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Ramiro Debbe Physics Department Brookhaven National Laboratory

RECENT RESULTS FROM BRAHMS CIPANP 2003 New York May 2003. Ramiro Debbe Physics Department Brookhaven National Laboratory. Introduction. We report comprehensive results of our analysis of the 200 GeV Au-Au data. This work concentrates on the 5% most central events .

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Ramiro Debbe Physics Department Brookhaven National Laboratory

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  1. RECENT RESULTS FROM BRAHMS CIPANP 2003 New York May 2003 Ramiro Debbe Physics Department Brookhaven National Laboratory R. Debbe CIPANP 2003

  2. Introduction We report comprehensive results of our analysis of the 200 GeV Au-Au data. This work concentrates on the 5% most central events. This work is based on the PhD theses of two NBI students: Djamel Ouerdane and Peter Christiansen All results presented today are PRELIMINARY. R. Debbe CIPANP 2003

  3. Introduction cont. BRAHMS is one of the five RHIC experiments. BRAHMS is designed to study the bulk properties of the collisions. We measure charged particle production in a wide rapidity range and transverse momenta extending up to ~5 GeV/c. These measurements are done with two conventional spectrometers with small acceptance. We put special emphasis on our Particle Identification capabilities with a combination of Time of Flight and Čerenkovdetectors. R. Debbe CIPANP 2003

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  5. BRAHMS Coverage R. Debbe CIPANP 2003

  6. H1 & C1 TOFW C1 π threshold RICH Particle Identification Mid-rapidity Spectrometer Forward Spectrometer R. Debbe CIPANP 2003

  7. d2n/pTdpT=A(p0+pT)-n R. Debbe CIPANP 2003

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  12. Mean Transverse momentum P K  R. Debbe CIPANP 2003

  13. Net Charge as function of y The net charge is fitted to : A cosh(y/b) D. Kharzeev PLB378(96)238 2=7.4/6 A = 8.5 0.3 b = 2.4 0.1 Total number of protons in y range: -3, 3 R. Debbe CIPANP 2003

  14. K+p/pion Y = 0 R. Debbe CIPANP 2003

  15. Anti-proton/pion at y=0 R. Debbe CIPANP 2003

  16. K+P/ at y=3 R. Debbe CIPANP 2003

  17. Anti-proton/pion at y~3 R. Debbe CIPANP 2003

  18. R. Debbe CIPANP 2003

  19. RHIC data is “far” from the “resonance gas” ; the contribution of rescattering to the shape of distributions is small. Transverse flow is the dominant feature R. Debbe CIPANP 2003

  20. Thermal source with transverse flow Distributions of particles are assimilated to the counting of particles traversing a hyper-surface  beyond which the system decouples A change to a Boltzman distrib. Integration over y and phi produce the following function: Changing to a Boltzman distrib. And integrating over y and  produces the following function to fit the measured spectra. (T = tanh) R. Debbe CIPANP 2003

  21. Transverse flow at y=0 • pions • kaons • proton 2/NDF = 6.7 T = 0.53 T = 138. MeV Fits + -K+ P Pbar. Errors are statistical R. Debbe CIPANP 2003

  22. Transverse flow at y~1 2/NDF = 6.6 T = 0.57 T = 115 MeV R. Debbe CIPANP 2003

  23. Transverse flow at y~2 2/NDF = 56/30 T = 0.47 T = 135. MeV R. Debbe CIPANP 2003

  24. Transverse flow at y~3 2/NDF = 1.2 T = 0.42 T = 140 MeV R. Debbe CIPANP 2003

  25. Transverse flow at y=3 The presence of transverse flow in the system is most evident in the shape of the proton distribution. Even though a fit to a thermal source with transverse flow does not fail, the comparison to the distribution at y=0 supports the assertion that transverse flow is much reduced at y=3. R. Debbe CIPANP 2003

  26. Summary • BRAHMS measurements in a range of up to 2 units of rapidity around 0, are consistent with a thermalized system that exhibits strong transverse flow (≥0.5). • Hadronization at RHIC happens when the system is dilute. Secondary interaction (pion wind ) are not the main contributors to the shape of the distributions. • Transverse flow is reduced at y~3. R. Debbe CIPANP 2003

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