Multiplicity Fluctuations in 200 GeV Au-Au Collisions

Zhengwei Chai

Brookhaven National Laboratory

for the Collaboration

APS April Meeting, Denver, 2004

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Collaboration

Birger Back, Mark Baker, Maarten Ballintijn, Donald Barton, Russell Betts, Abigail Bickley, Richard Bindel, Wit Busza (Spokesperson), Alan Carroll, Zhengwei Chai, Patrick Decowski,

Edmundo García, Tomasz Gburek, Nigel George, Kristjan Gulbrandsen, Clive Halliwell, Joshua Hamblen, Adam Harrington, Michael Hauer, Conor Henderson, David Hofman,

Richard Hollis, Roman Hołyński, Burt Holzman, Aneta Iordanova, 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, Christof Roland, Gunther Roland, Joe Sagerer, Helen Seals,

Iouri Sedykh, Wojtek Skulski, Chadd Smith, Maciej Stankiewicz, Peter Steinberg, George Stephans, Andrei Sukhanov, Marguerite Belt Tonjes, Adam Trzupek, Carla Vale,

Sergei Vaurynovich, Robin Verdier, Gábor Veres, Peter Walters, Edward Wenger, Frank Wolfs, Barbara Wosiek, Krzysztof Woźniak, Alan Wuosmaa, Bolek Wysłouch

ARGONNE NATIONAL LABORATORY BROOKHAVEN NATIONAL LABORATORYINSTITUTE OF NUCLEAR PHYSICS PAN, KRAKOW MASSACHUSETTS INSTITUTE OF TECHNOLOGY

NATIONAL CENTRAL UNIVERSITY, TAIWAN UNIVERSITY OF ILLINOIS AT CHICAGOUNIVERSITY OF MARYLAND UNIVERSITY OF ROCHESTER

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•Particle production in Au-Au collisions is dominated by overlapping geometry of the colliding ions, thus the particle multiplicity mainly depends on the number of participants Npart.

•Dynamical fluctuations other than statistical and Npart fluctuations may provide insights on the intrinsic mechanisms of the particle production.

•Event-by-event multiplicity fluctuation could be a useful signature of the QGP-Hadron Gas phase transition due to the large difference of the degree of freedom between the two phases.

•Dynamical fluctuations are also related to particle correlations, such as jets, resonances and clusters.

Fluctuations in Particle Production

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Event-by-event fluctuation observable (C)

• Study multiplicity fluctuation using

• (C) = RMS of C distribution

N 1+N 2

N1 - N

2

21

21

NNNNC

• (C) = 1 for pure statistical fluctuations

• Npart fluctuations suppressed in (C)

• (C) ≠1 indicates additional fluctuations

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PHOBOS Detectors

Beryllium Beam Pipe

Paddle Trigger Counters

Spectrometer Detectors (Silicon)

Ring Multiplicity Detectors (Silicon)

Cerenkov Trigger Counters Time of Flight Counters

Octagon Multiplicity Detectorand Vertex Detector (Silicon)

Octagon

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PHOBOS Capability in Charged Particle Multiplicity Analysis PHOBOS Multiplicity Detectors Acceptance

Coverage

≤

≤

5.4η 5.4-

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Constructing Multiplicity in Au-Au Collisions

• Octagon silicon sensors provide1. Number of hits (Nhit)2. Sum of the angle-corrected dE for charged particles (E)

• Nhit=Nmax(1-exp(-E/Emax))

• Emax/Nmax: average dE by a charged particle in selected bin

• Occupancy-corrected multiplicity N = E /(Emax/Nmax)• Multiplicities N1, N2 in forward and backward equal size bins N1, N2 (C)

21

21

NNNNC

Energy (E)

Num

ber o

f hits

(N

hit)

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Preliminary Fluctuation Analysis Result

• Data (C) agrees with Rec.Hijing+Geant (C)

• Data and Rec. MC (C) dominated by detector responses

• Estimated systematic error 5% (not shown)

Phobos Prelim. DataRec. Hijing+GeantHijing (half )(

C)

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Preliminary Fluctuation Analysis Result

• Data and Rec. MC (C) agree very well

• Hijing (C) increases with the separation in pseudo-rapidity space

• Estimated systematic error 5%(not shown)

(C

)

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Fluctuation Sources in Rec. MC Multiplicity

• Acceptance Effects

• Secondaries

• dE/dx Fluctuations• Landau fluctuation• Velocity () variation

• Hijing non-statistical fluctuations (physics)

(C

)

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Preliminary Fluctuation Analysis Result

• Data and Rec. MC (C) increase with the bin size

• Hijing (C) increases with the bin size

• Estimated systematic error 5%(not shown)

(C

)

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Summary and Outlook

NNS• Analyzed multiplicity fluctuation of the charged particle production in Au-Au collisions at =200GeV over wide pseudo-rapidity range (-3.0<<+3.0)

• The measured fluctuations in the Data are consistent with that in reconstructed Au-Au MC (Hijing + Geant)

• Current new dynamic fluctuation search is complicated by dominant detector responses

• The physics fluctuations grow with increasing bin separation () and width () and may be explained by jets or particle production in clusters

• Further studies are being extended to the full acceptance(-5.4<<+5.4) for a variety of beam energies