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Bulk signatures & properties (soft particle production). Does the thermal model always work ?. Data – Fit ( s ) Ratio. Particle ratios well described by T ch = 160  10 MeV, m B = 24 5 MeV Resonance ratios change from pp to Au+Au  Hadronic Re-scatterings!.

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Bulk signatures & properties (soft particle production)

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Bulk signatures & properties

(soft particle production)


Does the thermal model always work ?

Data – Fit (s) Ratio

  • Particle ratios well described by Tch = 16010 MeV, mB = 24 5 MeV

  • Resonance ratios change from pp to Au+Au  Hadronic Re-scatterings!


Strange resonances in medium

Short life time [fm/c]

K* < *< (1520) < 

4 < 6 < 13 < 40

Rescattering vs.

Regeneration ?

Medium effects on resonance and their decay products before (inelastic) and after chemical freeze out (elastic).

Red: before chemical freeze out

Blue: after chemical freeze out


ResonanceProduction in p+p and Au+Au

Life time [fm/c] :

 (1020) = 40

L(1520) = 13

K(892) = 4

++ = 1.7

Thermal model [1]:

T = 177 MeV

mB = 29 MeV

UrQMD [2]

[1] P. Braun-Munzinger et.al., PLB 518(2001) 41

D.Magestro, private communication

[2] Marcus Bleicher and Jörg Aichelin

Phys. Lett. B530 (2002) 81-87.

M. Bleicher, private communication

Rescattering and regeneration is needed !


Resonance yields consistent with a hadronic re-scattering stage

  • Generation/suppression according to x-sections

p

p

D

p

Preliminary

r/p

p

p

D

L*

D/p

More D

K

Chemical freeze-out

f/K

f Ok

p

p

r

p

p

Less K*

K*/K

p

r

K*

Less L*

L*/L

K

K

f

0.1

0.2

0.3

K


  • Blast wave fit of p,K,p (Tkin +b) + Tchem

  • Dt ~ 6 fm/c

    Based on entropy: Dt ~ (Tch/Tkin – 1) R/bs

  • Dt does not change much with centrality

  • because slight DT reduction is compensated by slower expansion velocity b in peripheral collisions.

preliminary

More resonance measurements are needed

to verify the model and lifetimes

Lifetime and centrality dependence from (1520) / and K(892)/K

G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239

Life time:

K(892) = 4 fm/c

L(1520) = 13 fm/c

  • Model includes:

  • Temperature at chemical freeze-out

  • Lifetime between chemical and thermal freeze-out

  • By comparing two particle ratios (no regeneration)

  • results between :

  • T= 160 MeV =>  > 4 fm/c(lower limit !!!)

  •  = 0 fm/c => T= 110-130 MeV

(1520)/ = 0.034  0.011  0.013

K*/K- = 0.20  0.03 at 0-10% most central Au+Au


hadronic phase

and freeze-out

QGP and

hydrodynamic expansion

initial state

Balance function (require flow)

pre-equilibrium

Resonance survival

hadronization

Rout, Rside

Rlong (and HBT wrt reaction plane)

dN/dt

time

5 fm/c

1 fm/c

10 fm/c

20 fm/c

Chemical freeze out

Kinetic freeze out

Time scales according to STAR data


BRAHMS: 10% central

PHOBOS: 10%

PHENIX: 5%

STAR: 5%

Identified Particle Spectra for Au-Au @ 200 GeV

  • The spectral shape gives us:

    • Kinetic freeze-out temperatures

    • Transverse flow

  • The stronger the flow the less appropriate are simple exponential fits:

    • Hydrodynamic models (e.g. Heinz et al., Shuryak et al.)

