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Nuclear Matter

Nuclear Matter. Course I Properties of strongly interacting systems Course II Creating and investigating nuclear matter under extreme conditions Joachim Stroth , GSI/Univ. Frankfurt. Discovery of the Micro-Cosmos.

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Nuclear Matter

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  1. Joachim Stroth, GSI/Univ. Frankfurt Nuclear Matter Course I Properties of strongly interacting systems Course II Creating and investigating nuclear matter under extreme conditions Joachim Stroth, GSI/Univ. Frankfurt

  2. Joachim Stroth, GSI/Univ. Frankfurt Discovery of the Micro-Cosmos • It all started with the observation of Radioactivity. In the late 19th Century Henri Becquerelle discovered Ionising Radiation emerging from Uranium. We now know that a,b and g-Rays stem from transitions in the nucleus. This event can be viewed as the birth of Nuclear Physics. • Further Discoveries: • In Cathode Rays:Electron (Thompson) • In Cosmic Rays:Positron, Myon (Anderson), Pion (Powell) • With Accelerators:Anti-Proton, and and and Decay patterns for the dacay of pions of the type p+ m+ + n  e+ + 3 n

  3. Joachim Stroth, GSI/Univ. Frankfurt The Atomic Nucleus • Ernest Rutherford, the real father of nuclear physics found something very heavy and tiny in the interior of atomic nuclei. • The observed angular distribution of a-particles was in agreement with the assumption of pure electromagnetic scattering off an object with • M >> Ma • R < 3  10 –14 m • The probability for an interaction can be calculated for thin targets:

  4. Joachim Stroth, GSI/Univ. Frankfurt e- e- q Electron Beam as Particle Microscope • Scattering of electrons off point-like objects is ... .. excellently described by: Exchange of Photons e- e- E,p E´,p´ g Z

  5. Experiments on elastic scattering of Electrons at Energies of < 1 GeV (l  0.2fm) Fourier-Transform ofthe Form Factor yields the Charge Distribution Joachim Stroth, GSI/Univ. Frankfurt 100 ds/dW [rel. Einh.] 10-2 10-4 40Ca 48Ca 10-6 0.08 Ca 10-8 r[fm-3] Pb 10-10 0.02 20 30 40 50 60 q [Grad] 0 2 4 6 8 10 R [fm] The Charge Distribution of Nuclei e- e- Nobel Price in Physics 1961 Hofstaedter g Z

  6. Joachim Stroth, GSI/Univ. Frankfurt Digging deeper with Deep-Inelastic Scattering

  7. Joachim Stroth, GSI/Univ. Frankfurt The Form Factor of Protons

  8. Joachim Stroth, GSI/Univ. Frankfurt Nobel Price 1990 Kenndall, Friedmann, Taylor Struktur des Nukleons • Experiments with Electron Beams at the SLAC up to 20 GeV (l  0.1fm) • Essential Observations: • Nucleons do have diffuse surfaces • Nucleons can be transformed into excited states • Nucleons are composite particles which contain point-like constituents

  9. Joachim Stroth, GSI/Univ. Frankfurt Constituents of the Atomic Nucleus <qq>  0 99.9% of the Matter around us consits out of Nucleons Nucleus (R  1-10 fm) Protons up-anddown-Quarks R  1fm; m  1GeV R < 10-4fm; m  10 MeV Neutrons GluonsandvirtualQuarksandAnti-Quarks <qq> = 0 Strong Interaction: QCD

  10. Joachim Stroth, GSI/Univ. Frankfurt The Nucleon is a Complex Object • Hadrons are very complex excitations of valence quarks in the present of quark and gluon condensates.

  11. Joachim Stroth, GSI/Univ. Frankfurt The Particle Zoo • According to current understanding point-like particles

  12. Joachim Stroth, GSI/Univ. Frankfurt The Particle Zoo II • Bosons carry the interaction.

  13. Joachim Stroth, GSI/Univ. Frankfurt The Nature of the Strong Force • Along the successful description of electro-weak interaction by gauge theory, the strong interaction can be described by the exchange of gluons.

