Recent Results from the BRAHMSExperiment at RHIC

Paweł Staszel, Jagellonian Universityfor the BRAHMS Collaboration

Eighth Workshop on Non-Perturbative QCDParis, 7 – 11 June, 2004

2P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

BRAHMS

BRAHMS

The Relativistic Heavy Ion Collider

Au+Aud+Au

p+p

Top energy:sNN=200GeV

3P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

I.G. Bearden7, D. Beavis1, C. Besliu10, B. Budick6, H. Bøggild7 , C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1, E. Enger12,

J. J. Gaardhøje7, M. Germinario7, K. Hagel8, O. Hansen7, A.K. Holme12, H. Ito11,

A. Jipa10, J. I. Jordre10, F. Jundt2, C.E.Jørgensen7, R. Karabowicz3, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5, G. Løvhøjden2, Z. Majka3,

A. Makeev8, B. McBreen1, M. Mikkelsen12, M. Murray8, J. Natowitz8, B.S.Nielsen7,

K. Olchanski1, D. Ouerdane7, R.Planeta4, F. Rami2, D. Röhrich9, B. H. Samset12,

D. Sandberg7, S. J. Sanders11, R.A.Sheetz1, P. Staszel3,7, T.S. Tveter12, F.Videbæk1, R. Wada8, Z. Yin9, and I. S. Zgura10

1Brookhaven National Laboratory, USA, 2IReS and Université Louis Pasteur, Strasbourg, France3Jagiellonian University, Cracow, Poland, 4Institute of Nuclear Physics, Cracow, Poland

5Johns Hopkins University, Baltimore, USA, 6New York University, USA7Niels Bohr Institute, University of Copenhagen, Denmark

8Texas A&M University, College Station. USA, 9University of Bergen, Norway 10University of Bucharest, Romania, 11University of Kansas, Lawrence,USA

12 University of Oslo Norway

50 physicists from 12 institutions

The BRAHMS Collaboration

4P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Agenda of this talk

General Characteristics of the Au+Au sNN=200GeV - particle production - nuclear stopping - statistical model description (particle ratios) - transvers dynamics (particle pt spectra)

Nuclear modification of spectra Au+Au (QGP)Rapidity evolution of nuclear modification for

d+Au (CGC)Summary

5P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Charged Particle Multiplicity

0-5%

5-10%

10-20%

20-30%

30-40%

40-50%

Energy density: Bjorken 1983

eBJ = 3/2 (<Et>/ R20) dNch/dh

4.0 GeV/fm3

(<Et>=0.5GeV, 0=1fm/c)

0-5% central Au+Au:Total charged particlemultiplicity: 4630370(PRL 88, 202301(2002)) 50% increase over p+pbar (UA5)

p+p

6P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Limiting FragmentationShift the dNch/d distribution by the beam rapidity, and scale by Npart. Lines up with lower energy limiting fragmentation

Au+Au sNN=200GeV (0-5% and 30-40%)Au+Au sNN=130GeV (0-5%)Pb+Pb sNN=17GeV (9.4%)

7P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Baryon stopping

6 order polynomial

Gaussians in pz

y = yb - yy = 2.03 0.16y = 2.00 0.1

p

p

y

y

BB

yT dyydy

dNm cosh)(

Total E=25.72.1TeV72GeV per participant

8P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Baryon stopping II

scaling broken

empirical sc

aling

SNN=63 GeV ???

y =0.58yp

8.9

LHC

y = 2.2, E/A=2800GeV (Ebeam/A=3500GeV, yp=8.9)

?

