understanding the physics of heavy ion collisionslss.fnal.gov/conf2/c110529/salgado.pdf · impact...

Understanding the Physics of Heavy Ion Collisions

[email protected] http://cern.ch/csalgado

Carlos A. SalgadoUniversidade de Santiago de Compostela

Rencontres de Blois 2011[Including news from Quark Matter 2011 - Last week]

mailto:[email protected]

mailto:[email protected]

http://csalgado.web.cern.ch

http://csalgado.web.cern.ch

2

QCD: An apparently simple lagrangian hides a plethora of emerging phenomena

Asymptotic freedom; confinement; chiral symmetry breaking; mass generation; new phases of matter; a rich hadronic spectrum; etc

High-energy heavy-ion collisions are the experimental tools to access (some of)

these properties

Rencontres de Blois 2011 Understanding heavy-ion collisions

Some of these properties appear at high-temperatures or densities

3

QCD at high-temperatures

[MILC Collaboration 2006]

Equation of state

First example: Equation of State (EoS)

Naïve estimation:Let’s fix µ = 0, the pressure of an ideal gas (ofmassless particles) is proportional to the number of d.o.f: P ! NT 4. So,

P! ! 3 " T 4 ; PQGP ! (2 " 2 " 3! "# $

quarks

+ 2 " 8! "# $

gluons

) " T 4

So, one expects a large difference (factor # 10) between the two

phases.Lattice results (Karsch et al.)

0.0

1.0

2.0

3.0

4.0

5.0

1.0 1.5 2.0 2.5 3.0 3.5 4.0

T/Tc

p/T4

pSB/T4

3 flavour2+1 flavour

2 flavour

Frascati, May 2006 QGP and HIC – p.19

First example: Equation of State (EoS)

Naïve estimation:Let’s fix µ = 0, the pressure of an ideal gas (ofmassless particles) is proportional to the number of d.o.f: P ! NT 4. So,

P! ! 3 " T 4 ; PQGP ! (2 " 2 " 3! "# $

quarks

+ 2 " 8! "# $

gluons

) " T 4

So, one expects a large difference (factor # 10) between the two

phases.Lattice results (Karsch et al.)

0.0

1.0

2.0

3.0

4.0

5.0

1.0 1.5 2.0 2.5 3.0 3.5 4.0

T/Tc

p/T4

pSB/T4

3 flavour2+1 flavour

2 flavour

Frascati, May 2006 QGP and HIC – p.19

Two broken symmetries in the QCD vacuum confinement chiral symmetry is broken

Restored at high-temperatures ← asymptotic freedom

Phase diagram

[Fodor, et al. 2004]


4

SPS@CERN - Fixed target√

s � 20AGeV

pA, SU, PbPb - 90’s

Towards the highest energies


4


s � 20AGeV



RHIC@BNL - Collider√

s = 20...200AGeV

CuCu, AuAu, dAu2000 - ...

x10


4


s � 20AGeV



RHIC@BNL - Collider√

s = 20...200AGeV

CuCu, AuAu, dAu2000 - ...

x10

LHC@CERN - Collider (pp), PbPb, pPb

Energy frontier of HI Starting November 2010

x30

√s = 2.76...5.5ATeV


5

Kinematical reach in nuclear collisions

Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY

Present nuclear DISand Drell-Yan in p+A


5


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY

Present nuclear DISand Drell-Yan in p+Ad+Au @ RHIC0 < y < 3.2


5


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY

p+Pb @ LHC (7 TeV+2.75 TeV)


