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

3

(Net)-proton rapidity distribution

• AGS energies – centrality dependence– energy dependence

B. Back et al., E917 Collaboration. Phys. Rev. Lett. 86 (2001) 1970

4

(Net)-proton rapidity distribution

• SPS, 158 GeV/nucl., NA49 - central collisions

5

Rapidity distributions of produced hadrons at SPS

• Rapidity distributions of both produced hadrons and net-protons peak at (or near) midrapidity

6

Net-proton rapidity distribution

BRAHMS, submittedto PRL, nucl-ex/0312023

dNdy • RHIC

• central Au+Au

• Npart=3578

7

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

9

Rapidity distributions at RHIC

Rapidity distributions of

• produced hadrons peak at midrapidity

• net-protons peak at forward midrapidity

10

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

11

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

14

Top 5% central collisions

Kaon inverse slopes

15

K-/K+ vs pbar/p

62.4 GeV

16

K/ vs rapidity at 200 GeV

BRAHMS

• Indication of divergence at large y

17

K/ vs rapidity at 62.4 GeV

BRAHMSpreliminary

• Clear splitting of the ratio for positive and negative particles

18

K/ vs s

• The Horn

19

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-

-

20

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

22

Kaon slopes vs pbar/p

100

300

200

T [MeV]SPS - NA49 RHIC 62.4 GeV

BRAHMS preliminary

RHIC 200 GeV BRAHMS

23

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

24

25

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