    • Hydro-like parameters (Blastwave)

  • Blastwave parameterization e.g.:

    • Ref. : E.Schnedermann et al, PRC48 (1993) 2462

      Explains: spectra, flow & HBT


Blastwave: a hydrodynamic inspired description of spectra

Spectrum of longitudinal and transverse boosted thermal source:

bs

R

Ref. : Schnedermann, Sollfrank & Heinz,

PRC48 (1993) 2462

Static Freeze-out picture,

No dynamical evolution to freezeout


STAR preliminary

Heavy (strange ?) particles show deviations in basic thermal parametrizations


Blastwave fits

  • Source is assumed to be:

    • In local thermal equilibrium

    • Strongly boosted

  • , K, p: Common thermal freeze-out at T~90 MeV and <>~0.60 c

  • : Shows different thermal freeze-out behavior:

    • Higher temperature

    • Lower transverse flow

  • Probe earlier stage of the collision, one at which transverse flow has already developed

  • If created at an early partonic stage it must show significant elliptic flow (v2)

Au+Au sNN=200 GeV

STAR Preliminary

 68.3% CL

95.5% CL

99.7% CL


Collective Radial Expansion

From fits to p, K, p spectra:

  • <r >

    • increases continuously

  • Tth

    • saturates around AGS energy

  • Strong collective radial expansion at RHIC

  • high pressure

  • high rescattering rate

  • Thermalization likely

Slightly model dependent

here:

Blastwave model


Dynamics indicate common freezeout for most particles

Chemical FO temperature

About 70 MeV difference between Tch and Tth: hadronic phase


z

y

x

Collective anisotropic flow


Elliptic Flow(in the transverse plane)for a mid-peripheral collision

Flow

Y

Out-of-plane

In-plane

Reaction

plane

Flow

X

Dashed lines: hard

sphere radii of nuclei

Re-interactions  FLOW

Re-interactions among what? Hadrons, partons or both?

In other words, what equation of state?


Anisotropic Flow

y

f

x

z

x

Transverse plane

Reaction plane

A.Poskanzer & S.Voloshin (’98)

“Flow” is not a good terminology

especially in high pT regions

due to jet quenching.

0th: azimuthally averaged dist.  radial flow

1st harmonics: directed flow

2nd harmonics: elliptic flow


Hydrodynamics describes the data

Strong collective flow:

elliptic and radial

expansion with

mass ordering

Hydrodynamics:

strong coupling,

small mean free path,

lots of interactions

NOT plasma-like


v2 measurements

Multistrange v2 establishes partonic collectivity ?


# III: The medium consists of constituent quarks ?

baryons

mesons


Ideal liquid dynamics –reached at RHIC for the 1st time


A more direct handle?

  • elliptic flow (v2) and other measurements (not discussed)  evidence towards QGP at RHIC

    • indirect connection to geometry

  • Are there more direct handles on the space-time geometry of collisions?

    • yes ! Even at the 10-15 m / 10-23 s scale !

  • What can they tell us about the QGP and system evolution?


Volumes & Lifetimes= 2nd Law Thermodynamics

  • Ideal Gas

  • Relativistic Fermi/Bose Gasm=0

  • Pions (3) vs. QGP (37)


The Bottom line…

if a pion is emitted, it is more likely to emit another

pionwith very similar momentumif the source is small

Creation probability r(x,p) = U*U

F.T. of pion source

Measurable!

Probingsource geometry through interferometry(Hanbury-Brown & Twiss (HBT) – photons from stars

p1

r1

x1

p source

r(x)

1 m

x2

r2

p2

experimentally measuring this enhanced probability: quite challenging

5 fm


Bose-Einstein correlations


~

P(p1,p2)/P(p1)P(p2) = 1 + | r(p1 - p2) |2

HBT (GGLP) Basics

  • In the simplest approximation, the technique has not changed since before most of you were born

    Goldhaber, Goldhaber, Lee, and Pais, PR 120:300 (1960)

  • For identical bosons/fermions

P(p1,p2;r1,r2) =

Who made first use of this pedagogic picture?

Gaussian source in xi yields Gaussian correlation

in conjugate variable qi=p1i-p2i

But this (plane wave) approximation neglects many effects


HBT Complexities

  • We have neglected

    • Final state interactions

      • Coulomb interaction

      • Strong interaction

      • Weak decays

    • Position-momentum correlations

    • Things more subtle, such as special relativity

State of the art analysis incorporates most of these, but not all


Au+Au

R ~ 6 fm

p+p

R ~ 1 fm

d+Au

R ~ 2 fm

Correlation functions for different colliding systems

STAR preliminary

C2(Qinv)

Qinv (GeV/c)

Different colliding systems studied at RHIC

Interferometry probes the smallest scales ever measured !


