Zbigniew Majka Hot Matter Physics Division M.Smoluchowski...

Zbigniew Majka, M.Smoluchowski Institute of Physics, Jagiellonian University, Kraków, Poland, [email protected]

HHototMMatteratterPPhysicshysicsDDivisionivision

Kielce Physics Workshops, October 15-17, 2004

Zbigniew Majka Hot Matter Physics Division

M.Smoluchowski Institute of PhysicsJagiellonian University



The BRAHMS CollaborationI.Arsene10, I. G. Bearden7, D. Beavis1, C. Besliu10, B. Budick6, H. Bøggild7, C. Chasman1, C.H.Christensen7,

P. Christiansen7, J. Cibor3, R. Debbe1, E. Enger12, J. J. Gaardhøje7, M. Germinario7, K. Hagel8, H. Ito1, A.Jipa10, F. Jundt2, J. I. Jørdre9, C. E. Jørgensen7, R. Karabowicz4, E. J. Kim1,11, T. Kozik4 ,

T. M. Larsen12, J. H. Lee1, Y. K. Lee5, S. Lindal12, R. Lystad9, G. Løvhøiden12, Z. Majka4, A. Makeev8, M. Mikelsen12, M. Murray8, 11, J. Natowitz8, B. Neumann11, B. S. Nielsen7, D. Ouerdane7, R. Planeta4,

F. Rami2, C. Ristea10, O. Ristea10, D. Röhrich9, B. H. Samset12, D. Sandberg7, S. J. Sanders11, R. A. Scheetz1, P. Staszel7, T. S. Tveter12, F. Videbæk1, R. Wada8, Z. Yin9, I. S. Zgura10

1Brookhaven National Laboratory, Upton, New York, USA2IReS and Université Louis Pasteur, Strasbourg, France

3Institute of Nuclear Physics, Krakow, Poland4 M. Smoluchkowski Inst. of Physics, Jagiellonian University, Krakow, Poland

5Johns Hopkins University, Baltimore, USA6New York University, New York, USA

7 Niels Bohr Institute, University of Copenhagen, Denmark8Texas A&M University, College Station, Texas, USA

9 University of Bergen, Bergen, Norway 10 University of Bucharest, Romania

11University of Kansas, Lawrence, Kansas, USA 12University of Oslo, Oslo, Norway



Review of the BRAHMS experiment results

Overall goal:

Concise review of the BRAHMS experiment abilities.

Presentation of a representative experimental results from BRAHMS.

(Also data from other experiments will be recall for comparison.)

Conclusions.



BNL/RHIC/BRAHMS/DC-pictures



Summary of RHIC runs

RHICrun

Collidingsystem

√sNN

[GeV]Dates of BRAHMSdata taking

I Au+AuAu+Au

56130

2000 (June 15)

2000 (summer)

II Au+AuAu+AuAu+Aup+p

13020019.6

200

2002 (winter)

2001 (fall)

2001 (winter)

2001/02 (winter)

III d+Aup+p

200

200

2002/03 (winter)

2003 (spring)

IV Au+AuAu+Aup+p

20062.4

200

2003/04 (winter)

2004 (spring)

2004 (spring)

Au +Au 56 bunches

of ~ 109 ionsin each ring

To control:• Time of interaction• z-distribution of the

interaction

Currently analyzedA few results available



Designed to measure charged hadrons: p, K, πIdentification of particles over a broad range of:angles – 2.3o – 95o momenta (up to 30 GeV/u, σ(dp/p) ~ 1%)

0 < |y| < 4 0.2 < pt < ~ 3GeV/c

• Small solid angles:MRS = 6.5 msrFS = 0.8 mrs

• Rotation around the nominal IP

Drawback:A small region of thePhase-space per settingGlobal detectors:

BBC, ZDC, MA, ICSpectrometers:Magnets, Tracking Devices, ToF, Cherencov

•Triggers for DAQ• Overall characteristics:

# collision vertex# collision centrality# particle density

•Particle identification •Particle momentum

# particle ratios# particle spectra

Experimental set up



The charged particle multiplicity

Centralit[%]

η = 0 η= 1.5 η = 3.0 η = 4.5 Nch Npart

0 – 5 625 ± 55 627 ± 54 470 ± 44 181 ± 22 4630 ± 370 357

η-6 -4 -2 0 2 4 6

η/d

chdN

0

100

200

300

400

500

600

700 0-5%

5-10%

10-20%

20-30%

30-40%

40-50%

= 200 GeVNNs√Au+Au @

PL, B523 (2001) 227

PRL, 88 (2002) 202301

The particle densities are sensitive to:•the energy loss of colliding nuclei

•the relative contribution of: ** “Soft” processes –

non-perturbative QCD mechanisms,involve the longer length scales

** “Hard” partonic processes –and the interactions of these partonsin a high energy environment.

(Two Component Parameterization)



The charged particle multiplicity(comparison to 130 GeV and p+p )

[GeV]NNs10 210 310

>)pa

rt /(

1/2<

N0≈ηη

dN/d

0

1

2

3

4

5

BRAHMSRHIC combinedE866 (AGS)NA49 (SPS)PHOBOS

)pUA5/CDF (p

dNch

/dη/

(0.5

Npa

rt)

The particle production in the Au+Au central collisionsexceeds by 40-50 % particle production in p+p collisions

14% increase over 130GeV

=> nucleus–nucleus collisions far from being the simple superposition of elementary collisions



The charged particle production per participant pair

Fragmentation:

Particle production stays constant for differentcollision geometry, different energies at rapidity0.5 – 1.5 units below beam rapidity.

