From Tc to Qs:
Quarks and Gluons at High Temperatureand High Density
rd3 International Symposium
Quest for the Origin of Particles and the Universe
KMI, Nagoya, JapanBerndt Mueller
January 5-7, 2017

1965
A year of momentous discoveries
Rolf Hagedorn

Penzias & Wilson

Cosmic microwave background

Exponential mass spectrum
2What is the hottest matter?
§ The CMB discovery raised the question: What kind of matter filled theuniverse at its hot beginning?

§ Hagedorn’s exponential mass spectrum hypothesis implied that matter, in theform of a dense gas of hadron resonances, cannot exceed TH ≈ 180 MeV.

§ In the early 1970s scientists realized that temperatures in this range can bereached in collisions of heavy nuclei.First experiments at LBNL (Bevalac)confirmed this concept in the years 1975−1980.

§ The insight that all hadrons are composed of quarks and gluons suggested
that TH may not be the highest possible temperature, but that matter would
dissolve into a novel type of plasma containing quarks and gluons (ca. 1978).

§ This led to experiments at AGS, SPS, RHIC and LHC and motivated theorists
to calculate properties of quarks and gluons at high temperature on thelattice.

§ The experiments at RHIC showed (and the LHC confirmed) that matter above
Tc ≈ 155 MeV is composed of unconfined quarks and gluons and flows likean almost inviscid liquid with η/s near the quantum limit (4π)-1.
3

RHIC: Champion of versatility

PHENIXSTARLHC: Champion of energy5

LHC: Champion of energy
CMS

ATLAS

5

Exploring the Phases of Nuclear Matter
RHIC is ideally suited to explore theQuark-Gluon Plasma and map the QCD
matter phase diagram.
RHIC has defined a multi-year program
to execute its scientific mission. We justcompleted Year 3.
Major components of this program are:• Search for a possible critical point inthe QCD phase diagram• Find unambiguous evidence for therestoration of chiral symmetry• Discover novel phenomena caused
by topological QGP excitations• Unravel the mechanism behind thenear “perfect” fluidity of the QGP
discovered at RHIC

Range of matter
explored at RHIC

Range of matter
explored at RHIC
(location unknown)(location unknown)
Internalfix
edtar

SPSgetIn addition, RHIC is the first and only
polarized proton collider in the world. Itis uniquely positioned to elucidate thedynamics of spin in QCD. RHIC has
already discovered that gluons make up
part of the spin of the proton.

6?

Atomicnuclei

Standard model of the “Little Bang”

7

Hot QCD matter properties & probes
Which properties of hot QCD matter can we hope to determine and how ?
Easyfor
LQCD

Very
Hard for
LQCD

Hardfor
LQCD
Easyfor
LQCD

Tµν⇔ ε , p, s

Equation of state: spectra, coll. flow, fluctuations

η=1d 4 x Txy (x)Txy (0)∫TShear viscosity: anisotropic collective flow⎫⎪⎪2⎪ Momentum/energy diffusion:
4π α s C R−
† − a+−a+ê =dyiU∂A(y)UA(0)⎬N c2 − 1 ∫⎪ parton energy loss, jet fragmentation⎪
4πα s† a0iab0ib
κ=dτ
UF(τ)tUF(0)t⎪3N c ∫⎭
4π 2α sC R−† a+i−a+q̂ =dyUF(y)UF(0)i2Nc − 1 ∫µνΠem(k) = ∫ d 4 x eikx j µ (x) j ν (0)1ln U †E a (x)UE a (0)|x|→∞ | x |mD = − lim

QGP Radiance: Lepton pairs, photons

Color screening: Quarkonium states
8Scientific Methodology§ Cosmology:• One universe, but many causally disconnected domains (after inflation)• Precision measurements + concordance model simulations• Global fits to multiple observables§ Relativistic heavy ion collisions:• Many independent events with the same global constraints• Precision measurements + concordance model simulations• Global fits to multiple observables (just beginning now)
• Example: E-by-E fluctuations of locally conserved quantitities (Q, B)
Lattice gauge theory:

Ratios are independent of the (unknown) freeze-out volume9

Chemical freeze-out… from fluctuations of conserved quantum numbers (Q, B):

hadron abundances
fluctuations

Consistency of freeze-out parameters from mean hadron abundances andfrom fluctuations (Q, B) opens the door to search for a critical point in theQCD phase diagram by looking for enhanced critical fluctuations as functionof beam energy.

