Two-particle angular correlations in p+p and Cu+Cu at PHOBOS

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1 Two-particle angular correlations in p+p and Cu+Cu at PHOBOS Wei Li Massachusetts Institute of Technology for the Collaboration 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions (Quark Matter 2006), November 14-20, 2006, Shanghai, China

2 Collaboration Burak Alver, Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Richard Bindel, Wit Busza (Spokesperson), Vasundhara Chetluru, Edmundo García, Tomasz Gburek, Joshua Hamblen, Conor Henderson, David Hofman, Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, Chia Ming Kuo, Wei Li, Willis Lin, Constantin Loizides, Steven Manly, Alice Mignerey, Gerrit van Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski, Robert Pak, Corey Reed, Christof Roland, Gunther Roland, Joe Sagerer, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, 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 9 PhDs in progress

3 Outline Introductions and motivations Two-particle angular correlations in p+p Two-particle angular correlations in Cu+Cu Summary

4 Motivations PYTHIA -3<η<3 (no weak decay) Two-particle correlation function PHOBOS MC 6-6

5 Motivations PYTHIA -3<η<3 (no weak decay) Two-particle correlation function PHOBOS MC No high p T trigger! 6 All charged particles are included (soft physics)! Study particle correlations over a broad region -3<η<3. Shed light on the gross features of multi-particle production in p+p and A+A collisions. -6

6 Experimental setup PHOBOS apparatus Octagon

7 Experimental setup Uniquely large acceptance: -3<η<3 and almost full azimuthal angle φ. η Single-layer silicon detector: φ PHOBOS Octagon detector: No pt information, only (η,φ) of all charged particles. Need corrections for secondary particles. Holes for vertex detector and spectrometer: Acceptance correction needed.

8 Methodology Two-particle correlation function: Foreground: F n Background: B $ Fn (#!, #") % R( #!, #") =< ( n & 1) ' & 1( > ) B n( #!, #") * II (%", %#) ~ $ n (" 1, " 2, # 1, # 2) = 4 1 d! n n( n & 1)! d" d" d# d# n d! 1 d! 2 2 I I n n n( %", %#) ~ $ n (" 1, # 1) $ n (" 2, # 2) = n! n d" 1d# 1 n! n d" 2d# 2 Event 1 Event 2

9 Two-particle correlations in p+p

10 Two-particle correlation function in p+p Foreground Background

11 Two-particle correlation function in p+p Foreground Background correlation function (uncorrected):

12 Two-particle correlation function in p+p Foreground Background correlation function (uncorrected): Secondary effects: δ-electron, γ conversion etc.

13 Two-particle correlation function in p+p Foreground Background Two particle correlation function: correlation function (uncorrected): corrections by MC 6 Secondary effects: δ-electron, γ conversion etc. -6

14 Cluster model Isotropic cluster model: Clusters are produced at the end of the collisions. They are emitted independently. They decay isotropically in their c.m.s into hadrons. C.Quigg, Phys. Rev. D 9, 2016 (1974) E. L. Berger, Nucl. Phys. B 85, 61 (1975).

15 Cluster model Isotropic cluster model: Clusters are produced at the end of the collisions. They are emitted independently. They decay isotropically in their c.m.s into hadrons. C.Quigg, Phys. Rev. D 9, 2016 (1974) E. L. Berger, Nucl. Phys. B 85, 61 (1975). :clusters

16 Cluster model Isotropic cluster model: Clusters are produced at the end of the collisions. They are emitted independently. They decay isotropically in their c.m.s into hadrons. C.Quigg, Phys. Rev. D 9, 2016 (1974) E. L. Berger, Nucl. Phys. B 85, 61 (1975). :clusters

17 Cluster model Isotropic cluster model: Clusters are produced at the end of the collisions. They are emitted independently. They decay isotropically in their c.m.s into hadrons. C.Quigg, Phys. Rev. D 9, 2016 (1974) E. L. Berger, Nucl. Phys. B 85, 61 (1975). :clusters Cluster model is a very generic model. It is not clear whether it has any significance in QCD. Or it is just a phenomenological description.

