1. Overview of Relativistic Heavy-Ion Collisions at SIS Energies
고려대학교
홍 병 식
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2. Schematic Understanding of the Relativistic HI Collisions
Evolution
Pre-
equilibrium
Thermalization
QGP?
Mixed phase
Hadronization
(Freeze-out) +
Expansion
V>0.9c
Compression
Thermalization
Some of the energy they had before is transformed into heat
and new particles right here !
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3. Nuclear Phase Diagram T(MeV) Density(n0) Early Universe (RHIC) ~150
~10
Early Universe
(RHIC)
Color Superconductor
Neutron Star
Hadron Gas
Quark-Gluon Plasma
Phase Transition
Atomic Nuclei
SIS explores Nonperturbative regime of QCD
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4. HE Heavy-Ion Accelerators
c.m. Energy
(GeV)
Status
SIS 18
(GSI, Germany) 2A
(A=mass number)
Running
AGS
(BNL, USA) 5A
Finished
SIS 200 8A
Just approved; Plan to run from ~2010
SPS
(CERN, Switzerland)
20A
Finish soon
RHIC
200A
Running since 2000
LHC
5500A
Plan to run from ~2007
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5. Heavy-Ion Collisions at SIS
Properties of hot and dense nuclear matter by studying
Nuclear Equation-of-State (EoS)
In-medium properties of hadrons
Test of QCD
Experimental Observables
Nuclear stopping phenomenon
Nonstrange meson production
Collective flow
Strangeness production
Comparison to various models
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6. CBM
Experiments at GSI
HADES
KaoS
FOPI
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7. FOPI Setup Au+Au@1.5AGeV 1 K- in 104 events -IPNE Bucharest, Romania
HI-Beam
-IPNE Bucharest, Romania
-ITEP Moscow, Russia
-CRIP/KFKI Budapest, Hungary
-Kurchatov Institute Moscow, Russia
-LPC Clermont-Ferrand, France
-Korea University, Seoul, Korea
-GSI Darmstadt, Germany
-IReS Strasbourg, France
-FZ Rossendorf, Germany
-Univ. of Heidelberg, Germany
-Univ. of Warsaw, Poland
-RBI Zagreb, Croatia
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8. KaoS Setup
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9. PID & Detector Acceptance
Examples of FOPI
dE/dx vs p/Z in drift chambers
Bethe-Bloch parameterization
Additional use of plastic to differentiate Z
Ru+Ru at 400A MeV
Phase-space covered
by the FOPI detectors p
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10. Collision Centrality
Peripheral
Central
FOPI invented the Erat variable which is extremely sensitive, especially, for the most central collisions.
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11. Particle Spectra
B. Hong et al., (FOPI)
Phys. Rev. C66, (2002)
Ru+Ru at 400A MeV
Two independent detectors (CDC and HELITRON) give identical results.
Nice backward and forward symmetry
Dotted lines: fit functions by the Siemens-Rasmussen blast model
PRL 42, 880(1979)
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12. Particle Spectra
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13. Stopping Mean rapidity shift of protons defined by
where yb(yt) is the beam(target) rapidity
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14. Stopping Introduce a new variable to test a nuclear transparency
We use the heaviest isobaric nuclei available(9644Ru & 9640Zr)
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15. Stopping 0.4A GeV Ru(Zr)+Ru(Zr)
B. Hong et al., (FOPI)
Phys. Rev. C66, (2002)
0.4A GeV Ru(Zr)+Ru(Zr)
Experimental data support the transparency scenario.
We need higher energy data to figure out which model is valid:
More stopping (CBUU model)
More transparency (IQMD model)
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16. Stopping Rp steeper Trend predicted by IQMD.
B. Hong et al., (FOPI)
Nucl. Phys. A 721, 317c (2003)
1.5A GeV Ru(Zr)+Ru(Zr)
Rp steeper
More transparency
Trend predicted by IQMD.
Absolute values of Rp are not described quantitatively.
