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The Experimental Quest for In-Medium Effects

The Experimental Quest for In-Medium Effects. Romain Holzmann GSI Helmholtzzentrum f ü r Schwerionenphysik, Darmstadt at 23 rd Indian-Summer School of Physics and 6 th HADES Summer School: Physics @ FAIR October 3-7, 2011 in Rez/Prague, Czech Republic.

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The Experimental Quest for In-Medium Effects

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  1. The Experimental Quest for In-Medium Effects Romain Holzmann GSI Helmholtzzentrum für Schwerionenphysik, Darmstadt at 23rd Indian-Summer School of Physics and 6th HADES Summer School: Physics @ FAIR October 3-7, 2011 in Rez/Prague, Czech Republic • Lecture I: Pedestrian’s approach • Lecture II: Experiments galore • Lecture III: HADES at GSI

  2. Lecture I:A pedestrian’s approach to medium effects Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  3. Mass of composite systems • Naively, the mass of a composite object is • the sum of the masses of its constituents. • Binding energy reduces the mass slightly: • molecules, atoms: 10-8 effect nuclei: 10-2 effect Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  4. atom 10-10 m atomic nucleus 10-14 m nucleon 10-15 m M » Σmi M   mi M   mi binding energy effect  10-8 binding energy effect  10-2 The origin of hadron masses 1 GeV >> 20 MeV nucleon: mass not determined by sum of current quark masses !!! ► Could say: mass given by energy stored in motion of quarks and by energy of gluon fields (m = E/c2) Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  5. M l,q [MeV/c2] Leptons Quarks t ~175000 105 104 ~4600 b 1777 ~1200 t c 103 80-140 106 s m 102 nt 4-8 2-4 10 d u 0.511 1 nm e 10-1 10-2 10-3 10-4 10-5 ne 10-6 Masses of quarks and leptons “mass” means here current mass = weak mass • Masses of elementary particles • (quarks, leptons) are generated • by interaction with the Higgs field • search for Higgs particle @ LHC Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  6. Phenomenology of quark masses Quark masses are not directly observable, they are parameters in models fitted to hadron properties. Systematics of (current) quark masses (from PDG full report, 2000): • Picture taken from • Zhu et al., PLB647 (2007) 366 each dot represents one model fit! Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  7. The evolution of the universe T time 15 billion years • Two steps • in mass generation: • Electro-weak transition • (Higgs mechanism) • ► weak mass • = current mass • Chiral transition • (hadronization) • ► strong mass • We observe the • constituent mass: • M = Mw + Ms 3 oK 1 billion years 20 oK 300.000 years 3.000 oK From the Big Bang to the galaxies: expansion & cooling 109oK ~100 MeV 3 minutes 2. 1 millionth of a second (1 μs) 1012oK ~100 GeV 1. Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  8. b b c c s u,d s u,d Dyson-Schwinger approach: non-perturbative ansatz for momentum-dependent quark mass function C. Fischer et al., Ann. Phys. 324 (2008) 106 Mass generation in QCD-inspired model Weak masses through interaction with Higgs boson Constituent quark masses mq= mweak + mstrong (p = momentum of quark) Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  9. The strong interaction • Hadron physics deals with phenomena mediated by • the strong force … • … the theory of which is Quantum Chromo Dynamics (QCD) Nucleus (R  1-10 fm; M  A x GeV) Quarks (R < 10-4fm; M 10 MeV) Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  10. Coupling strength between two quarks Coupling strength between two quarks Coupling strength between two quarks perturbative QCD:aS<< 1 perturbative QCD:aS<< 1 perturbative QCD:aS<< 1 non-perturbative QCD: aS 1 f non-perturbative QCD: aS 1 non-perturbative QCD: aS 1 Quarks are confined! QCD: running coupling constant αs ~1 fm Asymptoticfreedom (Physics Nobel prize 2004) Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  11. QCD: quarks  jets • The quark-quark potential • increases at large distances: Jet production in e+e- collisions Quarks are confined and by trying to separate them jets of hadrons materialize ► first experimental confirmation in e+e- collisions at SLAC Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  12. perturbative QCD:aS<< 1 non-perturbative QCD: aS 1 Non-pertubative QCD • At low energy the QCD equations • cannot be solved explicitely: • fall back on models • solve on the lattice • explore symmetries ofLQCD with Nf = 3 Chiral symmetry: In the limit of zero mass left- and right-handed quarks decouple But: M(quark) > 0  symmetry broken ! Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  13. qR qR qL qR qL qL gluon (g) gluon (g) gluon (g) Coupling to the condensate generates hadron masses qR qR qL qL qR qL Chiral symmetry breaking in a nutshell • The QCD Lagrangian is invariant against independent global SU(3) flavor rotations of left- and right-handed quarks: •  left- and the right-handed worlds decouple • This symmetry isexplicitly brokenby the finite • massesof the current (u,d,s) quarks. • On top of this, chiral symmetry isspontaneously broken, • and much more strongly so, because of the existence of • a non-vanishing vacuum expectationvalue • of the scalar quark condensate: • Analogy: the spontaneous orientation of the • elementary magnetic dipoles in a ferromagnet Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  14. Ferromagnetic: rotational symmetry about 1 axis Paramagnetic: full rotational symmetry (3d) magnetisation M ferro magnetic para magnetic temperature T TCurie Phase transition: ferromagnetism  paramagnetism Restoration of full rotational symmetry: vanishing of magnetisation Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  15. The ground state of QCD (i.e. vacuum) does not share the chiral symmetry • of the QCD Lagrangian. The vacuum is populated by scalar quark-antiquark • pairs in 3P0-states: quark-antiquark pairs with J=0+: • A left-handed quark qL can be converted into a right-handed quark qR • by interaction with a scalar qq pair: ►chiral symmetry breaking + Due to the condensate chiral symmetry is broken! But, it can be restored for = annihilate Spontaneous chiral symmetry breaking Non-zero chiral condensate: Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  16. 1535 1520 If chiral symmetry were to hold in the hadronic sector we would expect chiral partners with same spin but opposite parity to be degenerate in mass: ≈ 290 ≈ 600 1232 938 1260 600 nucleon ≈ 490 ≈ 470 135 770 vector meson Mass split is large, comparable to hadron masses ! scalar meson  Chiral symmetry is broken in the hadronic sector Chiral symmetry breaking in the hadronic sector Observation: Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  17. , . p - beams The chiral condensate as order parameter • The chiral condensate in QCD is an order parameter for • the breaking (or restoration) of chiral symmetry (like magnetization in ferromagnet!) • Hadron masses determined in a non-trivial way by chiral symmetry • breaking, i.e. via the interplay with the condensate ► calculated within models! • If chiral condensate could be changed by external parameters - like , T - and • if it were possible to study how this affects hadron masses, then • Deeper understanding of chiral symmetry breaking and restoration, and of hadron mass generation elementary reaction: ,   V+X mV (=0;T=0) heavy ion reactions: A+AV+X mV (>>0;T>>0) Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  18. SIS 18 SIS 300 SPS SIS 18 SIS 300 SPS SIS 18 SIS 300 SPS freeze-out regions S. Leupold, Trento Workshop 2005 J. Wambach et al. Quark condensates 2-quark condensate 4-quark condensate Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  19. However,is not an observable!! + higher order terms hadronic spectral function: QCD sum rules • QCD sum rules provide a link between hadronic observables and condensates: • (T. Hadsuda and S. Lee, PRC 46 (1992) R34; S. Leupold and U. Mosel, PRC58 (1998) 2939) • Chiral condensate related only to integral over hadronic spectral functions; •  spectral function are constrained, but not determined • Hadronic models are still needed for specific predictions of hadron properties !! Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  20. Model predictions for in-medium masses of mesons K. Saito, K. Tushima, and A.W. Thomas PRC 55 (1997) 2637 Quark-meson coupling model (QMC) V. Bernard and U.