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, the Early Years

, the Early Years. Presented in the spirit(s) of Charles Dickens:. The Ghost of Past What was built and why The Ghost of Present What has been accomplished The Ghost of Future What is still to come. Collaboration (Jan 2002).

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, the Early Years

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  1. , the Early Years Presented in the spirit(s) of Charles Dickens: • The Ghost of Past • What was built and why • The Ghost of Present • What has been accomplished • The Ghost of Future • What is still to come G.S.F.Stephans Epiphany 2002

  2. Collaboration (Jan 2002) ARGONNE NATIONAL LABORATORYBirger Back, Alan Wuosmaa BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Alan Carroll, Joel Corbo, Nigel George, Stephen Gushue, Dale Hicks, Burt Holzman, Robert Pak, Marc Rafelski, Louis Remsberg, Peter Steinberg, Andrei Sukhanov INSTITUTE OF NUCLEAR PHYSICS, KRAKOWAndrzej Budzanowski, Roman Holynski, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak MASSACHUSETTS INSTITUTE OF TECHNOLOGYWit Busza (Spokesperson), Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane, Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, Michel Rbeiz, Corey Reed, Christof Roland, Gunther Roland, Leslie Rosenberg, Pradeep Sarin, Stephen Steadman, George Stephans, Gerrit van Nieuwenhuizen, Carla Vale, Robin Verdier, Bernard Wadsworth, Bolek Wyslouch NATIONAL CENTRAL UNIVERSITY, TAIWANChia Ming Kuo, Willis Lin, Jaw-Luen Tang UNIVERSITY OF ROCHESTERJoshua Hamblen , Erik Johnson, Nazim Khan, Steven Manly,Inkyu Park, Wojtek Skulski, Ray Teng, Frank Wolfs UNIVERSITY OF ILLINOIS AT CHICAGORussell Betts, Edmundo Garcia, Clive Halliwell, David Hofman, Richard Hollis, Aneta Iordanova, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter, Joe Sagerer UNIVERSITY OF MARYLANDAbigail Bickley, Richard Bindel, Alice Mignerey G.S.F.Stephans Epiphany 2002

  3. Goals of , • Measure numerous observables quickly & accurately • Perform several unique measurements • Large multiplicity phase space coverage • Particle measurements extended to low p^ • Large event sample • Eliminate the word “preliminary” from relativistic heavy ion vocabulary • Good (to be)published data: Thanks to the collaboration • Wild physics speculation: Blame GSFS G.S.F.Stephans Epiphany 2002

  4. Detectors used by , • Multiplicity array (Si sensors) • Almost 4p coverage and high granularity • 2 Arm Spectrometer (Si sensors) • 2 Tesla magnetic field • PID using dE/dx • Time-of-Flight wall for extended PID • Trigger counters (Scintillator Paddles & Cherenkov T0) • ZDCs common to all RHIC experiments G.S.F.Stephans Epiphany 2002

  5. Frodo (to scale) G.S.F.Stephans Epiphany 2002

  6. Spectrometer The 42-ton monster Spectrometer module Trigger paddles All held together by excellent engineering! ~4p Multiplicity array G.S.F.Stephans Epiphany 2002

  7. Detector Performance I Detectors signals stable and well understood G.S.F.Stephans Epiphany 2002

  8. Detector Performance II ~137,000 total Si channels 15 Excellent signal/noise Before RHIC blasts Very few dead channels (even after RHIC assault) 10% G.S.F.Stephans Epiphany 2002

  9. x z Events Dt (ns) Triggering on Interactions Positive Paddles Negative Paddles ZDC N ZDC P Au Au PN PP Valid Collision 3<|h|<4.5 G.S.F.Stephans Epiphany 2002

  10. Determining Centrality of Interaction For more discussion, see later talk by Andrzej Olszewski… Data • HIJING +GEANT • Glauber calculation • Model of paddle trigger Paddle signal Data+MC Nparticipants G.S.F.Stephans Epiphany 2002