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17. Stopping
0.4A GeV Ru(Zr)+Ru(Zr)
Zr+Zr
Ru+Ru
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18. Stopping
1.5A GeV Ru(Zr)+Ru(Zr)
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19. Comparison Eb(GeV) dyp/yb Nf 1) Nb 2) Mpr 3) Remark
0.256
9.46
6.14
0.21
1.5A
0.258
23.4
9.70
0.41
More Transparent
Number of projectile nucleons in forward hemisphere
Number of projectile nucleons in backward hemisphere
Mixing parameter: more transparent for a larger Mpr
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20. Collective Flow
Reaction plane
time
reaction plane
transverse plane
(at midrapidity)
v2< v2 >0
elliptic flow
RN=(1+ v2)/(1-v2)
v1<0 v1 >0
sideward flow
px = v1 pt
Fourier expansion of azimuthal distribution gives the phase space distribution w.r.t. the reaction plane.
S. Voloshin & Y. Zhang, Z. Phys. C70, 665 (1996)
J.Y. Ollitrault, Nucl. Phys. A638, 195c (1998)
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21. Sideward Flow –integrated
FOPI Collaboration,
Phys. Rev. C67, (2003)
pt integrated sideward flow is sensitive to
EoS
MDI (especially at projectile rapidity)
σNN (especially at low beam energies less than ~100A MeV)
SM(soft EoS with MDI) well describe data
Better agreement for larger collision system
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22. Sideward Flow –differential
Differential directed flow (DDF) for
Au+Au collisions at 400A MeV
DDF shows a clear sensitivity on the EoS.
IQMD deviates at large y and large pt for Z=1.
SM(soft EoS with MDI) well describe data.
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23. Sideward Flow -warning
IQMD fails to reproduce the measured integrated sideward flow for Z=2 particles at 90A MeV
Remember that IQMD also fails to reproduce the centrality dependence of the nuclear stopping for Ru+Ru at 400A MeV
previous slides
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24. Elliptic Flow -systematic study
FOPI Collaboration,
Nucl. Phys. A679, 765 (2001)
pt dependence
Centrality
dependence
Eb dependence
A dependence
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25. Elliptic Flow –transition energy
Our data agree well with the Plastic Ball data.
Transition from in-plane to out-of-plane azimuthal enhancement near 100A MeV
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26. Elliptic Flow -comparison
Model cannot explain the experimental observation.
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27. Strangeness Production
Motivation (reminder)
Study
the in-medium effect due to the chiral symmetry restoration 
Equation-of-State
By using
the production yields
the momentum distribution
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28. Phase-space distribution
Ni+Ni 1.93A GeV
KaoS Collaboration, Phys. Lett. B 495, 26 (2000)
Isotropic thermal source
central (b≤4.4 fm)
non-central
Fit function : 2
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29. K-/K+ Ratio FOPI measures the target rapidity region:
Eur. Phys. J. A9, 515 (2000)
Nucl. Phys. A 625, 307 (1997)
with
without
in-medium potentials
RBUU calculation by
E.Bratkovskaya,
W.Cassing (Giessen)
similar trends by
G.Q.Li (Stony Brook)
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30. Equivalent Energy Analysis
KaoS Collaboration, Phys. Rev. Lett. 78, 4007 (1997)
Ni+Ni at various beam energies
40° < θlab < 48°
Use equivalent beam energies to correct
for different production thresholds
1.0 GeV/u for K+
1.8 GeV/u for K-
each corresponds to
K+ yield at 1.0 GeV/u is almost
the same as K- yield at 1.0 GeV/u.
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31. Equivalent Energy Analysis
KaoS Collaboration, Phys. Rev. Lett. 78, 4007 (1997)
Considering the pp→K+/-+X cross section, there is about factor of 7 enhancement in K- production in medium.
Parameterizations by
H. Müller, ZPA353, 103 (1995)
Indicates the importance of the multiple collisions for the strangeness production
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32. Determination of the EoS
KaoS Collaboration, Phy. Rev. Lett. 86, 39 (2001)
Comp. between Au+Au & C+C
Purpose: disentangle soft EoS effect and in-medium effect
Baryon density (ρB) depends on the nuclear compressibility
Au+Au will reach much higher ρB
Subthreshold K+ production by multiple scattering means ~ρB2 at least → will increase the K+ yield in larger collision system → more important at lower beam energies
But UKN depends linearly or less than linearly on ρB → will reduce the K+ yield in larger collision system
MAuAu/MCC(K+) favors the soft Equation-of-State.
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33. Collective Flow of K+ (v1)
Ni+Ni 1.93A GeV
FOPI Collaboration,
Z. Phys. A 352, 355 (1995)
Striking results on the kaon sideflow from the FOPI triggered a lot of discussions.
