August 8, 2013
Recent Results from the
RHIC Beam Energy Scan
Nu Xu
(1) College
(2) Nuclear
Nu Xu
Many Thanks to Organizers!
of Physical Science & Technology, Central China Normal University, Wuhan, 430079, China
Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
1/27
Outline
(1) Introduction
- The QCD phase structure and STAR physics program
(2) Selected Recent Results
- RHIC Beam Energy Scan-I results
(3) Summary and Outlook
(4) CEE – CSR-External-Target-Facility
Experiment
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
2/27
Relativistic Heavy Ion Collider
Brookhaven National Laboratory (BNL), Upton, NY
PHOBOS
PHENIX
STAR
BRAHMS
- RHIC: High-energy
RHIC
heavy-ion collider
(i) Dedicated QCD collider
(ii) √sNN = 200 - 5 GeV
(iii)v U,
Pb, Au,cCu,
d, p
= 0.99995
= 186,000
miles/sec
Au + Au at 200 GeV
AGS
- RHIC: The highest energy
polarized proton collider
√s = 200, 500 GeV
5 - 30GeV e + 100, 255 GeV p
5 - 30GeV e + 5 – 100GeV A
TANDEMS
Student Lecture, “Quark Matter 2006”, Shanghai, Nov. 14 - 20, 2006
Animation M. Lisa
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
3/27
STAR Experiment
Magnet
MTD
BEMC
HFT
Nu Xu
TPC
FGT
TOF
BBC
EEMC
HLT
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
4/27
Particle Identification at STAR
TPC
TOF
TPC
TPC
π
K
p
d
e, μ
TOF
Charged hadrons
Log10(p)
Hyperons & Hyper-nuclei
MTD
HFT
Jets
EMC
Neutral particles
Jets & Correlations
High pT muons
Heavy-flavor hadrons
Large, homogenous, collision energy independent acceptance
Multiple-fold correlations for the identified particles!
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
5/27
QCD Phase Structure
1
Tini, TC
LHC, RHIC
2
TE
RHIC, SPS
LHC+RHIC
sQGP properties
√sNN ~ 0.1 - 5 TeV
Nu Xu
1
2
3
3 Large μB
FAIR, CSR
Future eRHIC
Cold nuclear
matter
properties
e + ion collisions
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
6/27
Phase Diagram
Phase diagram: A map shows
that, at given degrees of
freedom, how matter organize
itself under external
conditions.
Water: H2O
The QCD Phase Diagram:
structure of matter with quarkand gluon-degrees (color
degrees) of freedom.
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
7/27
Beam Energy Scan at RHIC
Study QCD Phase Structure
- Signals for onset of sQGP
- Signals for phase boundary
- Signals for critical point
Observables:
1st order phase transition
(1) Azimuthally HBT
(2) Directed flow v1
Partonic vs. hadronic dof
(3) RAA: N.M.F.
(4) Dynamical correlations
(5) v2 - NCQ scaling
Critical point, correl. length
(6) Fluctuations
(7) Di-lepton production
BES-I: √sNN = 7.7, 11.5, 19.6, 27, 39GeV
Nu Xu
- http://drupal.star.bnl.gov/STAR/starnotes
/public/sn0493; arXiv:1007.2613
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
8/27
STAR Hadron Spectra
√sNN = 39 GeV Au+Au Collisions
p+ STAR Preliminary
K0s
K+
p
Nu Xu
L
X-
W-
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
9/27
(1) Bulk Properties at Freeze-out
Cleymans, Redlich
Chemical Freeze-out: (GCE)
- Central collisions => higher values of
Tch and μB!
Kinetic Freeze-out:
- Central collisions => lower value of
Tkin and larger collectivity β
- The effect is stronger at lower energy.
