August 4-9, Quark Matter 2005

System and Rapidity System and Rapidity Dependence of Dependence of Baryon/Meson Ratios at Baryon/Meson Ratios at RHICRHIC

Eun-Joo KimEun-Joo KimUniversity of KansasUniversity of KansasFor the BRAHMS collaborationFor the BRAHMS collaboration

August 4-9, Quark Matter 2005

OutlineOutline

• The BRAHMS experiment• p/ ratios for different centrality

bins• p/ ratios for different systems• p/ ratios at different rapidities• Summary

August 4-9, Quark Matter 2005

BBroad RARAnge HHadron MMagnetic SSpectrometers

• AuAu, CuCu, pp sNN= 200 GeV• MRS at 90o (y=0) and full FS data at 4o (~3.2)• PID by TFW2, C4,TFW2, C4, RICHRICH

August 4-9, Quark Matter 2005

Particle IdentificationParticle Identification

C4C4

• TFW2 : /K ~ 2.5 GeV/c, K/p ~ 4.0 GeV/c with 2 cut• C4 : /K ~ 9 GeV/c• RICH : /K ~ 25 GeV/c, p ~ 35 GeV/c

MRS MRS TFW2TFW2 FS RICHFS RICH

August 4-9, Quark Matter 2005

Centrality dependent pbar/Centrality dependent pbar/- -

ratios 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

pp at y~0 : PHENIX preliminary pp at y~0 : PHENIX preliminary

BRAHMS PreliminaryBRAHMS Preliminary

• No Anti-Lambda No Anti-Lambda Feed-Down Correction!Feed-Down Correction!• Errors are statistical Errors are statistical only…only…

August 4-9, Quark Matter 2005

p/p/increases with system increases with system sizesize

++

--

August 4-9, Quark Matter 2005

Comparison of AuAu & CuCuComparison of AuAu & CuCu

pbar/- ratios are similar for different collision systems, and for a comparable number of binary collisions at y~0

and ~3.2

August 4-9, Quark Matter 2005

p/p/ ratios in CuCu collisions ratios in CuCu collisions

Centrality dependence for p/+ ratios is stronger

at ~3.2 than y~0, but pbar/- shows only slight centrality dependence at both

rapidities.

++ ++

-- --

August 4-9, Quark Matter 2005

pp

p/p/+ ratios vs. <Npart> in + ratios vs. <Npart> in CuCuCuCu

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

Rapidity and <NRapidity and <Npartpart> > dependencedependence

Y=0

~3.2

Strongrapidity dependence

pp

pp

August 4-9, Quark Matter 2005

Recombination & Recombination & CoalescenceCoalescence

Recombination and parton coalescence model describe

ratios at midrapidty and suggest radial flow

August 4-9, Quark Matter 2005

<pT> decrease with y : p ~ 10%,~ 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)

Point : BRAHMS AuAu Curve : 3D Hydro (Hirano)Histo : AMPT

AuAu sNN= 200 GeV y~0

PRC72,014908(2005)

<p<pTT> vs. rapidity and > vs. rapidity and centralitycentrality

August 4-9, Quark Matter 2005

3D-Hydro Model for AuAu3D-Hydro Model for AuAu

- 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

PHENIX : PRC69,034909(2004)PHENIX : PRC69,034909(2004)

BRAHMS PreliminaryBRAHMS Preliminary

August 4-9, Quark Matter 2005

SummarySummary

BRAHMS has studied the pT/centrality/rapidity/system dependence of the p/ratios for AuAu, CuCu and

pp - p/ ratios are enhanced in AA collisions compared to

pp - No other system dependence is observed - p/+ and pbar/- ratios show similar interplay between soft and hard processes for different

systems - However, there is strong rapidity dependence (baryo-chemical potential?) (p/ ratio)/<Npart> at constant independent of

system

August 4-9, Quark Matter 2005

The BRAHMS CollaborationThe BRAHMS CollaborationI.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, USA2IReS and Université Louis Pasteur, Strasbourg, France

3Jagiellonian University, Krakow, Poland4Johns Hopkins University, Baltimore, USA

5New York University, USA6Niels Bohr Institute, University of Copenhagen, Denmark

7Texas A&M University, College Station. USA,8University of Bergen, Norway

9University of Bucharest, Romania10University of Kansas, Lawrence,USA

11University of Oslo, Norway

48 physicists from 11 institutions

August 4-9, Quark Matter 2005

Corrections in AuAuCorrections in AuAu

August 4-9, Quark Matter 2005

Net-p distributions? Net-p distributions?

Dynamics for Baryon/Meson is similar to p/+ and pbar/-?

August 4-9, Quark Matter 2005

p/p/ratios on Nratios on Ncollcoll

August 4-9, Quark Matter 2005

August 4-9, Quark Matter 2005