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34. Collective Flow of K+ (v1)
FOPI Collaboration,
Phys. Lett. B486, 6 (2000)
K+ sideflow can be used to study in-medium effect
Strong pt- dependence
Antiflow w.r.t. baryons at small pt
Flow in baryon direction at large pt
Magnitude of flow changes with collision centrality
Favors repulsive potential and increased kaon mass
1.7A GeV Ru + Ru
Rapidity interval: -1.2 < y(0) < -0.5
<bgeo>=3.8fm
<bgeo>=2.3fm
RBUU model calculations by
E.Bratkovskaya & W.Cassing
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35. Collective Flow of K+ (v2)
Au+Au 1A GeV
KaoS Collaboration,
Phys. Rev. Lett. 81, 1576 (1998)
b≤5 fm
due to the absorption
5<b≤10 fm
b>10 fm
due to the scattering
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36. Collective Flow of K+ (v2)
RBUU model
calculations by
G.Q. Li et al.,
Phys. Lett. B 381, 17 (1996)
with in-medium potential
without in-medium potential
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37. F Production K+K- invariant mass spectra Ni+Ni at 1.93A GeV
FOPI Collaboration,
Nucl. Phys. A714, 89 (2002)
K+K- invariant mass spectra
Ni+Ni at 1.93A GeV
Φ-yield = K--yield at the same incident energy!
Systematics: Φ/K- = %
Theoretical Expectations: ??
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38. Long-Term Future Exploring nuclear matter at the highest-density
B. Friman et al.,
Eur. Phys. J. A3, 165(1998)
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39. Motivation-Strangeness
QGP already
at 30A GeV?
Unique maximum in AA
When this enhancement
of hyperons starts?
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40. Motivation-e+e- pair
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41. Motivation-Charm SIS18: strangeness production near threshold (1-3 n0)
SIS200: charm production near threshold (5-10 n0)
In-medium effects
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42. Simple Estimates of Open Charms
Quark-meson Coupling model
Sibirtsev, K. Tsushima, A.W. Thomas,
EPJA6, 351 (1999)
(dc)
PYTHIA calculation for
open charm meson production
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43. More explicit channel, e.g.,
Simple Estimates
B. Hong, JKPS43, 685 (2003)
More explicit channel, e.g.,
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44. More Motivations Indications for deconfinement at high baryon density
Anomalous charmonium suppression
Temperature of Hot Nuclear Matter
Virtual photons decaying into e+e- pairs
Equation-of-State
Flow measurement (direct, v2, radial, etc.)
Critical Point
Event-by-Event fluctuations
Color Superconductivity
Precursor effects at T > TC
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45. How? Accelerator Side Detector Side
Require high intensity for rare particle measurements: ~109 ions/sec (cf. ~107 ions/sec at the SPS)
High spill fraction: 0.8 (cf at the SPS)
Detector Side
Identification of hadrons at high momentum with high track density environment (~1000 for 25A GeV Au+Au)
Identification of electrons with pion suppression by 104 – 105 (need two electron detectors)
Reconstruction of particle vertices with high resolution
Large acceptance
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46. 2nd Generation Fixed Target Exp.
Magnetic field: 1-2 T
Silicon Pixel/Strip: hyperons and D’s
RICH: electrons, high momentum pions & kaons
TRD: electrons from the J/Psi decay
TOF
Start: diamond pixel
Stop: RPC
CBM Detector Concept
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47. Conclusions Stopping Collective flow Particle Production
New experimental approach exploiting N/Z shows incomplete mixing for the most central collisions.
Collective flow
Fourier analysis of azimuthal distributions reveals the detailed event shape over full phase-space.
Particle Production
Pion spectra provides an information of the Coulomb interaction and the modification of the delta-spectral function.
Kaon yields and spectra favor the in-medium modification of kaon masses (it also favors a soft EoS).
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48. Conclusions –continued-
Nuclear EoS is not understood yet.
But many promising experimental observables such as collective flow and strangeness production are available to constrain it.
Evidence for in-medium effects from strange particle observables.
It exists, but more accurate (high statistics) data are needed.
But difficult near threshold energy
Future
CBM experiments at the future GSI facility
We can start the CBM experiment in ten years (far future).
But it takes more than ten years to design and build it.
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