What is the bulk viscosity Of QCD matter? - …mstrick6/qcdseminar/spring16/denicol.pdf ·...

with:

J.F. Paquet, S. Ryu, C. Shen, B. Schenke, S. Jeon, C. Gale

Kent State University 10.March.2016

What is the bulk viscosity

Of QCD matter?

Gabriel S. Denicol (BNL)

2

Shear viscosity of QCD matter exhibits surprising features near phase transition region

What about bulk viscosity?

“h/s”

3

What is bulk viscosity?

Non-equilibrium contribution to pressure Pressure =

thermodynamicpressure

> 0 < 0

Resistance to expansion

Resistance to compression

(Shock waves)(HIC,universe)

“dP”

4

Shear viscosity

Resistance to deformation

Sources of viscosity and dissipation

Resistance to volume change

Bulk viscosity

5

Bulk to shear viscosity ratio for several gases

Some known examples

In many cases, bulk viscosity can be larger than shear viscosity

M. Cramer, Phys. of fluids 24, 066102 (2012)

6

Bulk to shear viscosity ratio for several gases

Some known examples

M. Cramer, Phys. of fluids 24, 066102 (2012)

Comment: bulk viscosity from non-relativistic Boltzmann equation is zero

7

pions gas pQCD

Bulk viscosity ~1000 times smaller than shear

What about nuclear matter?some understood limits

Arnold et al, PRD 74, 085021 (2006)

Prakash et al, Phys. Rept. 227, 321 (1993)

8

QCD is not conformal

Lattice QCD calculations demonstrate that the EoS

of QCD matter deviates from that of a conformal fluid

Bulk viscosity couldbecome large in this

region

Near phase transition? we do not know

?

9We need guidance from experiment!

Extrapolations and models Finazzo et al, JHEP 1502, 051 (2015)

What is the bulk viscosity

Of QCD matter?

Extract it from experiment

11

Initial state

Pre-equilibriumdynamics

QGP as a relativisticfluid

Hadronization Transport/Freezeout

0 ~1 ~10

fm/c

~20

Ultra-relativistic Heavy Ion Collisions

Best (and often only) option to understand certainproperties of bulk nuclear matter

MADAI collaboration

Goal: use all data available to extract transport properties of QCD matter & understand initial state

12

Initial state

Pre-equilibriumdynamics

QGP as a relativisticfluid

Hadronization Transport/Freezeoutfm/c

Bulk QCD matter is only created transientlyNeed to reverse-engineer its properties

MADAI collaboration

Very large expansion rate! If bulk is sufficientlylarge, it should be possible to see it.

0 ~1 ~10 ~20

Ultra-relativistic Heavy Ion Collisions

13

Extraction of shear viscosityShear viscosity can be estimated using elliptic

flow data

Song et al, PRL 106, 192301 (2011)

The QGP is an almost perfect fluid with a shear viscosity ~10 times smaller than predictions from pQCD

14

Extraction of shear viscosity

IP-Glasma model offered a very good descriptionof flow harmonics

Gale et al, PRL 110, 1, 012302 (2013)

Shear viscosity can be estimated using elliptic and triangular flow data

15

Strong correlation between flow harmonics and initial geometry

shear viscosity reduces the hydrodynamic response to the initial gradients

provides good way toextract shear viscosity

16

What you will see in this talk

We investigate the effect of bulk viscosity on basic heavy ion collision observables

✔ Does bulk viscosity have a considerable effect on basic heavy ion observables? Is it needed to fit the data?

✔ Can it be extracted? What observable should we use?

✔ Does the inclusion of bulk viscosity change our current understanding of the transport properties of the QGP?

Questions addressed:

Fluid-dynamical model:

Improving the fluid-dynamical modeling of HIC

18

Hydrodynamic modeling of heavy ion collisions

Initial state and pre-equilibrium dynamics description of early time-dynamics and thermalization

IP-Glasma “initial condition”

Fluid-dynamical expansion of QGP and Hadron Gas

Transport description of Hadron Gas Matter described by cross sections and decay probabilities

UrQMD

thermalization “by hand”

fluid elements convertedto particles

EoS, viscosities, ...

+ EoM for dissipative currents

19

Fluid-dynamical equations

Inclusion of bulk viscous pressure, shear-stress tensor, and all couplings

GSD&Niemi&Molnar&Rischke, PRD 85, 114047 (2012)

For collisions at lower energies, baryon number diffusion is also included

20

✔ Switching to UrQMD at T=const.

