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Results from the BRAHMS experiment at RHIC

Dieter Röhrich Fysisk institutt, Universitetet i Bergen

for the

BRAHMS collaboration

• Experimental setup• Stopping• Particle production

– Charged particle pseudo-rapidity distribution– Rapidity dependence of ratios of identified particles

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BRAHMS collaboration

I.G. Bearden7, D. Beavis1, C. Besliu10, Y. Blyakhman6, J. Bondorf7, J.Brzychczyk4, B. Budick6, H. Bøggild7, C. Chasman1, C. H. Christensen7, P. Christiansen7, J.Cibor4, R.Debbe1,

J. J. Gaardhøje7, K. Grotowski4, K. Hagel8, O. Hansen7, H. Heiselberg7, A. Holm7, 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.Videbæk1, R. Wada8 and A.Wieloch3.

1Brookhaven National Laboratory, USA 2IReS and Université 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, 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

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RHIC physicsAugust 2000 & August 2001

2:00 o’clock

4:00 o’clock6:00 o’clock

8:00 o’clock

10:00 o’clock

STARPHENIX

RHIC

AGS

LINACBOOSTER

TANDEMS

9 GeV/uQ = +79

1 MeV/uQ = +32

HEP/NP

g-2

U-lineBAF (NASA)

BRAHMS: Lpeak = 3.3 1025 cm-2 s-1

Lave = 1.7 1025 cm-2 s-1

Rcoll= 350 HzPHOBOS

6 b-1

2 wks

August 2000 and 2001

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BRAHMS detector

– Centrality detectors• Tiles• Silicon strips• Beam-Beam counters • Zero-degree

calorimeters

– Two movable spectrometers• Midrapidity spectrometer

• Forward Spectrometer

• Broad RAnge Hadron Magnetic Spectrometer

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Global detectors: SiMA, TMA, BB, ZDC

• SiMA (-2.0< <2.0) • TMA (-2.2< <2.2)• Beam-Beam (3 < | | < 4)

97% (geom)

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Centrality determination

• Multiplicity measurement– Si strips + tiles

• Corrected for vertex position dependence

1m

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Forward & midrapidity spectrometers

FS: 2 TPC, 2 TOF, C1-threshold, 3 Drift Ch. Mod., RICH, 4 Dipoles

2.5 - 30 deg. = 1.5 - 4

MRS: 2 TPC, 1 Dipole, 1TOF

30 - 90 deg. = 0 - 1.5

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First BRAHMS collision at 100 AGeV+100AGeV

T1

MTPC1

T2

MTPC2

MRS: 90 deg

6.5 msr

FS: 6 deg

0.8 msr

Dipole Magnets

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Spectrometer acceptanceAugust 2000 & 2001

FFS

BFS

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TPC tracking and vertex reconstruction

MTPC1

z

y

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Hadron identification MRS (90, 40 deg)

m2=p2( t2 / L2 -1)

p-bar

K p

=0

=3

p

K

0

p, pbar

K±

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Hadron identificationFS (4 deg & 200AGeV) (1)

TOF (H1) and Cherenkov (C1) veto in FFS

C1,H1,T2

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Hadron identificationFS (4 deg & 200AGeV) (2)

K- p-

K+ p

• C1 Cerenkov pion threshold ~2.7GeV/c

• C1 segmented in 32 6.35cm x 6.35 cm pixels.

• Mean # of tracks/event ~1.4• TOF resolution roughly 25%

better than in 2000

• TOF K/p in FFS up to 5GeV/c

• TOF pi/K in FFS to 3GeV/c

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Hadron identificationFS (200AGeV) (3)

• Full PID in FS• Ring Imaging Cerenkov

Detector (RICH)

• Secondary ToF counter (H2)

PID up to 25 GeV/c

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Proton rapidity distribution

• AGS energies – Central collisions

– Energy dependence

B. Back et al., E917 Collaboration, Phys. Rev. Lett. 86 (2001) 1970

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Stopping

• Rapidity loss– energy

dependence

F. Videbæk, nucl-ex/0106017

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Net proton rapidity distribution

• SPS • central (6%) Pb+Pb, 158 GeV/nucl. • NA49

• RHIC• central (6%) Au+Au, sNN= 130 GeV

• BRAHMS, STAR

G. Cooper et al. (NA49 Collaboration), Nucl. Phys. A661 (1999) 362c-365c

C. Adler et al. (STAR), subm. Phys. Rev. Lett.; F. Videbæk (BRAHMS), QM01

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Net proton rapidity distribution – model predictions

• FRITIOF 7.02 • HIJING

• BRAHMS (central) preliminary

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Antiproton/proton ratio – rapidity dependence

• SPS • central (14%) Pb+Pb, 158 GeV/nucl. • NA49

• RHIC• central (40%) Au+Au, sNN= 130 GeV

• BRAHMS

G. Cooper et al. (NA49), Nucl. Phys. A661 (1999) 362c;G. Veres et al. (NA49), Nucl. Phys. A661 (1999) 383c

I.G. Bearden et al., (BRAHMS), Phys. Rev. Lett. 87 (2001)

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Antiproton/proton ratio – centrality dependence

