zimanyi2010noani mitchell
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First Results from the RHICBeam Energy Scan Program
Jeffery T. MitchellBrookhaven National Laboratory
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Outline
The QCD Phase Diagram
The RHIC Beam Energy Scan Program
The Matter Created at the top RHIC Energy
Experimental Challenges at Low Energies
Recent Results from the Beam Energy Scan
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Phases of Nuclear Matter
3
The original goal of therelativistic heavy ion programwas to create matter at highenough temperature andpressure that nucleons and
mesons would decouple intoquarks and gluons. Effectively,we strive to recreate theconditions immediately after theBig Bang.
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
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The Phase Diagram of H2OThere are many similarities between the phase diagramsof H2O and QCD
4
First order phasetransition
Critical Point
Crossover
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
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A Schematic Phase Diagram of QCD
SB(T) 2
30(Nbosons 7/8 Nfermions)T
4
5
There are many similarities between the phase diagramsof H2O and QCD
First orderphasetransition
Critical Point
Crossover
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QCD Phase Transition
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QuantumChromodynamics (QCD)predicts a strong increasein the energy density ata critical temperature of
Tc~170 MeV.
There is a phasetransition from hadronicto partonic matter(quarks, gluons) at a
critical energy density of0~1 GeV/fm3
Z. Fodor et al., PLB 568 (2002) 73.
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But, there is much room forexperimental input
M. Stephanov hep-lat/0701002
Large sensitivityto model inputs(such as quarkmasses), latticesizes, and otherassumptions
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Each black andgreen pointrepresents thecritical pointlocation from
differentcalculations.
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Search for the QCD Critical Point:Experimental Strategy
By systematicallyvarying the RHIC beam
energy, heavy ioncollisions will be ableto probe differentregions of the QCDphase diagram.
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Simulated Collision Trajectories
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Shown are locations
on the phasediagram forcollisions atdifferent energiestaken at varioustimes after the
collision occurs.
The simulation isfrom Ultra-Relativistic QuantumMolecular Dynamics(UrQMD).
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How big is the target?
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M.Asakawa et al.,PRL 101,122302(2008)
From a hydrodynamicscalculation.
For a given chemicalfreeze-out point, 3isentropic trajectories(s/nB=constant) areshown.
The presence of thecritical point can deformthe trajectories describingthe evolution of theexpanding fireball in the(T,B) phase diagram.
A large region can beaffected, so we do notneed to hit the criticalpoint precisely.
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
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Energy Scan Results from the SPS
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Discontinuities in the average K/ ratio (the horn) and the kaon spectraslope (the step) are observed.
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Enter the Beam Energy Scan Program atthe Relativistic Heavy Ion Collider
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The Relativistic Heavy Ion Collider (RHIC)
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RHIC Specifications
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A llid i ll f b
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A collider is an excellent for a beamenergy scan
The detector occupancy in acollider is much less dependenton beam energy than in a fixedtarget accelerator. The acceptanceis independent of beam energy.
Fixed targetCollider
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Th RHIC B E S P
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The RHIC Beam Energy Scan Program:Overview
Species: Gold + Gold
Collision Energies [sqrt(sNN)]:200 GeV, 130 GeV, 62.4 GeV, 39 GeV, 19.6 GeV,18 GeV (2011), 11 GeV (STAR only)9.2 GeV (short test run), 7.7 GeV
Species: Copper + Copper
Collision Energies [sqrt(sNN)]:200 GeV, 62.4 GeV, 22 GeV
Species: Deuteron + Gold
Collision Energies [sqrt(sNN)]:200 GeV
Species: Proton + ProtonCollision Energies [sqrt(sNN)]:
500 GeV, 200 GeV, 62.4 GeV
Coming Soon:Uranium + Uranium
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200 GeV Au+Au Event Displays
A head-on collision produces hundreds of particle tracks inthe detector.
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Wh i h i i i l ?
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What is the initial temperature?
Hot matter emits thermal radiation, so thetemperature can be measured from theemission spectrum of thermal photons.
