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Charged-particle dN/d h from PHOBOS

Charged-particle dN/d h from PHOBOS. A. H. Wuosmaa (Argonne National Laboratory) for the PHOBOS Collaboration. Quark Matter 2001. The PHOBOS Collaboration. ARGONNE NATIONAL LABORATORY Birger Back, Nigel George, Alan Wuosmaa BROOKHAVEN NATIONAL LABORATORY

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Charged-particle dN/d h from PHOBOS

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  1. Charged-particle dN/dh from PHOBOS A. H. Wuosmaa (Argonne National Laboratory) for the PHOBOS Collaboration Quark Matter 2001

  2. The PHOBOS Collaboration ARGONNE NATIONAL LABORATORY Birger Back, Nigel George, Alan Wuosmaa BROOKHAVEN NATIONAL LABORATORY Mark Baker, Donald Barton, Alan Carroll, Stephen Gushue, George Heintzelman, Robert Pak, Louis Remsberg, Peter Steinberg, Andrei Sukhanov INSTITUTE OF NUCLEAR PHYSICS, KRAKOW Andrzej Budzanowski, Roman Holynski,, Jerzy Michalowski, Andrzej Olszewski, Pawel Sawicki , Marek Stodulski, Adam Trzupek, Barbara Wosiek, Krzysztof Wozniak MASSACHUSETTS INSTITUTE OF TECHNOLOGY Wit Busza* , Patrick Decowski, Kristjan Gulbrandsen, Conor Henderson, Jay Kane , Judith Katzy, Piotr Kulinich, Johannes Muelmenstaedt, Heinz Pernegger, 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, TAIWAN Willis Lin, JawLuen Tang UNIVERSITY OF ROCHESTER Erik Johnson, Josh Hamblen, Nazim Khan, Steven Manly, Inkyu Park, Wojtek Skulski, R. Teng, Frank Wolfs UNIVERSITY OF ILLINOIS AT CHICAGO Russell Betts, Clive Halliwell, David Hofman, Burt Holzman, Wojtek Kucewicz, Don McLeod, Rachid Nouicer, Michael Reuter UNIVERSITY OF MARYLAND Richard Bindel, Edmundo Garcia-Solis, Alice Mignerey *spokesperson

  3. Why study dNch/dh ? • dNch/dhis sensitive to all aspects of charged-particle production in heavy-ion collisions: • Interplay between hard and soft processes • Effects of shadowing, jet quenching • Reaction dynamics, re-scattering • Full distribution reflects a time integral of particle production throughout the collision and total entropy production • Lots of existing data for pp, pA, AB,AA • How do RHIC data fit into this picture?

  4. Charged-particle Multiplicity in Au-Au at RHIC Energies Influence of various physical effects on dNch/dh in very central collisions: (Wang & Gyulassy, Private communication)

  5. The PHOBOS Detector Octagon Multiplicity Detector All multiplicity detectors are silicon pad sensors Ring Multiplicity Detectors

  6. 5 4 3 2 1 0 1 2 3 4 5 5m 2m 1m Coverage of multiplicity detectors in h Schematic Multiplicity Detector h coverage for vertex at Z=0. h

  7. PHOBOS Multiplicity detectors Octagon 1 of 6 Rings

  8. What I will not discuss: • Event Selection • Vertex Determination • Centrality Determination • See Talks by: • R. Pak, Tuesday 3:20 • J. Katzy, Wednesday 4:40 • And see Poster by: • P. Decowski

  9. Count hits binned in h, centrality (b) Calculate acceptance A(ZVTX)for that event Find the occupancy per hit pad O(h,b) Fold in a background correction factor fB(h,b) DE deposition in multiplicity detectors for 1 event. f h dNch O(h,b) ×fB(h,b) Shits = dh A(ZVTX)

  10. “Measuring” the occupancy Method: Assume Poisson statistics 0-3% Octagon (central) Rings Ntracks/hit pad 50-55% (peripheral) h N=number of tracks/pad m =mean number of tracks/pad The numbers of empty, and occupied, pads determine the occupancy as a function of h,b

  11. 12 12 DE (“MIP”) 8 8 4 4 0 0 6 6 0 0 -6 -6 -4 -4 2 2 4 4 -2 -2 Discriminating background with DE Monte Carlo Data DE (“MIP”) h h Not from vertex Si From vertex DE vs. h in the Octagon

  12. 1.0 0.8 0.6 0.4 0.2 -6 -6 -4 -4 -2 -2 0 0 2 2 4 4 6 6 MC, Occupancy corrected Estimating remaining backgrounds 600 dNch/dh 400 MC “truth” fB=MCTruth/MCOcc 200 h Compare PHOBOS Monte Carlo “data” analyzed using occupancy corrections to “truth” - the difference gives corrections for remaining background. fB(h,b) h

  13. Octagon Rings dNch/dh for different centrality bins dNch/dh 45-55% 35-45% 25-35% dNch/dh 15-25% 6-15% 0-6% h h h Statistical Unc. only PHOBOS Prelim.

  14. PHOBOS Prelim. Centrality Dependence of Nch(|h|<5.4) HIJING Nch(|h|<5.4) Npart ±10% Systematic Uncertainty

  15. PHOBOS Prelim. Shapes of dNch/dh for different Npart %s Mean Npart 0-3 Data HIJING 354 15-20 216 35-40 102 dNch/dh dNch/dh Data HIJING (dNch/dh)/(½Npart) (dNch/dh)/(½Npart) h h Systematic error ±(10%-20%)

  16. Centrality dependence of dNch/dh|h PHOBOS Prelim. Solid lines: HIJING Symbols: Errors are systematic |h| <1 2-2.4 (dNch/dh)/(½Npart) 3-3.4 4-4.4 5-5.4 Npart

  17. Summary • First multiplicity distributions over 4p now available at for wide range of impact parameters • Nch(|h|<5.4)=4100±410 for the 3% most central collisions • Distributions are somewhat wider than predicted by some models • (dNch/dh)/(½Npart) in fragmentation region drops by ~½ from Npart=100 to 350 • Outlook: coming analyses: EbyE, d2N/dhdf (I. Park, Wed. 5:55)

  18. “The appetizers were truly delightful, and I am anxiously looking forward to the main course” -N. Khrushchev Or - We can’t wait for 200 GeV!

  19. Backup slides to follow:

  20. Data Monte Carlo Data and Monte Carlo Comparison of DE measured in the Octagon at |h|~3.0, with spectrum predicted by Monte-Carlo: Conclusion: MC is a good predictor of background.

  21. (dNch/dh)/(½Npart) h

  22. 1hit oct rings 2hits Counts 3hits Ntracks/hit pad 1 2 3 DE (MIPs) h Occupancy reality check Backup Method: Study DE spectra Can determine from DE relative yields of events with 1,2,3… hits/pad: gives independent measurement of Occupancy Good: fewer potentially unjustified assumptions Bad: Fitting procedure somewhat unstable, occasional large errors Very Good: We get the same answer in the end!!

  23. Comparison of all methods at mid rapidity MULT ARRAY

  24. 24 45 31 53 63 2-4 5-9 10-14 Total observed multiplicity 15-19 20-24 pp data from ISR W. Thome et al., Nucl. Phys. B129 (1977) 365. h

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