Materia a alta densidad(de SPS y RHIC a LHC)

Carlos PajaresUniversidade de Santiago de Compostela

Multiplicity

Parton Saturation

Elliptic Flow. sQGP, Perfect Liquid. EoS

Transverse Momentum Suppression

Charm, J/Ψ suppression

Fluctuations (Multiplicity, Transverse momentum, Balance, LONG range)

Percolation of Color Sources

Color Glass Condensate

XXXI Bienal Real Sociedad Española de Física. Granada. Sept. 2007

Energy density versus T/TC. Curve 1-2 quark flavours, curve 2-2 light plus oneHeavy flavour and curve 3-3 quark flavours.

MULTIPLICITY

ExtrapolationFrom lepton-Nucleon and p-A scaling on 2 2/ SQ Q

At LHC energy gives 9.5, i.e. 1800charged particles per unit rapidity

Linear energy data extrapolation gives6.5, 1200 charged particles

String percolation in between

Most of the models over 2500.

SATURATION OF PARTONS

Number of gluons. Size gluons Total Area

New Scale QS

s ( )( , )

2

2 2sS A2

s

QxG x Q R

Q

( , ) ( , , ) ( , ) 1 22 2 2

h T T dip T0Q dz d r z r Q r

* scattering h

( , ) ( , )2dip T T T Tr 2 d b N r b

*ln( / )

T T T

h

r x y

1 x y y

, parton carries emitting a new gluon

with probability

0p x P xp

ln ln

p

c s c 01ss k

1

N N xdp p

p x

ln!

n

0s

x1

n x

( , )

s s2dN

xG x Q e xd

The whole gluon cascade, (ordered in longitudinal momenta)

1p p gives

A more detailed treatment, is the BFKL eq

2 2

2 2

( )( )

2 ( ) ( )

xy T T T

s xz zy xyT T T T

N d z x yN N N

x z y z

2 2 22 2 0

0

ln ( )( ) exp

22

s

TT T

ss

r QeN r r Q

i. Grows as a power of the energy (Violation unitarity)ii. Diffusive behaviour, gluons can go inside non-perturbative region

2 2T QCDk

2 2

2 2

( )( )

2 ( ) ( )xy T T T

s xz yz xy xz zyT T T T

N d z x yN N N N N

x z y z

BK equation

Small x, interaction among gluon sources

Solution

– At lower x (higher energy) N is large but lower than 1 (solving theunitarity problem)

– At small rT, N is small (color transparency) BFKL is OK.

– The transition between small rT takes place at a characteristicvalue rT~1/QS(τ). (solving the infrared diffusion problem)

NEW SCALE QS (depends on y an A)

ELLIPTIC FLOW

Rcos( ) cos 2( - )3 3 3

1 R 23T T T T

Ed N d N d N1 2 2

dp p dp dyd 2 p dp dy

T

momentum anisotropy

pressure gradient is mainly along the direction of impact parameter (x axis)

in fluid, the p distribution will reflect the fluid profile. Spatial distribution is

2 2y x

2 2 2y x

p pV

p p

carried over

the momentum distribution. (partons or hadrons must interact each other)

eccentricity spatial anisotropy of the almond2 2y x

2 2y x

We expect

density of scatterings2

1 dnv

S dy

2v

Hydrodynamics perfect fluid result is for full thermalized system anda soft EoS

LHC?

Perfect fluid should have scaling properties

Limiting fragmentation

Centrality dependence

( ) ( )2 2 2 2y x xy

part 2 2y x

4

This scaling suggests that the collective flow is at the partonic stage

OK with coalescence models

Evidence

Perfect fluid

(interacting at partonic stage, soft EoS, low viscosity, fast thermalization)

/ behaviour2v

. for central collisions2v 0 2

scaling properties

Caveat .422

1vv 2

Transverse Momentum Suppression

Energy loss by medium induced gluonradiation

Photons in agreement with perturbative QCD

O.K. withEnergy loss dependence on Npart

Problems: Equally supressed as charged hadrons contrary to predictions (less supressed)

Non photonic electrons

Q=14 GeV2/fm

Azimuthal distribution of away-side charged hadrons

• For central collisions, suppressionof the back jet

• The widths of the back-to-backpeaks are independent of centrality (for pT (asso c)>6and 4<pT<6)

Gev/ctrigT8 p 15

Possibilities to look for supersonic jets

J/Ψ SUPPRESSION

hA

/J

WMax A

PX

P P

Data requires smaller σabs

at most 3mb (usually σabs= 4.2 mb)

No additional suppression seenat RHIC

0 mb

3 mb

Low x2 ~ 0.003(shadowing region)

σab=1mb34

Regeneration models fit the data.They predict, an increase of J/Ψ atLHC.

