# Presentation: 210718

## Hadronic dissipative effects on transverse dynamics at RHIC

- Tetsufumi Hirano
- Dept. of Physics
- The Univ. of Tokyo

- QM2008, Feb. 4-10, 2008

- TH, U.Heinz, D.Kharzeev, R.Lacey and Y.Nara, Phys.Lett.B636,299(2006);arXiv:0710.5795[nucl-th].

## Outline

- Motivation
- 3D QGP fluid + hadronic cascade model
- Mass ordering of v2(pT) revisited
- Violation of mass ordering for  mesons
- Summary

## Motivation

- To understand the QGP in H.I.C., one needs to understand the hadronic stage since

- Indispensable to disentangle these
- effects for understanding of unknowns,
- in particular, if one wants to extract viscous
- coefficient in the QGP.

## A Hybrid Approach: QGP hydro + hadronic cascade

- 0

- collision axis

- time

**Au**

**Au**

- QGP fluid

_**Initial condition**_:
- Transverse  Glauber
- Longitudinal  “BGK triangle”
_**QGP fluid**_:
- 3D ideal hydrodynamics
- (Hirano)
- massless free u,d,s+g
- gas + bag const.
- Tc = 170 MeV
_**Hadron gas**_:
- Hadronic cascade, JAM1.09
- (Nara)
- Tsw = 169 MeV

- hadron gas

- TH et al.(’06)

- (1D) Bass, Dumitru (2D) Teaney, Lauret, Shuryak, (3D) Nonaka et al., Hirano et al.

## Pseudorapidity Distribution

- Tune initial parameters
- with Tth = 100MeV
- to reproduce dN/deta.
- Then, switch to hadronic cascade below T=Tsw.
- Caveat: Rejecting in-
- coming particles at Tsw

## pT spectra for pi, K, and p

- Reasonable reproduction of yields and spectra
- in low pT region (pT<~1.5 GeV/c)

## Hadronic Dissipative Effect on v2

- Hadronic dissipation
- reduces v2 as
- expected.

- Note: Early chemical
- freezeout (Tch=170
- MeV) is
- implemented in
- pure hydrodynamic
- calculations.

## v2(pT) for pi, K, and p

- OK!

- Fail to reproduce data due to
- (absence of) fluctuation of geometry in the calcualtions.
- Miller&Snelling (’03), Bhalerao&Ollitrault(’06)
- Andrade et al (’06),Drescher&Nara (’07)
- Browniowski et al(’07)

## Pseudorapidity Dependence of Elliptic Flow

- Again, it fails to reproduce data due to eccentricity fluctuation

- v2 is largely suppressed in forward region due to hadronic dissipation.
- Hydro + cascade generates a right amount of elliptic flow.

## Hydro + Cascade at Work in Forward Rapidity Regions

- Adopted from S.J.Sanders
- (BRAHMS) talk @ QM2006

- hybrid model
- AMPT

## Origin of Mass Ordering

- Mass ordering behavior
- results from **hadronic**
**rescatterings**.
- Subtle interplay btw.  “perfect fluid QGP” and “hadronic corona”.

- b=7.2fm

- b=7.2fm

## Why they shift oppositely?

**protons**

**pions**

- pT

- v2(pT)

- v2

- <pT>

**must decrease with proper time**

**v****2**** for protons can be negative**
**even in positive elliptic flow**

**TH and M.Gyulassy, NPA769,71(06)**

**P.Huovinen et al.,PLB503,58(01)**

## What happens to strangeness sector?

## Distribution of Freeze-Out Time

- b=2.0fm

- (no decay)

- Early kinetic freezeout for multistrange hadrons: van Hecke, Sorge, Xu(’98)
- Phi can serve a direct information at the hadronization.

## -meson case

- in pT < 1 GeV/c

- Just after hadronization

- Final results

- T = Tsw = 169 MeV

- b=7.2fm

- b=7.2fm

- Caveat: Published PHENIX data obtained in pT>~1GeV/c for mesons

- Violation of mass ordering for phi mesons!
- Clear signal of early decoupling!

## phi/p Ratio as a function of pT

- pp collisions
- Pure hydro in AA
- collisions

- Hydro + cascade
- in AA collisions

- Clear signal for
- early decoupling
- of phi mesons

## Summary

- A QGP fluid + hadronic rescattering
- Reproduction of both pT dist. and v2(pT,m)
- Reproduction of integrated and differential v2 in forward rapidity regions
- Origin of mass ordering of v2(pT)
- Radial flow effect, not “mass effect”.
- Need QGP to get large integrated v2. Need hadronic rescattering to get correct mass ordering.
- Violation of mass ordering for phi mesons
- Clear signal to see this scenario
- Can serve a direct information of the QGP

## Is Mass Ordering of v2(pT) a “Direct” Signal of Perfect Fluidity?

- STAR white paper (’05)

- PHENIX white paper (’05)

- Lines: Results from _**Ideal**_ hydro
- Consequences of perfect fluid QGP?

## Additive Quark Model in Transport Codes (JAM/RQMD/UrQMD)

- For cross sections without exp. data,

- Expected to be very small for phi, Omega, etc.

## Hadronic Dissipation Suppresses Differential Elliptic Flow

- Difference comes from dissipation only in the hadron phase

- Caveat: Chemically frozen hadronic fluid is essential in differential elliptic flow. (TH and M.Gyulassy (’06))

- Relevant parameter: s/
-                       Teaney(’03)
- Dissipative effect is not so
- large due to small expansion
- rate (1/tau ~ 0.05-0.1 fm-1)

## Excitation Function of v2

- Hadronic Dissipation
- is huge at SPS.
- still affects v2 at RHIC.
- is almost negligible at LHC.