1
• Stopping• net proton rapidity spectra• pbar/p vs s
• Kaon production• K/ vs pbar/p• Kaon slopes vs pbar/p
Energy dependence of stopping and the K/ ratio
(BRAHMS data)
Dieter RoehrichUiB
2
From SPS to RHIC
• Particle production increases ...
• Projectile fragmentation region and central region
– overlap at SPS– are well separated at RHIC
• Antiproton/proton ratio at midrapidity resp. net-proton rapidity density change drastically with s
BRAHMS
NA49
AGS
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(Net)-proton rapidity distribution
• AGS energies – centrality dependence– energy dependence
B. Back et al., E917 Collaboration. Phys. Rev. Lett. 86 (2001) 1970
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(Net)-proton rapidity distribution
• SPS, 158 GeV/nucl., NA49 - central collisions
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Rapidity distributions of produced hadrons at SPS
• Rapidity distributions of both produced hadrons and net-protons peak at (or near) midrapidity
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Net-proton rapidity distribution
BRAHMS, submittedto PRL, nucl-ex/0312023
dNdy • RHIC
• central Au+Au
• Npart=3578
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Stopping (1)
8
Gaussians in pz:
2
2
2
))sinh((exp
pz
zN pym
y 2.03 0.16
Stopping (2)
Net-baryon after feed-down & neutron corrections
y 2.00 0.106 order polynomial
Gaussians in pz:
2
2
2
))sinh((exp
pz
zN pym
Rapidity loss:(Npart= 357 10)
py BB
partpp dy
dy
dNy
Nyyyy
0
)(2
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Rapidity distributions at RHIC
Rapidity distributions of
• produced hadrons peak at midrapidity
• net-protons peak at forward midrapidity
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SPS vs RHIC
dn/dy
net-protons pions
RHIC: 35-40 80
forward rapidity
(y4) at 200 GeV
SPS: 41 100
midrapidity at
40 AGeV/c
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How to compare SPS and RHIC data?
• use the antiproton/proton ratio: ratios at midrapidity (SPS) and at different rapidities (RHIC)
12
Kaon production
• K/ vs pbar/p
• Kaon slopes vs pbar/p
13
Fit: exponential
T
mmA Texp
Top 5% central collisions
AuAu 63 GeV
AuAu 200 GeV
Kaon spectra at RHIC
BRAHMS preliminary
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Top 5% central collisions
Kaon inverse slopes
15
K-/K+ vs pbar/p
62.4 GeV
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K/ vs rapidity at 200 GeV
BRAHMS
• Indication of divergence at large y
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K/ vs rapidity at 62.4 GeV
BRAHMSpreliminary
• Clear splitting of the ratio for positive and negative particles
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K/ vs s
• The Horn
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K-/- vs pbar/p
• SPS data and RHIC data agree at same pbar/p ratio
SPS- NA49 RHIC 62.4 GeV BRAHMS preliminary
RHIC 200 GeV BRAHMS
K-
-
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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
21
Kaon slopes vs s
• The Step
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Kaon slopes vs pbar/p
100
300
200
T [MeV]SPS - NA49 RHIC 62.4 GeV
BRAHMS preliminary
RHIC 200 GeV BRAHMS
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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
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Identified particle spectra
n
T
p
pA
0
1
Pions: power law Kaons: exponential
T
mmA Texp
Protons: Gaussian
2
2
2exp
Tp
A
Top 5% central collisions
