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Overview of Relativistic HeavyIon Collisions at SIS Energies 고려대학교 홍병식 12-8-2002 서울대 핵물리세미나 1 Schematic Understanding of the Relativistic HI Collisions Evolution PreThermalization equilibrium QGP? Mixed phase Hadronization (Freeze-out) + Expansion Compression Thermalization V>0.9c Some of the energy they had before is transformed into heat and new particles right here ! 12-8-2002 서울대 핵물리세미나 2 Nuclear Phase Diagram T(MeV) Early Universe (RHIC) Quark-Gluon Plasma ~150 Phase Transition SIS explores Nonperturbative regime of QCD Hadron Gas Atomic Nuclei 12-8-2002 Color Superconductor Neutron Star ~10 서울대 핵물리세미나 Density(n0) 3 HE Heavy-Ion Accelerators Accelerator c.m. Energy (GeV) Status SIS 18 (GSI, Germany) 2A (A=mass number) Running AGS (BNL, USA) 5A Finished SIS 200 (GSI, Germany) 8A Just approved; Plan to run from ~2010 SPS (CERN, Switzerland) 20A Finish soon RHIC (BNL, USA) 200A Running since 2000 LHC 12-8-2002 (CERN, Switzerland) 5500A 서울대 핵물리세미나 Plan to run from 4 ~2007 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 5 Experiments at GSI HADES CBM KaoS 12-8-2002 서울대 핵물리세미나 FOPI 6 FOPI Setup [email protected] 1 K- in 104 events -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 12-8-2002 서울대 핵물리세미나 7 KaoS Setup 12-8-2002 서울대 핵물리세미나 8 PID & Detector Acceptance Examples of FOPI Ru+Ru at 400A MeV Phase-space covered by the FOPI detectors p dE/dx vs p/Z in drift chambers Bethe-Bloch parameterization Additional use of plastic to differentiate Z 12-8-2002 서울대 핵물리세미나 9 Collision Centrality Peripheral Central • FOPI invented the Erat variable which is extremely sensitive, especially, for the most central collisions. E E ,i Erat i ||,i i 12-8-2002 서울대 핵물리세미나 10 Particle Spectra B. Hong et al., (FOPI) Phys. Rev. C66, 034901 (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 SiemensRasmussen blast model – PRL 42, 880(1979) 12-8-2002 서울대 핵물리세미나 11 Particle Spectra free NN NN 12-8-2002 서울대 핵물리세미나 12 Stopping Mean rapidity shift of protons defined by 0( ) y p | y ( 0 ) yt ( b ) | ( ( 0 ) 0( ) ( 0 ) ( dN (0) ) dy dy ( 0 ) dN (0) ) dy dy ( 0) where yb(yt) is the beam(target) rapidity 12-8-2002 서울대 핵물리세미나 13 Stopping Introduce a new variable to test a nuclear transparency Rp N yRu Zr N yZr Ru We use the heaviest isobaric nuclei available(9644Ru & 9640Zr) 12-8-2002 서울대 핵물리세미나 14 B. Hong et al., (FOPI) Phys. Rev. C66, 034901 (2002) Stopping 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) 12-8-2002 서울대 핵물리세미나 15 B. Hong et al., (FOPI) Nucl. Phys. A 721, 317c (2003) Stopping 1.5A GeV Ru(Zr)+Ru(Zr) • Rp steeper – More transparency • Trend predicted by IQMD. • Absolute values of Rp are not described quantitatively. 12-8-2002 서울대 핵물리세미나 16 Stopping 0.4A GeV Ru(Zr)+Ru(Zr) Zr+Zr Ru+Ru 2Ny Ny mix R Z 12-8-2002 N ZrZr ZrZr y Ny RuRu Ny RuRu d N d projectile traget y 서울대 핵물리세미나 ( 0) (0) d 1 (1 0.437 y ) 2 d N y ( 0) 17 Stopping 1.5A GeV Ru(Zr)+Ru(Zr) 2Ny Ny mix R Z 12-8-2002 N ZrZr ZrZr y Ny projectile traget RuRu Ny RuRu dN d y 서울대 핵물리세미나 (0) (0) d 1 (1 0.856 y ) N( 0) 2 dy 18 Comparison Eb(GeV) dyp/yb Nf 1) Nb 2) Mpr 3) 0.4A 0.256 9.46 6.14 0.21 1.5A 0.258 23.4 9.70 0.41 Remark More Transparent 1) Number of projectile nucleons in forward hemisphere 2) Number of projectile nucleons in backward hemisphere 3) Mixing parameter: more transparent for a larger Mpr N M N f Nb f Nb pr 12-8-2002 서울대 핵물리세미나 19 Collective Flow Reaction plane reaction plane transverse plane (at midrapidity) v1<0 v1 >0 sideward flow v2<0 v2 >0 elliptic flow z y x Fourier expansion of azimuthal distribution gives the phase space distribution w.r.t. the reaction plane. R d 3N (1 2v1 cos( ) 2v 2 cos( 2 ) ...) pt dpt dyd S. Voloshin & Y. Zhang, Z. Phys. C70, 665 (1996) px 12-8-2002 서울대 핵물리세미나 J.Y. Ollitrault, Nucl. Phys. A638, 195c (1998) = v1 pt RN=(1+ v2)/(1-v 20 2) Sideward Flow –integrated FOPI Collaboration, Phys. Rev. C67, 034907 (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 12-8-2002 서울대 핵물리세미나 21 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. 