak dependence on y for v 2 (p T ), the underlying spectra must be affecting the strong dependence of v 2 (  ).

17. June 8, 2006RHIC & AGS Users Meeting17 Dependence on y for AuAu at 200 GeV Dependence on y. Dependence on y. Particle production Particle production p-bar/  - ratio (Preliminary) p-bar/  - ratio (Preliminary) p T -integrated v 2 p T -integrated v 2 Weak Dependence on y. Weak Dependence on y. High p T suppression High p T suppression Charged hadrons Charged hadrons  ’s, K’s, protons (Preliminary)  ’s, K’s, protons (Preliminary) v 2 (p T ) (Preliminary) v 2 (p T ) (Preliminary)

18. June 8, 2006RHIC & AGS Users Meeting18 Current Investigations with BRAHMS The forward system is expanding under different conditions than at mid-rapidity. The forward system is expanding under different conditions than at mid-rapidity. The anisotropic azimuthal production is affected by these effects. The anisotropic azimuthal production is affected by these effects. BRAHMS can provide detailed studies of the systematics of the longitudinal expansion of the system. BRAHMS can provide detailed studies of the systematics of the longitudinal expansion of the system. z x x y AuAu CuCu

19. June 8, 2006RHIC & AGS Users Meeting19 Summary/Conclusions High p T suppression at forward rapidities indicates that there most likely is some interplay between energy loss and initial state effects. High p T suppression at forward rapidities indicates that there most likely is some interplay between energy loss and initial state effects. Systems with similar N part show similar behavior for particle ratios and high p T suppression, but other probes (like flow) should be able to distinguish them. Systems with similar N part show similar behavior for particle ratios and high p T suppression, but other probes (like flow) should be able to distinguish them. With the given systematics, there is little difference of the pion and charged hadron v 2 (p T ) over y. With the given systematics, there is little difference of the pion and charged hadron v 2 (p T ) over y. Correlations with  1 and  2 will help with the understanding of the evolution of the longitudinal expansion of the system. Correlations with  1 and  2 will help with the understanding of the evolution of the longitudinal expansion of the system.

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