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12-8-2002 서울대 핵물리세미나 1
Overview of Relativistic Overview of Relativistic Heavy-Ion Collisions Heavy-Ion Collisions at SIS Energiesat SIS Energies
고려대학교홍 병 식
12-8-2002 서울대 핵물리세미나 2
V>0.9c
Evolution
Hadronization (Freeze-out) + Expansion
Compression Thermalization
Pre-equilibrium
Thermalization QGP? Mixed phase
Some of the energy they had before is transformed into heat and new particles right here !
Schematic Understanding of the Relativistic HI Collisions
12-8-2002 서울대 핵물리세미나 3
Nuclear Phase Diagram
T(MeV)
Density(n0)
~150
~10
Early Universe(RHIC)
Color SuperconductorNeutron Star
Hadron Gas
Quark-Gluon Plasma
Phase Transition
Atomic Nuclei
SIS explores Nonperturbative regime of QCD
12-8-2002 서울대 핵물리세미나 4
HE Heavy-Ion Accelerators
Acceleratorc.m. Energy
(GeV)Status
SIS 18(GSI, Germany)
2A(A=mass number)
Running
AGS(BNL, USA)
5A Finished
SIS 200(GSI, Germany)
8AJust approved;
Plan to run from ~2010
SPS(CERN,
Switzerland)20A Finish soon
RHIC(BNL, USA)
200ARunning since
2000
LHC(CERN,
Switzerland)5500A
Plan to run from ~2007
12-8-2002 서울대 핵물리세미나 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
12-8-2002 서울대 핵물리세미나 6
Experiments at GSI
HADES
KaoS
FOPI
CBM
12-8-2002 서울대 핵물리세미나 7
FOPI Setup
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
[email protected] K- in 104 events
12-8-2002 서울대 핵물리세미나 8
KaoS Setup
12-8-2002 서울대 핵물리세미나 9
PID & Detector Acceptance
dE/dx vs p/Z in drift chambers Bethe-Bloch parameterization Additional use of plastic to differentiate Z
Ru+Ru at 400A MeVPhase-space covered by the FOPI detectors
p
Examples of FOPI
12-8-2002 서울대 핵물리세미나 10
Collision Centrality
• FOPI invented the Era
t variable which is extremely sensitive, especially, for the most central collisions.
ii
ii
rat E
EE
||,
,
Centr
al Peripher
al
12-8-2002 서울대 핵물리세미나 11
Particle SpectraRu+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)
B. Hong et al., (FOPI)Phys. Rev. C66, 034901 (2002)
12-8-2002 서울대 핵물리세미나 12
Particle Spectra
freeNNNN
12-8-2002 서울대 핵물리세미나 13
Stopping
)(0
)0(
)0()0(
)(0
)0(
)0()0()(
)0(
)(
)(||
dydydN
dydydN
yy
ybt
p
Mean rapidity shift of protons defined by
where yb(yt) is the beam(target) rapidity
12-8-2002 서울대 핵물리세미나 14
Stopping
RuZry
ZrRuy
p N
NR
We use the heaviest isobaric nuclei available(96
44Ru & 96
40Zr)
Introduce a new variable to test a nuclear transparency
12-8-2002 서울대 핵물리세미나 15
Stopping
• 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)
B. Hong et al., (FOPI)Phys. Rev. C66, 034901 (2002)
0.4A GeV Ru(Zr)+Ru(Zr)
12-8-2002 서울대 핵물리세미나 16
Stopping
• Rp steeper– More transparency
• Trend predicted by IQMD.
• Absolute values of Rp are not described quantitatively.
