FLUCTUATION as a signal of QGP:Present Experimental Results

Tapan NayakJan 6, 2003

• Large number particles in each event (at SPS, RHIC and LHC) allows for Event-by-Event physics

• Study of Event-by-Event Fluctuations become quite relevant.

Au+Au at RHIC

Event-by-Event Fluctuations

Thermodynamic Properties of Matter:Specific heat: Fluctuation in

Temp. or < pT >

• PRL 75 (1995) 1044 L. Stodolsky• Phys. Lett. B423 (1998) 9 E Shuryak

Compressibility: Multiplicity Fluctuation

(N)2 = < (N - < N >)2

PLB 430 (1998) 9 S. Mrowczynski

Study of thermodynamic quantities (or fluctuations in exptl. observables) can shed light on possible existence of phase transition and its nature.

Chiral Symmetry Restoration => Formation for Disoriented Chiral Condensates

Fluctuation in number of neutral to charged pions

• J.D. Bjorken 1992• Rajagopal & Wilczek 1993

Tricritical point of QCD phase diagram

Similar to behavior of strange quark mass and temperature in m-T plane

At the TRICRITICAL POINT:

singularities in thermodynamical observables

=> LARGE EVENT-BY-EVENT FLUCTUATIONS

Stephanov, Rajagopal and Shuryak PRL 81 (1998)

Disoriented Chiral Condensates (DCC)Normally: Each of the pion flavors are roughly equally populated. We define:

Formation of DCC: gives rise to a pulse of low

pT pions with a probability:

f

Large fluctuations in number of photons and charged particles

Chiral Symmetric pions

Centauro, anti-Centauro events

Measure Proposed by References

2/mean of the Gaussian, ratios

Baym & Heiselberg Jeon & Koch

PLB 469 (1999) 7; Phys. Rep. 351 (2001) 161; PRL 83 (1999) 5435

Wavelets Huang, Sarcevic, Thews & X-N Wang (for DCC)

PRD 54 (1996) 750

Correlator Stephanov, Rajagopal, Shuryak

PRD 60 (1999) 114028

Fluctuation in conserved Quantities

Jeon, Koch Asakawa, Heinz, Muller

PRL 85 (2000) 2076PRL 85 (2000) 2076

Balance Functions Bass, Danielewicz,Pratt

PRL 85 (2000) 2689

pTGazdzicki, Mrowczynski

Z. Phys. C54 (1992) 127

dynPruneau, Gavin ,Voloshin

nucl-ex/0204011

Space-time evolution of fluctuations are important!

MEASURES OF FLUCTUATIONS

SPMD : 2.35 < < 3.75

PMD : 2.9 < < 4.2

Min. Bias Nch Min. Bias Photons

158.A GeV Pb+Pb at SPS

STATISTICAL + DYNAMICAL

Gaussians for narrow bins incentrality

N : Particle MultiplicityNpart : No. of participantsni : No of particles produced by ith participant, accepted within the acceptance of detector

Participant model:

Multiplicity Fluctuation

= 2/ < N >

Multiplicity distributions are GAUSSIANS for narrow bins in centrality.

The physics (statistical + dynamical) is in the width of the distribution. The amount of fluctuation

• CENTRALITY• ACCEPTANCE

Data agree fairly well with participant model calculations

Multiplicity Fluctuationsfor various centralities

Charged Particles Photons

CentralPeripheral

Fluctuations of Ch. particles vs. Photons

Single event display => Charged particles superimposed on photons

• Top 5% central events ONLY• Bins in

• Discrete Wavelet Analysis

• Correlation Analysis:

N vs. Nch FLUCTUATIONS

Localized phase fluctuations

Data widths > M1 => Presence of localized

fluctuations in

• N

• Nch

• Correlated fluctuation

RMS WIDTHS OF DATA compared with GEANT & 4-types of MIXED EVENTS

Data width > M1 widthData width = M2 width

Data width > M3-and M3-ch

1. Phys.Lett.B420:169-179,19982. Phys.Rev.C64:011901,2001 3. nucl-ex/0206017, to be published in

PRC

Krzywicki & Serreau Phys. Lett.B 448 (1999) 257

Formation of DCC – upper limits

Not detectableNot detectable

Localized DCC domain

Centrality

0-5% central

Global DCC

Localized fluctuations decrease from central to peripheral. Upper limit for DCC-like localized fluctuations: 3x10-3

for central collisions.

RHIC Results so far

No indication of additional or decreased fluctuation observed so far.

Balance function width

PMD In STAR experiment at RHIC

PMD in Full STAR setup

PMD SuperModule

Preshower Detector, fine granularity

• Two planes: Veto + Pre-shower

• Total no. of cells: 82,944

• Gas detector with hexagonal cells• Coverage: 2.3 – 3.9

• Cell c.s.: 1.0 cm2, depth: 0.8 cm

• Area of the detector: 4.2m2

Photon Multiplicity Detector (PMD)

MUON ARM

In ALICE Experiment at CERN

Front View ofPMD

• Gas detector with hexagonal cells.

• 170,000 honeycomb cells (each of 0.22 cm2 area).• Two planes• Total area: 1.8m2

for each plane.

• Study of Fluctuations of various quantities provides a powerful means of observing QCD phase transition.

• Measurement at SPS gives• no evidence of non-statistical fluctuation• no indication of e-by-e correlated fluctuations (DCC-type) Upper limits of DCC production is set at 90% C.L.

• Event-by-event physics and fluctuations should be studied along with other signals as functions of centrality of the collision and various colliding systems.

SUMMARY

QCD phase transitions can be studied thru anomalousfluctuations and correlations – just as in real life situations.