results from the brahms experiment at rhic f.rami* for the brahms collaboration * institut de...
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Results from the BRAHMS Experiment at Results from the BRAHMS Experiment at RHICRHIC
F.Rami* for the BRAHMS Collaboration* Institut de Recherches Subatomiques
and Université Louis Pasteur, Strasbourg
Introduction The BRAHMS Experiment Main Physics Results Global features and event characterization Charged particle multiplicity distributions dNch/d vs. Centrality and SNN
Comparison to theoretical models Summary and Conclusion
Relativistic Heavy Ion Collider
2 O’clock IR
June 2000: Startup of RHIC
June - September 2000 First Physics Run
Au+Au @ two energies
SNN = 56 and 130 GeV
July 2001- January 2002 Second Physics Run
Au+Au @ SNN = 200 GeV (maximal design energy)
p+p (reference data)
PHOBOS
PHENIX
STAR
BRAHMS
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, 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 12
University of Oslo Norway
The BRAHMS Collaboration
~55 physicists from 12 institutions
The BRAHMS Experiment at RHIC
Perspective view of BRAHMS
Good Particle Identification over wide range of rapidities (0<|y|<4) and transverse momenta (0.2<pt<4GeV/c)
Forward Spectrometer2.3o < < 30o
Mid-Rapidity Spectrometer30o < < 95o
Basic information on momentum spectra and yields of charged hadrons as a function of y and pt
SiMA Silicon strips
TMA Scintillator tiles
BBC Čerenkov radiator
SiMA
TPM1
BBCTMA
BBC
Global Detectors in BRAHMS
ChargedParticleMultiplicity
Primary Vertex
BRAHMS Physics Program
Probing Hot and Dense Nuclear Matter by studying:
Reaction Mechanisms and Dynamics Different Observables: dNch/d, pt spectra
Baryon Stopping (anti-particle/particle ratios)
Strangeness Production
Collective Flow
High pt hadron spectra (Jet Quenching effects)
First Results dNch/d and anti-particle/particle ratios
I.Bearden et al, PRL87(2001)112305I.Bearden et al, PLB523(2001)227I.Bearden et al, nucl-ex/0112001 submitted to PRL
EVENT CHARACTERIZATION COLLISION CENTRALITY
Au+Au @ SNN=130GeV
Measured with Multiplicity Detectors (TMA and SiMA)
Central Peripheral
Define Event Centrality Classes Slices corresponding to different fractions of the cross section
Central b=0
Peripheral b large
For each Centrality Cut Evaluate the corresponding number of participants
Npart
(Glauber Model)
dNch/d measurements in BRAHMS
0 - 5 % 5 -10%
10-20% 20-30%
30-40% 40-50%
TPM1
BBC SiMA
TMA
I.Bearden et al, Phys.Lett.B523(2001)227Au+Au @ SNN=130GeV
Data from detectors Consistency
By combining all results Cover wide range -4.7 4.7
= -ln (tan(/2))
“Complete” distribution
Total Charged Particle Multiplicities
dN
ch/d
dNch/d distributions
Au+AuSNN=130GeV SNN=200GeV
I.Bearden et al (BRAHMS)PLB523(2001)227
0-5% 30-40%
Forward ’s No Centrality Dependence Mid-rapidity (0) Increase with centrality
Centrality Dependence Relative contributions of Soft and Hard processes
Nch(-4.7<<4.7)
I.Bearden et al (BRAHMS)Submitted to PRL
3860 300 4630 370
=0 Steady increase =3 Flat dependence (dNch/d scales with Npart)
Increase with Npart Onset of hard processes
D.Kharzeev and M.Nardi, PLB 507(2001)121
dNch/d = ANpart BNcoll
% of hard
SNN=130GeV 20% 7%
SNN=200GeV 25% 7%
dNch/d - Centrality Dependence
Superposition of Soft + Hard
Comparison to Model Predictions
1
2
3
HIJING – Jet quenching
HIJING – No Jet quenching
EKRT (Gluon Saturation)
Wang & Gyulassy, PRL86(2001)3496
BRAHMS
1
2
3
|
|
|
|
Both models HIJING and EKRT reproduce the measured multiplicities
Au+Au data much larger than pp Not a simple superposition Medium effects important role in AA collisions
It would be interesting to explore the Centrality Dependence in these models Stronger constraints
Central CollisionsFor Central Collisions
SUMMARY
BRAHMS has measured dNch/d distributions in Au+Au collisions at two energies SNN=130GeV and 200GeV
Combining different sub-detectors in BRAHMS “Complete” dNch/d distributions
At Forward ’s No Centrality Dependence (dNch/d scales with Npart) No Energy Dependence ( Limiting Fragmentation)
At Mid-rapidity dNch/d/(0.5<Npart>) increases with Centrality Influence of hard scattering processes Two component analysis Significant contribution at RHIC
dNch/d measured in central collisions can be reproduced by two different models HIJING (“Soft+Hard”) and EKRT (“Gluon Saturation”) It would be interesting to investigate the Centrality Dependence in these models Stronger Constraints
Limiting Fragmentation
Central Collisions (5%)
SNN=130GeV
SNN=200GeV
Pb+Pb at SPS
Fragmentation region
Appropriate frame = beam reference frame
No Energy Dependence from SPS to RHIC
Consistent with the Hypothesis of Limiting Fragmentation
Observed in several reactions pp, ppbar, p-emulsion, -emulsion
Deines-Jones et al, PRC (2000) 4903
SNN=17.2GeV
(Benecke et al, PRC 188(1969)2159)
dNch/d - Comparison to Model Predictions
SNN=130GeV
5% 5-10%
20-30% 40-50%
UrQMDBass et al,Prog.Part.Nuc.Phys.41(98)255
HIJINGWang and Gyulassy,PRD44(91)3501
AMPTZhang et al,PRC61(2001)067901Lin et al,PRC64(2001)011902
Parton scattering models give a good description of the data AMPT wider distributions (includes hadronic rescattering)
PLB523(2001)227
dNch/d - Comparison to Model Predictions
Au+Au @ SNN=200GeV
AMPTZhang et al,PRC61(2001)067901Lin et al,PRC64(2001)011902
High density QCDgluon saturationKharzeev and Levin,PLB523(2001)79
Differences forPeripheral Collisions but Small effect !
dN
ch/d
Stronger Constraints on the models ...
Important to use different observables to constrain models
Au+Au @ SNN=130GeV