9P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

•At y=0: -/+ = 1.0, K-/K+ = 0.95 ±0.05 pbar/p = 0.75 ±0.04•Good statistical model description with B= B(y), • At |y|<1 materanti-matter

Increasing y

PRL90,102301 (2003)

Chemical freeze-out

T115 Mev, T0.7c at y=0• Flow velocity decreases with rapidity. Lower density lower pressure less flow• Temperature increases with rapidity. Lower density faster freeze out higher temperature

Kinetic freeze-out

Phys. Rev. Lett. 90, 102301(2003)

BRAHMS preliminary

10P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

q

q

hadronsleadingparticle

leading particle

Schematic view of jet production Particles with high pt’s (above ~2GeV/c) are primarly produced in hard scattering processes early in the collision Probe of the dense and hot stage

Experimentally depletion of the high pt region in hadron spectra

In A-A, partons traverse the medium

p+p experiments hard scattered partons fragment into jets of hadrons

If QGP partons will lose a large part of their energy (induced gluon radiation) Suppression of jet production Jet Quenching

High pt Suppression Jet Quenching

11P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Charged hadron invariant spectra

RAA =Yield(AA)

NCOLL(AA) Yield(NN)

Scaled N+N reference

Nuclear Modification Factor

RAA<1 Suppression relative to scaled NN reference

Reference spectrum

p+pbar spectra (UA1)

SPS: data do not show suppression enhancent (RAA>1) due to initial state

multiple scatering (“Cronin Effect”)

BRAHMS, PRL91(2003)072305

12P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

High pt suppression in Au+Au @ SNN=200 GeV

BRAHMS, PRL91(2003)072305 mid-rapidity (=0) At central collisions clear suppression At peripheral no suppression (as expected)

forward rapidity (=2.2) the same trend no p+p reference large sys. errors

Yield(0-10%)/NCOLL(0-10%)Yield(40-60%)/NCOLL(40-60%)

RCP=

RCP shows suppression at both =0 and =2.2

13P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Control measurement: d+Au @ SNN=200

Suppression in AuAu dueto Jet Quenching or due toInitial State PartonSaturation (CGC)?

What about d+Au? - Jet Quenching – No - CGC - Yes/No?

Excludes alternative interpretation in terms of Initial State Effects Supports the Jet Quenching for central Au+Au collisions

+ back-to-back azimuthal correlation by STAR

14P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Data versusHydro-Jet Model

i Hydro description of the soft part of the produced matter

ii Hard part use a pQDC model (PYTHIA)

i+ii – generation of jets is evolving medium

Reasonable descriptionof data at both =0 and =2.2

Hirano & Nara (nucl-th/0307087)

15P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Evolution of RdAu with rapidity

Cronin like enhancement at =0 Clear suppression at =3.2

Low pt consistent with measured dNch/d

nucl-ex/0403005

16P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

pQCD versus data @ = 3.2

Geometrical shadowing with opacity from fit to PHENIX (y~0, 0)

A. Accardi, M. Gyulassy,

nucl-th/0402101

17P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Color Glass Condensate explanation

D. Kharzeev at al.hep-ph/0405045

=0

=1

=2.2

=3.2

quark dipole-nucleus scattering amplitudeTwo free parameters fitted to data:y0 – onset of saturationc - onset of quantum regime

Overal good description of RdAu

With general trend ofRdAu 1/Npart, this model accounts also for resonabledescription of RCP

18P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Rapidity dependence for d+AuSubmitted to PRL nucl-ex/0401025

Curves: Saturation Model from Kharzeev, Levin, Nardi NPA730 (2004) 448Kharzeev, Levin, Nardi NPA730 (2004) 448

19P. Staszel - Jagellonian University, KrakówEighth Workshop on Non-Perturbative QCD, Paris 2004

BRAHMS

Summary Large hadron multiplicies Almost a factor of 2 higher than at SPS ( higher ) Much higher than in pp ( medium effects)

Evolution of nuclear modification in d+Au data absence of the suppression in d+Au data at =0 supports Jet Quenching scenario forward data consistent with onset of suppression in the Color Glass Condensate

Suppression of high pt particles in central Au+Au collisions observed at =0 and 2.2 Consistent with a Jet Quenching scenario

Identified hadron spectra Broken lower energy scaling of rapidity loss Good description by statistical model large transvers flow