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S f Ph
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Sources of Photons
quark gluon
g
pQCD direct photons
from initial hardscatteringof quarks andgluons
g
r
Thermal photonsfromhadron gasafter
hadronization
g
g
Decay Photonsfrom hadrons(0, h, etc)
background
Thermal photons
from hot quark gluonplasma
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Di t Ph t S t (PHENIX)
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Direct Photon Spectra (PHENIX)
pQCD consistent with p+pdata down to pT=1GeV/c
Au+Au data lie above Ncoll-scaled p+p data for pT < 2.5GeV/c
Fitting the excess data yields:
TAuAu = 221 19stat 19syst MeV Lattice QCD predicts a phase
transition to quark gluonplasma at Tc~ 170 MeV
The initial temperature isabove the predicted criticaltemperature.
exp + TAA scaled pp
NLO pQCD (W. Vogelsang)Fit to pp
A. Adare et al.,PRL accepted
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Elli ti Fl
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Elliptic Flow
v2>0: in-plane emission of particlesv2
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Elliptic Flow: Excitation Function
There is atransition fromsqueeze-out
flow to in-plane flow atAGS energies
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Elliptic Flow Indicates that thematter behaves like a perfect fluid!
STAR 200 GeV Au+Audata (black dots) withvarioushydrodynamicalcalculations overlayed.
The system cannot bedescribed or simulatedunless the followingcondition is set:
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S li f Elli ti Fl
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Scaling of Elliptic Flow
Phys. Rev. Lett.98, 162301
(2007)
Mesons
Baryons
Quark-Like Degrees of Freedomare Evident
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H d
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HadronSuppression
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The medium isextremely opaque
near away
RAA(pT) d2
NAA
/ dpTdhNbinary d
2Npp / dpTdh
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Summary of RHIC 200 GeVAu+Au Collision Results
The matter is very hot with a temperature well abovethe expected critical temperature for a phasetransition to a Quark-Gluon Plasma
The matter behaves like a strongly interactingperfect fluid
The matter is described by quark degrees of freedom
The matter is very opaque
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Triggering at Low Energy
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Triggering at Low EnergyThe problem:
The placement of thetrigger detectors (BBCs)are not optimized for lowenergy running.They have a reducedacceptance, especially
below RHIC energies of ~20 GeV.
Fermi motion to therescue!
At low energies, Fermimotion is enough tobring nucleons back intothe BBC acceptance.
28Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Beam Quality at Low Energy
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Beam Quality at Low Energy
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The problem:The quality of the
RHIC beam tuningdegrades at lowerenergies. The beamposition is difficult tomonitor.
Each point representsthe vertex coordinateof an eventreconstructed fromthe tracks in theSTAR TPC.
Due to the lowerquality beam tune,some backgroundexists.
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STAR 7 7 GeV Au+Au Event Displays
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STAR 7.7 GeV Au+Au Event Displays
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Beam + Beam pipe collision
Downstream collision
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
PHENIX 7 7 GeV Au+Au Event Displays
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PHENIX 7.7 GeV Au+Au Event Displays
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
STAR Particle Identification:
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STAR Particle Identification:7.7 GeV Au+Au
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Excellent Particle Identification Demonstrated
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
STAR 7 7 G V P i l Id ifi i
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STAR 7.7 GeV Particle Identification
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PHENIX 0 Yields
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PHENIX 0 Yields
Enhanced pT reach
(Run-10)
Previous pT reach
(Run-4)
62 GeV
39 GeV
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PHENIX Dilepton Expectations at 39 GeV
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PHENIX Dilepton Expectations at 39 GeV
mee
1/Nevtd
N/dmee
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How does the dilepton excess and modification at SPSevolve into the large low-mass excess at RHIC?
200M simulated events in 20cm vertex
If excess is the same at 39 GeVas 200, expect a 6 result
Black: simulation withsame enhancement asat 200 GeVBlue: no enhancement
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
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Experimental Approaches to theBeam Energy Scan
1. Search for the onset of deconfinement. Breakdown of the constituent quark number scaling of
elliptic flow Disappearance of hadron suppression in central
collisions
Local parity violation
2. Search for direct signals of the critical point and/or phasetransition.
Fluctuation measurements Measurements of higher moments (kurtosis) Excitation functions
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Searching for the Onset of
Deconfinement
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Charged Particle Multiplicity
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Charged Particle Multiplicity
The dN/dh perparticipant pair
at mid-rapidityin central heavyion collisionsincreases withln s from AGSto RHIC
energies
The sdependence isdifferent for pp
and AAcollisions
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l l d ( )
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Multiplicity at 7.7 and 39 GeV (Raw)
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Identified Particle Yields
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Identified Particle Yields
Identified particle yields areconsistent with measurementsat the SPS.
