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Bulk signatures & properties (soft particle production)

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Bulk signatures & properties

(soft particle production)

Data – Fit (s) Ratio

- Particle ratios well described by Tch = 16010 MeV, mB = 24 5 MeV
- Resonance ratios change from pp to Au+Au Hadronic Re-scatterings!

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 !

- 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

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

BRAHMS: 10% central

PHOBOS: 10%

PHENIX: 5%

STAR: 5%

- 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

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

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

- 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

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

Chemical FO temperature

About 70 MeV difference between Tch and Tth: hadronic phase

z

y

x

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?

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

…

Strong collective flow:

elliptic and radial

expansion with

mass ordering

Hydrodynamics:

strong coupling,

small mean free path,

lots of interactions

NOT plasma-like

Multistrange v2 establishes partonic collectivity ?

baryons

mesons

- 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?

- 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!

p1

r1

x1

p source

r(x)

1 m

x2

r2

p2

experimentally measuring this enhanced probability: quite challenging

5 fm

~

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

- 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

- We have neglected
- Final state interactions
- Coulomb interaction
- Strong interaction
- Weak decays

- Position-momentum correlations
- Things more subtle, such as special relativity

- Final state interactions

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

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

- 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

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

STAR, PRL93 012301 (2004)

Expected evolution:

?

p1

p2

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…

random (non-)system:

all observers measure the

“whole source”

It’s collective flow !!

Direct geometrical/dynamical evidence

for bulk behaviour!!!

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”

- 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

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

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

- no threshold effect seen
- RO/RS ~ 1

RHIC

Heinz & Kolb, hep-ph/0204061

An important space-time

“puzzle” at RHIC

- actively under study

- 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

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

- 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

- e 10 GeV/fm3

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

- 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

- So far all pieces point

elliptic