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RHIC Physics Through the Eyes of PHOBOS

Moriond, March 2003. RHIC Physics Through the Eyes of PHOBOS. Wit Busza MIT. Relativistic Heavy Ion Collider. Why Collide Heavy Ions?. From Frank Wilczek. time.  s NN = 130 GeV. Gold. Gold. UA1, 900 GeV. anti-proton. proton.

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RHIC Physics Through the Eyes of PHOBOS

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  1. Moriond, March 2003 RHIC Physics Through the Eyes of PHOBOS Wit Busza MIT

  2. Relativistic Heavy Ion Collider

  3. Why Collide Heavy Ions? From Frank Wilczek time

  4. sNN = 130 GeV Gold Gold UA1, 900 GeV anti-proton proton

  5. Goal of Relativistic Heavy Ion Physics is to Obtain a Better Understanding of the Solutions of the QCD Lagrangian: • QCD Phase Diagram • Properties of QGP • Mechanism of Particle Production • Structure and Interactions of Relativistic Hadrons & Nuclei

  6. What Are the Correct Variables When Looking at AA Collisions? Spectator Nucleons Participating Nucleons Npart= 7 Ncoll.= 10 Nquarks +gluons = ? Ninelastic= 1 In calculating Npart or Ncoll  taken to be nucleon-nucleon inelastic cross-section. A priori no reason for this choice other than that it seems to give a useful parameterization. Will the following be equivalent to the above?  inel ~ (R1+R2)2 ~ (A11/3 + A21/3)2 ~ A2/3 Npart ~ A2/3(A11/3+ A21/3) ~ A Ncoll ~ A2/3(A11/3 * A21/3) ~ A4/3

  7. pA multiplicities were found to be proportional to Npart Busza et al., PRL 41(1978).285

  8. In no rest frame is this picture correct In rest frame of one nucleus: Soft components overlap, “gluon saturation effects”, shadowing etc. In rest frame of the center of mass of the system: The use and relevance of Npart is far from obvious when the collision is viewed from different frames of reference

  9. Central Collisions 200 GeV 19.6 GeV 130 GeV PHOBOS PHOBOS PHOBOS dN d  Peripheral Collisions 1. Is there an interesting state created in high energy hadronic (in particular AA) collisions?

  10. Evidence that shortly after the collision a high energy density* is created Number of Particles Produced at y=0 Total energy released ~2000GeV Max. initial overlap volume Initially released energy density >5GeV/fm3 Note: energy density inside proton ≈ 0. 5GeV/fm3 Energy of Collision * Strictly speaking it is the energy released in the transverse direction per unit volume

  11. Evidence that at y≈0 this high energy density state has the quantum numbers of the vacuum A+A central collisions K–/K+ Ratio of antimatter to matter p/p Energy of collision

  12. Evidence for interactions with the created state Peripheral Au+Au data Central Au+Au data D. Hardtke QM ‘02 • Disappearance of back-to-back correlations in central Au+Au • Away-side particles absorbed or scattered in medium • Jets seen in peripheral Au+Au and p+p • Azimuthal correlations • Small angle (Df ~ 0) • Back-to-Back (Df ~ p)

  13. Evidence that the created state has a high pressure Phobos data for 130 and 200 GeV Azimuthal Angular Distributions Peripheral Central “head on” view of colliding nuclei Also, PHOBOS sees very few low Pt particles All this is direct evidence of collective effects

  14. Evidence that most of the action ends very quickly after the collision v 2 0<h<1.5 PHOBOS preliminary h+ + h- 200 GeV Au+Au Preliminary v2200 Final v2130 (top 55%) 17% scale error Elliptic Flow v2 PHOBOS Au+Au 200 GeV 130 GeV <Npart>~190 130 GeV result: nucl-ex/0205021, submitted to PRL h

  15. Evidence that the system may reach some kind of equilibriuim Event by Event Fluctuations NA49, PRL 86 (2001) 1965 NA49, Phys Lett B459 (1999) 679 From Gunther Roland/MIT

  16. Further evidence that it may be reaching statistical equilibrium Gene Van Buren. QM’02 Particle ratios compared to statistical model STAR Preliminary

  17. 2. There are remarkable similarities between e+e-, pp & AA collisions Is this evidence that dynamics are dominated by the initial state interactions?