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Pions
Protons
Kaons
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Identified Particle Ratios
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Identified Particle Ratios
pbar/p
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Exploring the Horn
RHIC results so far are consistent with the SPS results
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Directed Flow (v1)
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Directed Flow (v1)Directed flowdescribescollective
sideways motion.
Directed flow issensitive to theEquation of State.Expect non-linear
behavior nearmid-rapidity neara 1st-order phasetransition..
ybeam at 200 GeV = 5.4
ybeam at 62 GeV = 4.2
ybeam at 9 GeV = 2.3
The 9.2 GeV data show a different trendcompared to the 200 and 62 GeV data. Results at7 GeV coming soon.
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Elliptic Flow vs Beam Energy
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Elliptic Flow vs. Beam Energyand System Size
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The scaling of elliptic flow persistsin 62.4 GeV Au+Au collisions. Dataat lower energies coming soon.Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Elliptic Flow at 39 GeV
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Elliptic Flow at 39 GeV
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No surprises at these energies.
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Elliptic Flow at 9 2 GeV
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Elliptic Flow at 9.2 GeV
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Pion Interferometry
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Pion Interferometry
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STAR 9.2 GeV: Phys. Rev. C81(2010) 024911.
x
adapted from
Annu. Rev. Nucl. Part. Sci. 200555:357-402Detector
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Freeze-out Volume from Pion Interferometry
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Freeze out Volume from Pion InterferometryA freeze-out volumecan be extracted fromthe interferometryresults:
Vfo = R2sideRlong
A minimum in thisquantity exists at ~7GeV
9 GeV results areconsistent with SPSresults.
The particle emission lifetime is
related to:
t Rout/RsideAn increase is expected nearthe critical point. This is notobserved.
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Local Parity Violation
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Local Parity Violation
Under a strong magnetic field,
when the system isdeconfined and chiralsymmetry is restored, localfluctuations may lead to parityviolation.
Experimentally, look forseparation of the charges inhigh energy nuclear collisions.
Searching for thedisappearance of this effect
can signal the location of thephase boundary.
D.E. Kharzeev et al., NPA 803 (2008) 227.K. Fukushima et al., PRD 78 (2008) 074033.
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Local Parity Violation Results
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Local Parity Violation Results
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The signal is consistent with local parity violation in 200 GeV and62.4 GeV Au+Au collisions. Lower energy results are coming soon.
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The Mach cone feat re
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The Mach cone feature
STAR : Phys. Rev. Lett. 102, 052302 (2009)
QM09 : Teiji Kunihiro
From a model withrelativistic dissipativehydrodynamics couplingdensity fluctuations tothermal energy. Thermallyinduced density fluctuationsand sound modes getsuppressed at the criticalpoint. The disappearance ofthe mach cone featurecould be a signature of thecritical point.
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PHENIX arXiv:0801.4545
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The Ridge Feature
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The Ridge Feature
There is a ridge feature that
extends in pseudorapidity. It persistsat 62 GeV.
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Searching for Signals of the
Critical Point and PhaseTransition
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Antiproton/Proton Ratio vs. pT
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Antiproton/Proton Ratio vs. pT
Fitting Procedure :y = a (mT - m) + b
Observable proposed as a signature offocusing near the critical point.No large drop in ratio observedfor intermediate p
T
range
Phys. Rev. C73, 044910 (2006)
Phys.Rev. C78, 034918 (2008)
STAR : PLB 655, 104 (2007)PRL 97, 152301 (2006) STAR
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Divergent Quantities at the Critical Point
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Divergent Quantities at the Critical PointNear the critical point, several properties of a system diverge. The rateof the divergence can be described by a set of critical exponents. For
systems in the same universality class, all critical exponent valuesshould be identical.
The critical exponent for compressibility, g:g )(
C
cT
T
TTk
The critical exponent for heat capacity, a:g )(0
C
c
T
T
TTT
kk a )(
C
cV
TTTC
The critical exponent for correlation functions, h: )2()(h dRRC
(d=3)
g
)(0
C
c
T
T
T
TT
k
k n
)( C
c
T
TT The critical exponent for correlation length, n:
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Susceptibilities at the Critical Point
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pConsider quarksusceptibility, cq at thecritical point.
cq = = n(T,m)/m
This is related to theisothermal compressibility:
kT = cq(T,m)/n2(T,m)
In a continuous phasetransition, kT diverges at
the critical point
B.-J. Schaefer and J. Wambach, Phys. Rev. D75
(2007) 085015.