Lattice studies indicate no suppression of J/Ψ at T=TC, only at T≥2TC. Ψ’ and

are supressed at

Defining SJ/Ψ,Ψ’ the survival probabilities once is substracted the absorption, as

60% J/Ψ are directly produced and 40% J/Ψ come from decays of Ψ’ and

/. . obsJ XS 0 6 S 0 4 S ' Cx and

' . . 7 1 1 6 mb / ' . . J 4 3 0 3 mb

Grandchamp, Rapp, BrownPRL 92, 212301 (2004)

ThewsEur.Phys.J C43, 97 (2005)

Sequential dissociation modelcc

'c

cT T

c

The prediction for LHC isa large suppression of J/Ψcorresponding to the directlyproduced J/ Ψ.

Clear difference at LHC between regeneration and sequential models

Narrowing of the Balance function with Centrality

1B

2 N N

The width sensitive to hadronization time.Delayed hadronization narrowbalance function (stronger correlation inrapidity for the charged particles)

number of identified charged pion pairs

in ( ) ( )y y y

Caveat: In PyTHIA and other modelswith short hadronization time are able todescribe data.

The narrowing is only observed at midrapidity

00.05

0.10.15

0.20.25

0.30.35

Data CentralData Peripheral

B(y)

a)

00.05

0.10.15

0.20.25

0.30.35

0 0.5 1 1.5 2

HIJING-GEANT

B(y)

y

b)

NPTarg fluctuations contribute in target

hemisphere (most string hadronic models)

Different Extreme Reaction ScenariosMULTIPLICITY FLUCTUATIONS

NPTarg fluctuations contribute in both

hemispheres (most statistical models)

NPTarg fluctuations contribute in

Projectile hemisphere

• Multiplicity fluctuations sensitive to reaction scenario

M. Bleicher M. Gazkzicki,M. GorensteinarXiv:hep-ph/0511058

Reflection, Mixing and Transparency

• Significant amount of mixing of particles projectile and target sources

String Hadronic Models

• String hadronic models shown (UrQMD, HSD, HIJING) belong to transparency class

• They do not reproduce data on multiplicity fluctuations

Projectile hemisphere

HSD, UrQMD:V. Konchakovskyi et al.Phys. Rev. C 73 (2006)034902

HIJING:M. Gyulassy, X. N. WangComput. Phys. Commun. 83(1994) 307Simulation performed by:M. Rybczynski

PERCOLATION COLOR SOURCES

Results for the scaled variance of negatively charged particles in Pb+Pb collisions at Plab=158 AGeV/c compared to NA49 experimental data. The dashed line corresponds to our results when clustering formation is not included, the continuous line takes into account clustering.

L.Cunqueiro,E.G.Ferreiro,F del Moral,C.P.

FLUCTUATIONS AT RHIC

T

randomP

random

2 2T T

T

F

p p

p

%

• Color strings are stretched between the projectile and target

• Strings = Particle sources: particles are created via sea qq production inthe field of the string

• Color strings = Small areas in the transverse space filled with color fieldcreated by the colliding partons

• With growing energy and/or atomic number of colliding particles, thenumber of sources grows

• So the elementary color sources start to overlap, forming clusters, verymuch like disk in the 2-dimensional percolation theory

• In particular, at a certain critical density, a macroscopic cluster appears,which marks the percolation phase transition

CLUSTERING OF COLOR SOURCES

(N. Armesto et al., PRL77 (96); J.Dias de Deus et al., PLB491 (00); M. Nardi and H. Satz).

• How?: Strings fuse forming clusters. At a certain critical density ηc(central PbPb at SPS, central AgAg at RHIC, central SS at LHC ) amacroscopic cluster appears which marks the percolation phase transition(second order, non thermal).

• Hypothesis: clusters of overlapping strings are the sources ofparticle production, and central multiplicities and transverse momentumdistributions are little affected by rescattering.

LONG RANGE CORRELATIONS

• A measurement of such correlations is the backward–forward dispersion

D2FB=<nB nF> - <nB> <nF>

where nB(nF ) is the number of particles in a backward (forward) rapidity

•In a superposition of independent sources model, is proportional tothe fluctuations on the number of independent sources (It is assumedthat Forward and backward are defined in such a way that there is a rapiditywindow to eliminate short range correlations).

• Cluster formation implies a decreasing number of independent sources.Therefore DBF decreases.

2BFD

( )2ND

.1 0

• Sometimes, it is a measured

B Fn a bn

with

/2 2BF FFb D D

• b in pp increases with energy. In hA increases with A

• Clustering of strings implies a suppression of b

Color Glass Condensate

As the centrality increases, Qs increases, αs decreases an b increases

1 2

2 2sat

S

2

2 2sat2

S

S

2 4con conS sat

1 2

k y ycon

dN 1R Q

dy

dN 1R Q

dy

1 dN

dy

dN dNR Q

dy dy

dNe

dy

2S

1b

1 c

Particle production in high energy is considered as a gluon production in background classical field. The spectrum becomes thermal with

Kharzeev, Levin, Satz

/sT Q 2

/1 T

in percolation( )

2T 1

c

pT

2F

during

If you can not get rid of the noise…. study the noise

Penzias and Wilson

RHIC IIFAIRLHC