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

2. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 2 I.G. Bearden 7, D. Beavis 1, C. Besliu 10, Y. Blyakhman 6, J.Brzychczyk 4, B. Budick 6, H. Bøggild 7, C. Chasman 1, C. H. Christensen 7, P. Christiansen 7,J.Cibor 4, R.Debbe 1, J. J. Gaardhøje 7,M. Germinario 7, K. Grotowski 4, K. Hagel 8, O. Hansen 7, A.K. Holme 12, H. Ito 11, E. Jacobsen 7, A. Jipa 10, J. I. Jordre 10, F. Jundt 2, C. E. Jørgensen 7, T. Keutgen 9, E. J. Kim 5, T. Kozik 3, T.M.Larsen 12, J. H. Lee 1, Y. K.Lee 5, G. Løvhøjden 2, Z. Majka 3, A. Makeev 8, B. McBreen 1, M. Murray 8, J. Natowitz 8, B.S.Nielsen 7, K. Olchanski 1, D. Ouerdane 7, R.Planeta 4, F. Rami 2, D. Roehrich 9, B. H. Samset 12, S. J. Sanders 11, I. S. Sgura 10, R.A.Sheetz 1, Z.Sosin 3, P. Staszel 7, T.S. Tveter 12, F.Videb₣k 1, R. Wada 8 and A.Wieloch 3. 1 Brookhaven National Laboratory, USA 2 IReS and Universit₫ Louis Pasteur, Strasbourg, France 3 Jagiellonian University, Cracow, Poland 4 Institute of Nuclear Physics, Cracow, Poland 5 Johns Hopkins University, Baltimore, USA 6 New York University, USA 7 Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark 8 Texas A&M University, College Station. USA, 9 University of Bergen, Norway, 10 University of Bucharest, Romania, 11 University of Kansas, Lawrence,USA, 12 University of Oslo Norway

3. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 3 1 MeV/u Q = +32 9 MeV/u Q = +79

4. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 4 BRAHMS DETECTOR FS:  GLOBAL MRS: -0.5<?<1

5. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 5 Global Detectors: SiMA, PTMA, BBC  SiMA 25 wafers segm. into 7 strips, ø=5.3cm, -2.0 <  < 2.0  PTMA 38 tiles, ø=13.9cm, -2.2 <  < 2.2 (-3<  <3)  BBC L=2.15m,  t =65ps = >  z ~1.0cm, 3 < |  | < 4.0 (2.1<|  |<4.7)

6. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 6 Centrality determination, Vertex distribution 1m

7. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 7 TPC tracks = >Vertex reconstruction and dN ch /d 

8. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 8 Charged particle pseudorapidity density 0-5% 5-10% 10-20% 20-30% 30-40% 40-50%  N=  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:   N(ch)d  = 3860±300 • Central 0-5% dN(ch)/d  (  =0) =550 • FWHM of distribution  = 7.2  0.8 BRAHMS Phys. Lett. B 523 (2001) 227; nucl-ex 0108016

9. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 9 dN ch / d  @ 200GeV pppp  4630  370 charged particles produced for 0-5% central 20% increase over 130GeV   = 7.5  0.5  dN(ch)/d  (  =0) =625, 14% increase over 130 GeV   50% increase over p+  pbar (UA5) => significant medium effects — BRAHMS @ 200 Bjorken energy density  BJ = (1/  R 2  0 ) d /d   5 GeV/fm 3 (d =dN *,  0 =1fm/c, R  6fm, = 0.5GeV/c) cf:  QGP critical  1 GeV/fm 3

10. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 10 Saturation of excitation in fragmentation region: SPS=>RHIC BRAHMS subm. to PRL- nuc-ex. 00112001 Shift data to beam frame of reference

11. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 11 dN/d  vs N part • Kharzeev and Levin (nucl-th/0108006) • Soft-Hard: dN/d  = (1-X) n pp /2 + X n pp =1049, =339, n pp =2.43 =>dN/d  =668 (with X=0.12) • High Density QCD-saturation: dN/dy =f(Npart,Q s 2,,  QCD,  s,y) with =0.25÷0.3 from HERA data => dN/d  =616÷634 (using dN/d  =549 at  s=130GeV)  =0  =4.5  =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 dN ch /d  = An part + BN coll : 36÷37% of hard component } (  =0)

12. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 12 dN ch (200GeV)/dN ch (130GeV) AMPT dashed line K&L solid line 0-5% 5-10% 30-40% 40-50%

13. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 13 BRAHMS Spectrometer

14. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 14 Back Forward Platform

15. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 15 Acceptance and Hadron Identification BRAHMS has large acceptance for identified particles, up to y~4 for  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

16. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 16 Proton and Kaon data

17. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 17 Hadron Identification: MRS (90-40deg), TOF m 2 = p 2 (t 2 /L 2 – 1)

18. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 18 Hadron Identification: FS (3-20deg), TOF ++ p K+ 4 deg C1 H1 T2

19. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 19 Hadron Identification: FS (3-20deg), TOF and C1

20. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 20 Ring Imaging Cherenkov for high momentum PID    R p>15GeV/c K>8 GeV/c  >4 GeV/c

21. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 21 N(pbar)/N(p) @ 130 AGeV Centrality and P t 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 P t 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  systematic correction is < 5%. Model dependent  not aplied to data.

22. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 22 Antiparticle/particle ratios vs P t @ 200GeV, (y=0) BRAHMS Perliminary

23. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 23 Antiparticle/particle ratios @ 200GeV p - /p = p - (pair) / [p+p(pair)] K - /K + = K - (pair) / [K + (pair)+K + (ap)] (p+p  p+  +K +)  +  - pair prod (& ch. exch). Midrapidity: near matter-antimatter balance BRAHMS Perliminary ” + ”  ”-

24. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 24 How consistent are models? BRAHMS PRL 87(2001)112305, nucl-ex/0106011

25. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 25 N(p-bar)/N(p) systematics 130GeV 200 GeV

26. Cracow Epiphany Conference, Pawel Staszel, Niels Bohr Institute 26 Summary First Au+Au  s nn =130, 200 GeV  dN/d  (y=0) = 550,  N ch (0-5%) = 3860,  FWHN  7.2,  N ch /0.5  22,  dN ch /d  (  =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 P t and centrality dependence, • Models inconsistent with data  dN/d  (  =0) = 625,  dNch/d  (  =0)  3.7 pr. part. pair,  N ch (0-5%) = 4630,  FWHN  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  crit  Decoupling of central and ' fragmentation ' regions = Partonic (color) description appears necessary = Central region dominated by matter-antimatter balance:  Qualitatively new physics regime To come: particle spectra, Strangeness, net baryon density, jet quenching,...