g )(C
cT
T
TTk
TBNBD
N kV
Tkk
mm
m 1
2
Grand Canonical Ensemble
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Multiplicity Distributions (PHENIX)
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Multiplicity Distributions (PHENIX)200 GeV Au+Au
62.4 GeV Au+Au
200 GeV Cu+Cu 62.4 GeV Cu+Cu
22.5 GeV Cu+CuRed lines
represent the NBDfits. The
distributions havebeen normalizedto the mean and
scaled forvisualization.Distributionsmeasured for
0.2
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Multiplicity Fluctuation ResultsNear the critical point, the multiplicity fluctuations should exceed thesuperposition model expectation No significant evidence for criticalbehavior is observed. Low energy results coming soon.
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Fluctuations Excitation Function
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pT
a
)(C
c
V
T
TTC
Fluctuations in mean pT arerelated to the criticalexponent a:
No increase in fluctuations have beenobserved. Results at 7 and 39 GeV are coming
soon.
SpT = (event-by-event pTvariance) [(inclusive pT
variance)/(meanmultiplicity per event)],normalized by theinclusive mean pT.Random = 0.0.
SpT is the mean of thecovariance of all particlepairs in an eventnormalized by theinclusive mean pT.
SpT can be related to theinverse of the heatcapacity.
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Like-Sign Pair Azimuthal Correlations
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g
62 GeVAu+Au,0-5%Central
200 GeVAu+Au,0-5%Central
PHENIXPreliminary PHENIXPreliminary
0.2 < pT,1 < 0.4 GeV/c, 0.2 < pT,2 < 0.4 GeV/c, |Dh|
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Searching for the Critical Point with
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gHBT Qinv Correlations
T. Csorgo,S. Hegyi,T. Novk,W.A.Zajc,
Acta Phys. Pol. B36 (2005) 329-337
a = Levy index of stability = ha = 2 for Gaussian sourcesa = 1 for Lorentzian sources
This technique proposes to searchfor variations in the exponent h. The exponent h can be extracted byfitting HBT Qinv correlations with a
Levy function:C(Qinv) = l exp( -|Rq/hc|a)
Measure a as a function of collisionenergy and look for a change fromGaussian-like sources to a sourcecorresponding to the expectationfrom the universality class of QCD.
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Fluctuations of Particle Ratios
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K/
p/
arXiv: 0901.1795
Results consistent with previous NA49measurements.
The event-by-event fluctuations of thekaon/pion ratio are expected toincrease at the critical point.
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Measuring skewness or kurtosis
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g
Skewness describes the asymmetry of the distribution Kurtosis describes the peakness of the distribution
For a Gaussian distribution, skewness and kurtosis are both zero. These measures are ideal for measuring non-Gaussian fluctuations.
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Kurtosis of proton/antiproton ratios
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STAR: PRL 105(2010) 022302,aXiv:1004.4959
No large non-Gaussian fluctuations seen.Lower energy results coming soon.
Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Summary and Outlook
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y At the top RHIC energies, the created matter is a hot, opaque, stronglyinteracting perfect fluid described by quark degrees of freedom.
The location of the phase transition and QCD critical point remains anopen question.
RHIC has embarked on an beam energy scan program to search for theQCD critical point.
In 2010, RHIC executed a very successful run covering beam energies of62.4, 39, 11, and 7.7 GeV.
First RHIC low energy results are consistent with measurements atsimilar energies from the SPS. So far, no clear signs of the critical point.
RHIC plans to run at 18 GeV in the upcoming run that will start inJanuary 2011.
Results have only just started to appear. We are looking forward to manynew results in the coming months!
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Auxiliary Slides
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Statistical Models: Estimating the Freeze-out
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Temperature
AuAu - s=130 GeV
Minimum ofc2 for: T=1665 MeV mB=3811 MeV
A. Andronic et al., Nucl. Phys. A772 (2006) 167.
Basic assumption: System is described by a grand canonical ensemble ofnon-interacting fermions and bosons in thermal and chemical equilbrium
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Statistical Model Fits
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neutron star
Baryonic Potential mB [MeV]
early universe
ChemicalTemperatureTch
[MeV]
0
200
250
150
100
50
0 200 400 600 800 1000 1200
AGS
SIS
SPS
RHIC
quark-gluon plasma
hadrongas
deconfinementchiral restauration
LatticeQCD
atomic
nuclei
For s > 10 GeV , chemical freeze-out very close to phase boundary
Extracted T & B values
71Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
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Statistical Model Results
Results from differentbeam energiesAnalysis of particle yieldswith statistical models
Freeze-out points reach QGPphase boundary at top SPSenergies
72Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Direct Photons: Comparisons to TheoryH d d i l d l
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Hydrodynamical models arecompared with the data
D.dEnterria &D.Peressounko
T=590MeV, t0=0.15fm/cS. Rasanen et al.