  14. Joachim Stroth, GSI/Univ. Frankfurt QCD: Confinement • If the distance between two quarks gets larger, more and more gluons contribute to the interaction between the quarks. • Hence the potential energy grows with increasing distance. • At some point, enough energy is stored in the field to produce a pair of quarks out of the vacuum.

  15. Joachim Stroth, GSI/Univ. Frankfurt t 10-10s Hadronisation 10-34s QGP GUT 10-43s x The Origin of Matter Matter was produced about 1 ms second after the Big Bang • Criteria of Sacharov for the cre-ation of matter out of radiation: • C and CP ViolationThe decay rate of quarks and anti-quarks are different • Violation of Baryon Number ConservationLeptons decay in quarks and vice versa • No thermal equillibrium • mB=0 if baryon number is not onserved Since particles are always produced in pairs, why is there only matter and no anti-matter left

  16. Joachim Stroth, GSI/Univ. Frankfurt HAGEDORN Production in Secondary Reaction Relative Yield 1 1E-10 1E-20 Atomic Mass Number 1E-30 1E-40 1E-50 1E-60 1E-70 1E-80 1E-90 1 10 Production of Heavy Nuclei • In the Bing Bang only the light-est nuclei could be formed! • Production of heavier nuclei: • Thermonuclear burning in starsup to Iron ! • Supernova Explosions:Neutron absorbtion with subsequent beta-decay ! • r-processNeutron Drip Line • s-process

  17. Joachim Stroth, GSI/Univ. Frankfurt Nuclear Matter has Exotic Properties • Let‘s quote some macroscopic properties of Nuclear Matter • Nuclear matter is extremely heavy 280 Million Tons per cm3 • Less than a mm3 is enough to built an aircraft carrier. • However, if one would burn it completely, the energy gain would be equivalent to 50 GW for a whole year. • Although we know Nuclear Matter only in small portions inside atoms, it exists in nature also in big portions: • Neutron Stars have a diameter of typically 10 km.

  18. Joachim Stroth, GSI/Univ. Frankfurt The Equation of State hard EoS k = 380 MeVsoft EoS k = 200 MeV • Around normal nuclear ground-state density the compressibility can be determined from Giant Monopole Resonances. • At higher densities the proper-ties can only be extracted from experiment on the basis of theoretical models. • Conditions: • E/A(ro) = -16 MeV • d(E/A)(ro)/dr = 0 • Compressibilityk = 9r2 d2 (E/A)/ dr2 = 200 - 400 MeV Compressional Energy E/A Density

  19. Joachim Stroth, GSI/Univ. Frankfurt The Effective Interactions between Nucleons • Hideki Yukawa described in 1934 the force between nucleons as an exchange of virtual particles. • If the exchanged particles carry mass, the range of the interaction is finite:

  20. Nuclei can be described assuming nucleons moving independently in a mean nuclear potential: PhenomenologicalSquare-well, Harmonic, Woods-Saxon Self-consistentHartree-Fock Nuclei form because of the strong effective interaction between nucleons. Although this „residual“ interaction is weaker than the bare strong force between quarks and gluons, it still overcomes Coulomb repulsion of protons by far. Joachim Stroth, GSI/Univ. Frankfurt The Formation of Nuclei

  21. Joachim Stroth, GSI/Univ. Frankfurt The Nucleus as a Liquid Drop • The nucleus in the ground state is cold Fermi liquid. At moderate excitation energies (E/nucleon << EB) nuclei behave like little droplets of water. The Coulomb Barrier: Potential energy of two touching spheres (if r=R0)

  22. Joachim Stroth, GSI/Univ. Frankfurt Heating Nuclear Matter • Nuclei store additional energy by transfering nucleons into levels between the Fermi-surface and the barrier: • Single Particle excitations • Collective Excitations • It can thermalize by forming a Compound Nucleus • And cool down by • (Fragmentation) • Particle Decay (a,p,n) • Electromagnetic transitions (g) • At E/A of 5 MeV the nuclei transform to a gas of nucleons.

