Novel Transport Phenomena with Chirality, Vorticity and Magnetic - - PowerPoint PPT Presentation

Novel Transport Phenomena with Chirality, Vorticity and Magnetic field

• Jun. 23~25, 2019

Jinfeng Liao

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Fascinating New Frontiers of XQCD

It is all about quarks & gluons — under extreme conditions!

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Spin: Chirality, Vorticity and Magnetic Field

SPIN UP SPIN DOWN Magnetic Polarization Rotational Polarization Chirality Polarization

~ B

~ !

~ P

Interesting interplay —> highly nontrivial phenomena!

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Fascinating New Frontiers of XQCD

~ B

~ !

QCD matter under extremely strong vorticity and magnetic fields!

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A Quantum Fluid of Spin

What happens to the spin DoF in the fluid??? A nearly perfect fluid (of energy-momentum)

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Chirality 2019 @ Tsinghua Beijing, Apr 2019

~100 people, 4.5 days

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Chirality 2015,2016,2017 @ UCLA Chirality 2018 @ Univ. Florence Chirality 2019 @ Tsinghua Univ.

Exciting Progress: See Recent Reviews

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

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Exciting Progress: See Recent Reviews

arXiv:1906.00936

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Interdisciplinary Interests

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Weyl semimetal (non-degenerated bands)

TaAs NbAs NbP TaP

Dirac semimetal (doubly degenerated bands)

ZrTe5 Na3Bi, Cd3As2

“Fluid Spintronics” Condensed matter, cold atomic gases, neutron stars, cosmology, plasma physics, etc [Chiral Matter workshops @ RIKEN, NTU]

Chirality

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Chirality & Chiral Symmetry

If a Dirac fermion’s mass is zero —> axial U(1) global phase symmetry!

Ψ → eiαγ5Ψ

L → L Jµ

5 = ¯

Ψγµγ5Ψ

Axial current Classically conserved

∂µJµ

5 = 0

In this case, chirality becomes well defined.

Right Handed (RH) Left Handed (LH)

L = ¯ Ψ(iγµ∂µ)Ψ

L → ¯ ΨLγµ∂µΨL + ¯ ΨRγµ∂µΨR

ΨR = 1 + γ5 2 Ψ ΨL = 1 − γ5 2 Ψ

Phase symmetries: independent U(1) for RH and LH sectors!

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Chiral Symmetry: Explicit Breaking

If a nonzero Lagrangian mass term is added: axial symmetry is explicitly broken.

m¯ ΨΨ = m ¯ ΨLΨR + ¯ ΨRΨL

• RH and LH get coupled together.

Axial current is no longer conserved:

∂µJµ

5 = 2im¯

Ψγ5Ψ

The mass controls the degree of such breaking. In QCD, for light flavors (u & d), Lagrangian mass is small:

mu,d ⌧ ΛQCD

QCD has chiral symmetry (to very good approximation)!

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The QCD Vacuum: Chiral Symmetry Breaking

The missing symmetries: while the Lagrangian has (approximate) chiral symmetry, the vacuum and hadron spectrum do not have that. QCD vacuum is not empty, but a complicated, nonperturbative, emergent form of condensed matter. [It accounts for 99% of the mass of our visible matter in universe.]

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Chiral Symmetry Restoration

* Spontaneously broken chiral symmetry in the vacuum is a fundamental property of QCD. * A chirally symmetric quark-gluon plasma at high temperature is an equally fundamental property of QCD!

Could we see direct experimental evidence for that?

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“Little Bang” in High Energy Nuclear Collision

* Quark-gluon plasma (QGP) is created in such collisions. * It is PRIMORDIALLY HOT ~ trillion degrees ~ early universe.

* Is chiral symmetry restored? CHIRAL FERMIONS

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Chiral Symmetry: Quantum Anomaly

* C_A is universal anomaly coefficient * Anomaly is intrinsically QUANTUM effect Chiral anomaly is a fundamental aspect of QFT with chiral fermions. V V A Broken at QM level: Classical symmetry:

[e.g. pi0—> 2 gamma]

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Topologically Nontrivial Gluon Fields

Twisting gluon fields around spacetime boundary Mobius strip Gluon topological structures play key role in confinement and chiral symmetry breaking.

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How to observe their effects experimentally?

From Gluon Topology to Quark Chirality

QCD anomaly: gluon topology —> chirality imbalance

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Quarks

Net chirality <—> topo fluctuations & chiral restoration

Vorticity & Polarization in Heavy Ion Collisions

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Rotating Quark-Gluon Plasma Ly = Ab√s 2 ∼ 104∼5~ ˆ z ˆ x

Pz = −A√s 2

Pz = +A√s 2

ˆ z ˆ x

QGP’s way of accommodating this angular momentum

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Quantifying Fluid Rotation

NR UR Heavy ion collisions:

∂ ∼ fm−1

ω ∼ 1022 s−1

v ∼ 0.1 c

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Jiang, Lin, JL, PRC2016; Shi, Li, JL, PLB2018; … The local vorticity pattern is strongly influenced by the bulk flow. The averaged vorticity reflects the global orbital angular momentum.