10Anisotropic flow
Nuclei collide rarely head-on, but mostly
with an offset:

Reactionplanezyx2π

Only matter in the overlap area getscompressed and heatedEvent-by-event fluctuations of thedensity introduce all Fourier components⎛⎞dN= N 0 ⎜ 1+ 2∑ vn ( pT , η )cos n (φ − ψ n ( pT , η ))⎟⎝
⎠dφnanisotropic flow coefficients

event plane angle
11

Flow analysis today
Gale, Jeon, Schenke, Tribedy, Venugopalan, arXiv:1209.6330

MC-Glauberat parton level

LHC

MC-Glauberat nucleon level

Does not work

RHIC
Gaussian gluons energy
density fluctuations:
BM & A. Schäfer,PRD 85 (2012) 114030
Moreland, Qiu & Heinz,
NPA 904-5 (2013) 815c
12Model-data comparison today
Data:

Model:
initial conditions, τ0, η/s, ζ/s, ….

ALICE

102ATLAS
10pT>0.5 GeV, |η|<2.5pT>0.5 GeV, |η|<2.5ATLAS Pb+Pb

ATLAS Pb+Pb

sNN=2.76 TeV

sNN=2.76 TeV

Lint = 7 µb-1

Lint = 7 µb-1

Pb+Pb

sNN=2.76 TeV
Lint = 7 µb-1

10Glauber 20-25%0oGel
ATLAS

4p(v )

2p(v 3)1p(v ).L1 20-25%P(v2 )pT>0.5 GeV, |η|<2.510110-1 centrality:

10-200-1%
5-10%
20-25%
30-35%
40-45%
60-65%

10-1
0.1

0.2

v2

0centrality:
0-1%
5-10%
20-25%
30-35%
40-45%

centrality:
0-1%
5-10%
20-25%
30-35%
40-45%

0.05

0.1

v3

1
0

0.01

0.00

0.05

0.10

0.15

0.20

0.00

v2
0.02

0.03

v4

0.04

0.05

13 η/s, …
extracted QGP properties:

0.05

0.10

v2

0.15

0.20

Calibrated posterior
distributions:J. Bernhard, S. Moreland,
S.A. Bass, J. Liu, U. Heinz
Phys. Rev. C94 (2016) 024907

Temperature-dependent viscosities
from the calibrated posterior:

14

Tiny drops of QGP?

Initialstate

FinalstateTiny drops of QGP?
Data-Theory
comparison
confirms
Initialhydrodynamicstatecollective flow

Finalstates-enhancement probes τQGP
Strangeness enhancement grows with fireball life-time / size and saturates
at grand canonical equilibrium in Pb+Pb collisions

Fireball life-time/size ➝J. Rafelski & BM,
PRL 48 (1982)1066

The LHC data, soon to be complemented by RHIC data from p+Au, will permit asystematic study of quark chemistry equilibration as function of the life-time andsize of the QGP fireball.
16

Future Science
2017-20s

17

Highlights of RHIC runs 2017-23▪ Run 2017:▪ High luminosity √s = 510 GeV transverse polarized p+p run (400 pb-1)▪ Study scale evolution of the Sivers effect in W-boson production;
possibly confirm sign change of the Sivers effect relative to DIS▪ Run 2018:▪ Isobar system (96Ru - 96Zr) comparison run (1.2B events each)▪ Test of signatures of Chiral Magnetic Effect▪ Runs 2019-20:▪ Low energy (√sNN = 7.7, 9.8, 14.5, 19.6 GeV) Au+Au runs using electroncooling to increase luminosity▪ Search for signs of critical phenomena in event-by-event fluctuations▪ Runs 2022-23+:▪ Full energy (√sNN = 200 GeV) Au+Au, p+p, p+Au, etc.
▪ Precision measurements of fully resolved jets and Upsilon statesusing the new sPHENIX detector

Transverse polarized p+p collisions
Access the dynamic structure of protons:
à Test and confirm QCD structure of color spin interactions
à Non-universality of transverse momentum dependent functions
à SiversDIS = − Siverspp
à Observable: AN for Drell-Yan and W+/- production
DIS:γq-scattering attractivepp:
qqbar-anhilation repulsive

à Test scale evolution of transverse momentum dependent functions
à Observable: compare magnitude of AN for Drell-Yan and W+/Scale: DY: Q2 ~ 16 GeV2W+/-: Q2 ~ 6400 GeV219

Probing Chiral Symmetry with Quantum Currents
The chiral anomaly of QCD creates fluctuating differences in the number ofleft and right handed quarks, characterized by a chiral chemical potential µ5.
In a chirally symmetric QGP, this imbalance generates an electric current
along the magnetic field (chiral magnetic effect).

