Energy and Centrality Dependence of MidRapidity Charged Particle

Energy and Centrality Dependence of Mid-Rapidity Charged Particle Multiplicity Measured with Aneta Iordanova University of Illinois at Chicago DNP 02

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

• 4 p Multiplicity Array Octagon, Vertex and Ring Counters • Mid-rapidity Spectrometer • TOF wall for high momentum PID • Triggering Scintillator Paddle Counters Zero Degree Calorimeter (ZDC) Čerenkov Counters DNP 02 Aneta Iordanova

Vertex Detector 8192 silicon channels • Outer Layer: 2 × 2048 channels, 0. 47 mm × 24. 1 mm • Inner Layer: 2 × 2048 channels, 0. 47 mm × 12. 0 mm Y 1 channel X Top f Beam pipe Z, h Bottom 50. 4 mm 62. 1 mm Used for • reconstruction of collision location (“vertex”) • multiplicity measurement DNP 02 Aneta Iordanova

Tracklet Two-hit combinations from Outer and Inner Vertex (Top or Bottom), pointing to the reconstructed vertex. Outer Layer hit Inner Layer Top Vertex Reconstructed Vertex DNP 02 Aneta Iordanova

Tracklet Reconstruction First Pass f. Search , h. Search Layer • |df| = |f. Search – f. Seed| < 0. 3 • |dh| =|h. Search – h. Seed| < 0. 1 • smallest dh combination. dh < 0. 1 Extrapolate f. Seed , h. Seed hit Seed Layer Top Vertex Reconstructed Vertex Second Pass Tracklets with a common hit in the “Search Layer” • smallest |dh| combination. DNP 02 Aneta Iordanova

Multiplicity Determination using Vertex detector Combinatorial Background Efficiency Correction Factor DNP 02 Aneta Iordanova

Efficiency Correction Factor (a) (from Monte Carlo) a depends on: • Azimuthal acceptance of detector • Z vertex position • Multiplicity in detector (hits) a ~ 0. 4 (Z=0 cm) to 0. 25 (Z=10 cm) Top f Outer Layer Inner Layer Nominal vertex position Bottom Inner Layer Outer Layer DNP 02 Aneta Iordanova

Efficiency Correction Factor for three different Zvertex positions 19. 6 Ge. V a DNP 02 Aneta Iordanova

Combinatorial Background Tracklets (b) Tracklets from hits by rotating Inner layers 1800 about the beam pipe. f Beam pipe Z, h Nbackground_tracklets = b Nreconstructed_tracklets T R U E DNP 02 Aneta Iordanova

Background Tracklets for 80 to 100 Hits in Outer Vertex Layer 19. 6 Ge. V Data Counts Monte Carlo dh dh b = 0. 76 DNP 02 Aneta Iordanova

Scaled charged-particle multiplicity as a function of Npart for Au+Au collisions 200 Ge. V 130 Ge. V |h|<1 19. 6 Ge. V PRELIMINARY DNP 02 Aneta Iordanova

Scaled charged-particle multiplicity as a function of Npart for Au+Au collisions (Two component fit) 200 Ge. V 130 Ge. V |h|<1 19. 6 Ge. V PRELIMINARY DNP 02 Aneta Iordanova

Scaled charged-particle multiplicity as a function of Npart for Au+Au collisions (Normalized by the corresponding pp value for each energy) |h|<1 200 Ge. V 130 Ge. V 19. 6 Ge. V PRELIMINARY Errors from Au+Au only DNP 02 Aneta Iordanova

Scaled charged-particle multiplicity as a function of Npart for Au+Au collisions (KLN saturation model) 200 Ge. V 130 Ge. V |h|<1 19. 6 Ge. V PRELIMINARY DNP 02 Aneta Iordanova

Comparison of central charged-particle multiplicity for different energies. PRELIMINARY PHOBOS 19. 6 Ge. V DNP 02 Aneta Iordanova

Conclusion • Phobos has measured charged-particle multiplicity dependence on centrality and energy in Au-Au collisions at √s. NN of 200, 130 and 19. 6 Ge. V. • The mid-rapidity scaled charged-particle multiplicity shows evidence for deviation from Npart scaling over the studied centrality range. • The mid-rapidity scaled charged-particle multiplicity dependence on energy follows the logarithmic rise. DNP 02 Aneta Iordanova