hot, dense, thermalized matter at rhic
DESCRIPTION
Hot, Dense, Thermalized matter at RHIC. LANL Barbara V. Jacak Stony Brook August 7, 2003. outline. Why collide heavy ions? The QCD phase transition the Relativistic Heavy Ion Collider + experiments Data show: Thermalization & pressure build up – early! - PowerPoint PPT PresentationTRANSCRIPT
Hot, Dense, Thermalized matter at RHIC
outline
Why collide heavy ions?The QCD phase transition
the Relativistic Heavy Ion Collider + experiments
Data show:Thermalization & pressure build up – early!(medium-induced) modification of jetsThe control experiment: d+AuMedium effects on fragmentation function?
Conclusions
Collide heavy ions at RHIC to
Create very high temperature and density matteras existed ~1 sec after the Big Banginter-hadron distances comparable to that in neutron starscollide heavy ions to achieve maximum volume
Study the hot, dense mediumis thermal equilibrium reached?transport properties? equation of state?do the nuclei dissolve into a quark gluon plasma?
Au + Au at s = 200 GeV/nucleon pairp+p and d+A to compareAlso polarized p+p collisions to study carriers of p’s spin
Quantum ChromoDynamics
Strong interaction field theory : colored quarks exchange gluons Parallels QED but gluons have color charge
unlike E&M where are uncharged they interact among themselves (i.e. theory is non-abelian):
curious properties
+ +…
short distance:force is weak (probe w/ high Q2, calculate with perturbation theory)large distance: force is strong (probe w/ low Q2, calculations must be non-perturbative) leads to confinementHigh temperature: force becomes screened by produced color-charges, confinement goes away
QCD Phase Transition
Basic (i.e. hard) questionshow does process of quark confinement work?how nature breaks symmetries massive particles from ~
massless quarks transition affects evolution of early universe
latent heat & surface tension matter inhomogeneity in evolving universeequation of state compression in stellar explosions
s = 200 GeV: start with pQCD & pp collisions
p-p hep-ex/0304038
Good agreementwith NLO pQCD
Works!A handle on initial NN interactions by scattering of q, g inside NWe also need:
2
/( , )
a Nf x Q
2
/( , )ch a
D z Q
Parton distribution functions
Fragmentation functions
Xc(A)
pQCD
BFKL, DGLAP
G-sat.
>2
RHIC
Log Q2
-Log10 x
0
In A+A: QCD in non-perturbative regime
T/Tc
Karsch, Laermann, Peikert ‘99
/T4
Tc ~ 170 ± 10 MeV (1012 °K)
~ 3 GeV/fm3
But, we look for physics beyond simple superposition of NN:
EquilibrationCollective effectsEnergy, color transport in dense mediumDeconfinement?
EOS
Lattice…
Physics is softLattice QCD says:Create these conditions to look for new physics
Experimental approach
Central region has max temperature & density
Head-on = “central” collisions max volume
pT
Thermalization? particle spectra, yieldsPressure developed? particle/energy flowsMedium properties? effects upon probe particlesDeconfinement? c and anti-c remain bound as J/?
RHIC at Brookhaven National Laboratory
RHIC is first dedicated heavy ion collider10 times the energy previously available!
4 complementary experiments
STAR
Is the energy density high enough?PRL87, 052301 (2001)
R2
2c
Colliding system expands:
dy
dE
cRT
Bj 22
11
02
Energy tobeam direction
per unitvelocity || to beam
4.6 GeV/fm3 (130 GeV Au+Au)
5.5 GeV/fm3 (200 GeV Au+Au)well above predicted transition!
history of heavy ion collisions
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
, e+e-, + Kpnd,
Real and virtual photons from q scattering sensitive to the early stages. Probe also with q and g produced early, & passing through the medium on their way out.
Hadrons reflect medium properties when inelastic collisions stop (chemical freeze-out).
high , pressure builds up
Particle production (lots!)
Central Au+Aucollisions
(~ longitudinal velocity)
sum particles under the curve,
find ~ 5000 charged
particles in collision final state
(6200 in 200 GeV/A central
Au+Au)
In initial volume ~ Vnucleus
Rescattering should be important!
Hadron pT spectra – all 4 experiments!
