**Novel Quantum Phenomena **
**in the Subatomic Swirls**

** Chiral Matter Workshop @ NTU Dec. 6~9, 2018**

**Jinfeng Liao**

Indiana University, Physics Dept. & CEEM

**Research Supported by NSF & DOE**

The Subatomic Swirls

**An exciting discovery from ****STAR Collaboration at RHIC: **

**The most vortical fluid!**

2

Introduction

Nuclear Physics: Exploring the Heart of Matter

**nuclear ****force**

**matter****molecule****atoms **

**atomic nucleus****proton**

**neutron**

**[a millionth of a mm]**

**[a trillionth of a mm]**

**The physical world has a hierarchy of structures.**

**Most basic ****entities: **

**quarks ****and ****gluons.**

**Quantum **

**Chromodynamics ****(QCD)**

Quantum Chromodynamics (QCD)

**The fundamental theory of strong nuclear force:**

**QCD, a non-Abelian gauge theory of quarks and gluons**

**Asymptotic Freedom: coupling becomes large ****at low energy or long distance scale.**

⇤_{QCD} ⇠ 200MeV R ⇠ 1 fm

**Nobel Prize 2004**

QCD Confinement: “The Missing Particles"

**This null result is by itself a remarkable FACT of Nature.**

Confinement problem:

Biggest challenge withinStandard Model!

Mathematics: one of the seven Millennium Problems!

**from Particle Data Group**

**QCD vacuum as “dual superconductor” with dual Meissner effect? **

**Color-magnetic topological condensate?**

*QCD dipole field *

Chiral Symmetry: Spontaneous Breaking

**Dirac ****Sea**

**Lagrangian ****(SM) mass****Constituent **

**mass**

m_{⇡} ⇡ 140MeV , m^{n} ⇡ 940MeV

**Vacuum ****condensate**

**It accounts for 99% of ****the mass of our visible **

**matter in universe.**

QCD as Topological Material

**Instantons**

Emergent Phenomena in QCD

**F. Wilczek **

**@ QM2014**

NP as Quantum Chromo Material Science

**This talk will focus on the “hot frontier”.**

**Temperature**

**Baryon Density**

**“Hot **

**Fron****tier”**

**“F****or****ce**** F****ro****nti****er****”**

**“Dense Frontier”**

Quark-Gluon Plasma (QGP):

A Subatomic Quantum Fluid

QCD in Hot Environment

**The “super” side is hard, and let’s attack the lambda point from ****the “right side”, when the system is just about to condense!**

**Why don’t we do the same for QCD?!**

**QCD at extreme temperatures: **

** At high enough T >> Lambda_QCD **

**A transition to a quark-gluon plasma (QGP) !****[mid ~ late 1970’s]**

QGP: A New Phase of Matter

**from Lattice QCD**

a relativistic pion gas

More precisely,

Hadron Resonance Gas

free QGP

RHIC LHC

*** Two benchmarks at low/high T**

*** A transition regime in the middle**

*** Crossover (instead of a phase transition)**

QGP: A New Phase of Matter

**The high T phase of QCD matter (a few hundred MeV & up) ****is a distinctive new phase, the quark-gluon plasma (QGP).**

**The liberated ****quarks & gluons**

**The restored ****chiral symmetry**

**Wuppertal-****Budapest **

**HotQCD**

Little Bangs in Heavy Ion Collisions (HIC)

**Relativistic Heavy Ion Collider**

**An artistic presentation: **

**“nuclei as heavy as bulls, **

**colliding into new phase of matter”**

**Large Hadron Collider**

The Setup of Heavy Ion Collision

**A typical off-central collision. **

**In-Plane****Out-of-Plane**

**Quark-gluon plasma is created in such collisions!**

QGP Shining Brightly!