- Stronger collectivity at higher energy
STAR: S. Das, L. Kumar, QM2012
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“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
10/27
(2) v1: Directed Flow
B. Schaefer et al., Phys. Rev. D75, (2007) 085015
(1) Lattice QCD calculations predict
a first order phase transition seen, as
a discontinuity in the density
(2) Slope of v1: manifestation of early
pressure in the system
(3) Soft point?
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“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
11/27
(3) BES Dependence of RAA
1) Suppression of high pT hadrons is one of the key signatures for
the formation of strongly interaction Quark-Gluon Plasma in
high-energy nuclear collisions
2) The suppression was not observed in low energy Au+Au
collisions, especially for √sNN ≤ 11.5GeV
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
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(4) Search for Local Parity Violation
in High Energy Nuclear Collisions
L or B
The separation between the
same-charge and oppositecharge correlations.
- Strong external EM field

- De-confinement and Chiral
symmetry restoration
Nu Xu
cos  +   - 2
AAA
AA
RP 
1) Parity-even observable,
assumptions must be tested
2) Energy dependence & UU collisions
- S. Voloshin, PRC62, 044901(00).
- STAR: PR103, 251601; PRC81, 054908(2009)
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
13/27
SS - OS
Dynamical Correlations
(1) Below √sNN = 11.5 GeV, the splitting between the same- and opposite-sign
charge pairs (SS-OS) disappear
(2) If QGP is the source for the observed splitting at high-energy nuclear
collisions  hadronic interactions become dominant at √sNN ≤ 11.5 GeV
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
14/27
(5) NCQ Scaling in v2


- m ~ mp ~ 1 GeV
- ss  φ not K+K-  φ
- h << pp, pp
In the hadronic case, no number
of quark scaling and the value of
v2 of φ will be small.
* Thermalization is assumed!
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
15/27
Collectivity v2 Measurements
STAR: Phys. Rev. Lett. 110 (2013) 142301
1) Number of constituent quark (NCQ) scaling in v2 =>
partonic collectivity => deconfinement in high-energy
nuclear collisions
2) At √sNN < 11.5 GeV, the v2 NCQ scaling is broken
indicating hadronic interactions become dominant.
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
16/27
RHIC BES-I Highlights
(1) Parton energy loss
(2) “Local Parity Violation”
(3) Partonic collectivity
STAR Preliminary
sQGP key signatures
turned off at √sNN < 11.5 GeV!
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
17/27
(6) Higher Moments
1) High moments for conserved quantum
numbers: Q, S, B, in high-energy nuclear
collisions
2) Sensitive to critical point (ξ correlation length):
N    2,
2
N    4.5,
3
N    7
4
3) Direct comparison with Lattice results:
 B3
S *  2 ,
B

 B4
 *  2
B
2
4) Extract susceptibilities and freeze-out
temperature. An independent/important test on
thermal equilibrium in heavy ion collisions.
References:
- A. Bazavov et al. 1208.1220 (NLOTE) // STAR: PRL105,
22303(2010) // M. Stephanov: PRL102, 032301(2009) // R.V. Gavai
and S. Gupta, PLB696, 459(2011) // S. Gupta, et al., Science, 332,
1525(2011) // F. Karsch et al, PLB695, 136(2011) // S.Ejiri etal,
PLB633, 275(06) // M. Cheng et al, PRD79, 074505(2009) // Y.
Hatta, et al, PRL91, 102003(2003)
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
18/27
Net-proton Higher Moments
BES-II
RHIC
BES-I
STAR net-proton results:
1) All data show deviations below
Poisson beyond statistical and
systematic errors in the 0-5%
most central collisions for κσ2
and Sσ at all energies. Larger
deviation at √sNN ~ 20GeV.
2) UrQMD model show monotonic
behavior in the moment
products.
3) Higher statistics needed for
collisions at √sNN < 20 GeV.
STAR Preliminary
Nu Xu
- STAR: X.F. Luo, QM2012
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
19/27
Summary
RHIC BES-I Results:
- Partonic QGP dominant: √sNN > 39GeV
Hadronic interactions become dominant: √sNN ≤ 11.5GeV
BES-II:
- High statistics data for energy region √sNN ≤ 20GeV.
