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Energy dependence of stopping and the K/ ratio (BRAHMS data) • Stopping • net proton rapidity spectra • pbar/p vs s • Kaon production • K/ vs pbar/p • Kaon slopes vs pbar/p Dieter Roehrich 1 UiB From SPS to RHIC • Particle production increases ... BRAHMS NA49 AGS • Projectile fragmentation region and central region – overlap at SPS – are well separated at RHIC • Antiproton/proton ratio at midrapidity resp. netproton rapidity density change drastically with s 2 (Net)-proton rapidity distribution • AGS energies – centrality dependence – energy dependence B. Back et al., E917 Collaboration. Phys. Rev. Lett. 86 (2001) 1970 3 (Net)-proton rapidity distribution • SPS, 158 GeV/nucl., NA49 - central collisions 4 Rapidity distributions of produced hadrons at SPS • Rapidity distributions of both produced hadrons and net-protons peak at (or near) midrapidity 5 Net-proton rapidity distribution dN dy • RHIC • central Au+Au • Npart=3578 BRAHMS, submitted to PRL, nucl-ex/0312023 6 Stopping (1) 7 Stopping (2) Net-baryon after feed-down & neutron corrections Gaussians in in pz:pz: Gaussians 2 2 (m(Nmsinh( y ) p ) sinh( y ) p z z ) N exp exp 2 2 22pz pz 6 order polynomial Rapidity loss: (Npart= 357 10) 2 y y p y y p N part yp 0 y 2.03 0.16 y 2.00 0.10 y dN( B B ) dy dy 8 Rapidity distributions at RHIC Rapidity distributions of • produced hadrons peak at midrapidity • net-protons peak at forward midrapidity 9 SPS vs RHIC dn/dy net-protons RHIC: forward rapidity (y4) at 200 GeV SPS: midrapidity at 40 AGeV/c 35-40 41 pions 80 100 10 How to compare SPS and RHIC data? • use the antiproton/proton ratio: ratios at midrapidity (SPS) and at different rapidities (RHIC) 11 Kaon production • K/ vs pbar/p • Kaon slopes vs pbar/p 12 Kaon spectra at RHIC AuAu 200 GeV Fit: exponential m m A exp T T AuAu 63 GeV Top 5% central collisions BRAHMS preliminary 13 Kaon inverse slopes Top 5% central collisions 14 K-/K+ vs pbar/p 62.4 GeV 15 K/ vs rapidity at 200 GeV BRAHMS • Indication of divergence at large y 16 K/ vs rapidity at 62.4 GeV BRAHMS preliminary • Clear splitting of the ratio for positive and negative particles 17 K/ vs s • The Horn 18 K-/- vs pbar/p K- SPS- NA49 RHIC 62.4 GeV BRAHMS preliminary RHIC 200 GeV BRAHMS • SPS data and RHIC data agree at same pbar/p ratio 19 K+/+ vs pbar/p • SPS data and RHIC data agree at same pbar/p ratio K+ + SPS- NA49 RHIC 62.4 GeV BRAHMS preliminary RHIC 200 GeV BRAHMS 20 Kaon slopes vs s • The Step 21 Kaon slopes vs pbar/p T [MeV] SPS - NA49 RHIC 62.4 GeV BRAHMS preliminary RHIC 200 GeV BRAHMS 300 200 100 22 Summary • Projectile fragmentation region and central region overlap at SPS and are well separated at RHIC • Antiproton/proton ratio at midrapidity changes drastically with s • Antiproton/proton ratio changes with rapidity at RHIC energies • Local systems (y1), characterized by the same pbar/p ratio, show identical K-/K+ and K/ ratios and kaon inverse slopes • The right side of the ’horn’ seems to be reproduced by going to forward rapidities at RHIC 23 24 Identified particle spectra Top 5% central collisions Pions: power law p A1 T p0 n Kaons: exponential Protons: Gaussian m m A exp T T pT2 A exp 2 2 25