# Presentation: 383283

## Collective flow

- Fabrice Retière
- Lawrence Berkeley National Laboratory

## Flow (in the transverse plane)A mid-peripheral collision

- Dashed lines: hard
- sphere radii of nuclei

- Reaction
- plane

- In-plane

- Out-of-plane

- Y

- X

- Re-interactions  **FLOW **
- Re-interactions among what? **Hadrons, partons or both?**
*In other words, what equation of state?*

**Flow**

- Flow

**Notes:**
There are two fundamental and complementary approaches for modelling the evolution of a dynamic system.
In a microscopic approach one tries to describe the individual motion of the systems’ fundamental constituents, in heavy ion collisions this is the quarks and gluons in the initial stages, and hadrons in the late stages of the reaction. Such a problem is treated in terms of kinetic transport equations supplemented with some collision terms. This is a very difficult approach and relies in large parts on some unknown physics on the microscopic level.
If the system is large and dense enough with sufficient rescattering, one can turn to a macroscopic description, where the system is treated in terms of density fields and thermodynamic quantities. In this approach one studies with the help of continuity equations, energy and momentum conservation the evolution of these fields together with flow velocities that build up due to pressure gradients in the field. An explicit ingredient in this thermodynamic prescription is the equation of state the relates the thermodynamic properties of the expanding medium.
The typical timescale of the microscopic description is the scattering rate of the individual particles, which is related to density distribution of the particles and the cross-sections for the individual processes.
In the macroscopic picture, the expansion rate dmuumu and the dilution rate tells you how rapidly the system is changing. For such a hydrodynamic prescription to be valid, a major requirement is that the scattering rate exceeds the expansion rate throughout the process.

## Outline

- Recent data on anisotropic flow
- v1, v2, v4 and non-flow issues
- Coping with a wealth of data self-consistently and quantitatively
- What flow? partonic or hadronic, or both?
- Summary

## Anisotropic flow, v1, v2, v4, ...

- Spectators

- Reaction
- plane

- ~-3

- ~3

- ~0

- v2 = 15%
- v2 = 15%, v4=4%

- v2 = 7%
- v2 = 7%, v1=**+**7%

- v2 = 7%
- v2 = 7%, v1=**-**7%

**Isotropic emission**

- Spectators

- X

- Y

- 1

- In-plane

- Out-of-plane

- 1.5

- 0.5

## Directed flow v1

- Directed flow v1

- 

- PHENIX preliminary
- Poster by Hiroshi Masui

- STAR, nucl-ex/0310029
- NA49, Phys. Rev. C 69 (2003) 034903
- Talks by M. Belt-Tonjes (PHOBOS),
- A.Tang (STAR)
- Posters by H. Masui (PHENIX), M. Oldenburg (STAR)

**v****2**** is positive**, i.e. v1 and
- v2 are in the same plane

- STAR

## v2 vs rapidity at RHIC

- STAR preliminary
- PHOBOS QM02

- This afternoon’s talk by M.B. Tonjes’s (PHOBOS) and U.Heinz (theory)
- M.Oldenburg’s poster (STAR)

## Higher harmonics v4 and v6

- Higher harmonics v4 and v6

- New constraints to models
- Hydro* does not get v2 and v4 simultaneously
- v2 scaled by 0.55 to match data
- Blast wave
- Parameters fixed to fit v2
- requires a 4th order parameters (see A. Poskanzer’s talk)

- STAR, Au-Au √s=200 GeV
- Talk by A. Poskanzer

- *P.Kolb
- Phys.Rev. C68 (2003) 031902

## Non-flow issues

- v2
- Scalar products(1)
- Sensitive to both flow and non-flow
-  correlation
- Disentangle jets from flow
- Lee-Yang zeroes(2) and high order cumulants
- Cumulants even from PHENIX(3)

- A. Tang’s talk
- N. Borghini’s talk
- M. Issah’s poster

- STAR preliminary, √s=200 GeV

*p-p is the non-flow baseline*

## Other data sensitive to flow are also becoming available 

- Spectra
- Different energy
- AGS energies
- SPS: 20, 30 40, 80, 60
- RHIC: 19.6, 130, 200
- Many particle species, e.g.
- , , 
- Charm
- Many centralities
- Different rapidities

- Two-particle correlations
- Source size (HBT)
- Different energy
- Different centrality
- Different rapidity
- Kaons
- Wrt reaction plane
- Source shift (Non-id correlation)
- Tuesday’s talk by A.Kisiel
- Including  correlation!

## Understanding flow

- Requires to describe the data (spectra, anisotropic flow, two-particle correlations):
- Self-consistently
- Quantitatively
- And understand the **evolution of the system**
- No definite conclusions can be made with only freeze-out parameterizations

## Understanding flow: models

- Hadronic cascades (RQMD, uRQMD, ...)
- Do well at SPS, except too long source size
- Flow too weak at RHIC
- Partonic cascades (MPC, AMPT, ...)
- Do a reasonable job at RHIC with huge partonic x-sections
- Hydro
- Do well for spectra and v2
- Do not reproduce source size and lifetime (from HBT)

- See for details:
- - Following talk by T.Hirano
- - This afternoon’s talks by S.Bass, U.Heinz,  D. Molnar, E.Shuryak, D.Teaney

## Understanding flow: parameterizations

- Self-consistent
- Quantitative  characterization of the freeze-out stage
- On the market
- “Krakow” single freeze-out*
- BudaLund**
- Blast Wave
- Do not describe the system evolution

- Snapshot of the
- freeze-out stage

- *Friday’s talk by W.Florkowski
- W.Broniowski et al., nucl-th/0212052, nucl-th/0212053, ...
- ** tuedsay’s talk and poster by M.Csanad
- M. Csanád, T. Csörgő, B. Lörstad and A. Ster, nucl-th/0311102 and nucl-th/0310040, ...

