Pion interferometry with the UrQMD transport model

1
Pion interferometry with the UrQMD transport
model

• Qingfeng Li
• (FIAS, AvH fellow)

Closely cooperate with Marcus Bleicher, Xianglei
Zhu, Horst
Stoecker, Hannah Petersen Also thanks to
UrQMD-group, NA49-Collaboration,
CERES-Collaboration, M.
Lisa, S. Pratt, T. Humanic, Nu Xu
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Outline

• Introduction of HBT interferometry.
• Model efforts to extract HBT parameters.
• Classic HBT puzzle
• Origin of the HBT puzzle
• Summary and outlook

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The crucial goal of high energy HICs (AGS-RHIC)
Skip!

• The new phase QGP from QCD theory
• How to detect it?
• The relative direct approach is to detect the
  electromagnetic radiation which it emits, BUT,
  with a huge amount of noise.
• J/? suppression Strangeness enhancement energy
  loss of hard partons density effect on vector
  mesonsDCC (disorientedchiral condensates )
  etc, etc

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The importance of the HBT
interferometry

• We know, the transition can only take place in a
  very small space-time.
• Correlations of two final-state particles are
  closely linked to the space-time of the region of
  homogeneity, or called as the HBT technique (by
  the pioneering work of Robert Hanbury-Brown and
  Richard Q. Twiss in astronomy).

Skip!
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Whats the HBT technique?
The quotient of two-particle and one-particle
spectra
The two-particle correlator C(q,K) is related to
the emission function S(x,K), Which is the
Wigner phase-space density of the particle
emitting system and can be viewed as the
probability that a particle with momentum K is
emitted from the space-time point x in the
collision region.
Skip!
For identical bosons,
Smoothness approx.
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Gaussian Parameterization
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• To better understand the three-dimensional
  spatio-temporal source distribution. Although the
  realistic source deviates from a standard
  Gaussian, it provides the standard description of
  experimental data.
• There exist quite a few different types of
  Gaussian parameterization under different
  coordinate system (CMS, LCMS, YKP, etc).

Nucl-ex/0505014
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LCMS Gaussian Parameterization

• Longitudinal co-moving system (out-side-long)

• is the incoherence or chaoticity factor, lies
  between 0 (complete coherence)
• and 1 (complete
  incoherence) in the real reactions.
• it will be affected by many factors other than
  the quantum statistics,
• for example,
• misidentified particles(contamination),
• the (long-lived) resonance,
• different technical details of
  Coulomb corrections
• Rol is the cross term and vanishes at
  mid-rapidity.

Skip?
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The out-side-long system sketch

• Long parallel to beam, and the longitudinal
  components of the pair velocity vanishes.
• Side perpendicular to beam and total pair
  momentum.
• Out perpendicular to ql and qs.

S
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L
O
K
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The survey of Pratt radii RL,RO, and RS

• RR(KT, Eb, b, (A,B), y, ?, (m1,m2))

Quite a few model endeavors Hydrodynamics
models matter in the collision region is taken
as a ideal, locally
thermalized fluid with the zero mean free path
(hydro/PYTHIA)UrQMD, RQMD hadronic dynamics
model with string degree of freedom.
Having potentials for baryons at
low beam energies. From UrQMD
ver2.0, the PYTHIA (v6.1) was added in order to
consider the hard
process. MPC Molnars Parton Cascade, (with the
stiffest effective EoS) AMPT A Multi-Phase
Transport model (hadronstringparton) HRM
Hadronic Rescattering Model (no
strings/partons) etc
Skip?
Next, we show the results of the source of two
negatively (except otherwise stated) charged
pions using UrQMD model.
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How to calculate numerically?

• Standard UrQMD (v2.2) output of final-state
  particles
• (http//www.th.physik.uni-frankfurt/urqmd)
• CRAB (v3.0) used to analyze the
  (three-dimensional LOS) correlation of two
  identical particles.
• (http//www.nscl.msu.edu/pratt/freecodes/crab/hom
  e.html)
• Three-dimensional Gaussian fitting.