✔ We solve the fluid-dynamical equations using a relativistic version of the KT algorithm – MUSIC

✔ lQCD + HRG EoS by Huovinen&Petrescky

✔ IP-Glasma initial state, t0 = 0.4 fm

SimulationIP-Glasma+MUSIC+UrQMD

PRL 115, 132301 (2015)

✔ h/s=const, ✔ z/s =

21

Integrated observables Tswitch = 145 MeV h/s = 0.095

bulk viscosity increases multiplicity, reduces <pT>, and reduces Vn

Surprisingly large effects of bulk viscosity

22

Integrated observables Tswitch = 145 MeV

bulk viscosity increases multiplicity, reduces <pT>, and reduces Vn

Value of shear viscosity extracted changes significantlyh/s=0.16 0.095

23

Effect of switching temperature

With only shear: changing Tsw is not enough to fit the data

Shear only

h/s=0.16

24

Effect of switching temperature

With bulk: fitting the data becomes possible

Shear + bulk

h/s=0.095

25

Effect of re-scatterings

Effect of re-scatterings is significantfor kaons and protons

<pT> is affected significantly

Tswitch = 145 MeV h/s = 0.095

26

Same conclusions remainWhat about RHIC?

h/s=0.06 Tswitch=165 MeV

Same bulk viscosity can also describe RHIC data

27

Results from Duke group

Model: Trento initial state + Hydro (bulk&shear) + UrQMD

shear not well constrained with just LHC datafinite bulk viscosity is favored

Similar findings also by Schenke&Monnai for MC-Glauber with valence quarks

Very good description of Multiplicity, mean-pT, and Vn

✔ h/s=0.095, ✔ z/s =

Best fit: overall agreement with data

✔ Tswitch=145 MeV,

p

K

p

X

LHC 2.76 TeV, 0-5%MUSIC + UrQMDALICE data

0 10 20 30 40Centrality (%)

0.1

1

10

100

1000

10000

dN/d

y

(L+S0)/2

W

Hadron chemistry is reasonably described

0.4 0.8 1.2 1.6 2pT (GeV)

0

0.05

0.1

0.15

0.2

v n{2

}

0.4 0.8 1.2 1.6 2pT (GeV)

0.4 0.8 1.2 1.6 2pT (GeV)

1

10

100

1000

10000

1/2

dN

/pTdp

T




n=2n=3

n=4

p

K

p

p

K

p

p

K

p

n=2

n=3

n=4

n=2

n=3

n=4

1/(2

ppT) d

N/d

p T

charged hadrons charged hadrons charged hadrons

Overall description of differential observables

Vn coefficients – different pT cuts

Good agreement at low pTDisagreement with data starts at high pT

1 2 3 4 5 6n

0.001

0.01

0.1

Pb+Pb, 2.76 TeV, 10-20%ATLAS data0.5< pT< 1.0 GeV

1.0< pT< 2.0 GeV

2.0< pT< 3.0 GeV

1 2 3 4 5 6n

0.001

0.01

0.1

Pb+Pb, 2.76 TeV, 20-30%ATLAS data0.5< pT< 1.0 GeV

1.0< pT< 2.0 GeV

2.0< pT< 3.0 GeV

v n{2

}

HBT radius – calculation by C. Shen et al

Good description of HBT

Bulk helps a little, butthis is mainly due to

the inclusion of UrQMD

Transverse momentum distribution

Protons: we describe STAR data, but not PHENIX!

0 0.4 0.8 1.2 1.6 2pT (GeV)

0

0.04

0.08

0.12

0.16

0.2

RHIC 200 GeV, 10-20%MUSIC + UrQMDPHENIX data

v2{4}

v3{2}

v4{2}

Good description of differential observables

34

EKRT model + second order viscous hydroNiemi et al, PRC 93, no. 2, 024907 (2016)

Good description without including bulk viscosity!But, chemical freeze-out at 175 MeV

35

Non-equilibrium contribution to pressure Pressure =

“dP”

Hydrodynamical picture works, if this is a perturbative correction to the thermodynamic pressure

PPCE = P0 + dP

Different descriptions of the same effect?

bulk?