BRAHMS: 10% centralPHOBOS: 10%PHENIX: 5%STAR: 5%
200 GeV/A Au+Au
Protons show velocity boost to beam.Expect if pressure build-up due to rescattering
Data well fit with: Tfo = 110-120 MeV & <t> = 0.5-0.6
Simple quark counting:K-/K+
= exp(2s/T)exp(-2q/T)
= exp(2s/T)(pbar/p)1/3
= (pbar/p)1/3
local strangeness conservation K-/K+=(pbar/p)
= 0.24±0.02 BRAHMS = 0.20±0.01 for SPS
Good agreement with statistical-thermal model of Beccatini et al. (PRC64 2001) w/T=170 MeV
At y=0
From y=0 to 3
PRL 90 102301 Mar. 2003
Evidence for equilibrated final hadronic stateBRAHMS
More evidence for equilibrated final state
Observed hadron ratios in agreement with thermal ratios!T(chemical freeze-out) ~ 175 MeV
Early state? a barometer called “elliptic flow”
Origin: spatial anisotropy of the system when created, followed by multiple scattering of particles in the evolving system spatial anisotropy momentum anisotropy
v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane
Almond shape overlap region in coordinate space
y2 x2 y2 x2
2cos2 vx
y
p
patan
v2 measured by the experiments
STAR
v2=0.05
130 GeV: 0.075< pt < 2.0 200 GeV: 0.150< pt < 2.04-part cumulants
200 GeV: 0.2< pt < 2.0
Preliminary
200 GeV: Preliminary
- Consistent results- At 200 GeV better pronounced decrease of v2 for the most peripheral collisions.
STARPreliminary
v2 predicted by hydrodynamics
STARPRL 86 (2001) 402
Hydro. CalculationsHuovinen, P. Kolb,U. Heinz
pressure buildup explosionhappens fast early equilibration !
Hydro can reproduce magnitudeof elliptic flow for , p. BUTmust add QGP to hadronic EOS!!
Similar conclusion reached byKo, Kapusta, Bleicher, others… rescattering must be very large!
central
a unique probe for physics of hot medium
hadrons
q
q
hadronsleadingparticle
leading particle
schematic view of jet productionProbe: Jets from hard scattered quarks
Observed via fast leading particles orazimuthal correlations between the leadingparticles
But, before they create jets, the scattered quarks radiate energy (~ GeV/fm) in the colored medium
decreases their momentum (fewer high pT particles)“kills” jet partner on other side “jet quenching”
Nuclear Modification of Hadron Spectra?
ddpdT
ddpNdpR
TNN
AA
TAA
TAA /
/)(
2
2
<Nbinary>/inelp+p
nucleon-nucleon cross section
1. Compare Au+Au to nucleon-nucleon cross sections2. Compare Au+Au central/peripheral
Nuclear Modification Factor:
If no “effects”: RAA < 1 in regime of soft physics RAA = 1 at high-pT where hard scattering dominates Suppression: RAA < 1 at high-pT
AA
AA
AA
pp
AuAubinaryAuAuAA Yield
NYieldR
/
2/pp
AuAupartAuAupartAA Yield
NYieldR
/
Au-Au s = 200 GeV: high pT suppression!
nucl-ex/0304022
Au-Au nucl-ex/0304022
jet correlations: Au+Au vs p+pSTAR PRL 90, 082302 (2003)
Central Au + Au
Peripheral Au + Au
22 2 2( ) ( ) (1 cos(2 ))D Au Au D p p B v
Back-to-back jets are suppressed in central collisions!
near side
away side
peripheral central
Suppression: a final state effect?
Hadronic absorption of fragments: Gallmeister, et al. PRC67,044905(2003)Fragments formed inside hadronic medium
Recombination of flowing partonsFries, Muller, Nonaka, Bass nucl-th/0301087Lin & Ko, PRL89,202302(2002)
Energy loss of partons in dense matterGyulassy, Wang, Vitev, Baier, Wiedemann…
PCM & clust. hadronization
NFD
NFD & hadronic TM
PCM & hadronic TM
CYM & LGT
string & hadronic TM
Hadron gas
1AuAuR Absent in d+Au collisions!d+Au is the “control” experiment
Not technically a realfinal state effect…
Suppression: an initial state effect?
Gluon Saturation (color glass condensate)
Wavefunction of low x gluons overlap; the self-coupling gluons fuse, saturating the density of
gluons in the initial state. (gets Nch right!)
• Multiple elastic scatterings (Cronin effect) Wang, Kopeliovich, Levai, Accardi
• Nuclear shadowing
Levin, Ryshkin, Mueller, Qiu, Kharzeev, McLerran, Venugopalan,
Balitsky, Kovchegov, Kovner, Iancu …
probe rest frame
r/ggg
dAu AuAuR R RdAu~ 0.5D.Kharzeev et al., hep-ph/0210033
1dAuR
decreases dAuR
Broaden pT :
PHENIX Preliminary 0
PHOBOS Preliminary
STAR Preliminary
Experiments show NO suppression in d+Au!
