1. Transverse dynamics at y=0 in BRAHMS Bjørn H. Samset Transverse dynamics at RHIC, March 2003 A story of centrality dependent pt spectra of identified charged hadrons measured with the BRAHMS experiment at RHIC Data from AuAu collisions at

2. Transverse dynamics at y=0 in BRAHMS Bjørn H. Samset Transverse dynamics at RHIC, March 2003 A story of centrality dependent pt spectra of identified charged hadrons measured with the BRAHMS experiment at RHIC Bjørn H. Samset PhD student, University of Oslo, Norway Been with BRAHMS for 4 years...

3. Transverse dynamics at y=0 in BRAHMS Bjørn H. Samset Transverse dynamics at RHIC, March 2003 A story of centrality dependent pt spectra of identified charged hadrons measured with the BRAHMS experiment at RHIC Bjørn H. Samset PhD student, University of Oslo, Norway Been with BRAHMS for 4 years... BRAHMS crater on Mercury, formed by a high energy collision at low centrality, plus some transverse flow.

4. Outline Bjørn H. Samset Transverse dynamics at RHIC, March 2003 ● The BRAHMS experiment at RHIC ● The analysis - extracting particle yields from BRAHMS data ● and centrality dep. of dN ch /d h at y=0 ● and centrality dep. of identified hadron p t spectra at y=0 ● Centrality dependence of like and unlike particle ratios vs. p t at y=0 ● Conclusions and future visions

5. Bjørn H. Samset Transverse dynamics at RHIC, March 2003 The experiment at

6. The BRAHMS collaboration Bjørn H. Samset Transverse dynamics at RHIC, March 2003 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, E. Enger 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, S. Lindal 12, G. Løvhøjden 12, Z. Majka 3, A. Makeev 8, B. McBreen 1, M. Mikkelsen 12, 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, 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

7. The BRAHMS experiment Setup used for AuAu data in 2001 Bjørn H. Samset Transverse dynamics at RHIC, March 2003

8. BRAHMS coverage for the AuAu run of 2001 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 MRS FS 25 GeV/c 4o4o 2.3 o (min) 90 o Coverage of the y-pt plane is achieved by rotating the two spectrometer arms and changing magnetic fields. Angles covered in 2001: 90 o, 60 o, 45 o, 40 o, 35 o, 20 o, 12 o, 8 o, 4 o, 3 o

9. Data analysis in Bjørn H. Samset Transverse dynamics at RHIC, March 2003 heading towards Centrality dependence of charged particle production at midrapidity Analysis mainly by E. J. Kim and J. H. Lee

10. Particle identification in BRAHMS Bjørn H. Samset Transverse dynamics at RHIC, March 2003 Midrapidity performance: ● Time-of-flight resolution of ~75 psec ● p /K separation up to ~2.5 GeV/c ● K/p separation up to ~4.0 GeV/c Forward spectrometer (example): ● RICH gives PID up to 25 GeV/c TOFW RICH

11. Select data from y-p t plots Bjørn H. Samset Transverse dynamics at RHIC, March 2003 90 o 60 o 40 o

12. Select data from y-p t plots Bjørn H. Samset Transverse dynamics at RHIC, March 2003 90 o 60 o 40 o

13. Select data from y-p t plots Bjørn H. Samset Transverse dynamics at RHIC, March 2003 90 o 60 o 40 o

14. Select data from y-p t plots Bjørn H. Samset Transverse dynamics at RHIC, March 2003 90 o 60 o 40 o

15. A word on extracting a yield from a p t spectrum Bjørn H. Samset Transverse dynamics at RHIC, March 2003 We need to extrapolate to integrate the spectra, and here we have to make an assumption about the spectral shape: ● Boltzman? ● p t exponential? ● m t exponential? There is a 20% difference in the yields extracted via the different fits - this goes into our systematic uncertainty. In the following we have used m t exponential fits unless otherwise noted.

16. Centrality dependence of charged particle production at midrapidity Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – Analysis of total y~0 data set from Run-2 (Au-Au ) Approx. 30M events

17. Centrality dependence of charged particle production at midrapidity Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – Analysis of total y~0 data set from Run-2 (Au-Au ) – Events divided into centrality classes (0-10,10-20,20-40,40-60 %) as determined by Multiplicity detector (-2.2<  <2.2).

18. Centrality dependence of charged particle production at midrapidity Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – Analysis of total y~0 data set from Run-2 (Au-Au ) – Divided into centrality classes (0-10,10-20,20-40,40-60 %) as determined by Multiplicity detector (-2.2<  <2.2). – PID by Time-Of-Flight, 3 s cut with respect to our momentum and tof resolutions Momentum

19. Corrections applied to the data Bjørn H. Samset Transverse dynamics at RHIC, March 2003 We need to apply a number of corrections to our raw number of particles to get the correct yield. We've corrected for: ● tracking efficiency, using a track embedding technique ● efficiency in matching spectrometer tracks to hits in the time- of-flight systems ● geometrical acceptance, using GEANT3.21 ● physics effects like multiple scattering, proton knockout from the beampipe etc., also evaluated with GEANT3.21 Caveats: The numbers I will show have not been corrected for L feed-down, and I will only show statistical errors.