= 6.6

laby

= 6laby

= 4laby

= 2laby

= 0laby


5


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY



= 6.6

laby

= 6laby

= 4laby

= 2laby

= 0laby

Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

ALICE CMSJets

PhotonsHadrons

|<0.9!D's ||<4!B's 2.4<|

pA Ap

(x)2sat,PbQ

PresentDIS+DY


5


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY


Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

(x)2sat,PbQ

PresentDIS+DY



= 6.6

laby

= 6laby

= 4laby

= 2laby

= 0laby

Ax-710 -610 -510 -410 -310 -210 -110 1

)2 (G

eV2

Q

1

10

210

310

410

510

610

710

810

ALICE CMSJets

PhotonsHadrons

|<0.9!D's ||<4!B's 2.4<|

pA Ap

(x)2sat,PbQ

PresentDIS+DY

New regions never explored in HICsmall-x and large-Q


6

Some jargon... centrality of the collision

A

ALongitudinal view Transverse view

Experimental access to different medium densities and geometries

Normally computed in a (probabilistic) geometrical model by Glauber


6


A


Impact parameter




6


A


Impact parameter



Participants


6


A


Impact parameter

Spectators



Participants


6


A


Impact parameter

Spectators



Participants

Multiplicity0 500 1000 1500 2000 2500 3000

-510

-410

-310

-210

0 - 5%

5 - 10

%

10 -

20%

20 -

30%

30 -

40%

40 -

50%

50 -

60%

Prob

abilit

ycentral

peripheral


7

What is the structure of the hadrons at high energy?

→ color coherence effects in particle production.

Is the created medium thermalized? How?

→ presence of a hydrodynamical behavior.

What are the properties of the produced medium?

→ identify signals of the presence of a medium in well-controlled observables.

What do we expect to learn?


Initial state: Saturation of partonic densities

(Color Glass Condensate)

8 Rencontres de Blois 2011 Understanding heavy-ion collisions

Checks of hydrodynamics(thermalization)

9

∂µTµν = 0

Tµν = (ε+ p)uµuν − pgµν + viscosity corrections

+ Equation of state


10

The essential measurement for hydro

x

y

φ

Outgoing particle

dβ

dt= − c2

� + P∇P

Recall the Euler equationtransverse

plane


10

The essential measurement for hydro

x

y

φ

Outgoing particle

dβ

dt= − c2

� + P∇P

Recall the Euler equationtransverse

plane

More momentum in these directionsdN

dφ∝ 1 + 2 v2 cos(2φ)

Elliptic flow normally measured by the second term in the Fourier expansion

� = 3P =⇒ ∇xP < ∇yP

Initial conditions at thermalization time need to be given (ex. CGC)


11

Ideal fluid behavior[Luzum, Romatschke 2008]

Lowest viscosity known

Ideal fluid behavior

“perfect liquid”

[Csernai, Kapusta, Mclerran 2006]

Finite-T pQCD

AdS/CFT “bound” [Policastro, Son, Starinets]

)c (GeV/tp0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

{4}

2v

0.05

0.1

0.15

0.2

0.25

0.310-20%20-30%30-40%10-20% (STAR)20-30% (STAR)30-40% (STAR)

RHIC

LHC


[ALICE 2010]

12

Higher harmonics


With high precision data, higher terms in the expansion identified For a symmetric medium odd terms are 0 Even-by-event fluctuations make them finite

Will allow precise tests of hydro

dN

dφ∝ 1 +

∞�

n=1

2 vn cos [n (φ− φn)]

[H. P

eter

sen,

QM

2011

]

[More in the talk by C. Loizides]

Hard Probes Long distance terms modified by the presence of medium

Nuclear PDFs and new (non-linear) evolution equations Probes of hot matter created in the interaction EW processes (no hadronization) used as benchmark

13

Nuclear PDFs Hadronization paradigmatic exampleJ/Ψ

σAB→h = f iA(x1, Q

2)⊗ f jB(x2, Q

2)⊗ σ(ij → k)⊗Dk→h(z, Q2)

If you know two ingredients you can extract the other[Tom LeCompte yesteday’s talk]


14

Nuclear PDFs

Initial conditions and error analysis for different NLO sets

0.20.40.60.81.01.21.4

0.20.40.60.81.01.21.4

10-4 10-3 10-2 10-1 10.00.20.40.60.81.01.21.4

10-4 10-3 10-2 10-110-4 10-3 10-2 10-10.00.20.40.60.81.01.21.4

This work, EPS09NLOHKN07 (NLO)nDS (NLO)

Q2=100 GeV2

Q2=1.69 GeV2

Pb Pb Pb

(,

2 =100GeV

2 )Pb

(,

2 =1.69GeV

2 )Pb

Large uncertainties especially for gluons - smaller at large virtualityNotice that parametrization bias effects are present

Bands to be considered as lower bounds

Chi2/dof

EPS09 0.79

HKN 1.58

nDS 0.76


15

Quarkonia suppression Simple intuitive picture [Matsui & Satz 1986]

Potential screened at high-T Bound states not possible Suppression of J/Psi in nuclear collisions

However, interpretation of the data is not clear

J/Psi suppressed also in pA (on top of nPDFs) Not good theoretical control over the suppression (Already J/Psi suppression not well understood in pp) Could LHC improve the situation?