Are the RdA numbers wrong due to inel?
STAR
Compare for charged hadrons at = 0 in min bias collisionsBoth compare to their own measured pp at s = 200 GeV
PHENIX sees ~10% of single diffractive and 30% of double diffractive in ppAnalysis approach: correct pp to 42 mb via trigger efficiency correction; 42mb to calculate Ncoll in d+Au~ same as <T(dAu)>* ppmeasin denominator
STAR triggers on forward n, sees all double diffractive and some single diffractive.
No room for PHENIX by 20-30% and STAR by 10%
A caveat
As noted in nucl-th/0307087, the values of RdAu do NOT include gluon shadowing
True!
Of course, it is also not included in Ncoll for Au-Au, to which the d-Au result is compared
Large theoretical uncertaintyTherefore inappropriate for experiments to simply
“pick one” (at this point)
Do see Cronin effect at RHIC
“Cronin” enhancement more pronounced in the charged hadron measurement
Larger effect in protons at mid pT
Implication of RdAu? RHIC at too high x for gluon saturation…
(h++h-)/2
0
0 RAA vs. predictions
PHENIX Preliminary
shadowing
anti-shadowing
Theoretical predictions:
d+Au: I. Vitev, nucl-th/0302002 and private communication.
Au+Au: I. Vitev and M. Gyulassy, hep-ph/0208108, to appear in Nucl. Phys. A; M. Gyulassy, P. Levai and I. Vitev, Nucl. Phys. B 594, p. 371 (2001).
Initial state: mult. scatt.,shadowing + final state dE/dx (Au+Au)
Also: Kopeliovich, et al (PRL88, 232303,2002)
predict RpA~1.1 max at pT=2.5 GeV projectile as color dipole
Centrality Dependence
Dramatically different and opposite centrality evolution of AuAu experiment from dAu control.
Jet Suppression is clearly a final state effect.
PHENIX Preliminary results, consistent with PHOBOS data in submitted paper
Au + Au Experiment d + Au Control
Back-to-back jets observed in d+Au
• jet pair production also looks independent of Ncoll
• observe no (big) suppression in back-to back jets!
• probably some jet broadening due to initial multiple scattering…
STAR
PHENIX preliminary
Particle mix observed at RHIC is different!
p/ ~1 at high pT
in central collisionsHigher than in p+por jets in e+e-collisions
Hydro. expansion at low pT
+ jet quenching at high pT?
Medium modified fragmentationfunction?
Vitev&Gyulassy nucl-th/0104066
Do the baryons scale with Ncoll?
hard/soft process interplay… Quark recombination?Medium modification of fragmentation function?
Baryon yields not suppresed Ncoll at pT = 2 – 4 GeV/c
Au+Au
To help sort it out, study initial state effects
=
d+Au PHENIX preliminary
low pT
high pT Initial state multiplescattering mechanism?NOT incoherent soft multiple scatterings…
Mesons vs. baryons Cronin effect? Should help sort out fragmentation function vs. parton recombination …
ProtonA. Andronic et. Al. Nucl-th/0303036
Deconfinement? Does colored medium screen c+cbar?
Don’t know yet about deconfinement, but don’t see EXTRA (thermal) J/
Look at J/
R.L. Thews, M. Schroedter, J. Rafelski Phys. Rev. C63 054905 (2001): Plasma coalesence modelfor T=400MeV and ycharm=1.0,2.0, 3.0 and 4.0.
L. Grandchamp, R. Rapp Nucl.
Phys. A&09, 415 (2002) and Phys. Lett. B 523, 50 (2001):Nuclear Absorption+ absoption in a high temperature quark gluon plasma
40-90%most central Ncoll=45
0-20%most central Ncoll=779
20-40%most central Ncoll=296
J/ in pp collisions
= 3.98 ± 0.62 (stat) ± 0.56 (sys) ± 0.41(abs) b
<pT> = 1.80 ± 0.23 (stat)
± 0.16 (sys) GeV
open charm via single e in 200 GeV Au+Au
Compare themeasurement to (PYTHIA) an event generator tuned for pp collisions…
no largesuppression- unlike lightquarks!
Spectra of electrons from c e + anythingphotonic sources are subtracted
Total charm quark cross section at RHIC
Same conclusion from 130 GeV/A Au+Au data!Cross section fits into expected energy dependence
Why no energy loss for charm quarks?