## Blast-wave

- T=106 ± 1 MeV
- <InPlane> = 0.571 ± 0.004 c
- <OutOfPlane> = 0.540 ± 0.004 c
- RInPlane = 11.1 ± 0.2 fm
- ROutOfPlane = 12.1 ± 0.2 fm
- Life time () = 8.4 ± 0.2 fm/c
- Emission duration = 1.9 ± 0.2 fm/c
- 2/dof = 120 / 86

- Spectra

- v2

- HBT

- Latest paper (long legacy),
- F.R and M.Lisa
- nucl-th/0312024

## Parameterization  parametersSystem deformation in the Blast Wave

- Final state eccentricity from
-  v2
- HBT with respect to reaction plane

- Y

- X

- Time

- Time

## Is flow partonic, hadronic or both? 

- Now, that we can characterize flow, let’s ask the most important question:

## Is flow partonic, hadronic or both?

- Partonic

- Hadronic

- Hadronisation

- 

- Photons
- (prompt)

- Resonances

- , K, p

- Charm

- Charm

- Photons
- (thermal)

- Photons
- (from hadrons)

-  Only the models with a partonic stage *reproduce* flow data
-  Hadronisation by quark coalescence. Wait for R. Fries’ talk.
-  Are resonance yields affected by a hadronic rescattering stage?
-  Do ,  and flow? Do they flow as , K, p?
-  What is the flow of photons not coming from hadron decay?
-  Do charm hadrons flow?

- Sketch by
- S. Bass

## Resonance yields consistent with a hadronic re-scattering stage

- Resonance yields consistent with a hadronic re-scattering stage

- Generation/suppression according to x-sections

- p

- 

- *

- 

- 

- K*

- 

- 

- 

- p

- K

- K

- p

- 

- 

- 

- 

- 

- More 

- Less K*

- 

- Chemical freeze-out

- K

- K

- Ok

- 

- p

- K

- K*/K

- 

- 0.1

- 0.2

- 0.3

- Less *

- Preliminary

## Significant  and  v2 Multi-Strange Baryon flow

- Significant  and  v2 Multi-Strange Baryon flow

- This afternoon’s talk by J. Castillo

- STAR preliminary
- AuAu √s = 200 GeV

## Do  and  flow as , K, p?Blast Wave  no (RHIC), hydro  ?

- Blast wave fits

- Hydro (P. Kolb & U. Heinz)
- nucl-th/0305084

-  and , STAR preliminary
- Preliminary NA57 and NA49 data
*Different flow profile for NA57*

- Central AuAu
- √s = 200 GeV

## The Blast Wave side of the story Early freeze-out of  and  

- The Blast Wave side of the story Early freeze-out of  and 

- v2 (STAR preliminary)

- ,K,p v2
- (PHENIX)

- Time

- 300

- 200

- 100

- Temperature (MeV)

-  and spectra
- STAR preliminary

- ,K,p spectra
- PHENIX (box) & STAR (circle)

-  asHBT (STAR)

- __ 1  contour

- Initial
- state

- 0.6

- 0.4

- 0.2

- <T> and eccentricity

- Initial
- flow ~0

- Glauber ~ 0.3

## Photon flow fully driven by 0 flow?

- This afternoon’s talk by M. Kaneta

- vertical bar : stat. error
- curves, gray box : sys. error

- phenix preliminary

- Note :
- Inclusive photon = including all of the decay effect from hadrons

- phenix preliminary

- phenix preliminary

**p****T**** [GeV/c]**

- , 200 GeV Au+Au

- , 200 GeV Au+Au

- , 200 GeV Au+Au

## Electron v2 and Charm flow

- J. Nagle, S. Kelly,
- M. Gyulassy, S.B. JN,
- Phys. Lett. B 557, pp 26-32
- And talk by S.Kelly

- Talk by M. Kaneta, posters by S. Sakai, T. Hashiya

- 0                      1                         2                      3

- 0.3
- 0.25
- 0.2
- 0.15
- 0.1
- 0.05
- 0
- -0.05
- -0.1

-  non-photonic electron v2

- pT [GeV/c]

- The data point : on <*p**T*> in the bin
- horizontal bar  : RMS of *dN/dp**T*

## Summary

- A wealth of data probing flow becoming available
- v1, v2, v4, v6, spectra, and two-particle correlations
- Data described quantitatively and self-consistently by parameterizations
- What about models? (please release your code)
- Data pointing to flow being a combination of partonic and hadronic flow at RHIC
- Final conclusion pending ...
- Outlook:
- More , charm, photons, non-id correlations
- My wish: so much data will make the models converge

## BudaLund

_**M. Csan**__**ád**_**, ****T. Csörgő, B. Lörstad and A. Ster **
**(Tuesday’s talk and poster)**

- Spectra

- Source size (HBT)

- nucl-th/0311102 and nucl-th/0310040

## Hadronization by quark coalescence: v2 scaling by quarks

- Approximate
- validity range

- Wait for R.Fries’s
- talk for full glory
- details

**Notes:**
Results, baryon - meson

- Simultaneous fit to
- Spectra
- v2
- HBT radii

- Example of self-consistencyThe Blast Wave parameterization

## Quantifying the flow strength 

- Y=0 and 1

- Y=2

- Y=3

- Mean flow velocity higher than 0.5 c
- Flow increases with energy density as quantified by dN/dY/Area
- No scaling with s
- No scaling rapidity
- But different flow profile used by BRAHMS