T=580MeV, t0=0.17fm/c
D. K. Srivastava
T=450-600MeV, t0
=0.2fm/c
S. Turbide et al.
T=370MeV, t0=0.33fm/c
J. Alam et al.
T=300MeV, t0=0.5fm/c
F.M. Liu et al.
T=370MeV, t0=0.6 fm/c
Hydrodynamical modelsagree with the data within afactor of ~2
A.Adare et al.arXiv:0912.0244
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Temperature fit summary
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p y
Significant yield of the exponential component (excess over the scaledp+p)
The inverse slope TAuAu = 2211919 MeV (>Tc ~ 170 MeV) p+p fit funciton: App(1+pt
2/b)-n
If power-law fit is used for the p+p spectrum, TAuAu = 24021 MeV
Lattice QCD predicts a phase transition to quark gluon plasma atTc ~ 170 MeV
74Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Direct Photons: Initial temperature
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p
From data: T in i > TAuAu ~ 220 MeVFrom models: T in i = 300 to 600 MeV for t0 = 0.15 to 0.6 fm/cLattice QCD predicts a phase transition to quark gluon plasma at Tc ~170 MeV
TC from Lattice QCD ~ 170 MeVTAuAu(fit) ~ 220 MeV
A.Adare et al.arXiv:0912.0244
75Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
PHENIX DetectorCentral Arm Tracking
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Central Arm Tracking
Drift Chamber
Pad Chambers
Time Expansion Chamb.
Muon Arm Tracking
Muon Tracker
Calorimetry
PbGl
PbSc
MPC
Particle Id
Muon IdentifierRICH, HBD
TOF E & W
Aerogel
TEC
Global Detectors
BBC
ZDC/SMD Local Polarim.
Forward Hadron Calo.
RXNP
DAQ and Trigger System
Online Calib. & Production
VTXReplaces HBDMuon Trigger:
mTr FEERPC station 3
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Elliptic Flow: Excitation Function
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p
77
There is atransition fromsqueeze-out
flow to in-plane flowbetween AGSand SPSenergies
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78Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
PHENIX 39 GeV Au+Au Event Displays
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STAR 9.2 GeV Au+Au Event Displays
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80Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Multiplicity Measurements!
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central
central
peripheralperipheral
energy s81Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
STAR 39 GeV Particle Identification
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J/: analyzed 25% of 62 GeV
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J/ ystatistics
per semi cen
83 Recombination
(e.g. Rapp et al.)J/ yield at 200 GeV isdominantly fromrecombination
Predict suppression
greater at 62 GeVJ/ yield down by 1/3Recombination down
1/10
600 M min. bias events 500 J/ measure J/ suppression
Key test of recombination!
83Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
CLAN ModelA Giovannini et al Z Phys C30 (1986) 391
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84
The CLAN model was developed toattempt to explain the reason thatp+p multiplicities are described by
NBD rather than Poissondistributions.
Hadron production is modeled asindependent emission of a numberof hadron clusters, Nc, each with amean number of hadrons, nc.
These parameters can be relatedto the NBD parameters:
Nc = kNBD log(1 + ch/kNBD) and = (ch/kNBD)/log(1 +ch/kNBD).
A+A collsions exhibit weakclustering characteristics,independent of collision energy.
A. Giovannini et al., Z. Phys. C30 (1986) 391.
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Enhancement of low pT particles?
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Velocity of Sound in the Medium
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87Jeffery T. Mitchell - Zimnyi Winter School / Ortvay Colloquium - 12/2/10
Quark Number Susceptibilities
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Q p
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STAR fluctuations
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Fluctuationsa
)(C
c
V
T
TTC
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Above Npart~30, the data can be described by a power law in Npart,independent of the pT range down to 0.2
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PHENIX PRELIMINARY
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Mach Cone at the SPS
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Mach Cone at the SPS
f = -900
Wave Energy at Circle BoundaryPb-Au 17.3 GeV 0-5%
CERESPreliminary