HBT results from UrQMD
description
Transcript of HBT results from UrQMD
Marcus Bleicher, WPCF 08/2007
HBT results from UrQMDHBT results from UrQMD
Marcus Bleicher & Qingfeng Li (FIAS)
Institut für Theoretische Physik
Goethe Universität Frankfurt
Germany
Marcus Bleicher, WPCF 08/2007
Thanks to the UrQMD groupThanks to the UrQMD group
• Katharina Schmidt
• Manuel Reiter
• Sascha Vogel
• Xianglei Zhu
• Daniel Krieg
• Horst Stoecker
• Hannah Petersen
• Diana Schumacher
• Stephane Haussler
• Mohamed Abdel-Aziz
• Qingfeng Li
Marcus Bleicher, WPCF 08/2007
OutlineOutline
• HBT: How, Why, What?
• UrQMD model calculations
• HBT puzzle(s)
• Model explanations on the HBT puzzle
• Summary and outlook
Marcus Bleicher, WPCF 08/2007
The toolThe tool
UrQMD : Ultra-Relativistic Quantum Molecular Dynamics
• out-of-equilibrium transport model, (rel. Boltzmann equation)
• Particles interact via :
- measured and calculated cross sections
- string excitation and fragmentation
- formation and decay of resonances
• Provides full space-time dynamics of heavy-ion collisions
Marcus Bleicher, WPCF 08/2007
Why the HBT technique is important to probe the QGP?
Why the HBT technique is important to probe the QGP?
• 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 (the relevant volume for particles of a given velocity, not the entire source, which can give partly the message of the source.
• A non-trivial structure in the excitation function of HBT might be seen IF there is a (phase) transition.
Marcus Bleicher, WPCF 08/2007
MotivationMotivation
At RHIC: look for signals of partonic matter. (large v2, mach cones, quenching,…)
At critRHIC/SPS:look for the mixed phase and the onset of deconfinement(long life times, large fluctuations, …)
E. Bratkovskaya, M.B. et al., PRC 2005
Marcus Bleicher, WPCF 08/2007
The promise…The promise…
• long life times in the mixed phase…
Rischke, Gyulassy, Nucl.Phys.A608:479-512,1996
~ Energy density
10 fold increase in life time during the mixed phase
Marcus Bleicher, WPCF 08/2007
Why use the UrQMD model?Why use the UrQMD model?
• Hydrodynamics failed to explain the decrease of HBT radii with kT (see, e.g. nucl-th/0305084)
• Might be due to the Corona effect at late stage?• Transport model, considering the full
rescattering process, might throw light on what other mechanisms generate the observed kT-dependence of the HBT radii
Marcus Bleicher, WPCF 08/2007
What’s the HBT technique?What’s the HBT technique?
32
3
31
3
32
31
6
),(
dp
Nd
dp
Nd
dpdp
Nd
KqC 21 ppq
2/)( 21 ppK
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 average momentum K is emitted from the space-time point x in the collision region.
For identical bosons, 24
24
|),(|
|),(|1),(
KxSxd
eKxxSdKqC
xiq
Marcus Bleicher, WPCF 08/2007
Gaussian ParameterizationGaussian Parameterization
• 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
From one- to two- to three dimensional parameterization (e.g. nucl-th/0510049 for reviews)
Yano-Koonin parametrization
Marcus Bleicher, WPCF 08/2007
LCMS Gaussian ParameterizationLCMS Gaussian Parameterization
• Longitudinal co-moving system (out-side-long)
)2exp(1),,( 2222222LOOLLLSSOOLSO qqRqRqRqRqqqC
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 (bosons: 1, fermions: -1 ), for example, misidentified particles(contamination), the (long-lived) resonance, different technical details of Coulomb correctionsRL,O,S are B-P radii, Rol is the cross term and vanishes at mid-rapidity.
Marcus Bleicher, WPCF 08/2007
The out-side-long system sketchThe out-side-long system sketch
• Long: parallel to beam, and the longitudinal components of the pair velocity vanishes.(Kz=0)
• Side: perpendicular to beam and average pair momentum K.
• Out: perpendicular to Long and Side.
K
L
O
S
K
KqqO
Marcus Bleicher, WPCF 08/2007
The survey of Pratt radii RL,RO, and RS
The survey of Pratt radii RL,RO, and RS
• R~R(KT, Eb, b, (A,B), y, , (m1,m2))
Next, we show the results of the source of two negatively (except otherwise stated) charged pions using UrQMD model.
Quite a few model endeavors: Hydrodynamics models: matter in the collision region is taken as an 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: Molnar’s Parton Cascade, (with the stiffest effective EoS)AMPT: A Multi-Phase Transport model (hadron+string+parton)HRM: Hadronic Rescattering Model (no strings/partons)etc…
Marcus Bleicher, WPCF 08/2007
How to calculate numerically?How to calculate numerically?