20. Corrections applied to the data Bjørn H. Samset Transverse dynamics at RHIC, March 2003 We need to apply a number of corrections to our raw number of particles to get the correct yield. We've corrected for: ● tracking efficiency, using a track embedding technique ● efficiency in matching spectrometer tracks to hits in the time- of-flight systems ● geometrical acceptance, using GEANT3.21 ● physics effects like multiple scattering, proton knockout from the beampipe etc., also evaluated with GEANT3.21 Caveats: The numbers I will show have not been corrected for L feed-down, and I will only show statistical errors. Now for the data...

21. Centrality dependence of charged hadron spectra at y=0 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 ● The charged hadron spectra have been fitted to a power law formula: in the range 0.2 < p t < 4.0 GeV/c ● dN/d h and values are calc. from the fit parameters, with BRAHMS PRELIMINARY

22. dN/d h at h =0 from charged hadrons Bjørn H. Samset Transverse dynamics at RHIC, March 2003 dN/d h per participant pair increases from 3.0 for peripheral collisions to 3.5 for central. This is consistent with what we showed in Phys.Rev.Lett.88:202301,2002 rises from ~0.55 GeV/c for peripheral collisions to ~0.60 GeV/c for central. BRAHMS PRELIMINARY

23. Charged hadron yield per N coll, comparison between central and peripheral Bjørn H. Samset Transverse dynamics at RHIC, March 2003 BRAHMS PRELIMINARY The ratio between the yield of charged hadrons from central and peripheral collisions ● increases up to p t ~2.3 ● drops as p t increases beyond this value

24. Particle spectra from central AuAu collisions Bjørn H. Samset Transverse dynamics at RHIC, March 2003 Recap of Cent: 0-10% Analysis by D. Ouerdane

25. Charged hadron spectra: p +, p - Bjørn H. Samset Transverse dynamics at RHIC, March 2003 BRAHMS PRELIMINARY

26. Charged hadron spectra: K +, K - Bjørn H. Samset Transverse dynamics at RHIC, March 2003 0-10% BRAHMS PRELIMINARY

27. Charged hadron spectra: p, p Bjørn H. Samset Transverse dynamics at RHIC, March 2003 0-10% BRAHMS PRELIMINARY

28. Comparison: 0-10% vs. 40-60% Bjørn H. Samset Transverse dynamics at RHIC, March 2003 BRAHMS PRELIMINARY We see no significant difference between the behaviors of p t spectra for central and peripheral events.

29. Inverse slope vs. mass and centrality Bjørn H. Samset Transverse dynamics at RHIC, March 2003 ● We see transverse flow at all rapidities, and all centralities at y=0 ● Inverse slope decreases with increasing rapidity ● Inverse slope decreases somewhat for less central events y=0, 0.9 y~3 BRAHMS PRELIMINARY

30. for p, K, p at y=0 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – The mean p t is evaluated from the exponential m t fits. – for all particle species increases from peripheral to central events – Values and centrality dependence is good agreement with preliminary Phenix data, except for the pions. Ours are higher, likely because of the m t fit. BRAHMS PRELIMINARY

31. dN/dy per participant pair at y=0 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 ● The yield per participant pair increases with participant number for all particle species ● K and p yields rise faster than p Statistical errors only. Dominant sources of systematic errors are N part numbers and extraction of yields. BRAHMS PRELIMINARY

32. K/ p ratio at y=0, 3 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 Recap of ● Positive and negative ratios are identical at y=0. ● At y=3 K - / p - drops below the positives Analysis by D. Ouerdane

33. Centrality dependent p - / p + ratios at y=0 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – The p - / p + ratio is flat over the range 0.5<pt<3.5GeV/c. – R(central) is equal within errors to R(peripheral) BRAHMS PRELIMINARY

34. Centrality dependent K - /K + ratios at y=0 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – The K - /K + ratios are almost flat over the range 0.5<pt<3.5GeV/c. There may be a dip at low p t – R(central) is again equal within errors to R(peripheral) BRAHMS PRELIMINARY

35. Centrality dependent p / p ratios at y=0 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – The p / p ratios for central events are flat over the range 0.5<pt<3.5GeV/c. – R(central) is equal within errors to R(peripheral) BRAHMS PRELIMINARY

36. K / p ratios at y=0 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – K - /  -, K + /  + ratios show an increase with p t – There is no significant difference between central and peripheral events. BRAHMS PRELIMINARY

37. p / p ratios at y=0 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – p/  -, p/  + ratios show an increase with centrality. – The ratios in central events reach 0.7~0.8 at 2GeV/c, while in peripheral events the ratios go up to 0.4~0.5. BRAHMS PRELIMINARY