16

Quarkonia at the LHC

Different quarkonia states have different suppression


[J. Schukraft QM2011]

[C. S

ilves

tre

QM

2011

]

Sequential suppression? Lattice QCD suggest that 1S quarkonia states melt at Excited states melt at T ∼ Tc

T ∼ 2Tc

)2 (GeV/cµµm7 8 9 10 11 12 13 14 )2

Even

ts /

( 0.1

4 G

eV/c

0

10

20

30

40

50

60CMS Preliminary

= 2.76 TeVNNsPbPb 0-100%, 0.0 < |y| < 2.4

< 20 GeV/cT

0 < p-1bµ = 7.28 intL

> 4 GeV/cµ

Tp

(fixed to MC)2 = 92 MeV/c!

dataPbPb fitpp shape

!(2S+3S) !(1S)PbPb

!(2S+3S) !(1S)pp

= 0.31"0.15+0.19 ±0.03

J/Ψ

What are the effects of a medium

in the jet evolution?

Jet quenching

18

What is a jet (naively)What is a jet?

Islamabad, March 2004 HIC and the search for the QGP - 4. Status. – p.28


DELPHI Interactive AnalysisRun: 26154Evt: 3018

Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992

TD TE TS TK TV ST PA

Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z


Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z

Experimental definition involves jet finding algorithms Ideally all the energy of the primary is reconstructed by the algo

[Nigel Gloveryesterday’s talk]

18



What is a jet?


high-pt partonsproduced with large virtuality

(this is the short distance part)



Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z


Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z



18



What is a jet?


What is a jet?


virtuality isreduced by

gluon radiation



Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z


Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z



18



What is a jet?


What is a jet?


What is a jet?



gluon radiationradiation along a

given direction: jet

This is often called a jet cone, although shape depends on

definition



Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z


Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z



18



What is a jet?


What is a jet?


What is a jet?


What is a jet?

!y






definition



Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z


Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z



18



What is a jet?


What is a jet?


What is a jet?


What is a jet?

!!






definition



Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z


Beam: 45.6 GeV

Proc: 1-Oct-1991

DAS : 25-Aug-199121:47:02

Scan: 19-Feb-1992


Act

Deact

14( 93) 0

( 0)

72(133) 0

( 13)

0( 0) 0

( 0)

17( 23) 0

( 23)

0( 18) 0

( 12)

0( 0) 0

( 0)

0( 0) 0

( 0)

X

Y

Z



19

RAA at 200 GeV

• Direct γ, π0 and η in Au+Au– Direct γ RAA with measured p+p reference!

=> RAA of η and π0 consistent, both show suppression=> RAA of γ is smaller than 1 at very high pT

0-10% central events

mesons

photons

Jet quenching at RHIC


Very large energy loss - large jet quenching parameter

dense partonic system

Photons don’t interact (no effect) quarks and gluons do (suppression)

19

RAA at 200 GeV

• Direct γ, π0 and η in Au+Au– Direct γ RAA with measured p+p reference!

