1. Eun-Joo Kim University of Kansas For the BRAHMS collaboration
System and Rapidity
Dependence of
Baryon/Meson Ratios at RHIC
Eun-Joo Kim
University of Kansas
For the BRAHMS collaboration
August 4-9, Quark Matter 2005

2. Outline The BRAHMS experiment p/p ratios for different centrality bins
p/p ratios for different systems
p/p ratios at different rapidities
Summary
August 4-9, Quark Matter 2005

3. Broad RAnge Hadron Magnetic Spectrometers
AuAu, CuCu, pp sNN= 200 GeV
MRS at 90o (y=0) and
full FS data at 4o (h~3.2)
PID by TFW2, C4, RICH
August 4-9, Quark Matter 2005

4. Particle Identification
MRS TFW2
FS RICH C4
TFW2 : p/K ~ 2.5 GeV/c, K/p ~ 4.0 GeV/c with 2s cut
C4 : p/K ~ 9 GeV/c
RICH : p/K ~ 25 GeV/c, p ~ 35 GeV/c
August 4-9, Quark Matter 2005

5. Centrality dependent pbar/p- ratios
Increase from peripheral
to central in AuAu
at sNN = 200 GeV
Ratio for peripheral AuAu
approaches to pp
Ratios at forward rapidity
turn over at lower pT
than midrapidity
BRAHMS Preliminary
No Anti-Lambda
Feed-Down Correction!
Errors are statistical only…
pp at y~0 : PHENIX preliminary
August 4-9, Quark Matter 2005

6. p/p increases with system size+ -
August 4-9, Quark Matter 2005

7. Comparison of AuAu & CuCu
pbar/p- ratios are similar for different collision systems,
and for a comparable number of binary collisions at y~0 and h~3.2
August 4-9, Quark Matter 2005

8. p/p ratios in CuCu collisions+ + - -
Centrality dependence for p/p+ ratios is stronger
at h~3.2 than y~0, but pbar/p- shows only
slight centrality dependence at both rapidities.
August 4-9, Quark Matter 2005

9. p/p+ ratios vs. <Npart> in CuCu
p/p+ ratio integrated over 1.5<pT<2.5 GeV/c
at forward rapidity increase with centrality;
smaller dependence seen at midrapidity
August 4-9, Quark Matter 2005

10. Rapidity and <Npart> dependence
Strong
rapidity
dependence
Y=0
h~3.2 pp pp
August 4-9, Quark Matter 2005

11. Recombination & Coalescence
Recombination and parton coalescence model describe
ratios at midrapidty and suggest radial flow
August 4-9, Quark Matter 2005

12. <pT> vs. rapidity and centrality
AuAu sNN= 200 GeV
y~0
Point : BRAHMS AuAu
Curve : 3D Hydro (Hirano)
Histo : AMPT
PRC72,014908(2005)
<pT> decrease with y : p ~ 10%, p ~ flat from y=0 to y~3
AMPT and 3D-Hydro model under-predict <pT>
3D-Hydro describe y-dependence qualitatively
with a single Tth value (Tth = 100 MeV, Tch = 170 MeV)
August 4-9, Quark Matter 2005

13. 3D-Hydro Model for AuAu
BRAHMS Preliminary
PHENIX : PRC69,034909(2004)
- p/p+ enhanced at forward rapidity, mainly from projectile?
- Still high - Cronin, recombination, or flow?
- The hydro calculation shown does not consider baryon nor isospin
chemical potentials: There is no rapidity dependence.
- Particle ratio is fixed at chemical freezeout temperature
August 4-9, Quark Matter 2005

14. Summary BRAHMS has studied the pT/centrality/rapidity/system
dependence of the p/p ratios for AuAu, CuCu and pp
- p/p ratios are enhanced in AA collisions compared to pp
- No other system dependence is observed
- p/p+ and pbar/p- ratios show similar interplay
between soft and hard processes for different systems
- However, there is strong rapidity dependence
(baryo-chemical potential?)
(p/p ratio)/<Npart> at constant h independent of system
August 4-9, Quark Matter 2005

15. The BRAHMS Collaboration
I.Arsene9,11, I.G. Bearden6, D. Beavis1, S.Bekele10, C. Besliu9, B. Budick5, H. Bøggild6 ,
C. Chasman1, C. H. Christensen6, P. Christiansen6, R.Clarke9, R.Debbe1,
J. J. Gaardhøje6, K. Hagel7, H. Ito1, A. Jipa9, J. I. Jordre8, F. Jundt2, E.B.Johnson10,
J.I.Jordre8, C.Jørgensen6, R. Karabowicz3, E. J. Kim10, T.M.Larsen6, J. H. Lee1,
Y. K.Lee4, S.Lindal11, G. Løvhøjden2, Z. Majka3 , M. Murray10, J. Natowitz7,
B.S.Nielsen6, D.Ouerdane6, R.Planeta3, F. Rami2, C.Ristea6, O.Ristea9,
D. Röhrich8, B. H. Samset11, S. J. Sanders10, R.A.Sheetz1, P. Staszel3, T.S. Tveter11,
F.Videbæk1, R. Wada7, H.Yang8, Z. Yin8, and I. S. Zgura9
1Brookhaven National Laboratory, USA
2IReS and Université Louis Pasteur, Strasbourg, France
3Jagiellonian University, Krakow, Poland
4Johns Hopkins University, Baltimore, USA
5New York University, USA
6Niels Bohr Institute, University of Copenhagen, Denmark
7Texas A&M University, College Station. USA,
8University of Bergen, Norway
9University of Bucharest, Romania
10University of Kansas, Lawrence,USA
11University of Oslo, Norway
48 physicists from 11 institutions
August 4-9, Quark Matter 2005

16. Corrections in AuAu
August 4-9, Quark Matter 2005

17. Net-p distributions?
PRL90,102301(2003)
Dynamics for Baryon/Meson is similar to p/p+ and pbar/p-?
August 4-9, Quark Matter 2005

18. p/p+ ratios on Ncoll
August 4-9, Quark Matter 2005

19. August 4-9, Quark Matter 2005

20. August 4-9, Quark Matter 2005