“dead cone” predicted by Kharzeev and Dokshitzer, Phys. Lett. B519, 199 (1991)
conclusions
Rapid equilibration! Strong pressure gradients, hydrodynamics worksConstituent scattering cross section is very large
EOS is not hadronic The hot matter is “sticky” – it absorbs energy
See energy loss, disappearance of back-to-back jetsd+Au data says: final state, not initial state effect
So, the stuff is dense, hot, ~ equilibrated AND NEW!
OK, why not announce QGP discovery?J/ suppression or not? Next runTinitial? direct photon analysis underway by PHENIXProperties not as expect for plasma – looks like gluon liquid
A couple of mysteries…
Hydro describes single + multi-particles
• How to increase R without increasing Rout/Rside???
EOS?initial T & r profiles? emissivity?
But FAILS to reproducetwo-particle correlations!
Elliptic flow of high momentum particles
pT (GeV/c)
v2baryons cross mesons(not expected from hydro)
Still flowing at pT = 8 GeV/c? Geometry? v2 a bit too big…interplay of flow + jets???
is d+Au same as p+Au?
p
n ZDC
Neutron tagged eventsenhance peripheral collisions
<Ncoll> = 5.0 / 3.6Could be Ncoll dependenced+Au looks very similar to p+Au
More on RdAu & Glauber calculation
What we actually doRdA= 1/Nevt d2Nparticle/ddpT
--------------------------------- <Ncoll>/pp,inel d2pp/ddpT
TheoreticallyRdA= 1/Nevt d2Nparticle,dAu/ddpT
--------------------------------- <TAB> d2pp /ddpT
As pointed out in nucl-th/0306044<Ncoll> = <TAB>* pp,inel ---------------------
1 – exp (- <TAB>* pp,inel )
We measure pp= 21.3mb
Evaluate trigger eff. for
full pp,inel and correct
particle yield by that
= 0.99982 for m.b.= 0.973 for leading n(absorbed in syst)
Why no big energy loss for heavy quarks?
no x4 suppressionfrom peripheral to central,as predicted fordE/dx=-0.5GeV/fm!
But (we squirm) - Is 40-70% peripheral enough? error bars still big!
Particle Composition at high pT
(h++h-)/20 ~ 50% greater in central than peripheral at mid pT
similar again for pT>5 GeV/c
Central
Peripheral
Run 2001/2002 Au-Au 200 GeV:s
Locate RHIC on phase diagram
Baryonic Potential B [MeV]
0
200
250
150
100
50
0 200 400 600 800 1000 1200
AGS
SIS
SPS
RHIC
quark-gluon plasma
hadron gas
neutron stars
early universe
thermal freeze-out
deconfinementchiral restauration
Lattice QCD
atomic nuclei
fit yields vs. mass (grand canonical ensemble)
Tch = 175 MeV B = 51 MeV
These are the conditions when hadrons stop interacting
T
Observed particles “freeze out” at/near the deconfinement boundary!
J/ suppression was observed at CERN at s=18 GeV/A
Fewer J/ in Pb+Pb than expected!Interpret as color screening of c-cbar
by the mediumInitial state processes affect J/ tooso interpretation is still debated...
collaboration
J/yield
Vitev: they can get v2 right
C. Adler et al. [STAR Collab.], arXiv: nucl-ex/0206006
K. Filimonov [STAR Collab.],arXiv: nucl-ex/0210027
b=7 fmb~7 fm
• There is a quantitative difference Calculations/fits with flat or continuously growing
2 .v const 2 / .ln Tv p
Check against high-pT data (200 AGeV)
Same for 0-50%
• The decrease with pT is now supported by data• For minimum bias this rate is slightly slower
See: N.Borghini, P.Dinh, J-Y.Ollitrault, Phys.Rev. C 64 (2001)
kT dependence of R
Centrality is in top 30%
•Broad <kT> range : 0.2 - 1.2 GeV/c •All R parameters decrease as a function of kT consistent with collective expansion picture. • Stronger kT dependent in Rlong have been observed.
kT : average momentum of pair
Comparison of kaon to pion
In the most 30% central
Comparison with hydrodynamic model
Recent hydrodynamic calculation by U.Heinz and P. F. Kolb(hep-ph/0204061)
kT dependence of Rlong indicates the early freeze-out?
Hydro w/o FS
Hydro at ecrit
• Assuming freeze out directly at the hadronization point. (edec = ecrit)
• Standard initialization and freeze out which reproduce single particle spectra.