**QGP is hot stuff: about trillion degrees !****Official Guinness World Record: **

**the highest man-made temperature! **

RHIC/LHC

QGP: An Old Phase of Matter

**The quark-gluon plasm is an old phase of matter! **

**The highest ever temperature was in the beginning of universe.**

**The QGP temperature was available back then. **

Anisotropic Explosion: Elliptic Flow

**relativistic hydrodynamics **

**@ 1~ 10 fm scale. **

**This response is very ****sensitive to fluid dissipation**

**from STAR**

QGP: Nearly Perfect Quantum Liquid

**QGP is a quantum fluid:**

s ⇠ n

⌘/s ⇠ p^{T} ⇠ / ^{dB}

**It has nearly perfect fluidity:**

**less dissipative than known substance; **

**very close to conjectured lower bound.**

**[A recent ravel: cold atomic gas ****with infinite scattering length]**

Vorticity & Magnetic Field

Fascinating New Frontiers

### B ~

### ~

### !

**QGP fluid in extremely strong**

**vorticity and magnetic fields**Rotating Quark-Gluon Plasma
L_{y} = Abp

s

2 ⇠ 10^{4}^{⇠5}~

ˆ z ˆ

x ^{P}^{z} ^{=} ^{A}^{p}^{s}

2

P_{z} = +Ap
s
2

ˆ z ˆ

x

**QGP’s way of accommodating ****this angular momentum**

Quantifying Fluid Rotation

**NR****UR**

**Heavy ion ****collisions: **

@ ⇠ fm ^{1}

! ⇠ 10^{22} s ^{1}

v ⇠ 0.1 c

**The averaged vorticity strongly increases toward low beam energy!**

**Jiang, Lin, JL, PRC2016; Deng & Huang, PRC2016; **

**Xia, Li, Wang, et al, PRC; Shi, Li, JL, PLB2018; …**

Rotating Quark-Gluon Plasma

**The angular momentum together with large (+Ze) nuclear charge**

**—> strong magnetic field!**

Strong Electromagnetic Fields

Strong Electromagnetic Fields

• Strongest B field (and strong E field as well) naturally arises!

[Kharzeev,McLerran,Warringa;Skokov,et al; Bzdak-Skokov;

**Deng-Huang; Skokov-McLerran; Tuchin; ...]**

• “Out-of-plane” orientation (approximately)
**[Bloczynski-Huang-Zhang-Liao]**

E, B ⇠ Z↵_{EM}

R^{2}_{A} ⇠ 3m^{2}⇡

**Quantitative simulations confirm the existence of such extreme fields!**

Strong Electromagnetic Fields

**[STAR measurements of dielectron directly from such fields, PRL2018]**

**Huang, Liao, et al PLB2012**

Spin & Rotational Polarization

Spin-Fluid Coupling

**How does a many-body system cope with a ****sizable angular momentum? **

**Orbital motion (vorticity); **

**Spin alignment (polarization).**

**Fluid vorticity **
**Macroscopic **

**Individual spin**

**Microscopic, quantum **

**???**

Spin & Rotational Polarization

**Dirac Lagrangian in rotating frame:**

**Under slow rotation: **

**Rotational **

**polarization effect!**

Rotational Polarization

**Rotational **

**polarization effect!**

**For thermally produced particles: **

**“equal-partition” of angular momentum**

### ~

### !

### dN / e

^{!}

^{~}

^{T}

^{· ~}

^{J}

**“Fluid Spintronics”**

From Vorticity to Spin Polarization

**Viscous fluid flow **

**—> vorticity **

**—> spin polarization**

Fluid Spintronics in the Subatomic Swirls

**STAR Collaboration, Nature 2017**

Fluid Spintronics in the Subatomic Swirls

**STAR Collaboration, Nature 2017**

! ⇡ (9 ± 1) ⇥ 10^{21}s ^{1}

**The most vortical fluid!**

**Low energy**

**High energy**

**Jiang, Lin, JL, PRC2016**

Rotational Suppression of Fermion Pairing

**[Yin Jiang, JL, PRL2016] **

**[Rotational Inhabitation: Chen, Fukushima, Huang, Mameda, PRD2016]**

**Let us consider pairing phenomenon in fermion systems. **

**There are many examples: **

**superconductivity, superfluidity, chiral condensate, diquark, … ****We consider scalar pairing state, with J=0. **

S = ~s~ _{1} + ~s_{2} J = ~~ L + ~S

**Rotation tends to polarize ALL **

**angular momentum, both L and S, **
**thus suppressing scalar pairing.**

L~

L~

### ~

### !

Chiral Magnetic Effect in the Subatomic Chiral Matter

Exciting Progress: See Recent Reviews

**Prog. Part. Nucl. Phys. 88, 1 (2016)[arXiv:1511.04050 [hep-ph]].**

**J. Liao, Pramana 84, no. 5, 901 (2015) [arXiv:1401.2500 [hep-ph]].**

**X.G. Huang, ROPP2016; Hattori, Huang, 2017.**

Chiral Anomaly

*** C_A is universal anomaly coefficient **

*** Anomaly is intrinsically QUANTUM effect**
**Chiral anomaly is a fundamental aspect of QFT with chiral fermions.**

**V**

**A** **V**

**Broken at QM level:**

**Classical symmetry:**

**[e.g. pi0—> 2 gamma]**

Chiral Restoration in QGP

*** Spontaneously broken chiral symmetry in the vacuum ****is a fundamental property of QCD.**

*** A chirally symmetric quark-gluon plasma at high temperature****is also a fundamental property of QCD!**

**Can we see direct experimental evidence for that?**

Chiral Restoration via Chiral Anomaly

J_{5}^{µ} = J_{R}^{µ} J_{L}^{µ}

### @

_{µ}

### J

_{5}

^{µ}

### = 2iM ¯

^{5}

### +C

_{A}

### ~E · ~B

**Low T**

**Strong spon. breaking**

**High T**

**Quantum Anomaly**

**Look for pure quantum anomaly effect in **
**hot QGP with chiral symmetry restoration! **

The Chiral Magnetic Effect (CME)