Energy available for the particle production saturates below top SPS energy.(Limiting Fragmentation Pictures)

Midrapidity

Significant increase of the particle productionwith the increasing collision energy=> the dissipated energy is transported into

central rapidity regionMidrapidity Fragmentation

dNch/dη/(0.5Npart) vs. η - ybeam



Rapidity dependence of charged antihadron to hadron ratio.Observation• No significant dependence on pT or centrality

in two selected rapidity intervals (y = 0, 2)=> yields integrated over centrality (0 – 20) %

and over pT within acceptance

# π--/ π+ K-/ K+ p/p ~ 1 0.95 – 0.67 0.75 – 0.23

# p/p and K-/ K+ ratios are essentially constantin the rapidity interval 0 – 1.

# particle production in central regionpredominantly from pair creation

# correlation of p/p and K-/ K+ ratios welldescribed by the statistical approach => an indication that the system is in

chemical equilibrium

PRL, 87 (2001) 112305

PRL, 90 (2003) 102301



Net protons rapidity density

12

7(highest rapidity measurementsnot yet completed)

Net protons rapidity density comparison

• With increasing energy the nucleus – nucleus collisons re more and more transparent(a depletion of the net-proton density at central rapidities)



• Charged particle density, dN ch/dη = 625 around η = 0 (integrated: ≈ 4600)• Particle production in central region predominantly from pair creation• the nucleus – nucleus collisions are quite transparent

Bjorken energy density(Au+Au at √SNN = 200 GeV, central collision for y = 0)

εBJ = 3/2 (1/πR2τ0) d<ET >/dη

(R = 6 fm, τ 0 =1 fm/c, d<E T > = dN ch<p T >,

dN ch/dη =625, <p T > 0.5 GeV/c,)

εQGPcritical ≈ 1 GeV/fm3≈ 4 GeV /fm3

≈ 30 • ρnormal nuclear matter

≈ 4 • density of baryon



⟨δy⟩ = 2.03 ± 0.16⟨δy⟩ = 2.00 ± 0.1

63 GeV ??

8.9

LHC(3.5 A TeV)⟨δ y⟩ = 2.2

⟨δ E⟩ /A = 2.8 TeV

•Between AGS (5 GeV) and SPS (17 GeV) <δ y> ~ ybeam,<δy⟩ = 0.58∗ybeam

Au+Au at √SNN = 200 GeV• Scaling is broken at RHIC energies• Relative rapidity loss : 35% < <δy>/yb < 44%• Energy loss: ΔE/A=75GeV;

ΔE(tot)=26TeV out of available 35 TeV

Rapidity loss - (<δ y> = ybeam- <y>)

Full stopping: <δ y> = ybeamFull transparency: <δ y> = 0

Rapidity loss



Invariant spectra of charged hadrons

• power law-shape• 99% of particles produced at pT < 2GeV/c• <pT> larger for larger system

(largest energy density)• the spectra are steeper at η =2.2 than at η =0



Large high pt suppression for central collisions as compared to semi-peripheral(also at forward rapidity)

High transverse momentum component of hadron spectra studiesNuclear modification factor :

ηησddpNdN

ddpNdRt

NNbin

tAuAupp

inelAuAu /

/2

2

><=

Pseudorapidity dependence of high pT

Au(100A GeV) + Au(100A GeV)

The evidences for strong nuclear effects

Jets energy loss



High pt at midrapidity study - d(100A GeV) + Au(100A GeV)

No high pt suppression at midrapidity

Cronin enhancement

RdAu/ RAuAu (at pT≈ 4GeV/c)≈ 4-5

Initial state effects are ruled out!

PRL 91 (2003) 072305



High pT study of identified hadrons

Au(100A GeV) + Au(100A GeV)

Dependence on the type of particlesMesons (pions and kaons)

experience suppressionwhile baryons (protons) do not

Hadronic flow or partonic mechanism?

Qualitative agreement with

parton recombination models

(need results from run IV for higher pt)



High pT study at 62.4 GeV - preliminary:

High pt suppression less important

(No high pt suppression at SPS)



High pt at forward rapidity study - d(100A GeV) + Au(100A GeV)

Submitted to PRL, March 2004

nucl-ex/0403005

Initial condition of colliding nucleiat forward rapidity

existence of the CGC



Conclusions from the BRAHMS experiments at RHIC:

•The matter that is created at RHIC differs from anythingthat has been investigated before.

• Indications (model dependent) for a collective gluonicstate (CGC) found.

• Results are consistent with strongly interactingdeconfined matter

However

No direct evidence for chiral symmetry restorationNo direct evidence for phase transition

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