Update on flow studies with PHOBOS S. Manly University of Rochester Representing the PHOBOS collaboration Flow Workshop BNL, November 2003

The Phobos Collaboration Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Bruce Becker, Russell Betts, Abigail Bickley, Richard Bindel, Andrzej Budzanowski, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski, Edmundo Garcia, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Stephen Gushue, Clive Halliwell, Joshua Hamblen, Adam Harrington, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Erik Johnson, Jay Kane, Nazim Khan, Piotr Kulinich, Chia Ming Kuo, Willis Lin, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Inkyu Park, Heinz Pernegger, Corey Reed, Michael Ricci, Christof Roland, Gunther Roland, Joe Sagerer, Iouri Sedykh, Wojtek Skulski, Chadd Smith, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale, Siarhei Vaurynovich, Robin Verdier, Gábor Veres, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Wožniak, Alan Wuosmaa, Bolek Wysłouch, Jinlong Zhang ARGONNE NATIONAL LABORATORYBROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS, KRAKOWMASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWANUNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLANDUNIVERSITY OF ROCHESTER

Flow in PHOBOS

  coverage  Data at 19.6, 130 and 200 GeV 1m 2m 5m  coverage for vtx at z=0

 Pixelized detector Hit saturation, grows with occupancy Sensitivity to flow reduced Can correct using analogue energy deposition –or- measure of occupied and unoccupied pads in local region assuming Poisson statistics Poisson occupancy correction

Poisson occupancy weighting

Acceptance (phase space) weighting Octagonal detector Require circular symmetry for equal phase space per pixel Pixel’s azimuthal phase space coverage depends on location Relative phase space weight in annular rings = -1

 z Dilutes the flow signal  Remove Background  Estimate from MC and correct flow signal Non-flow background +  Non-flow Backgrounds

Background suppression Works well in Octagon  dE (keV) cosh  Background! Technique does not work in rings because angle of incidence is ~90  Beampipe Detector Demand energy deposition be consistent with angle

  RingsN OctagonRingsP Spec holes Vtx holes

Determining the collision point High Resolution extrapolate spectrometer tracks Low Resolution octagon hit density peaks at vertex z position

  RingsN OctagonRingsP Spec holes Vtx holes Detector symmetry issues where SPEC vertex efficiency highest Most data taken with trigger in place to enhance tracking efficiency

Strategies:  Avoid the holes – Offset vtx method PHOBOS flow analyses based on subevent technique Poskanzer and Voloshin, Phys. Rev. C58 (1998) Azimuthal symmetry is critical  Use the holes – Full acceptance method  Use a different type of analysis, such as cumulants Track-based analysis: Avoids holes for reaction plane determination Uses tracks passing into spectrometer Hit-based analyses

  RingsN Octagon RingsP Offset vtx method Limited vertex range along z Subevents for reaction plane evaluation  Good azimuthal symmetry  Fewer events, no 19.6 GeV data  Gap between subevents relatively small Technique used for published 130 GeV data

  RingsN OctagonRingsP Full acceptance method Vertex range -10<z<10 Subevents for reaction plane evaluation vary with analysis  Good statistics, 19.6 GeV data in hand  Gap between subevents large  Requires “hole filling”

Dealing with the holes   RingsN Octagon RingsP Inner layer of vertex detector fills holes in top and bottom. Must map hits from Si with different pad pattern and radius onto a “virtual” octagon Si layer

Dealing with the holes   RingsN Octagon RingsP Fill spectrometer holes by extrapolating hit density from adjoining detectors onto a virtual Si layer. (Actual spec layer 1 is much smaller than the hole in the octagon.)

  RingsN OctagonRingsP Track-based method Vertex range -8<z<10 Subevents for reaction plane  Momentum analysis  200 GeV data  Gap between tracks and subevents large  Little/no background

Vertex measurement Reaction plane determined by hits in widely separated subevent regions, symmetric in ,  Track-based method – detector space

Correlate tracks in spectrometer to reaction plane to determine v 2 Track-based method – detector space

A question to this workshop: Are there non-flow correlations that stretch across 3-6 units of  ? v z (cm)  Full acceptance v 1 :  sep =6 Full acceptance v 2 :  sep =5.2 Offset vertex v 2 :  sep = Track-based analysis

v 2 vs. centrality and energy Preliminary v Final v PHOBOS Au-Au 130 GeV result: PRL 89:222301, 2002 |  |< v2v2

v (hit) v (track) PHOBOS Preliminary 200 GeV Au-Au v 2 vs. centrality, method comparison |  |<1 track hit v2v2

PHOBOS preliminary h + + h GeV Au-Au track-weighted centrality averaging 0<  <1.5 (top 55%) v2v2 17% scale error v 2 vs.  p T

v 2 vs.  and energy Preliminary v Final v Hit-based result v & v similar PHOBOS Au-Au v2v2  ~ GeV result: PRL 89:222301, 2002

A. Poskanser showed in his talk that STAR agrees with the PHOBOS v 2 (  ). It will be interesting to see if it is possible to deconvolute the STAR and BRAHMS results in the forward region to determine what fraction of the drop in v 2 (  ) comes from dN/dp T and what fraction comes from v 2 (p T ).

Directed flow: MC analysis, resolution and background corrected, used event plane from 1 st harmonic Input flow A little Quark Matter preview

Preliminary directed flow sensitivity PHOBOS preliminary h + + h - Au-Au data A little Quark Matter preview

Flow at PHOBOS: What’s new? 200 GeV analyses  Finalizing systematics  Plan to release soon final results in 3 bins of centrality Directed flow (v 1 )  Still optimizing analysis and working to understand fine points of data analysis using full acceptance technique  Goal is to release preliminary v 1 (  ) at 19.6, 130 and 200 GeV for Quark Matter