Nontrivial Vorticity Structures

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Low energy High energy

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

???

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Spin & Rotational Polarization

Dirac Lagrangian in rotating frame: Under slow rotation: Rotational polarization effect!

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[CAN BE STUDIED ON THE LATTICE: Yamamoto, Hirono; …]

Rotational Polarization in Thermal Source

Rotational polarization effect! For thermally produced particles: “equal-partition” of angular momentum

~ !

dN ∝ e

~ !· ~ J T

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Expect larger signal at LOW beam energy HIC!

Subatomic Swirls

An exciting discovery from STAR Collaboration at RHIC: The most vortical fluid!

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Fluid Spintronics in the Subatomic Swirls

STAR Collaboration, Nature 2017

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ω ≈ (9 ± 1) × 1021s−1

The most vortical fluid!

Rotational Polarization

Existing puzzles: Splitting between hyperons & anti- hyperons; Local polarization azimuthal patterns.

Jiang, Lin, JL, PRC2016; Shi, Li, JL, PLB2019; Becattini, et al; Csernai, et al;

• Q. Wang, et al; …

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Hydrodynamics & Transport Theory with Spin

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[Talks by: H. Taya, R. Ryblewski, E. Speranza, A. Kumar, Gallegos Pazos, @ Chirality 2019] [Talk by Hongo and by Yang @ this conference ]

Rotational Suppression of Fermion Pairing

[Yin Jiang, JL, PRL2016; Huang, Fukushima, Mameda, Chernodub, …]

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 = ~ s1 + ~ s2

~ J = ~ L + ~ S

Rotation tends to polarize ALL angular momentum, both L and S, thus suppressing scalar pairing.

~ L ~ L

~ !

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Chiral Phase Transition

Maybe in low energy collisions: In-medium mass correction due to rotation??

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Color Superconducting Pairing

Maybe also for nucleon-pairing?!

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Isospin Matter under Rotation

Large isospin density in low energy collision: Possible effect from rotation?

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[Hui Zhang, Defu Hou, JL, arXiv: 1812.11787.] Spin-1 Rho condensation is favored by rotation!

Magnetic Field & Anomalous Transport in Heavy Ion Collisions

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The angular momentum together with large (+Ze) nuclear charge —> strong magnetic field!

Strong Electromagnetic Fields

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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 ∼ γ ZαEM R2

A

∼ 3m2

π

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Quantitative simulations confirm the existence of such extreme fields!

Strong Electromagnetic Fields

[Many interesting B-field induced effects: di-electron; polarization splitting; quarkonium v2; D meson v1; …] Huang, Liao, et al PLB2012

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The Chiral Magnetic Effect (CME)

~ J = Q2 2⇡2 µ5 ~ B

Chirality & Anomaly & Topology Magnetic Field Electric Current Q.M. Transport

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[Kharzeev, Fukushima, Warringa, McLerran, …]

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 = Q2 2⇡2 µ5 ~ B

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CME <=> 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 macroscopic chiral anomaly — a remarkable phenomenon!

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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

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Chiral Transport Theory

Usual (classical) transport equation: [Son, Yamamoto; Stephanov, Yin; Chen, Wang, et al; Hidaka, Pu, Yang; Huang, Shi, Jiang, JL, Zhuang; …] Chiral transport equation:

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Fluid Dynamics That Knows Left & Right

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

[Son, Surowka; Kharzeev, Yee; Hidaka, Yang; …]

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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

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From CME Current to Charge Separation

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

strong radial blast: position —> momentum

+ +

• -

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Experimental Observable

Very difficult measurement: * Zero average, only nonzero variance; * Correlation measurement with significant backgrounds; * Signal likely very small These correlations are sensitive to CME contributions, however they are also sensitive to many non-CME backgrounds!

x (In-plane) y (Out-of-plane)

φ1 φ2

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CME & Backgrounds

CME expectation:

γSS < 0 , δSS > 0

γOS > 0 , δOS < 0

Transverse Momentum Conservation (TMC)

γ < 0 , δ < 0

Local Charge Conservation (LCC) Resonance decay: similar to LCC

γOS > 0 , δOS > 0

Background contribution to gamma is due to nonzero v2!!

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Fighting with Backgrounds

Many interesting proposals

• f new observables!

Bzdak, Koch, JL, 2012

A two-component decomposition model:

STAR PRL2014

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Current Experimental Status for CME

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Most measurements based on: gamma correlator + certain procedure to constrain backgrounds

Key challenge: weak signal versus strong backgrounds. Many new measurements at RHIC and LHC to help address this. Need quantitative predictions to help exp search!

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arXiv:1611.04586 arXiv:1711.02496

Badly needed: Quantitative predictions for CME signal in heavy ion collisions!

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Anomalous Viscous Fluid Dynamics (AVFD)

AVFD: Anomalous-Viscous Fluid Dynamics

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The AVFD Framework

arXiv:1611.04586 arXiv:1711.02496 A versatile tool to quantitatively understand and answer many important questions about CME in HIC!

