what did we learn at rhic?
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What did we learn
at RHIC?Tetsufumi HiranoTetsufumi Hirano
Dept. of PhysicsDept. of Physics
The University of TokyoThe University of Tokyo
原子核・ハドロン物理:横断研究会
My Charge(?)
• 「原子核・ハドロン物理:横断研究会」におけるレビュー講演 原子核の他分野の方々に当該分野の現状を報告
• SPIRESを使って引用数の多いRHIC実験論文を理論屋(現象論屋)の立場から眺めてみよう。– 良い点:限られた時間で(客観的に)重要な
トピックスに絞れる– 悪い点:最新の結果に触れられない
• (私個人として、)何が分かって、何を目指すべきか。
What is RHIC?
Relativistic Heavy Ion Collider(2000-)
sideview
frontview
STAR
STAR
Purpose: Create a transient state of the QGPat high temperature and energy density ina laboratory and investigate its property.
これまでのRUNRun Ions sNN Luminosity
1 Au+Au 130 GeV 1 b-1
2 Au+Au 200 GeV 24 b-1
p+p 200 GeV 0.15 pb-1
3 d+Au 200 GeV 2.74 nb-1
p+p 200 GeV 0.35 pb-1
4 Au+Au 200 GeV 241 b-1
Au+Au 62.4 GeV 9.1 b-1
p+p 200 GeV 324 nb-1
5 Cu+Cu 200 GeV 4.8 nb-1
Cu+Cu 62.4 GeV 190 b-1
p+p 200 GeV 3.8 pb-1
6 p+p 200 GeV 10.7 pb-1
p+p 62.4 GeV 0.1 pb-1
7 Au+Au 200 GeV 813 b-1
8d+Au
p+p
200 GeV
200 GeV予定
織田さん(CNS)のトーク@ RCNP (‘07)から
•Size dependence•Energy dependence•Control experiment•(spin)
加速器側で制御できるのはせいぜい当てる原子核とエネルギー
FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007)
STAR PHENIX PHOBOS BRAHMSYields & Spectra 2 4 (1) 7 1
Elliptic flow 5 (3) 2(1)HBT 1 1
High pT 6 (4) 6 (3) 2Baryon 1
Etc. (incl. white paper) 4 (1) 3 (1) 1 (1) 1 (1)
Total 18 (8) 17 (6) 8 (1) 4 (1)
カッコ内はそのうち TOPCITE 250+
Dynamics of Heavy Ion Collisions
Time scale10fm/c~10-23sec<<10-4(early universe)
Temperature scale 100MeV~1012K
Freezeout
“Re-confinement”
Expansion, cooling
Thermalization
First contact (two bunches of gluons)
# of binary collisions
x
y
Thickness function:
Woods-Saxon nuclear density:Gold nucleus:0=0.17 fm-3
R=1.12A1/3-0.86A-1/3
d=0.54 fm
in = 42mb @200GeV
# of participants
1 -( survival probability )
Ncoll & Npart
Centrality (検出器側の制御)
PHENIX: Correlation btw. BBC and ZDC signals
•Npart and Ncoll as a functionof impact parameter•Categorize events with Npart or Ncoll
Au+Au 200 GeV
FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007)
STAR PHENIX PHOBOS BRAHMSYields & Spectra 2 4 (1) 7 1
Elliptic flow 5 (3) 2(1)HBT 1 1
High pT 6 (4) 6 (3) 2Baryon 1
Etc. (incl. white paper) 4 (1) 3 (1) 1 (1) 1 (1)
Total 18 (8) 17 (6) 8 (1) 4 (1)
カッコ内はそのうち TOPCITE 250+
Centrality Dependence of Multiplicity
PHENIX, PRL86,3500(‘01)Cited 194 times
•EKRT: final state saturation (Eskola et al.)•HIJING: event generator (string+jet) (Wang-Gyulassy)•Saturation Model: color glass condensate (Kharzeev-Levin)
PHOBOS,PRC65,061901(’02)Cited 105 times
•Nch ~ 5000(700) in very central collisions (at midrapidity)•~90% from soft particle production•Serves a severe test for models of particle production
Energy DensityBjorken formula (’83)
c from lattice
•Assuming =1fm/c, well above c from lattice in central collision at RHIC•Necessary condition to study the QGP at RHIC
Volume of cylinder
Sorry, I could not find the original paper.PHENIX, PRL87,052301(’01)Cited 121 times
Particle Relative Yield
STAR,NPA757,102(’05)Cited 408 times
•Tch = 157 +- 6 MeV, B = 22 +- 4 MeV•Really equilibrated in peripheral collisions?•Just fitting parameters?
