Hadronic dissipative effects on transverse dynamics at RHIC

1
Hadronic dissipative effects on transverse
dynamics at RHIC

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

TH, U.Heinz, D.Kharzeev, R.Lacey and Y.Nara,
Phys.Lett.B636,299(2006)arXiv0710.5795nucl-th.
QM2008, Feb. 4-10, 2008
2
Outline

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

3
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.
4
A Hybrid Approach QGP hydro hadronic cascade
TH et al.(06)
hadron gas

• Initial condition
• Transverse ? Glauber
• Longitudinal ? BGK triangle
• QGP fluid
• 3D ideal hydrodynamics
• (Hirano)
• massless free u,d,sg
• gas bag const.
• Tc 170 MeV
• Hadron gas
• Hadronic cascade, JAM1.09
• (Nara)
• Tsw 169 MeV

time
QGP fluid
collision axis
0
Au
Au
(1D) Bass, Dumitru (2D) Teaney, Lauret, Shuryak,
(3D) Nonaka et al., Hirano et al.
5
Pseudorapidity Distribution
Tune initial parameters with Tth 100MeV to
reproduce dN/deta. Then, switch to hadronic
cascade below TTsw. Caveat Rejecting in- coming
particles at Tsw
6
pT spectra for pi, K, and p
Reasonable reproduction of yields and spectra in
low pT region (pTlt1.5 GeV/c)
7
Hadronic Dissipative Effect on v2
Hadronic dissipation reduces v2 as expected.
Note Early chemical freezeout (Tch170 MeV) is
implemented in pure hydrodynamic calculations.
8
v2(pT) for pi, K, and p
Fail to reproduce data due to (absence of)
fluctuation of geometry in the calcualtions. Mille
rSnelling (03), BhaleraoOllitrault(06) Andrade
et al (06),DrescherNara (07) Browniowski et
al(07)
OK!
9
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.
10
Hydro Cascade at Work in Forward Rapidity
Regions
hybrid model AMPT
Adopted from S.J.Sanders (BRAHMS) talk _at_ QM2006
11
Origin of Mass Ordering
b7.2fm

• Mass ordering behavior
• results from hadronic
• rescatterings.
• Subtle interplay btw. perfect fluid QGP and
  hadronic corona.

b7.2fm
12
Why they shift oppositely?
protons
pions
v2(pT)
v2
ltpTgt
pT
v2 for protons can be negative even in positive
elliptic flow
must decrease with proper time
P.Huovinen et al.,PLB503,58(01)
TH and M.Gyulassy, NPA769,71(06)
13
What happens to strangeness sector?
14
Distribution of Freeze-Out Time
(no decay)
b2.0fm
Early kinetic freezeout for multistrange hadrons
van Hecke, Sorge, Xu(98) Phi can serve a direct
information at the hadronization.
15
f-meson case
Just after hadronization
Final results
b7.2fm
b7.2fm
T Tsw 169 MeV
in pT lt 1 GeV/c
Violation of mass ordering for phi mesons! Clear
signal of early decoupling!
Caveat Published PHENIX data obtained in
pTgt1GeV/c for f mesons
16
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
17
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

18
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?
19
Additive Quark Model in Transport Codes
(JAM/RQMD/UrQMD)
For cross sections without exp. data,
Expected to be very small for phi, Omega, etc.
20
Hadronic Dissipation Suppresses Differential
Elliptic Flow
Difference comes from dissipation only in the
hadron phase

• Relevant parameter Gs/t
• Teaney(03)
• Dissipative effect is not so
• large due to small expansion
• rate (1/tau 0.05-0.1 fm-1)

Caveat Chemically frozen hadronic fluid is
essential in differential elliptic flow. (TH and
M.Gyulassy (06))
21
Excitation Function of v2

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