• SPS • Pb+Pb, 158 GeV/nucl. • NA49

• RHIC• Au+Au, sNN= 130 GeV

• BRAHMS

G. Cooper et al. (NA49), Nucl. Phys. A661 (1999) 362c;G. Veres et al. (NA49), Nucl. Phys. A661 (1999) 383c I.G. Bearden et al., (BRAHMS), Phys. Rev. Lett. 87 (2001)

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Antiproton/proton ratio – energy dependence

• Energy systematics • RHIC, Au+Au sNN= 130 GeV

sNN= 200 GeV

RHIC, central Au+Au, BRAHMS

J.J. Gaardhøje, (BRAHMS), CIPPQG (2001)

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Particle production dNch/d @ snn= 130 GeV

• Charged particle pseudorapidity distribution

– SiMA, TMA, BB, TPC– Consistency between 4

independent detector systems

• Central 0-5% N(ch)d =

4050 ± 300

– dN(ch)/d (=0) = 553

1 36– FWHM of distribution

= 7.6 0.7

0-5%

10-20%

20-30%

30-40%

40-50%

5-10%

600

BRAHMS subm. Phys. Lett. B (2001)

65 AGeV + 65 AGeV

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Number of Participants

From HIJING

• dN/d ~ 3.2 per participant nucl. pair at =0 for central (0-5%); <Npart>=346

• Enhancement of particle production for central collisions at mid-rapidity

• At high rapidities ( >3) particle production scales with Npart

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dNch/dvs. participant nucleon pairs

@ snn=130 GeV

SPS

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dNch/d and model predictions

snn=130 GeV

C. E. Jørgensen, Thesis NBI 2001

FRITIOF

HIJING

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Particle production dNch/d @ snn= 200 GeV

• Charged particle pseudorapidity distribution– SiMA, BB

• Central 0-6% N(ch)d =

5100 ± 300

– dN(ch)/d (=0) = 610

50– FWHM of distribution

= 7.9 1.0

100 AGeV + 100 AGeV

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dNch/dvs. participant nucleon pairs @ snn=200 GeV

• Soft-Hard:

dN/d=(1-X) npp <Npart>/2

+ X npp <Ncoll>

with <Ncoll>=1049, <Npart>=339, npp=2.43 =>dN/d=668 (with X=0.9)

• High Density QCD-saturation:

dN/dy = f( Npart, Qs2, ,QCD,s,y)

with =0.3 from HERA data

=> dN/d=620 (using dN/d=549 at s=130 GeV)

Kharzeev and Levin (nucl-th/0108006)

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dNch/dvs. participant nucleon pairs - energy dependence

• 130 AGeV• 4000 charged part. observed• Nch 23.5 pr. part. pair• cf. Nch 17 in p+p at

s=130GeV• 35-40% increase over p+p

Syst

?BRAHMS

200 AGeV

• 200 AGeV• 5100 charged part. observed• Nch 30 pr. part. pair• cf. Nch 20 in p+p at

s=200GeV• 50% increase over p+p

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Rapidity dependence of ratios of identified particles - how consistent are the models @ snn= 130GeV?

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Rapidity dependence of K/K+ ratio @ snn= 130GeV

BRAHMS

preliminary

BRAHMS

preliminary

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Transverse momentum dependence of ratios of identified particles (1)

snn= 130GeV

• Ratios at y 0

• 0-40% central

• No observed dependence on centrality

• No strong pt-dependence

• N()/N(+) = 0.990.02

• N(K)/N(K+) = 0.900.06

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Transverse momentum dependence of ratios of identified particles (2)

snn= 130GeV

• Ratios at y 0

• 0-40% central

• N(K)/N() increases

with pt (0.16 – 0.6)

• N(p)/N() increases

with pt ;

pbar(p) > for pt > 2 GeV/c

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Ratios of identified particles and jet quenching

• Kaon/pion ratio as probes of jet quenching and initial density in AA collisions P. Levai, SQM2001

• Anomalous antiproton to negative pion ratio as revealed by jet quenching

I. Vitev, M. Gyulassy, hep-ph/0108045

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Thermal models at RHIC

F. Becattini, J. Cleymans, A. Keranen, E. Suhonen, K. Redlich,

Phys.Rev. C64 (2001) 024901

BRAHMS Preliminary

y2 y0

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Summary: Au+Au snn=130 & 200 GeV

RESULTS: 65 + 65• Nch (0-5%) 4050• dN/d (y=0) 553; FWHM 7.6• dN/d (y=0) 3.14 pr. part. pair

• Pbar/p = 0.64 ± 0.05 ± 0.06 (y 0)

= 0.66 ± 0.05 ± 0.06 (y 0.7)

= 0.41 ± 0.05 ± 0.06 (y 2)

/+ = 0.990.02 (y 0)

• K/K+ = 0.900.06 (y 0)

= 0.830.1 (y 2.5)

• No (weak) pt and centrality dependence

RESULTS: 100 + 100 • Nch (0-5%) 5100

• dN/d (y=0) 610. FWHM 7.9

• dN/d (y=0) 3.6 pr. part. pair

• Central mult increases by 14%

• Pbar/p 0.48 ± 0.08 (y 2)

/+ = 0.990.01 (y 3)

• Large y and pt coverage to come