Results from BRAHMS experiment at RHIC Pawel Staszel Niels Bohr Institute for the BRAHMS...

Results from BRAHMS experiment at RHIC

Pawel Staszel

Niels Bohr Institute

for the BRAHMS Collaboration

Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 2

I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J.Brzychczyk4, B. Budick6, H. Bøggild7, C. Chasman1, C. H. Christensen7,

P. Christiansen7,J.Cibor4, R.Debbe1, J. J. Gaardhøje7,M. Germinario7 ,K. Grotowski4, K. Hagel8, O. Hansen7, A.K. Holme12, H. Ito11, E. Jacobsen7, A. Jipa10, J. I. Jordre10,

F. Jundt2, C. E. Jørgensen7, T. Keutgen9, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5, G. Løvhøjden2, Z. Majka3, A. Makeev8, B. McBreen1, M. Murray8, J. Natowitz8,

B.S.Nielsen7, K. Olchanski1, D. Ouerdane7, R.Planeta4, F. Rami2, D. Roehrich9, B. H. Samset12, S. J. Sanders11, I. S. Sgura10, R.A.Sheetz1, Z.Sosin3, P. Staszel7, T.S. Tveter12, F.Videb₣k1, R.

Wada8 and A.Wieloch3. 1Brookhaven National Laboratory, USA 2IReS and Universit₫ Louis Pasteur, Strasbourg, France

3Jagiellonian University, Cracow, Poland 4Institute of Nuclear Physics, Cracow, Poland 5Johns Hopkins University, Baltimore, USA 6New York University, USA 7Niels

Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark 8Texas A&M University, College Station. USA, 9University of Bergen, Norway, 10University of Bucharest, Romania,

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


1 MeV/uQ = +32

9 MeV/uQ = +79


BRAHMS DETECTOR

FS: 1< <3.6h

GLOBAL

MRS: -0.5<?<1

Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute5

Global Detectors:SiMA, PTMA, BBC

SiMA 25 wafers segm. into 7 strips, ø=5.3cm, -2.0 < h < 2.0

PTMA 38 tiles, ø=13.9cm, -2.2 < h < 2.2 (-3<h<3)

BBC L=2.15m, st=65ps => sz ~1.0cm, 3 < |h| < 4.0 (2.1<|h|<4.7)


Centrality determination,Vertex distribution 1m


TPC tracks =>Vertex reconstruction and dNch/dh


Charged particle pseudorapidity density

0-5%

5-10%

10-20%

20-30%

30-40%

40-50%

N=SdE /<dE> N=ADC/ADC(sing. part.) Background corr.due to

secondaries: 6-25%(SiMA), 20-40%(TMA), 37-50%(BB)

Consistency between 4 independent. detector systems: SiMA, TMA, BB, and TPC.

65 AGeV+65 AGeV: ò N(ch)dh= 3860±300 Central 0-5% dN(ch)/dh (h=0) =550 FWHM of distribution

Dh= 7.2 ± 0.8

BRAHMS Phys. Lett. B 523 (2001) 227; nucl-ex 0108016

Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute

9

dNch/dh @ 200GeV

p`p

4630 ± 370 charged particles produced for 0-5% central 20% increase over 130GeV

Dh= 7.5± 0.5 dN(ch)/dh (h=0) =625, 14% increase over 130

GeV »50% increase over p+ pbar (UA5) => significant medium effects

—

BRAHMS @ 200

Bjorken energy density

eBJ = (1/pR2t0) d<Et>/dh ³ 5 GeV/fm3

(d < Et>=dN * <pt> , t0=1fm/c,

R»6fm, <pt> = 0.5GeV/c)

cf: eQGPcritical » 1 GeV/fm3


Saturation of excitation in fragmentation region: SPS=>RHIC

BRAHMS subm. to PRL- nuc-ex. 00112001

Shift data to beam frame of reference


dN/dh vs Npart

Kharzeev and Levin (nucl-th/0108006)