No Coulomb corrections in all above
calculations Available choices n-n-n, (this
work) w/n-w-n
(standard procedure),
n-w-w/w-n-w (Bowler procedure)
better fitting Procedure
Its very Important!
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R.vs.KT_at_AGS
1,Good agreement 2,Deviations shown at small kT
for RL and RS
lt11?T
lt5 ?T
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The mass dependence of lifetime of resonances
better agreement
The green lines We consider the Mass
dependence Of lifetime of Resonances.
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R.vs.KT_at_SPS-NA49
good agreement
lt7.2 ?T
lt10 ?T
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R.vs.KT_at_SPS-CERES
Large deviation shown In RO ?might be due
to Different Coul. treatments
lt5 ?T
What a DIFFERENCE in last 2 slides!
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R.vs.KT_at_RHIC
Large deviation shown in RO
lt15 ?T
lt15 ?T
lt10 ?T
lt5 ?T
What a SIMILARITY in last 2 slides!
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R.vs.b_at_RHIC GeV
RO in central collisions.
Shifted lines by 5 fm
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R.vs.(A,B)_at_RHIC GeV
RO in central AuAu, CuCu, and pp collisions.
Surface-like emission Corona effect
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ROL.vs.y_at_CERES
good agreement
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R.vs.y_at_NA49
good agreement
Weak y-dependence in all HBT radii For RS, it
decreases slowly with rapidity. ---
But, Why?
For kT100-200 MeV/c
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ROL.vs.y_at_NA49
good agreement
For better statistics, the modulus Of the three
components of relative momentum q is used in
Gaussian fitting. Therefore, only the modulus
of ROL is Obtained in our current calculations.
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R.vs.Eb_at_small KT
1, How to improve the HBT radii at AGS and
SPS energies? ---the mass dependence of
the resonance lifetimes. (the RO/RS
changes little) 2, How to improve the HBT radii
at RHIC? --- reduce (or 0) string
formation time? (tremendous number of
collisions make it almost impossible to
calculate the HBT interferometry)
?the idea in HRM and checked for
elliptic flow in UrQMD ---consider Partons?
?the idea in AMPT Not yet in
UrQMD model
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Whats the (classical) HBT puzzle?

• Model calculations of RO/RS or (RO2-RS2)1/2 are
  obviously larger than the experimental data

It is related to duration time (in the absence
of flow)
How to improve it? ---hadronic potentials Should
also be studied More carefully?
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Flow puzzle---thanks Hannah and Xianglei
At Eblt10 A GeV, the flow can be well reproduced
with a HMw potential.
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The time evolution of the HBT puzzle
In the late stage, HBT puzzle occurs.
Corona effect
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The (argued) disadvantages in the UrQMD
calculations

• No potentials for baryons in the above
  calculations (only cascade mode used).
• No string-string interaction although the string
  degree of freedom exists.
• No deconfined quarks nor gluons.

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Potential contributions ---especially the Coulomb
pot.

• The contributions of nuclear potentials are weak.
• Besides B-B Coulomb interaction, we further
  considered the Coulomb potential between B-M and
  M-M.
• (see PRC 72, 034613 (2005) J. Phys. G 32, 151
  (2006) J. Phys. G 32,407(2006) )
• So far, the potentials in UrQMD are
  non-relativistic and needed to update for
  investigations especially at SPS and RHIC. ---one
  more question the calculation time becomes too
  long for HBT calculations (to guarantee a good
  statistics)
• Method w-n-w (Bowler) Coul. in UrQMD no Coul
  in CRAB Coul. in Gaussian fitting.

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Coulomb contribution at AGS(Eb4 A GeV)
The Coulomb contributes to a higher Rs, lower
Ro, and thus better Ro/Rs
Inspired by CERES paper NPA714,124 (2003)
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Coulomb contribution at SPS(Eb160 A GeV)
The consideration of Coulomb interaction also
give a better Ro/Rs at SPS
But it looks that the Ro/Rs keeps increasing
slowly with beam energy. ?the Coulomb might
not fully Explain the HBT puzzle at RHIC?
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At RHIC HRM and AMPT calculations.
AMPTHBT is sensitive to The parton-scattering Cr
oss sections.
HRM considering only the hadron
rescattering (with sudden collisions ), No parton
degree of freedom
From nucl-ex/0505014 by M. Lisa
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Comments

• Partons are required or not?
• Corona effect? But,differences are mostly
  washed out after rescattering? see
  nucl-th/0602058 by H. Boggild, Ole Hansen, and
  T.J. Humanic.
• relativistic potential (especially the Coulomb)
  treatments?
• ? it needs more efforts

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Summary and outlook

• Good (quantitatively) agreement of the calculated
  HBT radii with data from AGS to RHIC.
• The decay of resonances affects the HBT radii.
• HBT puzzle is also seen by the comparison of our
  calculations with data, especially at RHIC
  energies
• A relativistic EoS for nuclear matter should be
  updated in UrQMD model.
• Is it necessary to consider new degree of freedom
  in our UrQMD model in order to solve the HBT
  puzzle thoroughly???
• The Volume, density,and MFP of pion freeze-out,
  etc, which are very sensitive to the HBT Radii,
  will be shown soon later.

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Thanks for listening