The e-cooling at RHIC has started.
RHIC: Unique opportunities for exploring
QCD phase structure
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
20/27
Exploring the QCD Phase Structure
1
Tini, TC
LHC, RHIC
2
TE
RHIC, SPS
LHC+RHIC
sQGP properties
2
3
FAIR, CSR
Future eRHIC
Cold nuclear
matter
properties
e + ion collisions
Hadronic
Matter
RHIC BES-II
QCD phase
structure and
critical point
1
Partonic Matter
√sNN ~ 0.1 - 5 TeV
3 Large μB
√sNN ≤ 20 GeV
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
21/27
STAR: Upgrade Plan ( - 2025)
-HF-I: Charm
- Di-lepton
sQGP properties
2013
2014
2015
- QCD phase
structure
- Critical Point
2016
2017
2018
2019
- HF-II: B, ΛC
- Jet, gamma
CNM, spin
2020
2021
2022
- CNM, CGC
- Phase structure
with glue
2013
2024
2025
2026
HF, (e,μ)
BESII
HFT/MTD
e-Cooling, iTPC
HF’, pA
eSTAR
HFT’, Tracking, EM/HCAL (West side)
EMCAL (East side)
physics
Nu Xu
upgrade
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
22/27
高能核核碰撞中的QCD相结构示意图
Tini, TC
LHC, RHIC
早期宇宙
发展演化
部分子物质
(QGP)
强子物质
Partonic Matter
1
2
TE
RHIC, SPS
3 Large μB
FAIR, CSR
CEE 兰州重离子加速器
低温高密核物质测量谱仪
2
3
1)
2)
3)
4)
低温、高重子密度
强子相互作用
手征对称自发破缺
对称能Esym()
Hadronic
Matter
1
强关联的核物质
重子化学势
CEE – CSR-External-Target-Facility Experiment
Nu Xu
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
23/27
HIRFL-CSR 重离子加速器
SFC:
 10 AMeV (H.I.), 17~35 MeV (p)
SSC:
100 AMeV (H.I.),  110 MeV (p)
CSRm: 1000 AMeV (H.I.),  2.8 GeV (p)
SSC
N
SFC
RIBLL1
RIBLL2
CSRe
外靶实验
装置(CEE)
CSRm
RIBLL1:
RIBLL2:
CSRm:
Nu Xu
几十AMeV RIBs
百AMeV RIBs
冷却储存环
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
24/27
CEE 概念性设计
低温高密核物质测量谱仪（CEE）
二极磁铁
飞行时间探测器
多丝漂移室
微像素
定位探测器
靶
零度角量能器
重离子束
T0探测器
时间投影室
内飞行时间探测器
技术亮点:
Nu Xu
1)
2)
3)
4)
硅像素定位探测器 (华中师范大学)
高计数率高精度飞行时间探测器 (清华大学、中国科学技术大学)
高精度三维径迹探测器TPC (中科院上海应用物理所)
新型数据获取系统 (中国科学技术大学)
“QCD Phase Transition and Relativistic Heavy-Ion Physics”, August 8 – 10, Chengdu, China
25/27
(CEE) 总结
1)利用当前最新技术在中国大型重离子加速器
HIRFL-CSR(HIAF)上建设性能先进的多功能中
高能重离子物理实验谱仪：
－ 三年完成基本实验设备建设
－ 高重子密度下的QCD相结构, 对称能高密行为, …
2)在中高能核物理领域建立一支由高校－中科院
研究所密切结合的优秀科研团队
3)为国家中长期高能核物理规划, 核探测技术发
展及其应用做贡献
哈尔宾工业大学，华中师范大学，山东大学，清华大学，中国科学技术大学,
中国科学院近代物理所，中国科学院上海应用物理所
Nu Xu
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