37

IP-Glasma + MUSIC + UrQMD LHCz/s(T) h/s=0.095Ryu et al, PRL 115, 132301 (2015)

IP-Glasma initial conditions lead to

high mean pT

Bulk viscosityreduces mean

pT

PRL 115, 132301 (2015)

38

Evolution of initial state

Smooth Initial conditions(v2=0 in central collisions)

Fluctuations in nucleon positions(odd harmonics)

sub-nucleonic fluctuations (vn distributions&correlations)

proton-nucleus collisions

l~5 fm

l~1 fm

l~0.4 fm

l~0.4 fmor smaller

e(x,y) Coarse-grainingsize

IP-Glasma event

l = 0.1 fm l = 0.2 fm

l = 0.4 fm l = 0.8 fm l = 1.6 fm

0-5% class

Effect of smoothing

0.4 0.8 1.2 1.6(fm)

0.3

0.35

0.4

0.45

0.5<

p T>

shear only

shear+bulk

data

Effect of initial thermalization scale

p (G

eV)

Correlation to initial thermalization scale

L (fm)

<p T

> (

GeV

)

shear only

<L>-1 = <e>/<e> p

Correlation to initial thermalization scale

L (fm)

shear only

<L>-1 = <e>/<e>

<pT> ~ <L>-1

<p T

> (

GeV

) p

43

Summary/conclusions

We studied the effect of bulk viscosity the transverse momentum spectra and azimuthal

momentum anisotropies

✔ Bulk viscosity has a considerable effect on multiplicity, transverse momentum, and flow harmonics

✔ For IP-Glasma initial conditions, bulk viscosity improves the agreement between theory and experiment

✔ The mean transverse momentum is linearly related to the initial energy density gradients

It should be possible to extract it

Nk/Np

0 0.4 0.8 1.2 1.6 2pT (GeV)

0

0.2

0.4

0.6

0.8


0 0.4 0.8 1.2 1.6 2pT (GeV)

0

0.2

0.4

0.6

0.8


Np/Np

Nk/Np

Np/Np

Particle ratios

Pion to proton ratio is well describedKaons are slightly over-predicted

0.4 0.8 1.2 1.6 2pT (GeV)

0

0.1

0.2

0.3

v 2{2}


0.4 0.8 1.2 1.6 2pT (GeV)

0

0.1

0.2

0.3

v 2{2}


p

pK

p

pK

Diffential elliptic flow

Reasonable descriptionUrQMD is an important factor for this

46

Bulk viscosity from kinetic theory

Weinberg (matter coupled to radiation)

Dusling&Schaefer (pure glue)

14-moment approximation (Anderson-Witting equation)

47

Model: IP-Glasma + MUSIC (bulk&shear)

large bulk viscosity around “Tc” is favored by dataConsistent with our previous findings (recently confirmed by Duke group)

Extraction of z/s(T) and h/s with MADAI Emulator

z/s(T) parametrized as a Breit-Wigner distribution

0.4 0.8 1.2 1.6T/Tc

0

0.1

0.2

0.3

0.4

0.5

Parameters extracted

z/s(T) band = 1 sigma

“Tc” = 0.177 0.022 GeV+-

h/s = 0.077 0.037+-

LHC energy

48

h/s

z/s(Tc)

non-conformal holographyprediction

Correlation between Bulk and Shear

Increasing z/s leads to a reduction of h/s flow harmonics

Value of z ismuch larger than expectedFinazzo et al, arXiv:1412.2968

49

Event-by-event fluctuations changed the game

Centrality dependence of vnv2 distributions (measured by ATLAS)

PhD thesis of C. Shen Renk&Niemi, PRC 89 (2014) 6, 064907

Cannot be described by Glauber and KLN

Difficult to describe

v2 and v

3 with the

same shear viscosity

Hydrodynamic models should describe, not only event-averaged observables, but also distributions/correlations of observables

50

IPsat model + Yang-Mills evolution IP-Glasma:

Gale et al, PRL 110 (2013) 1, 012302

Schenke et al, PRC86 (2012) 034908

h/s=0.2

Very good description of flow harmonic coefficients

Prediction of vn distribution

51

Also able to describe event-by-event distributions of flow

NLO-improved pQCD + saturationEKRT model:

Central

PeripheralWhy can only EKRT and IP-Glasma describe this data?

Niemi et al, arXiv:1505.02677

What is the bulk viscosity Of QCD matter? - …mstrick6/qcdseminar/spring16/denicol.pdf ·...

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