### J = ~ Q ^{2}

### 2⇡ ^{2} µ _{5} B ~

**Chirality & Anomaly & Topology**

**Magnetic **
**Field**
**Electric **

**Current**

**Q.M. Transport**

Intuitive Picture of CME

**Intuitive understanding of CME: **

**Magnetic polarization —>**

**correlation between micro. **

**SPIN & EXTERNAL FORCE**

**Chiral imbalance —> **

**correlation between directions of **
**SPIN & MOMENTUM**

## ⊗

**Transport current along magnetic field**

J =~ Q^{2}

2⇡^{2} µ_{5} B~

From Micro. Laws To Macro. Phenomena

**Micro. Laws: **

**Symmetry; **

**Lagrangian; **

**Conservation laws;**

**……**

**Macro. Phenomena: **

**Thermodynamics; **

**Transport; **

**Fluid Dynamics;**

**……**

**Quantum **
**Field **
**Theory **

**Kinetic **

**Theory** **Fluid **

**Dynamics**

**Weakly ****Interacting**

**Strongly****Interacting**

**WHAT ABOU the “SEMI”-SYMMETRY??? **

**i..e ANOMALY?!**

**— classical symmetry that is broken in quantum theory**

CME = Macroscopic Chiral Anomaly

Anomaly -->

Chirality -->

*** This is a non-dissipative current!**

*** Indeed the chiral magnetic conductivity is P-odd but T-even! **

**(In contrast the Ohmic conductivity is T-odd and dissipative.)**
**CME is a quantum/anomalous transport current **

**as macroscopic manifestation of microscopic quantum anomaly.**

Fluid Dynamics That Knows Left & Right

**[Son, Surowka, 2009;…]**

**conservation **
**law:**

**constituent **
**relation:**

**CME**
**CVE**

**Microscopic quantum anomaly emerges as **
**macroscopic anomalous hydrodynamic currents!**

**It would be remarkable to actually “see” this new ****hydrodynamics at work in real world materials!**

Looking for CME in Heavy Ion Collisions

**The quark-gluon plasma is a ****subatomic CHIRAL MATTER.**

**In-Plane****Out-of-Plane**

**Can we observe CME in **
**heavy ion collisions?? **

**1) (nearly) chiral quarks ****2) chirality imbalance ****3) strong magnetic field **

From Gluon Topology to Quark Chirality

**QCD anomaly: gluon topology —> chirality imbalance **

From CME Current to Charge Separation

**[Kharzeev 2004; Kharzeev, McLerran, Warringa,2008;…]**

**strong radial blast:**

**position —> momentum**

**+ +**

**- -**

**Very difficult measurement: **

*** Zero average, only nonzero variance; **

*** Correlation measurement with significant backgrounds; **

*** Signal likely small**

Latest Exp. Search Status

**[From Z. Ye, STAR Summary Talk @ QM2018]**

**ALICE @ LHC 2.76TeV: signal level possibly about 8~10% **

**(upper limit ~30%)**

**CMS @ LHC 5.02TeV: signal level no more than 7%**

**The trend with beam energy seems in line with expectation! **

**STAR @ RHIC 200GeV: “**

**naive” statistical interpretation: ( 8.5 +/- 1.2 ) %**

**arXiv:1611.04586**

**arXiv:1711.02496**

**Badly needed: **

**Quantitative ****predictions for ****CME signal in ****heavy ion **

**collisions!**

Anomalous Viscous Fluid Dynamics (AVFD)

**AVFD: **

**Anomalous-Viscous Fluid Dynamics**

The AVFD Framework

**arXiv:1611.04586****arXiv:1711.02496****We now have a versatile tool to **

**quantitatively understand and answer many important **
**questions about CME in heavy ion collisions!**

The AVFD Framework

**[We now also have MUSIC-AVFD!]**

The AVFD At Work

**[arXiv:1611.04586; arXiv:1711.02496]**

**Zero B Field****Nonzero B Field**

The AVFD At Work

**[arXiv:1611.04586; arXiv:1711.02496]**

**Left-handed****Right-handed**

The Charge Separation from AVFD

AVFD Predictions v.s Experimental Data

**Excellent agreement!**

**Shi, Jiang, JL, et al: arXiv:1611.04586 [CPC]; **

**arXiv:1711.02496 [Annals of Physics]**

Chiral Magnetic Wave (CMW)

**CMW: gapless collective excitation in chiral fluid **

** —> charge quadrupole of QGP —> elliptic flow splitting ****[Burnier, Kharzeev, JL, Yee, PRL2011; **

**& arXiv: 1208.2537]**

**[STAR, PRL2015]**

**charge quadrupole ****due to CMW transport**

**[STAR@RHIC]**

**[Also seen by ALICE@LHC]**

There Are Electric Fields Too!

**Chiral matter in strong electric field:**

**Chiral Electric Separation Effect (CESE)**
**[Huang, JL, PRL2013; Jiang, Huang, Liao, PRD2014]**

**QED plasma****QCD plasma**

Summary & Outlook

Summary: the Subatomic Swirls

**Subatomic swirls as ****the most vortical fluid ****with the strongest B field**

**Quark-Gluon Plasma: **

**A Subatomic Chiral Fluid **

The hottest material

The new, 5th state of

matter

The oldest state of matter:

early cosmos

The most perfect fluid

**Spin ****Polarization**

**CME**