STAR, PRL92,112301(’04)Cited 161 times
pT spectra
•Blue-shifted spectra are evidence of radial flow•Blast wave model gives = 0.48+-0.07 in 0-5% bin.•Quantitative interpretation needs dynamical model.
PHENIX, PRC69,034909(’04)Cited 268 times
Blast wave model (thermal+boost)
FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007)
STAR PHENIX PHOBOS BRAHMSYields & Spectra 2 4 (1) 7 1
Elliptic flow 5 (3) 2(1)HBT 1 1
High pT 6 (4) 6 (3) 2Baryon 1
Etc. (incl. white paper) 4 (1) 3 (1) 1 (1) 1 (1)
Total 18 (8) 17 (6) 8 (1) 4 (1)
カッコ内はそのうち TOPCITE 250+
What is Elliptic Flow?
How does the system respond to spatial anisotropy?
J.Y.Ollitrault,PRD46,229 (’92)
Hydro behavior
Spatial Anisotropy
Momentum Anisotropy
INPUTINPUT
OUTPUTOUTPUT
Interaction amongInteraction amongproduced particlesproduced particles
dN
/d
No secondary interaction
0 2
dN
/d
0 2
2v2
x
y
Multiplicity Dependence of v2
STAR, NPA757,184(’05)Cited 410 timesSTAR, PRC66,034904(’02)Cited 162 times
Particle Density
Re
sp
on
se
= (
ou
tpu
t)/(
inp
ut)
•Experimental data reach “hydrodynamic limit”for the first time at RHIC•But, only one data point?
P.F.Kolb et al.,PRC62,054909(’00)
pT dependence of v2
STAR, PRC72,014904(’05)Cited 127 times
PHENIX,PRL91,182301(’03)Cited 242 times
•A hydrodynamic model based on perfect fluidsreasonably describes pi, K, p, Lambda data in low pT region. •How small is viscosity?•How fragile/robust? See our recent papers
Hydro calculations: P.Huovinen
Hydrodynamic ModelFinal stage:Free streaming particles Need decoupling prescription
Intermediate stage:Solve energy-momentum conservation. Need EoS and/or transport coefficients
Initial stage:Particle production,pre-thermalization, instability?Instead, initial conditions for hydro simulations
0z
t
FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007)
STAR PHENIX PHOBOS BRAHMSYields & Spectra 2 4 (1) 7 1
Elliptic flow 5 (3) 2(1)HBT 1 1
High pT 6 (4) 6 (3) 2Baryon 1
Etc. (incl. white paper) 4 (1) 3 (1) 1 (1) 1 (1)
Total 18 (8) 17 (6) 8 (1) 4 (1)
カッコ内はそのうち TOPCITE 250+
Two-Particle Correlation FunctionC2
Bertsch-Pratt equation
•Inverse problem to get source information
Bertsch-Pratt parameterization
p1
p2
reaction planez
Rlong
KT
Rout
Rside
x
y
Two-pion correlation function
Bird’s eye view View from beam axis
q
1
C2
q
1/R
KT Dependence of HBT Radii
PHENIX, NPA757,184(’05)Cited 410 timesPHENIX, PRL88,192302(’02)Cited 128 timesSTAR, PRL87,082301(’01)Cited 193 times
•Hydro models do not give correct source sizes.•HBT puzzle in a narrow sense•Last interaction point Hydro description is not valid.
Hydro(-based) calculationSoff, Kolb,Hirano,…
FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007)
STAR PHENIX PHOBOS BRAHMSYields & Spectra 2 4 (1) 7 1
Elliptic flow 5 (3) 2(1)HBT 1 1
High pT 6 (4) 6 (3) 2Baryon 1
Etc. (incl. white paper) 4 (1) 3 (1) 1 (1) 1 (1)
Total 18 (8) 17 (6) 8 (1) 4 (1)
カッコ内はそのうち TOPCITE 250+
Tomography
* 平野哲文、浜垣秀樹、「ジェットで探るクォークグルーオンプラズマ」、日本物理学会誌 2004 年 12 月号
CT (computed tomography) scan
“Tomography”1. Known probes: Spectra reliably calculable via pQCD2. Good detector: RHIC experiments!3. Interaction btw. probes and unknowns: Recent development in this field
Jet Tomography
g g
g
Tool 1. Jet quenching
High “density” matter
Tool 2. Jet acoplanarity
180 deg. correlation?
Bjorken(’82)Gyulassy,PlümerWang (’90)
Bjorken(’82)Appel (’86)Blaizot & McLerran (’86)
pT
RAA 1
binary collision scaling
Au+Au 0-10% central•b=2.8 fm
•Ncoll = 978•Npart = 333
•Npart/Ncoll = 0.341
participant scaling0.341
Nuclear Modification Factor
(null result)
High pT Spectrum in pp Collisions
PHENIX, PRL91,241803(’03)Cited 193 times
•NLO pQCD works at RHIC•Important for AA collisions•Serves a reference spectrum
Nuclear Modification Factor
PHENIX, PRL88,022301(‘02)Cited 402 times
•RAA < 1 for the first time at RHIC•Significant suppression in central collisions
char
gedSTAR, PRL89,202301(’02)Cited 292 times
Di-hadron Distribution
STAR, PRL90,082302(’03)Cited 341 times
•Disappearance of away-side peaks in central collisions•Away side jet may be gone.
4<pT,trigger<6 GeV/c2 GeV/c<pT,associate<pT,trigger
???
Initial vs. Final
Importance of pA (dAu) collisions
D.Kharzeev et al., PLB561, 93(‘03).
•Saturation Npart scaling(Later, ∃Cronin peak even within CGC)•ggg (no back-to-back)
I.Vitev and M.Gyulassy,PRL89, 252301(‘02)
•Jet quenching•dNg/dy =500-1200 @ RHIC
Results from d-Au Collisions
STAR,PRL91,072304(’03)Cited 314 times
PHENIX, PRL91,072303(’03)Cited 276 times
Results from d-Au Collisions
PHOBOS, PRL91,072302(’03)Cited 169 times
BRAHMS, PRL91,072305(’05)Cited 204 times
•Neither suppression nor disappearance in d+Au•Jet quenching scenario turns out to be favored.•This does not mean saturation models are killed.
High pT at forward
BRAHMS, PRL91,072305(’03)Cited 204 times
=0
=2.2
•More suppression at forward, or initial state effect?
Kinematic EffectJet quenchingSpectrum shift
pT
(1/p
T)d
N/d
p T “parallel shift”
pT(1
/pT)d
N/d
p T Different slope,but same shift
00
Ratio at a fixed pT.
TH and Y.Nara, PRC68,064902(’03)
•R can be less than unity.•But, insufficient to explain data
Saturation effect in d+Au?
BRAHMS, PRL93,242303(’04)Cited 153 times
•Forward rapidity Small x in a nucleus•Manifestation of Color Glass Condensate?
Cronin Peak Suppression
D.Kharzeev et al.,PRD68,094013(’03);PLB599,23(’04).
•Cronin peak disappears as moving away from midrapidity.•Qualitatively consistent with data
preliminary
H.Fujii, talk at RCNP workshop(’07)
y=0,1,2,3
Di-Hadron spectra revisited
PHENIX, PRL97,052301(’06)Cited 143 times
2.5<pT,trigger<4.0 GeV/c1.0<pT,associated<2.5 GeV/c
4.0<pT,trigger<6.0 GeV/c0.15<pT,associated<4.0 GeV/c
STAR,PRL95,152301(’05)Cited 131 times
•Where does the lost energy go?•Mechanism? (Mach cone? Deflected jets?)
FIND CN *** AND TOPCITE 100+*** = STAR, PHENIX, PHOBOS, BRAHMS (as of Nov.15,2007)
STAR PHENIX PHOBOS BRAHMSYields & Spectra 2 4 (1) 7 1
Elliptic flow 5 (3) 2(1)HBT 1 1
High pT 6 (4) 6 (3) 2Baryon 1
Etc. (incl. white paper) 4 (1) 3 (1) 1 (1) 1 (1)
Total 18 (8) 17 (6) 8 (1) 4 (1)
カッコ内はそのうち TOPCITE 250+
No Suppression for Baryons
C.Seife, Science298,718(2002)
Baryon Enhancement
PHENIX, PRL91,172301(’03)Cited 126 times
PHENIX, PRC69,034909(’04)Cited 268 times
•Baryons are not suppressed in intermediate pT
•Mechanism of enhancement?
Recombination as a Third Component
Low pT (bulk, hydro)
High pT (fragmentation)
““Third Component”Third Component”Intermediate pIntermediate pTT (~2-5 GeV/c) (~2-5 GeV/c)
RecombinationRecombination
Soft-Hard Soft-Hard CoalescenceCoalescence
Soft-Softrecombination
Elliptic Flow Scaling
STAR, PRC72,014904(’05)Cited 127 times
qq qbarqbar+
= mesonmeson
qq qq
+
+
= baryonbaryon
meson(n=2)
baryon(n=3)
Voloshin(’02), Molnar, Lin(’03), Fries,Nonaka,Muller,Bass(’03),Hwa,Yang(’04),Pratt,Pal(’05)…
Summary1. One day experimentで、粒子生成メカニズムに制
限をつけることができる。素朴な2成分モデルでは、ソフトな生成は90%近い。
2. 中心衝突では、エネルギー密度は十分格子QCDから予言されている臨界値を超えている。~5GeV/fm3 @ τ =1fm/c
3. 化学平衡が切れる温度は160MeV程度。擬臨界温度に近い。4. 光速の50%近い横膨張速度が得られている。大きな圧力(勾配)。5. 完全流体QGPを仮定したダイナミクスと楕円型フローの実験結果が
よく合う。6. HBT半径は流体模型では合わない。7. ミニジェットの収量は中心衝突では20%程度まで減っており、終状
態相互作用の結果である。8. 前方ラピディティでは、作られたミニジェットが減っており、CGC
の発展方程式の振る舞いとコンシステント。9. 消えた後方ジェットは、マッハ錐状(?)に出ている。10. バリオンの収量は中間横運動量領域(2-6GeV/c)で減らない。
楕円型フローのスケーリング的振る舞いから、クォーク再結合模型が有力。 •個々のモデルはそれなりにうまくいっている。
•しかし、統一的な記述は未だに得られず。
Talk by T.Hallman @ ICHEP04
contd.
Inconsistency• Some hydro model does not reproduce relative yields.
Need chemical potential for hadrons
Importance of viscosity at a hadronic level (hadronic corona)• The number of partons obtained from jet tomography is smaller than that
from hydro.
Need chemical non-equilibrium process in QGP fluids.• Energy per particle from CGC is larger than data.
Need pdV work (e.g., hydrodynamic approach)• CGC gives a large eccentricity at initial state and overshoot elliptic flow
data as an initial condition for ideal hydro.
Need viscosity in QGP fluids• Twice larger radial flow to understand data in intermediate pT via
recombination than the one obtained from hydro simulations.
Need quantitative and dynamical anaysis of recombination mechanism• …
Current Status of Dynamical Modeling
Pro
per
tim
e
Transverse momentum
CGC Geometric Scaling
Shattering CGC
Hydrodynamics•viscosity•non chem. eq.
Parton energy loss•Inelastic (light)•Elastic (heavy)
Hadroniccascade
Low pT High pT
RecombinationCoalescence
“DGLAP region”
(N)LOpQCDBefo
re
colli
sions
Part
on
pro
duct
ion
Pre
-equili
bri
um
“Perf
ect
” fluid
QG
P o
r G
P
Dis
sipati
ve
hadro
ngas
Fragmentation
Interaction
Intermediate pT
fluctuationInstability?Equilibration?
Our studies reduce model ambiguities
• TH,PRL86,2754(’01);PRC65,011901(’02).
First realistic full 3D hydro. No Bjorken boost invariant ansatz.• TH and K.Tsuda, PRC65,061902(’02).
Introduce chemical freezeout in hydro. Get correct particle ratios and spectra simultaneously for the first time.
• TH and Y.Nara, PRC66,041901(’02);PRL91,082301(’03); PRC68,064902(’03);PRC69,034908(’04).
Jet quenching in QGP fluids. Realistic matter profile for jet quenching analysis.
• TH and Y.Nara, NPA743,305(’04).
CGC initial condition in hydro. Remove some issues for initial conditions in hydro simulations.
• TH and M.Gyulassy, NPA769,71(’06); TH et al., PLB636,299(’06).
Hadronic cascade after QGP evolution. Remove issues for final decoupling.
(Incomplete) Reference List• RHIC white papers (BRAHMS,PHOBOS,STAR,PHENIX)
– Nucl.Phys.A757,1(‘05)
• Review papers– Quark Gluon Plasma 3, Eds. R.C.Hwa and X.-N. Wang (World
Scientific, Singapore, 2004)• Hydro: P.F.Kolb and U.W.Heinz, P.Huovinen
• Jet quenching: M.Gyulassy,I.Vitev,X.-N.Wang,B.-W.Zhang
• CGC: E.Iancu and R.Venugopalan
• …
– Hydro• TH, proceedings of Quark Matter 2004
(J.Phys.G30.S845(’04)),ISMD04(Acta.Phys.Pol.B36,187(’05)), YKIS06(Prog.Theor.Phys.Supplement168,347(’07))
– Femtoscopy• M.A.Lisa, S.Pratt,R.Soltz,U.Wiedemann,nucl-ex/0505014
– ReCo• R.Fries, proceedings of Quark Matter 2004,nucl-th/0403036
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