fluctuation as a signal of qgp: present experimental results
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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.
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