  11. Multiplicity Measurements • Unrivaled phase space coverage • High granularity in f and h • Low mass detectors situated very close to the beam pipe • Multiple detectors and/or independent analysis methods for the same observable • MC and data combined for a very detailed understanding of systematics G.S.F.Stephans Epiphany 2002

  12. f h Octagon&Ring hits +5.4 -5.4 Single-event display Vertex tracklets G.S.F.Stephans Epiphany 2002

  13. Energy Dependence of Central Multiplicity |h|£16% most central AA collisions Phys Rev Lett 85, 3100 (2000) & 88, 22302 (2002) G.S.F.Stephans Epiphany 2002

  14. Centrality Dependence I dNch/dh /<Npart>/2 |h|£1 AuAu Kharzeev/Nardi HIJING: PRL 86, 3496 (2001) EKRT: hep-ph/0106330 KN scaling PLB 507,121 (2001) nucl-ex/0105011 Accepted: Phys Rev C G.S.F.Stephans Epiphany 2002

  15. Centrality Dependence II |h|£1 AuAu See: Kharzeev and Levin, Phys. Lett. B523, 79 (2001) To be submitted to PRL G.S.F.Stephans Epiphany 2002

  16. (mini)jet (mini)jet Soft Scattering Two Component Parameterization “soft” “hard” xis the fraction of particles produced by hard scattering At RHIC:npp~2.3, x~10% Hard Scattering G.S.F.Stephans Epiphany 2002

  17. Two Component Parameterization For Symmetric systems, colliding pairs: From geometry, the number of collisions: where n is the average number of binary collisions In old language: • Ratio to pp is a mix of nuclear geometry and the fraction of hard scattering Note: Asymmetric systems (pAu, SiAu, etc.) will have different ratios between NColl and NPart G.S.F.Stephans Epiphany 2002

  18. Model Comments • Fit of AuAu centrality data to two component parameterization extrapolates very close to pp data. • Underlying physics of two-component model and saturation model are very different! • Hopefully, further study (as well as other systems including pA) will help to differentiate the two. • Note: Several different ‘saturation’ calculations agree that gluon densities are “large” on the QCD scale. G.S.F.Stephans Epiphany 2002

  19. 2-Component Energy Prediction ~20 at LHC dN/dh~3500 G.S.F.Stephans Epiphany 2002

  20. Peripheral Central Shapes I 130 GeV AuAu Data PRL 87, 102303 (2001) Distributions get narrower for more central collisions. Full dN/dh distribution yields the total number of charged particles. For 3% most central <Nch> = 4200  470 G.S.F.Stephans Epiphany 2002

  21. Shapes II 130 GeV PRL 87,102303 (2001) Note crossover G.S.F.Stephans Epiphany 2002

  22. Shapes III PHOBOS 2000/2001 UA5: Alner et al., Z. Phys. C33,1 (1986) 7-10% syst error Fragmentation Fragmentation 200 GeV shape from Phys Rev Lett 88, 22302 (2002) G.S.F.Stephans Epiphany 2002

  23. Multiplicity Conclusions (so far) • Whatever measure or model is used, systems being created are dense & denser. • Extensive results on energy, centrality, and rapidity dependence • Data have significant impact on theory • Initial conditions and subsequent evolution • Global properties and fundamental interactions • Rules out or severely restricts many proposed exotic processes • Much more to come… G.S.F.Stephans Epiphany 2002

  24. Charged Multiplicity Future • Soon: 20 GeV AuAu (RHIC injection energy, run in November specifically for Phobos) and 200 GeV pp (currently running) • Later: More details, fluctuations, event shape… • Next Run: More species and energies G.S.F.Stephans Epiphany 2002

  25. Observation: Centrality data at both beam energies rise for the most central events (systematics? physics? mean p?) |h|£1 AuAu G.S.F.Stephans Epiphany 2002