+electric charge separation

Spin

BMomentum! e2!
J=µ5 B
22π

B≈1018 Gauss+−µ52 ≠ 0−
μ5 > 0JJ ≠ 0

Probing Chiral Symmetry with Quantum Currents
The chiral anomaly of QCD creates fluctuating differences in the number ofleft and right handed quarks, characterized by a chiral chemical potential µ5.
In a chirally symmetric QGP, this imbalance generates an electric current
along the magnetic field (chiral magnetic effect).

Au+Au 200 GeV: 30-40%
0.15 < p < 0.5 GeV/cT

3.3 18B≈10ππ+Gauss+
3.2−−0.0500.05

Observed Ach

FIG. 2.

0.1

30-40% central

0−0.1(a)3.1

r = 3.1985 ± 0.2903−0.04(b)

−0.02

00.02

0.04

Ach(Color online) (a) pion v2 {2} as a function of ob-

Slope parameter r (%)

3.42v2 (%)

electric charge separationv2(π-) - v (π+) (%)

Charge asymmetry of elliptic flow
as function of total charge asymmetry

Probing Chiral Symmetry (Run-18)
Current understanding: backgrounds unrelated to the chiral magnetic effectmay be able to explain the observed charge separation
96
40Zr + 4096 Zr vs.

96
44Ru+ 4496 Ru

Relative difference in charge
separation effects (Ru vs Zr)

Isobar collisions will tell us what fraction of the charge separationis due to CME to within +/- 6% of the observed signal, allowing fora 5σ measurement if CME is 1/3 of the observed effect.
21

Critical behavior?
The moments of the distributions of conserved charges are related
to susceptibilities and are sensitive to critical fluctuations

Higher moments like kurtosis*varianceκσ2 change sign near the critical point

Non-monotonic trend observed in BES-I with limited statistical precision!
22

Beam Energy Scan II
2760

300

200 √s = 62.4 GeV
39

Temperature (MeV)250

The Phases of QCD

27
19.6

Quark-Gluon Plasma

14.5

200

11.5

B E S -I I

150
100

1st Orde 7.7
r Pha
se TransitionCriticalPoint?

ronHad50

9.1

Gas

Nuclear
MatterVacuum
00

200

400

600

800

1000

Color
Superconductor
1200

1400

1600

Baryon Chemical Potential μB(MeV)κσ2−1Model independent structure ofnet baryon number kurtosis

Possible Scenario
Near Critical Point

23

LEReC Layout
Cooling sections

Injection Section

Laser
24

sPHENIX

High-rate capable, large acceptance detector
built around the former BaBar 1.5T solenoid,
with full EM and hadronic calorimetry andprecision tracking and vertexing,

Outer HCal
Magnet coil
Inner HCal
EMCal
Vertexer/Tracker
Japan (RIKEN)
contributes theouter Si tracker

25microscopic resolving power [1/fm]

Probing scales in the medium
50

vac

10m
ediu

LHC
5RHICmiu
medumcal srm

Jets probe sub-thermallength scalesΥ(1s)Upsilon states probe
thermal length scalesΥ(3s)perfect liquidalethemTcuumuvac

Υ(2s)1How does the perfect
fluidity of the QGP
emerge from theasymptotically freetheory of QCD?

sPHENIX

2Tc

3Tc

temperature26

Jets & Upsilon statessPHENIX
capabilities
Complete calorimetricjet spectroscopy

Completely resolved
Upsilon spectroscopy

27

Rate enabled measurements
Example: Length dependent jet quenching
Length dependent suppression RAA

Length dependent energy loss
in photon tagged jet events

28

RHIC & LHC complementarity

Beyond RHIC30

2015 NSAC Long Rang Plan
RECOMMENDATION III
We recommend a high-energy, high-luminosity polarizedElectron Ion Collider as the highest priority for new facility
construction following the completion of FRIB.
The EIC will, for the first time, precisely image gluons in nucleons andnuclei. It will definitively reveal the origin of the nucleon spin and will
explore a new Quantum Chromodynamics (QCD) frontier of ultra-dense
gluon fields, with the potential to discover a new form of gluon matter
predicted to be common to all nuclei. This science will be made possibleby the EIC’s unique capabilities for collisions of polarized electrons withpolarized protons, polarized light ions, and heavy nuclei at high luminosity.

