heavy ion collisions at high energy

QCD MATTER CREATED AT THE LHC

BARBARA ERAZMUS CNRS/IN2P3 FRANCE

CRETE CENTER FOR THEORETICAL PHYSICS MAY 28, 2013

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2

HEAVY ION COLLISIONS AT HIGH ENERGY

Extreme states of matter

• QCD phase diagram

• Deconfinement

• Chiral symmetry restoration

Universal character of wave functions of large nuclei

• Dense gluonic system

• Saturation

• Color glass condensate

3

HERA demonstrated that the gluon distribution in a proton rises very fast with decreasing x at fixed Q

RHIC

LHC

In this range saturation of the rapidly growing gluon distribution at saturation scale Qs

ALICE | DIS | 22 Avril 2013 | B. Erazmus 4

ALICE | SIPB | 21 March 2013 | B. Erazmus 6

A LARGE ION COLLIDER EXPERIMENT

Not shown: ZDC (at ±114m)

L3 MagnetT0/VZEROTrigger/Centrality

TPCTracking, PID (dE/dx) ITS

Low pT trackingPID + Vertexing

MUON μ-pairs

TOFPID

TRDElectron ID (TR)

HMPIDPID (RICH) @ high pT

PHOSγ, π0, jets

PMDγ multiplicity

ACORDECosmic trigger

FMDCharged multiplicity

Dipole

EMCALγ, π0, jets

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ALICE – dedicated heavy-ion experiment at the LHC

• particle identification (practically all known techniques)• extremely low-mass tracker ~ 10% of X0

• excellent vertexing capability• efficient low-momentum tracking down to ~ 100 MeV/c

vertexingHMPID

ITS TPC

TRD

TOF

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LHC Heavy-Ion running • Two heavy-ion runs at the LHC so far:

• in 2010 – commissioning and the first data taking• in 2011 – already above nominal instant luminosity!

• p–Pb run just finished at the beginning of this year

• Followed by Long Shutdown–1 (LS1)

year system energy √sNN

TeVintegrated luminosity

2010 Pb – Pb 2.76 ~ 10 mb-1

2011 Pb – Pb 2.76 ~ 0.1 nb-1

2013 p – Pb 5.02 ~ 30 nb-1

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GLOBAL EVENT PROPERTIES

State and dynamical evolution of the bulk matter characterized by

soft particles (below a few GeV/c)

multiplicity distributions (initial energy density)

spectra, yields (hadronization process)

flow (collective transport phenomena)

correlations (space-time evolution)

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MULTIPLICITY DISTRIBUTIONS

ALICE | DIS | 22 Avril 2013 |

ALICE PRL 105 (2010)


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INITIAL DENSITY AND TEMPERATURE FROM BJORKEN FORMULASEE CMS PRL 109 (2012)

Lattice QCD predictions : Tc 155 MeV – 175 MeV

The conditions of the formation of a quark gluon plasma are reached in the early stages of the collisions

(2.6 times RHIC)

(+30% RHIC)

IDENTIFIED PT SPECTRA

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model comparisons:- VISH2+1 (viscous hydro)- HKM (hydro+UrQMD)

-Kraków (viscous corr., lower the effective Tch)- EPOS (hydro+UrQMD)

p (GeV/c)T

Large radial flow in most central events:<βT> = 0.65 ± 0.02 (~10% higher w.r.t. RHIC)

increases with centrality

Comparison with hydro models: radial flow and kinetic freeze-out temperature Tkin

Tkin = 95 ± 10 MeV (same as RHIC within errors)

Dat

a/M

odel

1/N

1/(2

πp

) d2 N

/(dp

dy

) (G

eV/c

)-

2T

Tev

10-3

Krakow

EPOS

10-1

10

103

106

105

0-5% Central collisions

π+ + π- (× 100)

K+ + K (× 10)

p + p (× 1)

-

= 2.76 TeVNN

ALICE, Pb-Pb s

STAR, Au-Au s = 200 GeVNN

PHENIX, Au-Au s = 200 GeVNN

VISH2+1

HKM

1

1.5π+ + π-

1

1.5K+ + K-

1

1.5 p + p

0 1 2 3 4 5

•

ALI

CE

Col

labo

ratio

n, P

hys.

Rev

. Let

t. 10

9, 2

5230

1 (2

012)

+

arX

iv:1

303.

0737



13



Large radial flow in top central events:<βT> = 0.65 ± 0.02 (~10% higher w.r.t. RHIC)




•

Dat

a/M

odel

1/N

1/(2

πp

) d2 N

/(dp

dy

) (G

eV/c

)-

2T

Tev 10-4

10-2 HKM

1

102

105

104


π+ + π- (× 100)

K+ + K (× 10)-

p + p (× 1)

ALICE, Pb-Pb s = 2.76 TeVNN

= 200 GeVNN

STAR, Au-Au s


VISH2+1

Krakow

EPOS

1

1.5π+ + π-

1

1.5K+ + K-

1

1.5 p + p

0 1 2 3 4 5

p (GeV/c)T

ALI

CE

Col

labo

ratio

n, P

hys.

Rev

. Let

t. 10

9, 2

5230

1 (2

012)

+

arX

iv:1

303.

