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August 8, 2013Recent Results from the RHIC Beam Energy Scan Study emergent properties of matter with QCD degrees of freedomNu Xu(1) College of Physical Science & Technology, Central China Normal University, Wuhan, 430079, China (2) Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA

Many Thanks to Organizers!

Outline

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

r elativistic h eavy i on c ollider brookhaven national laboratory bnl upton ny

PHOBOS

BRAHMS

RHIC

PHENIX

STAR

AGS

TANDEMS

Relativistic Heavy Ion ColliderBrookhaven National Laboratory (BNL), Upton, NY

- RHIC: High-energy
heavy-ion collider
(i) Dedicated QCD collider
(ii) √sNN= 200 - 5 GeV
(iii) U, Pb, Au, Cu, d, p
- RHIC: The highest energy
polarized proton collider
√s= 200, 500 GeV
eRHIC: The EIC (2025)
5 - 30GeV e + 100, 255 GeV p
5 - 30GeV e + 5 – 100GeV A

v = 0.99995c = 186,000 miles/sec

Au + Au at 200 GeV

Student Lecture, “Quark Matter 2006”, Shanghai, Nov. 14 - 20, 2006

Animation M. Lisa

STAR Experiment

Magnet

MTD

BEMC

TPC

TOF

BBC

EEMC

HFT

FGT

HLT

Particle Identification at STAR

TPC TOF TPC

TPC

K pd

π

e, μ

TOF

Log10(p)

Charged hadrons

Hyperons & Hyper-nuclei

MTD

HFT

Jets

EMC

Neutral particles

Jets & Correlations

High pTmuons

Heavy-flavor hadrons

Large, homogenous, collision energy independent acceptance

Multiple-fold correlations for the identified particles!

QCD Phase Structure

TE

RHIC, SPS

2

Large μB

FAIR, CSR

Tini, TC

LHC, RHIC

3

1

LHC+RHIC

sQGP properties

√sNN ~ 0.1 - 5 TeV

Future eRHIC

Cold nuclear matter properties

e + ion collisions

1

2

3

Emergent properties of QCD matter

Phase Diagram

Phase diagram: A map showsthat, at given degrees offreedom, how matterorganizeitself under externalconditions.

Water: H2O

The QCDPhase Diagram:

structure of matter with quark-

and gluon-degrees (color

degrees) of freedom.

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

- http://drupal.star.bnl.gov/STAR/starnotes

/public/sn0493; arXiv:1007.2613

BES-I: √sNN = 7.7, 11.5, 19.6, 27, 39GeV

STAR Hadron Spectra

√sNN = 39 GeV Au+Au Collisions

p+

STAR Preliminary

K0s

K+

p

L

X-

W-

(1) Bulk Properties at Freeze-out

Cleymans, Redlich

Kinetic Freeze-out:
Central collisions => lower value of
Tkinand larger collectivity β
Stronger collectivity at higher energy
STAR: S. Das, L. Kumar, QM2012

Chemical Freeze-out: (GCE)

- Central collisions => higher values of

Tch and μB!

- The effect is stronger at lower energy.

(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?

(3) BES Dependence of RAA

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

The suppression was not observed in low energy Au+Au collisions, especially for √sNN ≤ 11.5GeV

L or B

(4) Search for Local Parity Violation in High Energy Nuclear Collisions

The separation between the same-charge and opposite-charge correlations.

- Strong external EM field

- De-confinement and Chiral

symmetry restoration

AAA AA

Parity-even observable, assumptions must be tested
Energy dependence & UU collisions
- S. Voloshin, PRC62, 044901(00).

- STAR: PR103, 251601; PRC81, 054908(2009)

Dynamical Correlations

STAR Preliminary

SS - OS

Below √sNN= 11.5 GeV, the splitting between the same- and opposite-sign charge pairs (SS-OS) disappear

If QGP is the source for the observed splitting at high-energy nuclear collisions  hadronic interactions become dominant at √sNN ≤ 11.5 GeV



(5) NCQ Scaling in v2



m ~ mp ~ 1 GeV
ssφnot K+K-φ
h<< p, 
In the hadronic case, no number
of quark scaling and the value of
v2ofφ will be small.
* Thermalization is assumed!

Collectivity v2 Measurements

STAR: Phys. Rev. Lett. 110 (2013) 142301

Number of constituent quark (NCQ) scaling in v2 => partonic collectivity => deconfinement in high-energy nuclear collisions

At √sNN< 11.5 GeV, the v2 NCQ scaling is broken indicating hadronic interactions become dominant.

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!

(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):

3) Direct comparison with Lattice results:

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.Ejirietal, PLB633, 275(06) // M. Cheng et al, PRD79, 074505(2009) // Y. Hatta, et al, PRL91, 102003(2003)

Net-proton Higher Moments

BES-II

RHIC

BES-I

STAR net-proton results:

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.

UrQMD model show monotonic behavior in the moment products.

Higher statistics needed for collisions at √sNN< 20 GeV.

- STAR: X.F. Luo, QM2012

STAR Preliminary