Soft-Hard:

dN/dh = (1-X) npp <Npart>/2 + X npp<Ncoll>

<Ncoll>=1049, <Npart>=339, npp=2.43

=>dN/dh=668 (with X=0.12)

High Density QCD-saturation:

dN/dy =f(Npart,Qs2,l,LQCD,Ös,y)

with l=0.25÷0.3 from HERA data

=> dN/dh=616÷634

(using dN/dh=549 at Ös=130GeV)

h=0

h=4.5

h=3

130: A= 0.97 ± 0.08, B =0.22 ±0.04

200: A= 1.12 ± 0.1, B =0.24 ±0.04

Fit to dNch/dh = Anpart + BNcoll:

36÷37% of hard component}(h=0)


dNch(200GeV)/dNch(130GeV)AMPT dashed line K&L solid line

0-5% 5-10%

30-40% 40-50%


BRAHMS Spectrometer


Back Forward Platform


Acceptance and Hadron Identification

BRAHMS has large acceptance for identifiedparticles, up to y~4 for p and 3.5 for p. In MRS: PID via TOF vs mom.p separation upto~3GeV/c.

In FS: TOF1,C1, TOF2,RICH in various combinations


Proton and Kaon data


Hadron Identification: MRS (90-40deg), TOF

m2 = p2(t2/L2 –1)


Hadron Identification: FS (3-20deg), TOF

p+

p

K+

4 deg

C1

H1 T2


Hadron Identification:FS (3-20deg), TOF and C1


Ring Imaging Cherenkov for high momentum PID

´

q Þ R

p>15GeV/c

K>8 GeV/c

p>4 GeV/c


N(pbar)/N(p) @ 130 AGeV Centrality and Pt dependence

Antiproton absorbtion correction to p-bar/p ratio: 5 % for FS at 4 deg, 2 % for MRS at 90 and 40 deg. Proton production (? and Be–tube): 10% and 6% (low Pt bin) for MRS at 90 and 40 deg., respectively. Hyperon decays: p-bar/p » anti-hyperon/hiperon then weak-decay would not affect p-bar/p ratio. Fritiof 7.02 + GEANT Þsystematic correction is < 5%. Model dependent Þ not aplied to data.


Antiparticle/particle ratios vs Pt @ 200GeV, (y=0)

BRAHMS Perliminary


Antiparticle/particle ratios @ 200GeV

p-/p = p-(pair) / [p+p(pair)]

K-/K+ = K-(pair) / [K+(pair)+K+(ap)]

(p+p ® p+L+K+)

p+p- pair prod (& ch. exch).

Midrapidity: near matter-antimatter balance

BRAHMS Perliminary

”+” » ”-


How consistent are models?BRAHMS PRL 87(2001)112305, nucl-ex/0106011


N(p-bar)/N(p) systematics

130GeV

200 GeV


Summary First Au+Au Ösnn=130, 200 GeV

dN/dh(y=0) = 550, Nch(0-5%) = 3860, DhFWHN»7.2,

Nch/0.5<Npart> » 22,

dNch/dh(h=0) » 3.1 pr. part. Pair, p-bar/p vs y shows increase but still

incomplete transparency p-bar/p » 0.64, 0.66, 0.41 at y=0, 0.7, 2,

respectively Weak Pt and centrality dependence, Models inconsistent with data

dN/dh(h=0) = 625, dNch/dh(h=0) » 3.7 pr. part. pair, Nch(0-5%) = 4630, DhFWHN»7.5, Nch/0.5Npart » 28, p-bar/p vs y shows increase but still

incomplete transparency p-bar/p higher at mid- and central rapidity.

RESULTS: 65+65 RESULTS: 100+100

Large energy density > 5 ecrit

Decoupling of central and fragmentation regions

Partonic (color) description appears necessary

Central region dominated by

matter-antimatter balance: Þ Qualitatively new physics regime

To come: particle spectra, Strangeness,

net baryon density,

jet quenching,...

Results from BRAHMS experiment at RHIC Pawel Staszel Niels Bohr Institute for the BRAHMS...

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