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First Results from the PHOBOS Experiment at RHIC :

Explore the First Results from the PHOBOS Experiment at RHIC, detailing the charged particle multiplicity near mid-rapidity in central Au+Au collisions at two different energies. This study sheds light on the physics goals of RHIC, such as creating high-energy density and studying the deconfinement phase transition. The analysis includes information on energy densities, nucleus-nucleus collisions, and detector setups, offering valuable insights into the scattering processes involved. Stay informed on the latest developments in this field based on the research conducted by the DPF2000 Collaboration.

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First Results from the PHOBOS Experiment at RHIC :

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  1. First Results fromthe PHOBOS Experiment at RHIC: Charged Particle Multiplicity Near Mid-Rapidity in Central Au+Au Collisions at s=56 and 130 AGeV Judith Katzy, MIT Judith Katzy DPF2000

  2. PHOBOS Collaboration ARGONNE NATIONAL LABORATORY Birger Back, Nigel George, Alan Wuosmaa BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Mathew Ceglia, Alan Carroll, Stephen Gushue, George Heintzelman, Hobie Kraner ,Robert Pak,Louis Remsberg, Joseph Scaduto, Peter Steinberg, Andrei Sukhanov INSTITUTE OF NUCLEAR PHYSICS, KRAKOW Wojciech Bogucki, Andrzej Budzanowski, Tomir Coghen, Bojdan Dabrowski, Marian Despet, Kazimierz Galuszka, Jan Godlewski , Jerzy Halik, Roman Holynski, W. Kita, Jerzy Kotula, Marian Lemler, Jozef Ligocki, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki , Andrzej Straczek, Marek Stodulski, Mieczylsaw Strek, Z. Stopa, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak, Pawel Zychowski JAGELLONIAN UNIVERSITY, KRAKOW Andrzej Bialas, Wieslaw Czyz, Kacper Zalewski MASSACHUSETTS INSTITUTE OF TECHNOLOGY Wit Busza*, Patrick Decowski, Piotr Fita, J. Fitch, C. Gomes, Kristjan Gulbrandsen, P. Haridas, Conor Henderson, Jay Kane , Judith Katzy , Piotr Kulinich, Clyde Law, Johannes Muelmenstaedt, Marjory Neal, P. Patel, Heinz Pernegger, Miro Plesko, Corey Reed, Christof Roland, Gunther Roland, Dale Ross, Leslie Rosenberg, John Ryan, Pradeep Sarin, Stephen Steadman, George Stephans, Katarzyna Surowiecka, Gerrit van Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch NATIONAL CENTRAL UNIVERSITY, TAIWAN Yuan-Hann Chang, Augustine Chen, Willis Lin, JawLuen Tang UNIVERSITY OF ROCHESTER A. Hayes, Erik Johnson, Steven Manly, Robert Pak, Inkyu Park, Wojtech Skulski, Teng, Frank Wolfs UNIVERSITY OF ILLINOIS AT CHICAGO Russell Betts, Christopher Conner, Clive Halliwell, Rudi Ganz, Richard Hollis, Burt Holzman,, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter UNIVERSITY OF MARYLAND Richard Baum, Richard Bindel, Jing Shea, Edmundo Garcia-Solis, Alice Mignerey Judith Katzy DPF2000

  3. Relativistic Heavy Ion Collider 13 June: 1st Phobos AuAu Collisions @ s = 56 AGeV 24 June: 1st Phobos AuAu Collisions @ s = 130 AGeV 2001: AuAu Collisions @ s = 200 AGeV species: pp , AuAu energies: 30-200AGeV Judith Katzy DPF2000

  4. RHIC physics goal Create high energy density over a large volume quark gluon plasma deconfinement phase transition chiral symmetry restoration Study QCD Judith Katzy DPF2000

  5. Nucleus - Nucleus Collisions - the scattering process Hadronic scattering via p, r, w exchange AGS: s = 4.8 GeV SPS: s = 17 GeV Partonic scattering via gluon exchange? Rescattering? Minijets? RHIC: s = 53-200 GeV d N/ dh is sensitive to the scattering process (hard vs soft) Judith Katzy DPF2000