1.5A GeV Ru(Zr)+Ru(Zr)
B. Hong et al., (FOPI)Nucl. Phys. A 721, 317c (2003)
12-8-2002 서울대 핵물리세미나 17
Stopping
NNNNN
R RuRu
y
ZrZr
y
RuRu
y
ZrZr
y
mix
y
Z
2
yNy
yN
d
d
d
d tragetprojectile
)0(
)0(
)0()437.01(
2
1
0.4A GeV Ru(Zr)+Ru(Zr)
Ru+Ru
Zr+Zr
12-8-2002 서울대 핵물리세미나 18
Stopping
yNy
yN
d
d
d
d tragetprojectile
)0(
)0(
)0( )856.01(2
1
NNNNN
R RuRu
y
ZrZr
y
RuRu
y
ZrZr
y
mix
y
Z
2
1.5A GeV Ru(Zr)+Ru(Zr)
12-8-2002 서울대 핵물리세미나 19
Comparison
Eb(GeV) dyp/yb Nf 1) Nb
2) Mpr 3) Remark
0.4A 0.256 9.46 6.14 0.21
1.5A 0.258 23.4 9.70 0.41 More Transparent
1) Number of projectile nucleons in forward hemisphere2) Number of projectile nucleons in backward hemisphere3) Mixing parameter: more transparent for a larger Mpr
NNNN
Mbf
bf
pr
12-8-2002 서울대 핵물리세미나 20
Collective Flow
tim
e
reaction plane
transverse plane(at midrapidity)
v2<0 v2 >0 elliptic flow
RN=(1+ v2)/(1-v2)
v1<0 v1 >0sideward flow
px = v1 pt S. Voloshin & Y. Zhang, Z. Phys. C70, 665 (1996)J.Y. Ollitrault, Nucl. Phys. A638, 195c (1998)
Fourier expansion of azimuthal distribution gives the phase space distribution w.r.t. the reaction plane.
...))2cos(v2)cos(v21( 21
3
dyddpp
Nd
tt
R
x
yz
x
yz
x
yz
x
yz
Reaction plane
12-8-2002 서울대 핵물리세미나 21
Sideward Flow –integrated
• 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
FOPI Collaboration,Phys. Rev. C67, 034907 (2003)
12-8-2002 서울대 핵물리세미나 22
Sideward Flow –differential
• Differential directed flow (DDF) for – Au+Au collisions at 40
0A MeV• DDF shows a clear se
nsitivity on the EoS.• IQMD deviates at larg
e y and large pt for Z=1.
• SM(soft EoS with MDI) well describe data.
12-8-2002 서울대 핵물리세미나 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
12-8-2002 서울대 핵물리세미나 24
Elliptic Flow -systematic study
pt dependence
Centralitydependence
Eb dependence
FOPI Collaboration,Nucl. Phys. A679, 765 (2001)
A dependence
12-8-2002 서울대 핵물리세미나 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
12-8-2002 서울대 핵물리세미나 26
Elliptic Flow -comparison
• Model cannot explain the experimental observation.
12-8-2002 서울대 핵물리세미나 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 distributi
on
12-8-2002 서울대 핵물리세미나 28
Phase-space distributionKaoS Collaboration, Phys. Lett. B 495, 26 (2000)
Ni+Ni 1.93A GeVNi+Ni 1.93A GeV central (b≤4.4 fm)non-central
)/exp(1
3
3
Tmdp
d
m TT
Fit function :
Isotropic thermal source
2
12-8-2002 서울대 핵물리세미나 29
K-/K+ Ratio
withwithout
in-medium potentials
RBUU calculation byE.Bratkovskaya, W.Cassing (Giessen)similar trends byG.Q.Li (Stony Brook)
FOPI measures the target rapidity region:Eur. Phys. J. A9, 515 (2000)Nucl. Phys. A 625, 307 (1997)
12-8-2002 서울대 핵물리세미나 30
Equivalent Energy Analysis KaoS Collaboration, Phys. Rev. Lett. 78, 4007 (1997)
Ni+Ni at various beam energies
40° < θ lab < 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
GeVss th 23.0
K+ yield at 1.0 GeV/u is almost the same as K- yield at 1.0 GeV/u.