  23. Joachim Stroth, GSI/Univ. Frankfurt Hadronic Matter Baryonen M[GeV] Mesonen • Nucleons are composite particles and can therefore transform into excited states. • Is the temperature of nuclear matter high enough, internal degrees of the nucleons are excited. • e.g.: N + N = N + D= N + N + p • These excited states are often called resonances, since their decay width is rather large (due to the strong interaction). N(1520) N(1440) a1 f 1 p,n r,w k,h p 0

  24. Joachim Stroth, GSI/Univ. Frankfurt The Melting of Resonances • Exiting nucleons by inelastic electron scattering • on liquid hydrogen (protons):Resonances are clearly visible (most prominent the D33) • on nuclei:no higher-lying resonances seem to survive

  25. Joachim Stroth, GSI/Univ. Frankfurt QCD: Spontaneous Breaking of Chiral Symmtery • The groundstate of QCD is characterized by a non-vanishing field of quark – anti-quark pairs, the so-called chiral condensate. • This is a non-perturbative effect of QCD

  26. Joachim Stroth, GSI/Univ. Frankfurt Baryonen M[GeV] M[GeV] Baryonen M[GeV] Mesonen Mesonen Mesonen N(1520) N(1440) a1 N(1520) f 1 N(1440) 1 1 p,n a1 N(1520) f N(1440) r,w p,n a1 r,w k,h f p,n k,h r,w k,h p p 0 p 0 0 Vakuum<qq>  0 Vakuum<qq> > 0 Vakuum<qq>  0 Spontaneously Broken Chiral Symmetry • How can almost massless quarks combine to hadron with a mass of typicall 1 GeV and more? • The ground state of QCD is spotaneously broken – the vaccum is filled by a condensate of scalar quark – anti-quark pairs! • Light mesons (M<<1 GeV)p, h, K • No parity doubletts M(r)  M(a1) The bare quarks gain dynamically mass by coupling to the quark – ant-quark pairs.

  27. Joachim Stroth, GSI/Univ. Frankfurt Probing the Chiral Condensate • Expectation value of the chiral condensate in a simplified model, as a function of baryon density and temperature of nuclear matter. • Already in ordinary nuclei the condensate is reduce as compared to vacuum.

  28. Joachim Stroth, GSI/Univ. Frankfurt Medium Modifications of Hadrons • Spectral function of the r-meson in medium

  29. Joachim Stroth, GSI/Univ. Frankfurt The Quark-Gluon Phase of Nuclear Matter • At very high energies and/or densities quarks are deconfined

  30. Joachim Stroth, GSI/Univ. Frankfurt Characteristic Energy Regimes • Heavy Ion Accellerators around the world

  31. Joachim Stroth, GSI/Univ. Frankfurt Dissipative Collisions • In a kinematically complete experiment the following obsevables are derived: • T CM scattering angle • TKEL Total Kinetc Energy Loss • MR,E Mass of Recoil Ion and Ejectile • The data show evidence for a smooth transfer of collective energy of motion into internal degrees od freedom

  32. Joachim Stroth, GSI/Univ. Frankfurt Multi-Fragmentation • The ALADIN Experiment! • Projectile Fragmentation in inverse Kinematics • Forward focusing (4p detection) • No detector Thresholds

  33. Joachim Stroth, GSI/Univ. Frankfurt The Liquid-Gas Phase Transition • Results of the ALADIN collaboration show evidence for transition from a liquid to a vapour phase of nuclear matter.

  34. At energies above a few 100 MeV/u the non-overlapping parts of the nuclei are abraised and continue on straight trajectories. Nucleons in these „pole caps“ are called spectators. The nucleons in the overlapp zone form the fireball and are called participants. A correlation plot of the two helps to select impact parameter, which is no direct observable: ZSUM (Small Angle Hodoscope) Sum of all Charge M (Large Angle Hodoscope) Multiplicity Joachim Stroth, GSI/Univ. Frankfurt Creating Nuclear Fireballs

  35. Joachim Stroth, GSI/Univ. Frankfurt Cross Properties of Expanding Fireballs • A nuclear fire ball is a hot, rapidly expanding gas of hadrons. • Below some critical density, all collisions between the particle stop and the system freezes out. • In the spectrometer all particles are identified by their mass and charge. • From the spectral shape it can be inferred, that the energy of the particles is composed of a thermal and collective part Kinetic Energy of a Particle: Ek = Eth + Eflow = 3/2 kT + m/2flow2