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The AVFD Framework

[We now also have MUSIC-AVFD!] 53

Demonstrating the AVFD

Upper: NO magnetic field Lower: with B field (along y+ direction)

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Demonstrating the AVFD

Upper: Left-Handed (LH), with B field (along y+ direction) Lower: Right-Handed (RH), with B field (along y+ direction)

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The Charge Separation from AVFD + + + + +

• - - --

Chirality imbalance —> R/L asymmetry —> charge asymmetry

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AVFD Predictions v.s Experimental Data

Excellent agreement! Many more detailed results reported in: Shi, Jiang, JL, et al: arXiv:1611.04586 [CPC]; arXiv:1711.02496 [Annals of Physics]

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Event-By-Event AVFD

Include EBE fluctuations: Important for better understanding: * Interplay between signal and BKG; * Experimental analysis methods

58

Implementing Local Charge Conservation

[Schenke, Shen, Tribedy, 2019]

To quantify background correlations in state-of-art hydro framework

59

[Koch, Oliinychenko, 2019]

New development of particlization: the best way to quantify LCC

EBE-AVFD+LCC

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First attempt at full characterization of signal + known major backgrounds

A Decisive Experiment: Isobaric Collisions

New opportunity of potential discovery: Isobaric Collision @ RHIC

~2 billion data collected successfully in RHIC 2018 run; processing and analysis underway!

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Key idea: contrasting two systems with identical bulk, varied magnetic fields. [Koch, et al, arXiv: 1608.00982]

Isobars: Identical Bulk with Varied B Field

Joint multiplicity-geometry cut: Vanishing difference in bulk properties, Sizable difference in magnetic fields!!!

Eccentricity is guaranteed the same! B field differs by 12~20% !

62

AVFD Predictions for Isobars

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Look for absolute difference between isobars (after joint-cut)! Look for consistency between delta- and gamma-correlators!

[Shi, Zhang, Hou, JL, arXiv:1807.05604; paper in preparation]

Chiral Magnetic Wave (CMW)

CME + CSE —> gapless collective excitations, the CMW [Kharzeev, Yee, 2010; Burnier, Kharzeev, JL, Yee, 2011] Wave: propagating “oscillations” of two coupled quantities e.g. sound wave (pressure & density); EM wave (E & B fields) EM wave Chiral Magnetic Wave

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CMW Induced Flow Splitting

CMW —> charge quadrupole of QGP —> elliptic flow splitting

[Burnier, Kharzeev, JL, Yee, PRL2011; and arXiv: 1208.2537] [STAR, PRL2015] [Also seen by ALICE@LHC]

charge quadrupole due to CMW transport

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CME & CME versus Beam Energy

66

CME CMW A consistent trend: Turning-off at low energy? Chiral breaking/ restoration?

Summary

67

Summary: Chirality, Vorticity & Magnetic Field

68

Chirality Topology Magnetic Field Vorticity

Backup Slides

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The Influence of the Magnetic Field

Strong influence by B field evolution; Significant theoretical uncertainty!

70

The Axial Charge Initial Condition

Very sensitive to initial axial charge; Significant theoretical uncertainty!

71

The Influence of the Viscous Transport

First calibration for the influence of the viscous transport on charge separation signal!

72

Flavor Dependence

Kaons are sensitive to anomalous transport of s-quarks. Theory expectation: u,d ~ s

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AVFD ALICE 2.76TeV

74

1 1.05 1.1

• 3
• 2
• 1

1 2 3 (a) Au+Au 200 GeV 20-30%

RΨm(∆S) ∆S″

• 3
• 2
• 1

1 2 3 (b) 40-50%

∆S″

m = 2 m = 3

• 3
• 2
• 1

1 2 3 (c) 60-70%

∆S″

σ

Ψ σ Ψ

EBE-AVFD for Testing Observables

New a key tool for understanding different observables’ responses and sensitivity to signal and backgrounds

Isobars: How to Choose Identical Systems?

Insight from initial conditions: joint cut on Multiplicity-Eccentricity

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[Shi, Zhang, Hou, JL, arXiv:1807.05604; paper in preparation]

Analyzing Actual EBE-AVFD Events for Isobars

100M EBE-AVFD events: Subject to joint-cut

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Post-selection double-check: Identical v2 ! Getting two identical sample of isobar events for contrast

Analyzing Actual EBE-AVFD Events for Isobars

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Magnetic Filed Induced Polarization

78 78

~ !

~ B

[Yu Guo, Shengqin Feng, Shuzhe Shi, JL, 1905.12613]

Magnetic Filed Induced Polarization

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[Yu Guo, Shengqin Feng, Shuzhe Shi, JL, 1905.12613]

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~ !

~ B

Vorticity

• nly

Vorticity + Magnetic field

For this to work: Requires long-lived late time magnetic field. Where does that come from??

Connecting Magnetic Field and Fluid Rotation

80

[X. Guo, et al, arXiv:1904.04704] Important at low beam energy!

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