• Standard UrQMD (v2.2) output of freeze-out 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/home.html)
• Three-dimensional Gaussian fitting.
• Present study: pi-pi correlations
Marcus Bleicher, WPCF 08/2007
World HBT data 1World HBT data 1
Marcus Bleicher, WPCF 08/2007
World HBT data 2
World HBT data 2
• First (up to now only) systematic comparison between transport model (RQMD) and experimental data(Mike Lisa, 2005)
Marcus Bleicher, WPCF 08/2007
Systematic analysis is neededSystematic analysis is needed
• Hydro is known to fail for HBT radii
• Transport models can provide a baseline
Use UrQMD for a systematic study
Marcus Bleicher, WPCF 08/2007
Transverse momentumdependence of the HBT radii
at various energies
Marcus Bleicher, WPCF 08/2007
UrQMD vs. data @ AGSUrQMD vs. data @ AGS
02468
(6A
GeV
)(2
A G
eV
)(8
A G
eV
)(4
A G
eV
)
kT (MeV/c)
data: ; th: th.
Eb L O S
02468
(10.7
A G
eV
)
0 100 200 300 40002468
Ri (
fm)
0 100 200 300 400 0 100 200 300 400 500
02468
10
02468
<11%T
<5% T
2/)( 21 TTppKT
•Good agreement•Deviations at small kT for RL
and RS
Marcus Bleicher, WPCF 08/2007
The mass dependence of lifetime of resonances
The mass dependence of lifetime of resonances
The green lines:We consider the Mass dependenceOf lifetime of Resonances.
M
02468 fm
(6A
GeV
)(2
A G
eV)
(8A
GeV
)(4
A G
eV)
kT (MeV/c)
data: ; th: th.
Eb L O S
02468 fm
(10.
7A G
eV)
0 100 200 300 40002468 fm
Ri (
fm)
0 100 200 300 400 0 100 200 300 400 500
02468
10
fm
02468 fm
better agreement
Time from phase shift?
Marcus Bleicher, WPCF 08/2007
UrQMD @ SPS-NA49UrQMD @ SPS-NA49
<7.2% T
0 200 400
NA49 data: ; th:
0 200 400 0 200 400
s=0 fm/c
0 200 400 600
RS (fm
)R
O (fm
)
(20A GeV)
kT (MeV/c)
(40A GeV)(30A GeV) (80A GeV) (160A GeV)
RL (fm
)
0
2
4
6
8
10
0
2
4
6
8
0 200 4000
2
4
6
8
Note the effect of short formation times: more early pressure
Marcus Bleicher, WPCF 08/2007
UrQMD @ SPS-CERESUrQMD @ SPS-CERES
<5% T
0
2
4
6
8
10CERES data: ; th:
0
2
4
6
8
0 200 4000
2
4
6
8
0 200 400 0 200 400 600
RS (fm
)R
O (fm
)
kT (MeV/c)
(40A GeV) (80A GeV) (160A GeV)
RL (fm
)
Marcus Bleicher, WPCF 08/2007
[email protected]@RHIC
0
2
4
6
8
10
15%T
0
2
4
6
8
exp.: ; th.:
0
2
4
6
8
0 200 400 600 8000
2
4
6
8
kT (MeV/c)
O SL
(62.
4 G
eV)
(30
GeV
)(1
30 G
eV)
sNN
(200
GeV
)
Ri (
fm)
0 200 400 600 800 0 200 400 600 800
<15% T
<15% T
<10% T
<5% T
Deviation for RO!
Marcus Bleicher, WPCF 08/2007
R.vs.b@RHIC GeVR.vs.b@RHIC GeV200s
0
5
10
15
20
25
RO (fm
)
th. exp. 0-5% 10-20% 30-50% 50-80%
+15 fm
+10 fm
+5 fm
+0 fm
100 200 300 400 500 6000
5
10
15
20
RS (fm
)
+15 fm
+10 fm
+5 fm
+0 fm
200 300 400 500 600
RL (fm
)
+15 fm
+10 fm
+5 fm
+0 fm
kT (MeV/c)
RO problems grow towards centralcollisions.
lines shifted by 5 fm each
Marcus Bleicher, WPCF 08/2007
-correlations at RHIC-correlations at RHICQ
. Li
, M
.B.,
H.
Sto
ecke
r, n
ucl-
th/0
602
032;
D
ata:
ST
AR
• Correlations are well described except for most central reactions
Marcus Bleicher, WPCF 08/2007
The HBT puzzle? The HBT puzzle?
• Model calculations of RO/RS or (RO2-RS
2)1/2 are usually larger than the experimental data
Duration time (in the absence of flow):
2
22 )(
SO RR
No indication of long life time in the data
1 10 100 1000 100000
2
4
6
8
(R2 O-R
2 S)1/
2 (fm
)
Eb (A GeV)
Circles: kT=100 MeV/c
Squares: kT=200 MeV/c
Stars: exp. data
Li, Bleicher, Stoecker, arXiv:0706.2091. JPG in press
Marcus Bleicher, WPCF 08/2007
The (argued) ‘disadvantages’ in the UrQMD calculations
The (argued) ‘disadvantages’ in the UrQMD calculations
• Hadronic potentials for baryons in the above calculations.