Centrality is in top 30%
kT dependence of Rout/Rside
A. EnikizonoQM2002
C.M. Kuo, QM2002 poster (PHOBOS) 200 GeV:
.)(25.009.016.1 syst @0.25 GeV/c
HBT PUZZLE
P.Kolb
Small Rout implies small
Large Rside implies large RSmall Rbeam impliessmall breakup ~10 fm/c
Jet Evidence in Azimuthal Correlations at RHIC
near-side correlation of charged tracks (STAR)trigger particle pT = 4-6 GeV/c distribution for pT > 2 GeV/c
signature of jets
also seen in (0) triggered events (PHENIX)trigger particle pT > 2.5 GeV/c distribution for pT = 2-4 GeV/c
M. Chiu, PHENIX Parallel Saturday
QM2002 summary slide (Peitzmann)
Identifying Jets - Angular Correlations
Remove soft background by subtraction of mixed event distribution
Fit remainder:Jet correlation in ; shape taken from PYTHIAAdditional v2 component to correct flow effects
PHENIX Preliminaryraw differential yields
2-4 GeV
Verify PYTHIA using p+p collisions
(neutral E>2.5 GeV + 1-2 GeV/c charged partner)
||<.35 ||>.35
ake cuts in to enhance near or far-side correlationsBlue = PYTHIA
In Au+Au collisions
1-2 GeV partner
(neutral E>2.5 GeV + charged partner)
||<.35 ||>.35
1/N
trig d
N/d
1/N
trig d
N/d
Correlation after mixed event background subtraction
Clear jet signal in Au + AuDifferent away side effect than in p+p
Jet strengthSee non-zero jet strength as partner pT increases!
jets or flow correlations? fit pythia + 2v2vjcos(2)
partner = .3-.6 GeV .6-1.0 GeV/c 2-4 GeV/c
1/N
trig d
N/d
v2
vj
1-2 GeV/c
How many particles are produced?
dNch/d = 640
Rises somewhat faster than Npart
Charged hadron correlations - small
•Fit charged correlations with v2 + Gaussian (fixed pT)•Jet signal visible via
Width of near-side Gaussian decreases with pT
No significant centrality dependence on near-side
Cor
rela
tion
wid
th
jT
pT Correlation width jT/pT
How do high pT yields scale?
vs. binary collisions:continuous decrease as
function of centralityfactor ~ 3.5 from
peripheral to central vs. participants:
first increase, then decrease as function of centrality
for Npart > 100 have 3 change (scaling or no?)
surface emission? re-interactions?accident?
18% scaling uncertainty from corrections
Opaque, expanding source would mean:
2222222 2)()( xtso YXRR
)(outX
)(sideY
29.13
5)(
)(
spheres
shellhalfs
R
R
65.012
5)(
)(
sphereo
shellhalfo
R
R
Opaque Expanding
Rischke RIKEN workshop (2002): Such strong xt correlations probably require a lack of boost-invariance...
Energy Dependence
Assumptions:in Lab in C.M.
Energy density (Bjorken):
2% most central at sNN=200 GeV:
5.5 GeV/fm3
From AGS, SPS to RHIC:
Transverse energy and charged particle multiplicity densities per participant consistent with logarithmic behaviour
d
dX
dy
dX
d
dX
dy
dX2.1
dy
dE
Rt
2
1
cfm
AfmR
/1
18.1 3/1
PHENIX preliminary
PHENIX preliminary
So, is there jet quenching?
Suppression observed to 8 GeV/c! (in 3 independent measurements)
Theory agrees with data when quark, gluon energy loss is included
NB: 2 examples here, others also must add some kind of medium modification of the fast quarks/gluons
In initial or final state?
Look at “transverse mass” mT2 = pT
2 + m02
— is distribution e-E/T?i.e. Boltzmann distribution from thermalized gas?
hadron spectra: , K, p and antiprotons
130GeV/A
yes !
Protons are flatter velocity boost to beamResult of pressure built up
Spectral shapes
<pT> for radially expanding hadrongas with Tth and <>
<pT> in pp with “Tch” = 170 MeV and <>=0pp no rescattering, flow or equilibrium
STAR
preliminaryF. Wang
min bias 200 GeV Au+ Au
v2 at high pT
Note pbar/p behavior
Centrality dependence only for pT > 3 GeV/c
Peripheral collisions have quite a few protons at mid-y
Anti-particle/particle ratios vs. rapidity
At y=0 (central coll.)
pbar/p = 0.75 ±0.04
K-/K+ = 0.95 ±0.05 = 1.01 ±0.04
Nearly baryon-free at central y, but not complete transparency
Larger contribution of protons nearer rapidity of the Au beams
PRL 90 102301 (Mar. 2003)
BRAHMS