  26. 70 cm 10 cm z -x y Spectrometer Magnetic Field G.S.F.Stephans Epiphany 2002

  27. Spectrometer Characteristics Momentum resolution 2% Particle ID using dE/dx d 10 GeV p K p dE/dx resolution »7% G.S.F.Stephans Epiphany 2002

  28. Spectrometer I: Chemistry 130 GeV Data Phys.Rev.Lett. 87, 102301 (2001) Stat.Syst. Using model of Redlich (QM ’01) T~165 implies mB=45±5 G.S.F.Stephans Epiphany 2002

  29. p/p vs Energy Particle Ratios @ 130 GeV K-/K+ vs Energy Phys Rev Lett 87, 102301 (2001) G.S.F.Stephans Epiphany 2002

  30. F E D C B A X[cm] Beam pipe Z[cm] Spectrometer II: Stopping ParticlesThe Ultimate in Low p^ For tracks stopping in the 5th Si layer: pp 50 MeV/c pK  140 MeV/c pp  200 MeV/c Note: At low p, particles are at y~0 for any angle G.S.F.Stephans Epiphany 2002

  31. dE/dx from p in Individual Layers 0 2 High signals from nuclear fragmentation can identifyp- 20 0 G.S.F.Stephans Epiphany 2002

  32. P K p Eloss Mp MC Results Eloss = (ΣdEi )/nhits, i=A-E Mi = (dE/dx)i * Ei (~1/2) (m2) G.S.F.Stephans Epiphany 2002

  33. Spectrometer Future • Soon: Particle ratios from 200 GeV AuAu • Later: • Spectra (with and without PID) • Extended PID • Low and high p^ • HBT • Beyond: Reaction plane, resonances (especially f at low p^), and much more… G.S.F.Stephans Epiphany 2002

  34. Future for , • Eagerly awaiting more beam energies and beam species (including pA) for systematic study • Continue the program discussed as well as many additional physics topics (flow…) • Far Future: Considering addition of electron identification to study charm production G.S.F.Stephans Epiphany 2002

  35. EM-Calorimeter Transition Radiation Detector Micro-Vertex One Possible Charming Future… Discussing upgrade to focus on charm production at RHIC. Measure single electrons from displaced vertices. Use existing spectrometer • Add • ALICE prototype TRD Electron-ID • EM-Calorimeter • Micro-Vertex Detector G.S.F.Stephans Epiphany 2002

  36. Conclusion • Early results have proven more robust and more interesting than (I) expected. • Detector (and analysis teams) have performed spectacularly. • Bright prospects for productive years ahead. • An even Happier 2002! G.S.F.Stephans Epiphany 2002

  37. For More Information… • PHOBOS web-site: www.phobos.bnl.gov • Physics Results • Charged particle multiplicity near mid-rapidity in central Au+Au collisions at 56 and 130 GeV Phys. Rev. Lett. 85, 3100 (2000) • Ratios of charged antiparticles-to-particles near mid-rapidity in Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102301 (2001) • Charged-particle pseudorapidity density distributions from Au+Au collisions at 130 GeV Phys. Rev. Lett. 87, 102303 (2001)  • Energy dependence of particle multiplicities in central Au+Au collisions Phys. Rev. Lett. 88, 22302 (2002) • Centrality Dependence of Charged Particle Multiplicity at h=0 in Au+Au Collisions at 130 GeV Accepted to Phys. Rev. C (December 2001); nucl-ex/0105011 Technical • Array of Scintillator Counters for PHOBOS at RHICNucl. Instr. Meth. A474, 38-45 (2001) • Silicon Pad Detectors for the PHOBOS Experiment at RHICNucl. Instr. Meth. A461, 143-149 (2001) • Development of a double metal, AC-coupled silicon pad detectorThe silicon detector for the PHOBOS experiment at RHICNucl. Instr. Meth. A389, 415 (1997) G.S.F.Stephans Epiphany 2002

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