0737

ALICE arXiv: 1303.0737


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Large radial flow in top central events:<βT> = 0.65 ± 0.02 (~10% higher w.r.t. RHIC)



-2)c 106

(GeV/105 ALICE, Pb-Pb NN = 2.76 TeV

s


) PHENIX, Au-

Au s = 200 GeV

y 3

NNd 10

Tp/(dπ+ + π- (× 100)N 10

2d

K+ + K - (× 10)) VISH2+1T 10-1

p + p (× 1)p HKMπ1/(2 10-3 0-5% Central collisions

Krakow

EPOSev

N1/

1.5

π+ + π-

1

Data/Model1.5

K+ + K-

1

1.5

p + p

1

0

1

2

T

Dat

a/M

odel

1/N

1/(2

πp

) d2 N

/(dp

dy

) (G

eV/c

)-

2T

Tev

p (GeV/c)T

10-6

1.5

10-4

10-2

1

102

104


π+ + π- (× 100)

K+ + K - (× 10)

p + p (× 1)

ALICE, Pb-Pb s = 2.76 TeVNN



VISH2+1

HKM

Krakow

1

π+ + π-

1

1.5K+ + K-

0 1 2 3 4 5

1

1.5 p + p

•

ALI

CE

Col

labo

ratio

n, P

hys.

Rev

. Let

t. 10

9, 2

5230

1 (2

012)

+

arX

iv:1

303.

0737 ➡ more peripheral events are more

challenging for the models

ALICE arXiv: 1303.0737


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MATTER AT CHEMICAL FREEZE-OUT

(from J. Cleymans et al, hep-ph/0511094)

well described by statistical models

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ANNIHILATION IN BARYON-ANTIBARYON CORRELATIONS

Deviation of proton yields from thermal models expectations

annihilation should be taken into account while determining yields

Steinheimer, Aichelin, Bleicher; arXiv:1203.5302Werner et al.; Phys.Rev. C85 (2012) 064907 Karpenko, Sinyukov, Werner;arXiv:1204.5351

(...)switching BB-annihilation one suppresses baryon yields, in the same time increases pion yield, thus lowering p/π ratio to the value 0.052, which is quite close to the one measured by ALICE(...)

→ annihilation must be seen in baryon-antibaryon correlations

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BARYON FEMTOSCOPY

increase of (anti)correlation

=decrease of the

radius orincrease of the

interaction cross-section

expected shape of the signal (MC)

measured correlationemission function (radius) cross-section

C ( ⃗q)= ∫ S ( ⃗r )∣ Ψ ( ⃗q , ⃗r )∣2 d

4 r

Maciej Szymański Quark Matter 2012

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PP CORRELATION FUNCTIONS

Shape dominated by Coulomb and Strong FSISignificant annihilation (from strong FSI) expected and measured Quark Matter 2012

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ANISOTROPIC ELLIPTIC FLOWSpatial deformation

Pressure Δpx > Δpy

Y

X

Zφ

xy

Azimuthal (φ) pressure gradients Anisotropic particle density

y2

y3

y4

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ELLIPTIC FLOW COEFFICIENTS

ALICE PLB 719 (2013)

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ELLIPTIC FLOW COEFFICIENTS

Hydro model using Glauber initial conditions for different values of the viscosity Schenke, Jeon, Gale Phys.Lett. B7012 (2011) Further constraints on viscosity and initial conditions provided by measurements of higher harmonics very sensitive to properties of the mediumALICE PRL 107

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HARD PROBES AT HIGH MASS AND HIGH PTHEAVY QUARKS, QUARKONIA, PHOTONS, JETS…

• Created at early stages of the collisions

• Production and propagation in medium provides information about parton energy loss

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REFERENCE COLLISIONSproton-proton

RHIC

J/ ψ SUPPRESSION

SPS ‘anomalou

s’ suppression

LHC

suppression / regenerat ion


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J/y elliptic flow

arXiv: 1303.5880

J/y produced by recombination of thermalized c-quarks should have non-zero elliptic flow– measurements give a hint for non-zero v2 – qualitative agreement with transport models, including regeneration– complementary to indications obtained from J/y RAA studies


D MESONS RAA

Average D-meson RAA:– pT < 8 GeV/c hint of slightly less suppression than for light hadrons– pT > 8 GeV/c both (all) very similarno indication of colour charge dependence


D MESONS v2

Non-zero D meson v2 observed Comparable to that of light hadrons

Simultaneous description of RAA and v2

c-quark transport coefficient in medium

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Ds MESONS RAA

Strong suppression (~ 4–5 )at pT above 8 GeV/c

Uncertainty will improve with future pp and Pb–Pb data taking

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REFERENCE COLLISIONSp - Pb

• Reference for Pb-Pb collisions ?• Cold nuclear matter ?• Unexpected collective effects ?

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COLD NUCLEAR MATTER EFFECTS VS. JET QUENCHING IN PB-PB…

Compatible with unity above 2-3 GeV/c

Jet quenching in Pb-Pb collisions is a final state effect <=> QGP opaque to energetic partons

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Phys. Rev. Lett. 110, 082302 (2013)

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THE RIDGE

• The near-side long-range ridge observed by CMS in pp and p-Pb seen by ALICE in p-Pb[JHEP 09 (2010) 091, PLB718 (2013) 795]

(zoomed)

Near-side ridge(Dj ~ 0, elongated in Dh)

Near-side jet(Dj ~ 0, Dh ~ 0)

Away-side jet(Dj ~ p, elongated in Dh)

2 < pT,trig < 4 GeV/c1 < pT,assoc < 2 GeV/c20% highest multiplicity

Dj (rad)Dh

1/N

trig d

2 Nas

soc/d

DhdD

j

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INTERPRETATIONFlow?

viscous hydro (arXiv:1112.0915)

Saturation?Color glass condensate (arXiv:1302.7018)

arXi

v:11

12.0

915

Rid

ge Y

ield

s pe

r Dh

0-20% 20-40% 40-60%

arXi

v:13

02.7

018Band: Calculation

Points: ALICE data

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CONCLUSIONS

Hot and dense matter created at the LHC behaves as a liquid

with low viscosity well described by hydrodynamical approaches

New precise hard probes allow to study the QGP

Recent measurements of proton-lead collisions reveal

surprising (collective ?) behaviour

heavy ion collisions at high energy

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