38. The BRAHMS experiment Additions since 2001 Bjørn H. Samset Transverse dynamics at RHIC, March 2003 C4 - Cherenkov counter Spectrometer triggers for pp and dA ● Extended pt coverage at midrap. ● Better timing resolution ● Allows triggering on events w. tracks in spectrometer for inc. data rate TOFWII second time-of-flight wall

39. What to expect from BRAHMS in the near future Bjørn H. Samset Transverse dynamics at RHIC, March 2003 Existing AuAu data: ● Analysis is ongoing away from midrapidity ● Our centrality dependent spectra will be extended out to y~3 pp and dAu data: ● pp data are being analyzed to serve as baseline for our AuAu data ● dAu data are being taken and analyzed as we get them. Now we only need the machine to deliver enough beam for a good high pt sample! A future AuAu run at full RHIC energy: ● C4 and TOFWII extend our capabilities at midrapidity, allowing for an even better comparison between mid and high rapidities ● Our p t coverage at midrapidity will go increase, nicely complementing the data we already have

40. Conclusions Bjørn H. Samset Transverse dynamics at RHIC, March 2003 BRAHMS has measured the transverse dynamics of charged hadrons at midrapidity from AuAu collisions at In brief, we have shown that ● for charged hadrons, increases as a function of centrality ● this also applies to each particle species individually ● the global behavior of identified particle spectra does not change with centrality ● like-particle ratios are constant as a function of p t and centrality ● the p/ p ratio shows an increase for more central events

41. Conclusions Bjørn H. Samset Transverse dynamics at RHIC, March 2003 BRAHMS has measured the transverse dynamics of charged hadrons at midrapidity from AuAu collisions at In brief, we have shown that ● for charged hadrons, increases as a function of centrality ● this also applies to each particle species individually ● the global behavior of identified particle spectra does not change with centrality ● like-particle ratios are constant as a function of p t and centrality ● the p/ p ratio shows an increase for more central events Thank you for listening

42. Comparison: 0-10% vs. 40-60% m t -m 0 Bjørn H. Samset Transverse dynamics at RHIC, March 2003

43. High pt, nuclear modification factor Bjørn H. Samset Transverse dynamics at RHIC, March 2003 Recap of  150  40-60% 55110-20% 7645-10% 9650-5%  N binary  cent. The lines show ratios of fits. Analysis by C. E. Jorgensen Numbers from nucl-ex/0206011

44. Calculating from m t spectra Bjørn H. Samset Transverse dynamics at RHIC, March 2003 We've fit our spectra with an m t exponential to extract the inverse slope. Using the fit functions for p t : we can extract the mean p t by integrating:

45. Analysis details 1: Track and event selection Bjørn H. Samset Transverse dynamics at RHIC, March 2003 ● All MRS 90 degree data set -> run4692 - run5983 -> BB, TPC, TOFW, BbVertex calibration ● No specific Trigger selection ● Centrality cut from latest calibration from DB ● Select Good MrsTracks ● Magnet Fiducial cut : 1cm (x,y) from edge ● Run-by-Run fitting - Diff(Vzdc-Vbb) : 4  cut - matching (Dang,Dy,Daly,Ty) : 3  cut

46. Analysis details 2: Acceptance maps Bjørn H. Samset Transverse dynamics at RHIC, March 2003 ● Flat distributions : p,  -> 10M at each setting -> -17.5cm < z <17.5cm,  z = 5cm ● New TPM2 geometry for 2001 data setting ● Selection : same as used in data -> remove bad TOFW slats -> Magnet Fiducial cut : 1cm (x,y) ● y-mt, y-pt map for , K, p -> Acceptance values below 4.5(5.5) are applied to data. (reduce edge effect)

47. Analysis details 3: Corrections Bjørn H. Samset Transverse dynamics at RHIC, March 2003 ● Track-by-Track corrections ● TPC efficiency : ~ 89%, 96% -> as a function of # of clusters ● TOFW : remove bad slats ● Corrections for particle species -> Multiple scattering :  p -> Decay correction : , K -> Absorption : pbar -> as a function of momentum

48. Bjørn H. Samset Transverse dynamics at RHIC, March 2003 @ Cent: 0-10%

49. Centrality dependence of charged particle production at midrapidity Bjørn H. Samset Transverse dynamics at RHIC, March 2003 – Analysis of total y~0 data set from Run-2 (Au-Au ) – Divided into centrality classes (0-10,10-20,20-40,40-60 %) as determined by Multiplicity detector (-2.2<  <2.2). – PID by Time-Of-Flight, 3 s cut with respect to our momentum and tof resolutions 1) Yields and from charged hadrons 2) Yields and from identified hadrons 3) Centrality and p t dependence of like and unlike particle ratios...and now for the data: