Explore the QCD Phase Diagram

Nu Xu
Lawrence Berkeley Na4onal Laboratory

Many Thanks to the Organizers
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Outline
1) Introduction
2) Recent experimental data
- High pT results- Partonic collectivity at RHIC

3) Outlook- Heavy quark measurementsthermalization- RHIC beam energy scan


Nu Xu

QCD tri-critical point

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Physics Goals at RHIC
- Identify and study the propertiesof the matter (EOS) with partonic
degrees of freedom.
- Explore the QCD phase diagram.

Nu Xu

Bulk Properties:

Penetrating Properties:(1) Spectra and anisotropies(2) Correlation and fluctuations(3) Heavy quark hadron collectivity(4) …

(1) Leading hadron spectra(2) Jets production(3) High pT triggered correlations(4) Heavy quark production …

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STAR Physics Focus
1) Heavy‐ion program‐ Study medium proper6es, EoS‐ pQCD in hot and dense medium

2) RHIC beam energy scan

‐ Search for cri6cal point‐ Chiral symmetry restora4on

Polarized spin program‐ Study proton intrinsic proper6es

Forward program‐ Study low‐x proper4es, search for CGC‐ Study elas4c (inelas4c) processes (pp2pp)‐ Inves4gate gluonic exchanges

Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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PHOBOSPHENIX

BRAHMS

RHIC

STAR‐ RHIC: The highest energy
heavy‐ion collider in the world!
√sNN = 200 ‐ 5 GeV

AGS

Au + Au, Cu + Cu, d + Au
‐ RHIC: The highest energy
polarized proton collider!

TANDEMS√s = 200, 500 GeV
Anima&on M. Lisa

Nu XuATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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STAR Detector
EMC barrel
EMC End Cap
RPSD
FMS
FPD

TPC

PMD

Complete
FTPC
Full azimuthal particle identification!
e, π, ρ, K, K*, p, φ, Λ, Δ, Ξ, Ω, D, ΛC, J/ψ, Υ …
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

Ongoing
R&D

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STAR Detectors: Full 2π particle identification!
TPC

TOF

EMC+EEMC+FMS(‐1 ≤ η ≤ 4)
DAQ1000

HFT

FGT
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Au + Au Collisions at RHIC

Central Event

Nu Xu(real‐Ome Level 3)

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Particle Identification at STAR
STAR TPCronsdeutensprotoskaonSTAR ToF

STAR EMCSTAR HFT

Strange hadrons
Nu Xu

Jets
ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

Heavy quark hadrons
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Log10(dE/dx)

Light Hadron PID at Large pT

Log10(p)1)
2)
3)

Low p:TPC
0.2 < pT < 5 GeV/c
ToF> 5 GeV/c
TPC(dE/dx at rela4vis4c rise extends PID beyond pT ~ 10 GeV/c)

Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Suppression and Correlation

In central Au+Au collisions: hadrons are suppressed and back-to-back ‘jets’
are disappeared. Different from p+p and d+Au collisions.
Energy density at RHIC: ε > 5 GeV/fm3 ~ 30ε0
Parton energy loss:
Bjorken“Jet quenching”:
Gyulassy & Wang
…
Nu Xu

1982
1992

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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High pT Results of pion Spectra

STAR preliminary

STAR preliminary

PYTHIA (V6.205, MSEL=1) and GEANT are used to get triggerefficiency to correct spectra in triggered events.
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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High pT Results for proton Spectra

STAR Preliminary

p+p collisions at RHIC:
pQCD based calculations provide a reasonable fit to data
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 200813/30

pion and proton RAA at High pTSTAR preliminary(1) STAR PID up topT ~ 12 GeV/c(2) At the highest pTRAA(π) ≤ RAA(p)⇒ Noeffects!

Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Heavy Flavor Energy Loss
STAR PRL, 98, 192301 (2007)

1) Non-photonicelectrons decayedfrom - charm andbeauty hadrons2) At pT ≥ 6 GeV/c,RAA(n.e.) ~ RAA(h±)!
contradicts to naïvepQCD predictions
Surprising results - challenge our understanding of the energy loss mechanism- force us to RE-think about the collisional energy loss
- Requires direct measurements of C- and B-hadrons.
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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γ-Jet Measurement in STAR
“Golden Probe” of QCD Energy Lossqγ
QCD Compton
ScaSeringgqγh- This probe is valuable for comparison with di-hadron correlations- Goal: Full reconstructed kinematics: real fragmentation function D(z)Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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High Mass: ϒSequential dissociation ofquarkonia is sensitive toenergy density of plasma

RHIC

ϒ (1S+2S+3S) → e+eRun 6: 200 GeV p+p

Run 7: 200 GeV Au+Au

preliminary

STAR high pT topological electron trigger works!
pQCD calculations are consistent with data!
Nu Xu

RHIC Science and Technology Review, BNL, July 7-9, 2008

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dNJet/dET (per event)

Reconstructed Jet in Au+Au
p+p(scaled by Nbin) Au+Au 10%
O HT‐Trig

MB-Trig: Good agreement with Nbin
scaled p+p collisions
HT-Trig: Large trigger bias persists atleast to 30 GeV.
Relative normalization systematic
uncertainty: ~50%
Resolution effect corrected assuming
Pythia fragmentation.

STAR Preliminary

Further statistics of MB is needed toassess the bias in HT Trigger.
Leading Order High Seed Cone(LOHSC)
R=0.4, pT = 1 GeV/c, seed = 4.6 GeV/c

Sta4s4cal errors only.
Nu XuFirst step towards jet reconstructionin heavy ion collisions.

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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18Search for Mach Cone
STAR: sub. to PRL, arXiv: 0805.0622

with Three Particle Correlations

neard+Au

Mediumaway
deflected jets
near

Au+Au
(0‐12%)

Mediumaway
Conical Emission

Nu Xu

cosϑ Mach =p /ε“Evidence of conicalemission …”

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The Ridge from STAR
STAR: Joern Putschke, J.Phys.G34:S679 (07)

JetRidge

Bulk Medium
Rich underlying physics: jet, bulk, jet-medium interaction, medium responses,…
N. Armesto et al.; R. Hwa; A. Majumder, et al.; E. Suryak; S. Voloshin; C.Y. Wong

Not fully understood.
Nu Xu

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Two Particle CorrelationsÄññref

Äñ
ñref

φΔ

Peak Amplitude

Peak η Width

STAR Preliminary
200 GeV62 GeVSTAR Preliminary

ηΔCollision Centrality ⇒Binary scaling

Hijing predic4ons

1) Amplitude and η widths: sharp transition
2) Deviations from binary scaling: physics unique to HI collisions
3) The observed correlation: Hijing under predicted the correlation
4) Inconsistent with the medium thermalization(?)
Modification of energetic ‘jets’ in the medium!
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 200821/30

φ -meson Flow: Partonic Flow

“φ-mesons are produced via coalescence of seemingly thermalized quarks
in central Au+Au collisions. This observation implies hot and dense matterwith partonic collectivity has been formed at RHIC”
STAR: Phys. Rev. Lek. 99 (2007) 112301// * STAR, Duke, TAMU** OZI rule
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Centrality Dependence
STAR: Phys. Rev. C77, 54901(2008)

200 GeV Au+Au[25[[[[[[[[[[[[[[20[[[[[[15[[v2 / !part (%)[3010500Charged hadrons

KS0#Hydro results

"

$100

200

300

400

Number of Participants Npart
S. Voloshin, A. Poskanzer, PL B474, 27(00).
D. Teaney, et. al., nucl‐th/0110037

 Larger v2/εpart indicates stronger flow in more central collisions.
 NO εpart scaling.
 The observed nq-scaling does not necessarily mean thermalization.
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 200823/30

sQGP and the QCD Phase Diagram
200 GeV Au+Au collisions at RHIC, stronglyinteracting matter formed:
Jet energy loss: RAA
Strong collectivity: v0, v1, v2
Hadronization via coalescence: nq-scaling

Questions:Has the thermalization reached, or how large is the η at RHIC?
When (at which energy) does this transition happen?
What does the QCD phase diagram look like?

Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Quark Masses
1)
2)

Higgs mass: electro-weaksymmetry breaking. (currentquark mass)
QCD mass: Chiral symmetry
breaking. (constituent quarkmass)➩ New mass scale comparedto the excitation of thesystem.
➩ Important tool for studying
properties of the hot/dense
medium at RHIC.
Total quark mass (MeV)

Nu Xu➩ Test pQCD predictions atRHIC.

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Decayed e pT vs. b- and c-hadron pT

Key: Directly reconstructed heavy quark hadrons!
Pythia calcula4on Xin Dong, USTC October 2005

Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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STAR Detector
MTD

EMC barrel
EMC End Cap

RPSD
FMS
FPD

TPC

PMD

CompleteOngoing
HFT

Nu Xu

FGT

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

R&D

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Charm Hadron v2- 200 GeV Au+Au minimum biased collisions (500M events).
- Charm collectivity ➱ drag/diffusion constants ➱ medium properties!
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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Charm Hadron RCP- 200 GeV Au+Au minimum biased collisions (|y|<0.5 500M events).
- Charm RAA ➱ energy loss mechanism, e.g. collisional vs. radiative!
Nu Xu

ATHIC 2008, Tsukuba, Japan, Oct. 13 - 15, 2008

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The QCD Critical Point- LGT prediction on the transition
temperature TC is robust.
- LGT calculation, universality, andmodels hinted the existence ofthe critical point on the QCD phase
diagram* at finite baryon chemical
potential.
- Experimental evidence for either
the critical point or 1st ordertransition is important for ourknowledge of the QCD phase
diagram*.
* Thermalization has been assumed
M. Stephanov, K. Rajagopal, and E. Shuryak, PRL 81, 4816(98)
K. Rajagopal, PR D61, 105017 (00)hkp://www.er.doe.gov/np/nsac/docs/Nuclear‐Science.Low‐Res.pdf
Nu Xu

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