=> RAA of η and π0 consistent, both show suppression=> RAA of γ is smaller than 1 at very high pT

0-10% central events

mesons

photons

Jet quenching at RHIC

Twooppositeassumptions

Alllostenergyistransferredtomedium

Hydroevolution[Satarov,Stoeker,Mishustin2005;

Casalderrey-Solana,Shuryak,Teaney2004]

Coloredwakes[Muller,Ruppert,Renk2006,

Chakraborty,Mustafa,Thoma2006]

Partonictransport[AMPT2006]

1

Atr

igg

er j

et

2

! M

B

C

Negligibleenergytransferred:Energylossisradiatedasgluons

Cherenkovradiation[Dremin

2005;Koch,Majumder,Wang2005]

Radiativeenergyloss

[Polosa,Salgado2006]

Kyoto,November2006

HardProbestoQGP–p.20

Calibration


Very large energy loss - large jet quenching parameter

dense partonic system

Photons don’t interact (no effect) quarks and gluons do (suppression)

20

Reconstructed Jets

[Jet reco in HIC: Cacciari, Rojo, Salam, Soyez 2010]


21

Inclusive jets are suppressed

In central collisions, only 1/2 of the jets are observed for two radius R[ATLAS 2010 - B. Cole QM2011]

Need to understand proton-proton referenceObserved jets are biased - is an unbiased measurement possible in HI?


R = 0.2 R = 0.4

22

Di-jet asymmetry at the LHC

Energy imbalance between two most energetic jets: Aj =ET1 − ET2

ET1 + ET2[ATLAS 2010 - B. Cole QM2011; CMS similar results]

Strong energy loss - points to a very dense partonic system


ET1

ET2

23


No strong change with respect to the vacuum jets


ET1

ET2

Azimuthal distribution of two most energetic jets[CMS 2011 - C. Roland QM2011; ATLAS similar results]

24


Energy taken by soft particles at large angles


[CMS 2011 - C. Roland QM2011]

� p�T =�

Tracks

−pTrackT cos (φTrack − φLeading Jet)

Where does the energy go?


A theory of jets in the medium In-medium parton shower not knownfrom QCD

Until recently only medium modificationoff single emitter computed

But coherence among different emittersis essential in the vacuum case:

ordering variables

26

Antenna emission in vacuum (QCD or QED)

k⊥, ω

tform �ω

k2⊥� 1

θ2q,gω

The transverse wavelength

λ⊥ �1

k⊥⇒ tform �

λ⊥θq,g

The transverse size of the pair : θqq̄ tform � λ⊥θqq̄

θq,g

�dNq�φ ∝ dω

ω

dθpk

θpkΘ (θpp̄ − θpk)

The spectrum integrated in azimuthal angle

So, when the gluon/photon “sees” a neutral object θq,g � θqq̄

Building block of parton showers in vacuum. Taking quark as reference:


27

Antenna radiation in medium

!pp !pp

Angular ordering in vacuum Anti-angular ordering

in the medium

dNq =αsCF

π

dω

ω

dθ

θ(Θ (cos θ − cos θqq̄) + A(θqq̄ , L)Θ (cos θqq̄ − cos θ))

Very striking result found in the medium Strict large angle emission - anti-angular ordering in soft limit

[Mehtar-Tani, Salgado, Tywoniuk 2010]


0 0.1 0.2 0.3 0.4

!

0

2

4

6

8

10

12

" d

N/d"

d!

vacuum

radiation

medium-induced

radiation

!-1

For an opaque medium, two vacuum-like de-coherent spectra Soft emission at large angle. Promising tool for in-medium shower Memory loss effect: radiation independent on initial color config.

28

Collisions at the TeV scaleimply completely new opportunities


29

First Z’s measured in nuclear collisions


Rapidity0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

dN/dy

0

10

20

30

40

50

60

CMS

POWHEG + PYTHIA 6.4

Paukkunen et al., CT10+isospin

Paukkunen et al., idem+EPS09

Neufeld et al., MSTW+isospin

Neufeld et al., idem+eloss

b) = 2.76 TeVNN

s at -1bµCMS PbPb 7.2

-8x10

Summary With LHC nuclear collisions at the TeV for the first time

Access to the small-x region of the wave function

Large virtualities: jets, EW bosons, etc...

Created medium (RHIC+LHC) very dense

Ideal fluid behavior

Higher statistics and new tools

Will allow to characterize the medium properties withunprecedented precision

Is it a liquid? Strongly coupled? Are quasiparticles the relevant degrees of freedom?..


understanding the physics of heavy ion collisionslss.fnal.gov/conf2/c110529/salgado.pdf · impact...

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