Fluctuation studies in Phobos Constantin Loizides for the collaboration Massachusetts Institute of Technology (loizides@mit.edu) Workshop on “Correlations and fluctuations ” Florence, Italy, July 8, 2006 Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 1
PHOBOS collaboration (July 2006) Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel, Wit Busza (Spokesperson), Zhengwei Chai, Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Ian Harnarine, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Jay Kane, Piotr Kulinich, Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Eric Richardson, Christof Roland, Gunther Roland, Joe Sagerer, Iouri Sedykh, Chadd Smith, Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Artur Szostak, Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Donald Willhelm, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Shaun Wyngaardt, Bolek Wysłouch ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 2
PHOBOS experiment (Run5) ZDC ,pp TOF ,pp Ring Paddle T0 Vertex 137000 Silicon Octagon Pad Channels Spectrometer NIM A499, 603-23 (2003) Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 3
Outline 1) Single-particle distributions 2) Unusual event search 3) Forward/backward multiplicity correlations 4) Two-particle angular correlations 5) Eccentricity fluctuations 6) Elliptic flow fluctuations Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 4
Charged hadron dN/dη-distributions (1) 19.6 GeV 62.4 GeV 130 GeV 200 GeV c e n t r a l i t y PHOBOS Au+Au preliminary (QM05) preliminary(QM05) Cu+Cu d+Au Au+Au : PRL 91, 052303 (2003) 62 GeV: nucl-ex/0509034 (PRC in press) Cu+Cu: nucl-ex/0510042 (prel., QM05) d+Au : PRL 93, 082301 (2004) Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 5
Charged hadron dN/dη-distributions (2) ● Rich data set of p+p, p+A and A+A ● Scaling features of charged hadron multiplicities – Npart scaling – Extended longitudinal scaling (aka Limiting Fragmentation) – Factorization of energy/centrality dependence – Universality of total multiplicity in A+A, p+p and e + +e - ● Seen over a wide range of collision energy Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 6
Charged hadron dN/dη-distributions (2) ● Rich data set of p+p, p+A and A+A ● Scaling features of charged hadron multiplicities – Npart scaling – Limiting Fragmentation – Factorization of energy/centrality dependence – Universality of total multiplicity in A+A, p+p and e + +e - ● Seen over a wide range of collision energy In all of the above, dN/dη is single-particle event average Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 7
2) Unusual event search ● Beyond the average dN/dη – Are there events with very large multiplicity? – Does the dN/dη shape vary from event to event? Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 8
Unusual events: Large total multiplicity QM05 QM05 200M min.bias #Events 2M 3% central Cut (scaled) 570 evts Use high-statistics Run-4 AuAu ● data and select 3% central data (with lose data-quality cuts) Look at events with a large ● number of hits: ~10 -4 (570/2M) events Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 9
Unusual events: Large total multiplicity x10 -4 Fraction of unusual events QM05 QM05 4 200M min.bias 570 evts #Events 2M 3% central Cut (scaled) 2 570 evts 0 Use high-statistics Run-4 AuAu Events with large number of hits ● ● data and select 3% central data are strongly correlated with beam (with lose data-quality cuts) rate Look at events with a large Rate of “unusual” events ● ● number of hits: ~10 -4 (570/2M) extrapolated to low luminosity is events consistent with zero Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 10
Unusual events: dN/dη-shape x10 -4 Fraction of unusual events Data QM05 Random 3 200 evts 2 QM05 Cut 1 200 evts 0 Devide dN/dη into individual bins Events with large χ 2 are again ● ● (η, vertex) to get the average and strongly correlated with beam rate its variance Rate of “unusual” events ● Calculate χ 2 for each event extrapolated to low luminosity is ● again consistent with zero Compare to “random” events: ● distinct tail ~10 -4 (200/2M) events Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 11
3) Forward/backward multiplicity fluctuations ● Beyond the average dN/dη – Quantify E-by-E correlations in particle- production over regions in η Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 12
Forward/backward multiplicity fluctuations Independent particle production ● σ 2 C = 1 Correlated particle production N B N F ● – Long range σ 2 C → 0 Δη Δη – Short range σ 2 C >1 ● Clusters of size k within Δη C , = N F − N B C k C N F N B 2 k C 2 C Use variance σ 2 C ● If limited rapidity window (Δη) k k eff Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 13
Extraction of σ 2 C ● Deal with large occupancy in the octagon – Use η-bin-dependent lower and upper dE/dx cuts on hits to suppress contribution from secondaries Hit distribution in η - ϕ space with |Z vtx |<10cm ● Deal with limited acceptance – Correct gap effects E-by-E with z-vertex dependent offset ϕ – Avoiding holes in octagon ● Only half acceptance in φ ● Correction ~2, found with MC η ● Deal with contribution of detector effect (see next slides) Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 14
Contributing sources of detector effects ● Acceptance effects ● Secondaries ● dE/dx fluctuations – Landau fluctuation – Velocity (β) variation Different contributions add in quadrature and resulting detector effects are flat in η Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 15
Removing detector effects ● Assuming σ 2 C, raw = σ 2 C + σ 2 C, det σ 2 Modified HIJING with randomized C, raw ● sign of particle η to force σ 2 C =1 σ 2 C – Direct access to σ 2 C, det σ 2 Correction slightly depends on ● C, det size of signal – Cure residual correlation σ 2 C, det → σ 2 C, det - α (σ 2 C -1) ● α=constant(η, Δη, cent) Systematic errors estimated to ● Δ σ 2 C =0.1 (averaged over η) Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 16
Verification with various MC For the same tuning, the reconstructed σ 2 C agrees with raw σ 2 C within the errors in all tested models Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 17
F/B results: σ 2 C vs. η for fixed Δη Au+Au, 200 GeV PHOBOS, nucl-ex/0603026, Δη=0.5 PRC RC in press Poissonian Centrality dependence in slope observed ● Models systematically lower (partially within errors) – HIJING & AMPT agree in peripheral, but diverge in central events ● At η=0, models and data yield σ 2 C =1 ● Induced “intrinsic” long-range correlations? – Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 18
F/B results: σ 2 C vs. Δη at fixed η=2 Au+Au, 200 GeV PHOBOS, nucl-ex/0603026, η=2 PRC RC in press Poissonian Monotonic rise with increasing Δη-bin width ● Particles produced in effective cluster size ● – Central: k eff =2-2.3 – Peripheral: k eff =2.6-2.8 Models do not simultaneously describe ● centrality and Δη dependence Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 19
Clusters in elementary collisions 2 /〈 k 〉 k eff =〈 k 〉 k Two-particle pseudo-rapidity correlation = Δη N F +N B Clusters in Au+Au are reminiscent - of results from p+p Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 20
Centrality dependence of σ 2 C Resonance gas PHOBOS data: nucl-ex/0603026 pp data, UA5, PLB 123:361 (1983) Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 21
Centrality dependence of σ 2 C Model short and long range ● contribution 2 = f SR 2 1 − f LR 2 C where short range 2 = k [ 1 − exp −/ short ] SR Resonance gas and long range PHOBOS data: nucl-ex/0603026 2 f ∫ d 1 d 2 exp − 1 − 2 2 = 1 − pp data, UA5, PLB 123:361 (1983) LR Model: M.Abdel-Aziz and M.Bleicher, 2 2 long nucl-th/0605072 Constrain parameters ● Cent. Extra- 200 GeV, 0-20% σ 2 polation C Model fit nucl-th/0605072 Δη Constantin Loizides (MIT), Correlations workshop, Florence, 07/08/2006 22
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