1 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

2 BRAHMS collaboration I.G. Bearden 7, D. Beavis 1, C. Besliu 10, Y. Blyakhman 6, J. Bondorf 7, 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, K. Grotowski 4, K. Hagel 8, O. Hansen 7, H. Heiselberg 7, A. Holm 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.Videbæk 1, R. Wada 8 and A.Wieloch 3. 1 Brookhaven National Laboratory, USA 2 IReS and Université 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, 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 RHIC physics August 2000 & August :00 o’clock 4:00 o’clock 6:00 o’clock 8:00 o’clock 10:00 o’clock STAR PHENIX RHIC AGS LINAC BOOSTER TANDEMS 9 GeV/u Q = MeV/u Q = +32 HEP/NP  g-2 U-line BAF (NASA) BRAHMS: L peak = 3.3  cm -2 s -1 L ave = 1.7  cm -2 s -1 Rcoll= 350 Hz PHOBOS 6  b -1 2 wks August 2000 and 2001

4 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

5 Global detectors: SiMA, TMA, BB, ZDC SiMA (-2.0<  <2.0) TMA (-2.2<  <2.2) Beam-Beam (3 < |  | < 4) 97%  (geom)

6 Centrality determination Multiplicity measurement –Si strips + tiles Corrected for vertex position dependence 1m

7 Forward & midrapidity spectrometers FS: 2 TPC, 2 TOF, C1-threshold, 3 Drift Ch. Mod., RICH, 4 Dipoles deg.  = MRS: 2 TPC, 1 Dipole, 1TOF deg.  =

8 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

9 Spectrometer acceptance August 2000 & 2001 FFS BFS

10 TPC tracking and vertex reconstruction MTPC1 z y

11 Hadron identification MRS (90, 40 deg) m 2 =p 2 ( t 2 / L 2 -1) p-bar  KK p  =0  =3 p K  0 p, pbar K±  

12 Hadron identification FS (4 deg & 200AGeV) (1) TOF (H1) and Cherenkov (C1) veto in FFS C1,H1,T2

13 Hadron identification FS (4 deg & 200AGeV) (2) K-K- p-p- K+K+ p C1 Cerenkov pion threshold ~2.7GeV/c C1 segmented in cm 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

14 Hadron identification FS (200AGeV) (3) Full PID in FS Ring Imaging Cerenkov Detector (RICH) Secondary ToF counter (H2) PID up to 25 GeV/c

15 Proton rapidity distribution AGS energies –Central collisions –Energy dependence B. Back et al., E917 Collaboration, Phys. Rev. Lett. 86 (2001) 1970

16 Stopping Rapidity loss –energy dependence F. Videbæk, nucl-ex/

17 Net proton rapidity distribution SPS central (6%) Pb+Pb, 158 GeV/nucl. NA49 RHIC central (6%) Au+Au,  s NN = 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

18 Net proton rapidity distribution – model predictions FRITIOF 7.02HIJING BRAHMS (central) preliminary

19 Antiproton/proton ratio – rapidity dependence SPS central (14%) Pb+Pb, 158 GeV/nucl. NA49 RHIC central (40%) Au+Au,  s NN = 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)

20 Antiproton/proton ratio – centrality dependence SPS Pb+Pb, 158 GeV/nucl. NA49 RHIC Au+Au,  s NN = 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)

21 Antiproton/proton ratio – energy dependence Energy systematics RHIC, Au+Au  s NN = 130 GeV  s NN = 200 GeV RHIC, central Au+Au, BRAHMS J.J. Gaardhøje, (BRAHMS), CIPPQG (2001)

22 Particle production dN ch /d  s nn = 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  % 10-20% 20-30% 30-40% 40-50% 5-10% 600 BRAHMS subm. Phys. Lett. B (2001 ) 65 AGeV + 65 AGeV

23 Number of Participants From HIJING dN/d  ~ 3.2 per participant nucl. pair at  =0 for central (0-5%); =346 Enhancement of particle production for central collisions at mid-rapidity At high rapidities (  >3) particle production scales with N part

24 dN ch /d  vs. participant nucleon  s nn =130 GeV SPS

25 dN ch /d  and model predictions  s nn =130 GeV C. E. Jørgensen, Thesis NBI 2001 FRITIOF HIJING

26 Particle production dN ch /d  s nn = 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  AGeV AGeV

27 dN ch /d  vs. participant nucleon  s nn =200 GeV Soft-Hard: dN/d  =(1-X) n pp /2 + X n pp with =1049, =339, npp=2.43 =>dN/d  =668 (with X=0.9) High Density QCD- saturation: dN/dy = f( Npart, Q s 2,,  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/ )

28 dN ch /d  vs. 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 5100 charged part. observed Nch  30 pr. part. pair cf. Nch  20 in p+p at  s=200GeV 50% increase over p+p

29 Rapidity dependence of ratios of identified particles - how consistent are the  s nn = 130GeV?

30 Rapidity dependence of K  /K +  s nn = 130GeV BRAHMS preliminary BRAHMS preliminary

31 Transverse momentum dependence of ratios of identified particles (1)  s nn = 130GeV Ratios at y  % central No observed dependence on centrality No strong pt-dependence N(   )/N(  + ) = 0.99  0.02 N(K  )/N(K + ) = 0.90  0.06

32 Transverse momentum dependence of ratios of identified particles (2)  s nn = 130GeV Ratios at y  % central N(K)/N(  ) increases with p t (0.16 – 0.6) N(p)/N(  ) increases with p t ; pbar(p) >      for p t > 2 GeV/c

33 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/

34 Thermal models at RHIC F. Becattini, J. Cleymans, A. Keranen, E. Suhonen, K. Redlich, Phys.Rev. C64 (2001) BRAHMS Preliminary y  2 y  0

35 Summary: Au+Au  s nn =130 & 200 GeV RESULTS: 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)   /  + = 0.99  0.02 (y  0) K  /K + = 0.90  0.06 (y  0) = 0.83  0.1 (y  2.5) No (weak) pt and centrality dependence RESULTS: 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)   /  + = 0.99  0.01 (y  3) Large y and pt coverage to come