12-8-2002 서울대 핵물리세미나 31
Equivalent Energy AnalysisKaoS 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
12-8-2002 서울대 핵물리세미나 32
Determination of the EoS Comp. between Au+Au & C+C
① Purpose: disentangle soft EoS effect and in-medium effect
② Baryon density (ρB) depends on the nuclear compressibility
③ Au+Au will reach much higher ρB
④ Subthreshold K+ production by multiple scattering means ~ρB
2 at least → will increase the K+ yield in larger collision system → more important at lower beam energies
⑤ 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.
KaoS Collaboration, Phy. Rev. Lett. 86, 39 (2001)
12-8-2002 서울대 핵물리세미나 33
Collective Flow of K+ (v1)
FOPI Collaboration,Z. Phys. A 352, 355 (1995)
Ni+Ni 1.93A GeV
Striking results on the kaon sideflow from the FOPI triggered a lot of discussions.
12-8-2002 서울대 핵물리세미나 34
Collective Flow of K+ (v1)
• 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
FOPI Collaboration,Phys. Lett. B486, 6 (2000) 1.7A GeV Ru + Ru
RBUU model calculations by E.Bratkovskaya & W.Cassing
<bgeo>=3.8fm <bgeo>=2.3fm
Rapidity interval: -1.2 < y(0) < -0.5
12-8-2002 서울대 핵물리세미나 35
Collective Flow of K+ (v2)KaoS Collaboration,Phys. Rev. Lett. 81, 1576 (1998)
Au+Au 1A GeV
2
2
21
21
)180()0(
)90()90(
v
v
NN
NNR
b≤
5 fm
5<
b≤
10 fm
b>
10 fm
due to the absorption
due to the scattering
12-8-2002 서울대 핵물리세미나 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
12-8-2002 서울대 핵물리세미나 37
Production• K+K- invariant mass spectra
Ni+Ni at 1.93A GeV
Φ-yield = K--yield at the same incident energy! Systematics: Φ/K- = 10 - 20 % Theoretical Expectations: ??
FOPI Collaboration,Nucl. Phys. A714, 89 (2002)
12-8-2002 서울대 핵물리세미나 38
Long-Term FutureExploring nuclear matter at the highest-density
B. Friman et al.,Eur. Phys. J. A3, 165(1998)
12-8-2002 서울대 핵물리세미나 39
Motivation-Strangeness
When this enhancement of hyperons starts?
QGP already at 30A GeV?
Unique maximum in AA
12-8-2002 서울대 핵물리세미나 40
Motivation-e+e- pair
12-8-2002 서울대 핵물리세미나 41
Motivation-Charm
SIS18: strangeness production near threshold (1-3 n0)SIS200: charm production near threshold (5-10 n0)In-medium effects
12-8-2002 서울대 핵물리세미나 42
Simple Estimates of Open Charms
PYTHIA calculation for open charm meson production
Quark-meson Coupling model Sibirtsev, K. Tsushima, A.W. Thomas,EPJA6, 351 (1999)
(dc)
(dc)
12-8-2002 서울대 핵물리세미나 43
More explicit channel, e.g.,
Simple EstimatesB. Hong, JKPS43, 685 (2003)
12-8-2002 서울대 핵물리세미나 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
12-8-2002 서울대 핵물리세미나 45
How?
• Accelerator Side– Require high intensity for rare particle measurements: ~10
9 ions/sec (cf. ~107 ions/sec at the SPS)– High spill fraction: 0.8 (cf. 0.25 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
12-8-2002 서울대 핵물리세미나 46
2nd Generation Fixed Target Exp.
• Magnetic field: 1-2 T• Silicon Pixel/Strip: hyp
erons 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
12-8-2002 서울대 핵물리세미나 47
Conclusions
• Stopping– New experimental approach exploiting N/Z shows incomplet
e mixing for the most central collisions.
• Collective flow– Fourier analysis of azimuthal distributions reveals the detail
ed event shape over full phase-space.
• Particle Production– Pion spectra provides an information of the Coulomb interac
tion 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).
12-8-2002 서울대 핵물리세미나 48
Conclusions –continued-
• Nuclear EoS is not understood yet.– But many promising experimental observables such as collec
tive 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.