18 Cluster-like correlation structure higher p T clusters lower p T clusters 6 e.g. Resonance decay -6

19 Cluster-like correlation structure average over Δφ 6-6

20 Cluster-like correlation structure Two-particle rapidity correlation function: average over Δφ scale error Δη short-range rapidity correlations -6

21 Parameterize cluster size (multiplicity) Quantitatively understand cluster phenomena Two-particle rapidity correlation function: ' R("#) = $ ) %("#) ( B("#) &1 *, + K. Eggert et al., Nucl. Phys. B 86:201, 1975

22 Parameterize cluster size (multiplicity) Quantitatively understand cluster phenomena Two-particle rapidity correlation function: ' R("#) = $ ) %("#) ( B("#) &1 *, + correlations between particles from one cluster ( + "(#$) %exp*& (#$)2 - ) 4' 2, Decay width: 2 K. Eggert et al., Nucl. Phys. B 86:201, 1975 δ

23 Parameterize cluster size (multiplicity) Quantitatively understand cluster phenomena Two-particle rapidity correlation function: k: cluster size K eff = " +1= Keff : effective cluster size ' R("#) = $ ) %("#) ( B("#) &1 *, + < k(k #1) > < k > +1=< k > + $ k 2 < k > correlations between particles from one cluster ( + "(#$) %exp*& (#$)2 - ) 4' 2, Decay width: 2 K. Eggert et al., Nucl. Phys. B 86:201, 1975 δ

24 Parameterize cluster size (multiplicity) Quantitatively understand cluster phenomena Two-particle rapidity correlation function: k: cluster size ' R("#) = $ ) %("#) ( B("#) &1 *, + correlations between particles from one cluster ( + "(#$) %exp*& (#$)2 - ) 4' 2, Decay width: 2 K. Eggert et al., Nucl. Phys. B 86:201, 1975 δ K eff = " +1= < k(k #1) > < k > Keff : effective cluster size +1=< k > + $ 2 k < k > B("#) : background distribution

25 Cluster size and decay width ' R("#) = $ ) %("#) ( B("#) &1 *, + ( + "(#$) %exp*& (#$)2 - ) 4' 2, scale error

26 Cluster size and decay width Keff = 2.44±0.08 δ = 0.66 ±0.03 (90% C.L.) Scale error: 5% for Keff 4% for δ (90% C.L.) ' R("#) = $ ) %("#) ( B("#) &1 *, + ( + "(#$) %exp*& (#$)2 - ) 4' 2, 2" scale error

27 Cluster size and decay width Keff = 2.44±0.08 δ = 0.66 ±0.03 (90% C.L.) Scale error: 5% for Keff 4% for δ (90% C.L.) ' R("#) = $ ) %("#) ( B("#) &1 *, + ( + "(#$) %exp*& (#$)2 - ) 4' 2, 2" scale error On average, every charged particle is correlated with about another 1.5 particles!

28 Clusters in p+p collisions Energy dependence of Keff and δ PHOBOS preliminary p+p PHOBOS preliminary scale error Cluster size increases with energy!

29 Clusters in p+p collisions Energy dependence of Keff and δ PHOBOS preliminary scale error UA5 HIJING ISR PYTHIA Cluster size increases with energy!

30 Clusters in p+p collisions Energy dependence of Keff and δ PHOBOS preliminary scale error UA5 HIJING ISR PYTHIA Expected from resonances (UA5 collaboration) Cluster size increases with energy!

31 Clusters in p+p collisions Energy dependence of Keff and δ PHOBOS preliminary scale error UA5 ISR HIJING PYTHIA Expected from resonances (UA5 collaboration) scale error Cluster size increases with energy!

32 Clusters in p+p collisions Multiplicity dependence of Keff and δ 410GeV 200GeV scale error scale error Cluster size increases with event multiplicity!

33 Clusters in p+p collisions Multiplicity dependence of Keff and δ scale error scale error Cluster size increases with event multiplicity!

34 Two-particle correlations in Cu+Cu

35 Two-particle correlations in Cu+Cu PHOBOS preliminary PHOBOS preliminary 0%-10%

36 Two-particle correlations in Cu+Cu PHOBOS preliminary PHOBOS preliminary 0%-10% Evolution of correlation structure from p+p to Cu+Cu: Clear elliptic flow signals which extends to very high Δη in Cu+Cu. Similar cluster-like structure as in p+p. -6

37 Two-particle correlations in Cu+Cu

38 Two-particle correlations in Cu+Cu

39 Two-particle correlations in Cu+Cu

40 Two-particle correlations in Cu+Cu

41 Two-particle correlations in Cu+Cu

42 Two-particle correlations in Cu+Cu More work will follow to subtract flow and study the medium effects on the correlation structures!