12-8-2002 서울대 핵물리세미나 22 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 23 Elliptic Flow -systematic study FOPI Collaboration, Nucl. Phys. A679, 765 (2001) Centrality dependence Eb dependence pt dependence A dependence 12-8-2002 서울대 핵물리세미나 24 Elliptic Flow –transition energy • Our data agree well with the Plastic Ball data. • Transition from in-plane to outof-plane azimuthal enhancement near 100A MeV 12-8-2002 서울대 핵물리세미나 25 Elliptic Flow -comparison • Model cannot explain the experimental observation. 12-8-2002 서울대 핵물리세미나 26 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 12-8-2002 서울대 핵물리세미나 27 Phase-space distribution Ni+Ni 1.93A GeV central (b≤4.4 fm) KaoS Collaboration, Phys. Lett. B 495, 26 (2000) non-central Isotropic thermal source 1 d 3 Fit function : 2 3 exp( mT / T ) mT dp 12-8-2002 서울대 핵물리세미나 28 FOPI measures the target rapidity region: Eur. Phys. J. A9, 515 (2000) Nucl. Phys. A 625, 307 (1997) K-/K+ Ratio RBUU calculation by E.Bratkovskaya, W.Cassing (Giessen) similar trends by G.Q.Li (Stony Brook) 12-8-2002 with without in-medium potentials 서울대 핵물리세미나 29 Equivalent Energy Analysis KaoS Collaboration, Phys. Rev. Lett. 78, 4007 (1997) Ni+Ni at various beam energies 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 s sth 0.23GeV 40° < θlab < 48° 12-8-2002 K+ yield at 1.0 GeV/u is almost the same as K- yield at 1.0 GeV/u. 서울대 핵물리세미나 30 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 12-8-2002 서울대 핵물리세미나 31 Determination of the EoS KaoS Collaboration, Phy. Rev. Lett. 86, 39 (2001) 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 ~ρB2 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. 12-8-2002 서울대 핵물리세미나 32 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. 12-8-2002 서울대 핵물리세미나 33 Collective Flow of K+ (v1) • K+ sideflow can be used to study inmedium effect – Strong ptdependence – 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 12-8-2002 FOPI Collaboration, Phys. Lett. B486, 6 (2000) 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 서울대 핵물리세미나 34 Collective Flow of K+ (v2) KaoS Collaboration, Phys. Rev. Lett. 81, 1576 (1998) Au+Au 1A GeV b≤5 fm 5<b≤10 fm N (90 ) N (90 ) 1 2v 2 R N (0 ) N (180 ) 1 2v2 b>10 fm 12-8-2002 서울대 핵물리세미나 due to the absorption due to the scattering 35 Collective Flow of K+ (v2) RBUU model calculations by with in-medium potential G.Q. Li et al., Phys. Lett. B 381, 17 (1996) without in-medium potential 12-8-2002 서울대 핵물리세미나 36 F Production • K+K- invariant mass spectra FOPI Collaboration, Nucl. Phys. A714, 89 (2002) Ni+Ni at 1.93A GeV - Φ-yield = K -yield at the same incident energy! Systematics: Φ/K = 10 - 20 % Theoretical Expectations: ?? 12-8-2002 서울대 핵물리세미나 37 Long-Term Future Exploring nuclear matter at the highest-density B. Friman et al., Eur. Phys. J. A3, 165(1998) 12-8-2002 서울대 핵물리세미나 38 Motivation-Strangeness Unique maximum in AA QGP already at 30A GeV? When this enhancement of hyperons starts? 12-8-2002 서울대 핵물리세미나 39 Motivation-e+e- pair 12-8-2002 서울대 핵물리세미나 40 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 41 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 42 Simple Estimates B. Hong, JKPS43, 685 (2003) More explicit channel, e.g., 12-8-2002 서울대 핵물리세미나 43 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 44 How? • Accelerator Side – Require high intensity for rare particle measurements: ~109 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 45 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 CBM Detector Concept – Start: diamond pixel – Stop: RPC 12-8-2002 서울대 핵물리세미나 46 Conclusions • Stopping – 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). 12-8-2002 서울대 핵물리세미나 47 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. 12-8-2002 서울대 핵물리세미나 48