• No string-string interaction although the string degree of freedom exists.
• Or, no deconfined quarks nor gluons and the interactions between them.
Marcus Bleicher, WPCF 08/2007
More collisions by setting zero formation time for strings
More collisions by setting zero formation time for strings
The difference BetweenC(qo) and C(qs)almost disappearsafter consideringzero formation timefor string.
It is very time consuminge.g. :SPS-E160:3events/hRHIC-s200:1event/d
A larger early pressure especially in the sideward direction leads to larger Rs
Marcus Bleicher, WPCF 08/2007
Ro/Rs at SPS(Eb=160 A GeV)
Ro/Rs at SPS(Eb=160 A GeV)
Zero-formation time
Leads to much smaller
Ro/Rs ratio mainly due to a larger Rs.
0 100 200 300 400 500 6000
2
4
6
8
10
(R
O
2 -RS
2 )1/2 (
fm)
kT (MeV/c)
NA49 data CERES data default
s=0 fm/c
Eb=160A GeV
Early stage,Early state!
Marcus Bleicher, WPCF 08/2007
At RHIC: How about other approaches?
At RHIC: How about other approaches?
From nucl-ex/0505014 byM. Lisa
AMPT:HBT is sensitive to The parton-scatteringCross sections.
HRM: considering onlythe hadron rescattering(with sudden collisions ),No parton degree of freedom
Marcus Bleicher, WPCF 08/2007
How to solve the HBT puzzleHow to solve the HBT puzzle
• reduce (or 0) string formation time for more pressure? (tremendous number of collisions make it almost impossible to calculate the HBT interferometry at RHIC) the idea in HRM and checked for elliptic flow and HBT at SPS in UrQMD• consider Partons? the idea in AMPT Not yet in UrQMD model
with the help of another model: qMD,
• consider optical potential for pions (chiral symmetry) see PRL94, 102302(2005), PRC73, 024901(2006)
and, hadronic potential should be also paid attention.
Marcus Bleicher, WPCF 08/2007
Rapidity studies
Marcus Bleicher, WPCF 08/2007
[email protected]@NA49
Weak y-dependencein all HBT radiiFor RS, it decreases slowly with rapidity.
NA49 data For kT<100 MeV/c
Weak y-dep, Why? strong x-p correlation
good agreement
Marcus Bleicher, WPCF 08/2007
Possible reason…Possible reason…
-2 -1 0 1 2
2
4
6
8
10
(NB
* ->X / N
Strin
g->X)
free
ze-o
ut
Ycm
Eb (A GeV)
20 40 160
kT<100 MeV/c
Different particle sources as function of rapidity: Direct production vs. decay
Marcus Bleicher, WPCF 08/2007
Energy dependence
Marcus Bleicher, WPCF 08/2007
R.vs.Eb
@small KT
R.vs.Eb
@small KT
• Overall reasonable agreement
• But, Ro/Rs too big
• Difference between CERES and NA49 (acceptance?)
1 10 100 1000 100000
2
4
6
8
0
2
4
6
8
0
2
4
6
8
10R
L (fm
)
Eb (A GeV)
exp (stars):k
T~150: E2,4,6,8,
E20,30,40,80,160 (NA49)k
T~170: s130
kT~200: E10.7,s62.4,s200
E40,80,160 (CERES)
Ro (fm
) R
s (fm
)
Circles: kT=100 MeV/c
Squares: kT=200 MeV/c
Marcus Bleicher, WPCF 08/2007
Mean free pathMean free path
• UrQMD seems to supports the finding of a (nearly) constant mfp.
• However, this is surprising within a microscopic analysis (here one expects mfp ~ R ~ 5 fm)
22/32 SLf RRV
Marcus Bleicher, WPCF 08/2007
Droplets: > 10-100 (Mishustin)
Taken from a talk by B. Lungwitz at CPOD 2007
UrQMD data from Lungwitz& Bleicher, arXiv:0707.1788
Marcus Bleicher, WPCF 08/2007
Summary and outlookSummary and outlook
• Good (quantitatively) agreement of the calculated HBT radii with data from AGS to RHIC.
• The decay of resonances affects the HBT radii (mainly at low kT).
• HBT puzzle is also seen by the comparison of our calculations with data, especially at RHIC energies (flow and HBT puzzles are twin.)
It seems essential to consider the interactions between new degrees of freedom.
1 10 100 1000 100000
2
4
6
8
(R2 O-R
2 S)1/
2 (fm
)
Eb (A GeV)
Circles: kT=100 MeV/c
Squares: kT=200 MeV/c
Stars: exp. data
Where are all the irregular structures expected when entering the mixed phase?