  18. Collision viewed in rest frame of CM: Central Collisions 200 GeV 19.6 GeV 130 GeV PHOBOS PHOBOS PHOBOS dN d  Peripheral Collisions Collision viewed in rest frame of one nucleus: Limiting fragmentation

  19. h ISR data Proton+Antiproton Limiting fragmentation: 24 31 45 53 63 4 2-4 900 GeV 3 546 GeV 5-9 200 GeV 2 Total observed multiplicity 10-14 53 GeV 1 15-19 UA5 20-24 0 -4 -2 0 -6 h-ybeam W. Thome et al., Nucl. Phys. B129 (1977) 365.

  20. Amazing similarity of AA and e+e- e+e- Au+Au (preliminary) e+e- Number of Particles Produced Eskola, QM ’01 Energy of Collision From P. Steinberg Au+Au dN/dh||h|<1

  21. 3. Some results inconsistent with naïve expectations: Data inconsistent with the following picture: e.g. impact parameter dependence of the number of particles produced at the center of mass of the collision PHOBOS Au+Au 200 GeV PRC 65 (2002) 061901R Slow quark Fast quark 130 GeV 19.6 GeV preliminary Au+Au yields normalized to corresponding pp value for all three energies pp 200GeV 130GeV 19.6GeV (PRELIMINARY) pp Errors from Au+Au only

  22. Hadrons Hadrons q q q q Hadrons Hadrons Leading Particle Leading Particle 4. Direct study of the properties of the produced state “X-Ray” of Medium Using Jets Leading Particle Leading Particle

  23. Preliminary sNN = 200 GeV Preliminary sNN = 200 GeV Charged Hadron Spectra

  24. Submitted to Phys.Lett. AuAu 200GeV Particle Production at high Pt Fast quark Ncollscaling pA AuAu Ncollscaling Relative Yield per participant PHOBOS Cronin effect data

  25. “Quenching” of leading partons in pA collisions? Skupic et al. Eichten et al. Baron et al. W. Busza Nucl.Phys. A544 (1992) 49c

  26. Summary • pp, pA, AA collisions are magnificent laboratories for the study of QCD • No doubt a very high energy density creates a fascinating medium. If it equilibrates, it does so quickly. If it is the QGP, the transition is almost certainly a cross-over • Main difficulty in interpretation of data is the separation of the initial and final state interactions • Data continues to surprise us • Smoothness of data with energy • Jet quenching • Similarity of AA with e+ e- • Why approx. Nparticipant scaling, even at high Pt?

  27. Collaboration (Jan 2003) Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley, Richard Bindel, Andrzej Budzanowski, Wit Busza (Spokesperson), Alan Carroll, Patrick Decowski, Edmundo Garcia, Nigel George, Kristjan Gulbrandsen, Stephen Gushue, Clive Halliwell, Joshua Hamblen, George Heintzelman, Conor Henderson, David Hofman, Richard Hollis, Roman Holynski, Burt Holzman, Aneta Iordanova,Erik Johnson,Jay Kane, Judith Katzy, Nazim Khan, Wojtek Kucewicz, Piotr Kulinich, Chia Ming Kuo,Jang Woo Lee, Willis Lin, Steven Manly, Don McLeod, Jerzy Michalowski, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Louis Remsberg, Michael Reuter, Christof Roland, Gunther Roland, Leslie Rosenberg, Joe Sagerer, Pradeep Sarin, Pawel Sawicki, Wojtek Skulski, Stephen Steadman, Peter Steinberg, George Stephans, Marek Stodulski, Andrei Sukhanov, Jaw-Luen Tang, Ray Teng, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Gábor Veres, Robin Verdier, Bernard Wadsworth, Frank Wolfs, Barbara Wosiek, Krzysztof Wozniak, Alan Wuosmaa, Bolek Wyslouch ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

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