  36. Joachim Stroth, GSI/Univ. Frankfurt A Typical 4p Experiment • Particle IDentification: • Momentum from the bending in a magnetic field • Chargeby Ionization Power • Mass from time-of-flight (combined with momen-tum measurement)

  37. Joachim Stroth, GSI/Univ. Frankfurt Particle Spectra • The emission pattern of part-icles show a rich structure if correlated with the reaction plane.

  38. Joachim Stroth, GSI/Univ. Frankfurt Creation of New Particles (Resonance Matter) • Short-lived particles (resonances) can be detected via particle correlations. • Observable  Invariant Mass • e.g.: N+N  N+D33  N+N+p

  39. Joachim Stroth, GSI/Univ. Frankfurt p D33 p hole Pions are Complicated • The pion is the lightest hadron. Its existence in nuclear matter is tightly linked to the excitation of the D33 resonance. • Data described by „two temperatures“ fit

  40. The KAOS Spectrometer features a compact dipole combined with a large quadrupole to enlarge acceptance. Various focal-plane detectors allow a dedicated kaon trigger. At 1 AGeV the energy in a single nucleon nucleon is not sufficient to produce kaons. In contrast to pion production is the kaaon production rising as the number of participating nucleons increases. Clear evidence for multi-step production mechanism pN  K+L, DN  K+LN Joachim Stroth, GSI/Univ. Frankfurt Strangeness Production

  41. Joachim Stroth, GSI/Univ. Frankfurt Medium Modification of Kaons • In medium kaons/anti-kaons experience a density dependent potential which lowers/increases their effective mass. • Hence the production of anti-kaons close to the production threshold is enhanced.

  42. Joachim Stroth, GSI/Univ. Frankfurt A Thermal Model for the Fireball • The Thermal Model assumes that all particles stem from a thermalized fireball, where all inelastic collisions stop at the same temperature. • By adjusting only two parameters, the baryon chemical potential and the temperature, relative particle yields can be explained.

  43. Joachim Stroth, GSI/Univ. Frankfurt Central Collision of two Gold NucleiAbout 95% of the velocity of light • Simulation: Univ. Frankfurt, Institut für Theoretische Physik

  44. Joachim Stroth, GSI/Univ. Frankfurt r e+ e- Probing the Interior of Fire Balls e.g. Au+Au @ 1 GeV/u = 2-30 T < 100 MeV n  p p   ++ K

  45. Joachim Stroth, GSI/Univ. Frankfurt The HADES-Spectrometer • Geometry 2p in f 18 < J < 85 • Online Pattern Recognition RICH (Ring Imaging Cherenkov Detectors) TOF (Organic Scintillators) SHOWER (Lead-Shower Detector) • Tracking ILSE (Super Conducting Magnet) MDC (Multiwire Drift Chambers)

  46. Sensitive to changes of in-medium properties of vector mesons (restoration of chiral symmetry) Experimental findings: Strong enhancement of lepton pairs below the vector meson region Enhancement already at Bevalac energies Joachim Stroth, GSI/Univ. Frankfurt Low-mass Dilepton Pairs

  47. Joachim Stroth, GSI/Univ. Frankfurt Ultra Relativistic Collisions

  48. Joachim Stroth, GSI/Univ. Frankfurt Multistrange Hyperons • Strangeness enhancement in the QGP should influence in particular the production of multi-strange baryons (hyperons). • Strong enhancement of W over X over L found (W : AA/pp = 17/1) WA97F. Antinori et al, Nucl. Phys. A 661 (1999) 130c

  49. Joachim Stroth, GSI/Univ. Frankfurt The Suppression of Charmonium • Anomalous suppression if screening in a deconfined phase occurs. • Effect establishes as a function of centrality NA50

  50. Joachim Stroth, GSI/Univ. Frankfurt Composition of a Neutron Star • Each arrow indicatesa different model for the neutron star • Each model represents an other EOS

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