43 Cluster parameterization in Cu+Cu R("#) -5 "# 5 R("#) Cu+Cu@200GeV "# 5-5 "# -5 5

44 Cluster parameterization in Cu+Cu R("#) Kef f=2.89±0.14 Keff =2.85±0.13 Keff =2.76±0.11 δ =0.78±0.06 δ =0.80±0.06 δ =0.81±0.05 (90% C.L.) (90% C.L.) (90% C.L.) Scale error: 7% for Keff 8% for δ (90% C.L.) R("#) Kef f=2.49±0.12 Keff= 2.19±0.12 δ =0.78±0.08 δ = 0.74±0.06 (90% C.L.) (90% C.L.) "# 5-5 "# "# Extract cluster parameters in Cu+Cu using two-particle rapidity correlation function 5 Cu+Cu@200GeV

45 Clusters in Cu+Cu scale error

46 Clusters in Cu+Cu p+p To first order, cluster size in Cu+Cu is similar to p+p. scale error

47 Clusters in Cu+Cu p+p To first order, cluster size in Cu+Cu is similar to p+p. In Cu+Cu, cluster size decreases with centrality. scale error

48 Clusters in Cu+Cu p+p To first order, cluster size in Cu+Cu is similar to p+p. In Cu+Cu, cluster size decreases with centrality. scale error Model comparison: AMPT shows the same trend but systematically lower in magnitude. HIJING remains constant.

49 Clusters from Cu+Cu to Au+Au " C 2 ~ K eff Phys. Rev. C74, (R) (2006) peripheral η=2 central Cu+Cu@200GeV Au+Au@200GeV Cluster sizes from the two methods are similar in magnitude. Cluster sizes decrease with centrality both in Cu+Cu and Au+Au.

50 Clusters from Cu+Cu to Au+Au " C 2 ~ K eff Phys. Rev. C74, (R) (2006) peripheral η=2 central Cu+Cu@200GeV Au+Au@200GeV Cluster sizes from the two methods are similar in magnitude. Cluster sizes decrease with centrality both in Cu+Cu and Au+Au. Ongoing studies of two-particle correlations in Cu+Cu and Au+Au!

51 Summary Correlation structures over broad (η,φ) range: Provide detailed information on multi-particle production. Observed short-range correlations in p+p and Cu+Cu have a natural interpretation in terms of clusters: Particles tend to be produced in clusters with a size of 2-3 in p+p. Clusters in Cu+Cu are similar to p+p but show a modification of particle correlations with centrality dependence in HI collisions.

52 Summary Correlation structures over broad (η,φ) range: Provide detailed information on multi-particle production. Observed short-range correlations in p+p and Cu+Cu have a natural interpretation in terms of clusters: Particles tend to be produced in clusters with a size of 2-3 in p+p. Clusters in Cu+Cu are similar to p+p but show a modification of particle correlations with centrality dependence in HI collisions. Future work: a comprehensive study of two-particle correlations in p+p, d+au, Cu+Cu and Au+Au!

53 Backup slides

54 Corrections uncorrected secondaries correction acceptance correction corrected

55 Normalized multiplicity distribution After normalized by the average multiplicity, the multiplicity distribution becomes acceptance independent!

56 Cluster decay width in Cu+Cu scale errors

57 Cluster model

58 V 2 modulation In our definition of two particle correlation function: $ Fn (#!, #") % R( #!, #") =< ( n & 1) ' & 1( > ) B n( #!, #") * V 2 modulation will be 2(v 2 ) 2 (n "1) since R("#) ~ 2(v 2 ) 2 (n $1)cos(2"#)

59 Clusters from Cu+Cu to Au+Au At rapidity window δη=2, " C 2 = K eff ( Δη <2)

60 Clusters from Cu+Cu to Au+Au 3.0 Cu+Cu 2.5 K eff Au+Au@200GeV from! C Cu+Cu@200GeV from K eff 3.0 Au+Au ! C 1.5 scale errors PHOBOS preliminary

61 Clusters from Cu+Cu to Au+Au Do clusters in A+A have anything to do with the geometry? scale errors