  6. Energy density in Au Au Collisions Spectator nucleons Produced (primary) particles Energy density? Participating nucleons d N d N y = 1/2 * ln( E+pL/E-pL) h = - ln (tan q/2 ) e ~ ~ d y d h Judith Katzy DPF2000

  7. PHOBOS Detector 1m Judith Katzy DPF2000

  8. Commissioning run set-up Judith Katzy DPF2000

  9. x z PHOBOS Trigger Positive Paddles Negative Paddles ZDC N ZDC P Au Au PN PP Judith Katzy DPF2000 First Collisions: June 13

  10. Examples of events Hits in SPEC Tracks in SPEC Hits in VTX 130 AGeV 130 AGeV 56 AGeV Judith Katzy DPF2000

  11. Monte Carlo Simulations generator: HIJING 1.35 simulations: Geant 3.21 Silicon Detector Response Very good under- standing of detector response Judith Katzy DPF2000

  12. Centrality Determination Data 6% 6% events with highest signal in paddle counters corresponds to 6% most central events of inelastic cross section Judith Katzy DPF2000

  13. Inelastic cross section from spectator neutrons (not in scale) ZDC B ZDC B 18 m Forward ns • Confirms • centrality measurement • paddle counter acceptance • for periphal collisions 130 AGeV Multiplicity Judith Katzy DPF2000

  14. Select 6% most central events based on paddles gives Extracting Npart MC Events/bin b Npart Npart Judith Katzy DPF2000

  15. z x Vertex Distribution Y X X Z Z Fiducial volume -25cm < Z < 15 cm Judith Katzy DPF2000

  16. Event Statistics • 56 AGeV • Collision Events : 6352 • Central Events : 382 • Central Events (–25 < z < 15) : 103 • 130 AGeV • Collision Events : 12074 • Central Events : 724 • Central Events (–25 < z < 15) : 151 Judith Katzy DPF2000

  17. Tracklets Reconstruction y z z • Two hit combinations that point to the vertex • Vertex tracklets dh<0.1, dh = h2 - h2, , • Spectrometer tracklets dR<0.02 , dR =  (dh2 – df2) • Redundancy essentially eliminates feed-down, secondaries, random noise hits x Judith Katzy DPF2000

  18. Uncorrected dN/dh Spectrometer Vertex 130 GeV 56 GeV • Final result extracted by integrating over Z Judith Katzy DPF2000

  19. 56 AGeV 130 AGeV dN/dh | |h|<1 408±12(stat) ±30(syst) 555±12(stat) ±35(syst) dN/dh | |h|<1 per participant pair 2.47±0.10±0.25 3.24±0.10±0.25 Ratio of density per participant pair 1.31±0.04±0.05 Final Results for dN/dh Judith Katzy DPF2000

  20. Comparisons with SPS and pp Submitted for publication • dN/dh obtained at RHIC is 70 % higher then at SPS • => increase of energy density by 70% • dN/dh per participating nucleon obtained in AuAu significantly • higher then in pp collisions • => AuAu collisions differ from simple superposition of pp Judith Katzy DPF2000

  21. Vertex magnet octagon The Central region of PHOBOS • Reconstruct charged particle multiplicity • in |h| < 5.5 over 4p event by event • search for events with high multiplicity (e.g.excess of entropy in QGP) • search for fluctuations (e.g. dcc) Judith Katzy DPF2000

  22. Bfield region 1 arm of the spectormeter • Spectrometer: • measure pt spectrum down to very low momentum • ->sensitive to collective phenomena over large volumes and DCC • reconstruct size of volume with high energy density and lifetime (HBT) • -> excess of entropy • reconstruct f mass and width -> look for unusual medium effects Judith Katzy DPF2000

  23. Status of PHOBOS Complete Detector Installed July 5 - 13 25000 Collisions Recorded at 130 AGeV more to come during August 2000 Judith Katzy DPF2000

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