Rlong

p1

qside

x1

p2

qout

Rside

qlong

x2

Rout

Rside

Rout

Reminder

  • Two-particle interferometry: p-space separation  space-time separation

source sp(x) = homogeneity region [Sinyukov(95)]

 connections with “whole source” always model-dependent

Pratt-Bertsch (“out-side-long”) decomposition designed to help disentangle space & time


p1

Rlong

q

Rside

p2

Rout

beam direction

More detailed geometry

Relative momentum between pions is a vector

 can extract 3D shape information

Rlong – along beam direction

Rout – along “line of sight”

Rside–  “line of sight”


central

collisions

mid-central

collisions

peripheral

collisions

Measured finalsource shape

STAR, PRL93 012301 (2004)

Expected evolution:

?


p1

p2

More information

Relative momentum between pions is a vector

 can extract 3D shape information

Rlong – along beam direction

Rout – along “line of sight”

Rside –  “line of sight”

Rout

Rside

study as K grows…


Why do the radii fallwith increasing momentum ??


Geometric substructure?

random (non-)system:

all observers measure the

“whole source”


Why do the radii fallwith increasing momentum ??

It’s collective flow !!

Direct geometrical/dynamical evidence

for bulk behaviour!!!


Flow-generated substructure

random (non-)system:

all observers measure the

“whole source”

  • Specific predictions ofbulk global collective flow:

  • space-momentum (x-p) correlations

  • faster (high pT) particles come from

    • smaller source

    • closer to “the edge”


Timescales

  • Evolution of source shape

    • suggests system lifetime is shorter than otherwise-successful theory predicts

  • Is there a more direct handle on timescales?


p1

q

p2

Disintegration timescale

Relative momentum between pions is a vector

 can extract 3D shape information

Rlong – along beam direction

Rout – along “line of sight”

 increases with emission timescale

Rside –  “line of sight”

Rout

Rside


Disintegration timescale - expectation

Rischke & Gyulassy, NPA 608, 479 (1996)

3D 1-fluid Hydrodynamics

with

transition

with

transition

“”

“”

  • Long-standing favorite signature of QGP:

  • increase in , ROUT/RSIDE due to deconfinement  confinement transition

  • expected to “turn on” as QGP energy threshold is reached


8

8

6

6

RO (fm)

4

4

RS (fm)

1.5

1.25

RO / RS

1.0

increasing collision energy

Disintegration timescale - observation

  • no threshold effect seen

  • RO/RS ~ 1

RHIC


Heinz & Kolb, hep-ph/0204061

An important space-time

“puzzle” at RHIC

- actively under study

Disintegration timescale - observation

  • no threshold effect seen

  • RO/RS ~ 1

  • toy model calculations suggest very short timescales

    • rapid, explosive evolution

    • too explosive for “real” modelswhich explain all other data

N()


hadronic phase

and freeze-out

QGP and

hydrodynamic expansion

initial state

pre-equilibrium

hadronization

Time scales according to STAR data

Balance function (require flow)

Resonance survival

Rout, Rside

Rlong (and HBT wrt reaction plane)

dN/dt

time

5 fm/c

1 fm/c

10 fm/c

20 fm/c

Chemical freeze out

Kinetic freeze out


Summary: global observables

  • Initial energy density high enough to produce a QGP

    • e 10 GeV/fm3

      (model dependent)

    • High gluon density

      dN/dy ~ 800-1200

    • Proof for high density matter but not for QGP


Summary of particle identified observables

Statistical thermal models appear to work well at SPS and RHIC

  • Chemical freeze-out is close to TC

  • Hadrons appear to be born

    into equilibrium at RHIC (SPS)

  • Shows that what we observe is

    consistent with thermalization

  • Thermal freeze-out is common

    for all particles if radial flow

    is taken into account.

    T and bT are correlated

  • Fact that you derive T,bT is

    no direct proof but it is consistent with thermalization


Conclusion

  • There is no “ “ in bulk matter properties

  • However:

    • So far all pieces point

      indeed to QGP formation

      - collective flow

      & radial

      - thermal behavior

      - high energy density

elliptic


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