Big Questions
Proton spin:
Quark orbitalang. mom.

Quark spin contributes only ~30% to the proton’s spin
How do quark and gluon dynamics generate
the remainder of the proton’s spin?

Gluon spin
Lattice
QCD
Quark spin

The EIC will definitively resolve this question.
Gluon saturation:

Qs

Low energy

Gluons proliferate at high energy (small Bjorken-x)
How does the gluon density saturate to avoid violationof fundamental principles like unitarity?
High energy

The EIC will explore this question using heavy nuclei.
e + p → e + p + J/ψ

Proton transverse structure:
Distribution of gluons

We know the 1-D (longitudinal) structure of amoving proton very well
What does the proton look like in 3 dimensions?

t∫Ld=10f-1

b2

0.12
0.1
0.08
0.06
0.04
0.02
01

4
03

0.16 < xV < 0.25
00.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.2

26
5

1

4

0

0.12
0.1
0.080.06
0.04
0.02
00.016 < xV < 0.025
00.2

0.4

0.6

0.8

11.2

1.4

1.6

321The EIC will definitively answer this question.

15.8 < Q2 + M2J/ψ < 25.1 GeV2xV

0.0016 < xV < 0.0025

00

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.2

bT (fm)

32

1.2

0.12
0.1
0.08
0.06
0.04
0.02
0
1.4

1.6

1.4

1.6

1.4

1.6

Partons at Q2 ~ few GeV2?

?

Qs(x,A)
Gluon
saturation

Sea partons(gluons and sea quarks)

Confinedvalencequarks

x10−N
Theoreticallyunder control
at weak coupling

0.001

0.01

EIC domain

0.1

1

JLab 12 GeV
program will
explore33

Key physics areas
Imaging using GPDs and TMDs
Proton spin decomposition
Q2 = 10 GeV2
current
data

0.5

sea quarks

pol sea quarks

gluons0with EIC data

0.00112) dxspin
g(x,Qfractional
gluon

1DSSV+-0.5

EIC 5×100
5×250

EIC 20×250 eRHIC-1

all uncertainties for ∆χ2=90.3

0.35
10.4

0.45

2(x,Qquark) dx spin
2 x fractional
0.001

Nuclei as a probes ofquark confinement

Nuclear parton
distributions

34

BNL EIC Design: eRHIC
eRHIC ERL + FFAG ring design @ 1033−1034/cm2s~20 GeV e− + 255 GeV p or 100 GeV/u Au.

Day-1 Detector

35

Primary eRHIC Design Goals
Luminosity:
1033 – 1034 cm-2 s-1

80% polarizedelectrons:
3 – 18 GeV

pe-

70% polarized protons
40 – 275 GeVLight ions (d, Si, Cu)
Heavy ions (Au, U)
10 – 110 GeV/uPol. light ions (3He)
17 – 184 GeV/u

Maximum Peak Luminosity
Accepted Luminosity for Initial Operation≥ 1034 cm-2s-1
1033 cm-2s-1

Center of Mass Energies (ep)

20 GeV - 140 GeV

Proton Polarization

70%

Electron Polarization80%

Detector forward acceptance:pT acceptanceforward neutron acceptance

200 MeV/c – 1.3 GeV/c
4 mradMinimized construction and operational cost of the accelerator
36

Summary§ RHIC is planning a unique forefront science program with
continued discovery potential as laid out in NSAC LRP:
§ Quantify the transport properties of the QGP near Tc using
heavy quarks as probes§ Measure gluon and sea quark contributions to proton spinand explore transverse momentum-spin dynamics of QCD§ High statistics map of the QCD phase diagram, including
search for a possible critical point§ Probe internal structure of the most liquid QGP using fullyreconstructed jets and resolved Upsilon states as probes§ Important machine and detector upgrades underway for
BES II (LEReC, iTPC, EPD)

§ Major detector upgrade underway (sPHENIX)§ Transition from RHIC to eRHIC in mid-2020s37