-G. Meißner NPA 489 (1988) 647 NJL-model decrease of  mass by 15% at normal nuclear matter density mass degeneracy of chiral partners reached at high baryon densities Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  21. F. Klingl et al. NPA 610 (1997) 297 NPA 650 (1999) 299 P. Mühlich et al., NPA 780 (2006) 187  spectral function (structure due to coupling to S11,P13 resonances) for rB: lowering of in-medium mass + broadening of resonance Model calculations of the ω spectral function Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  22. Calculation of the ρ spectral functions vacuum hadronic medium e.g. Leupold, Mosel, Post et al. NPA 741 (2004) 81, NPA 780 (2006) 187 + other calc. vacuum ρ Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  23. 33 D13 F15 Evidence for in-medium changes • Nucleon resonances excited in photoabsorption on nuclei: • "melting" of the resonances above the 33 • Bianchi et al. • Phys. Rev. C 54 (1996) 1688 • In the nuclear medium: • Fermi motion • collisional broadening • final-state effects Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  24. Kaons in the medium D.B. Kaplan et al., PLB 175 (1986) 57 G.E Brown et al., NPA 567 (1994) 937 T. Waas et al., PLB 379 (1996) 34 J. Schaffner-Bielich et al., NPA 625 (1997) 325 G. Mao et al., PRC 59 (1999) 3381 Dispersion relation: • Repulsive (attractive) potential for K+ (K-) • Models predict same trend, but differ quantitatively • Uncertainty on production cross section of K in the medium • Observables:yields (AA vs. NN), flow, pt distributions Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  25. L(1405) K- K- N-1 K- spectral function in nuclear matter Self-consistent coupled channel calculations L. Tolos, A. Ramos, E. Oset, arXiv:nucl-th/0702089 Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  26. Basic experimental approach: hadron decay in the medium: • reconstruct the invariant mass from 4-momenta of decay products: with vacuum • compare (listed in PDG) • ensure that decays occur in the medium: • select shortlived mesons ( • cut on low meson momenta : 1.3 fm; : 23 fm; : 46 fm ) • avoid distortion of 4-momenum vectors by final-state interactions •  dilepton spectroscopy: ρ, ω,  e+e- (orμ+μ- ) • real photons (and K+) are useful as well Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  27. Heavy-ion collisions: A+A Elementary reactions: , p, -beams Advantage: sizable effects due to high densities and temperatures (regeneration of mesons) Advantage: well controlled conditions: important for theoretical interpretation no time dependence of baryon density: B B(t); T=0; Disadvantage: any signal represents an integration over the full space-time history of the heavy-ion collision with strong variations in densities and temperatures Disadvantage: small medium effects since   0 and T=0 Goal (in both approaches): Test concepts for hadron mass generation by comparing predictions based on these concepts with experimental observations how hadron properties are changed in a strongly interacting environment. Pros and cons of HIC vs. elementary Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  28. Evolution of the universe • Rafelski 2005 hadronization ρ≈ few times ρ0 T ≈ 100 MeV Such conditions can be realized in heavy-ion collisions but treac≈ 10-23 s << 10-6 s ! Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  29. two colliding nuclei A+A @ 2 AGeV formation of highly compressed and heated collision zone explosion of collision zone: freeze-out of yields   e+  e+,+ e+,+ e- e-,- e-,- bremsstrahlung probe the full space-time evolution of the collision, being emitted through all stages of the reaction • dileptons: Dileptons as probes in heavy-ion reactions new forms of matter? medium modifications of hadrons? • hot & dense fireball: • photons and dileptonsareundistorted probes of strongly interacting matter Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  30. Mll > 1 GeV: direct decays of cc, bb + πo, γ Drell-Yan process: w πo,η g* N N R p g* Direct decays of VM: e- e+ w,ρ, g* Bremsstrahlung: R N Semi-leptonic D decays: D or D →leptons + meson(s) N N N Dilepton emitting processes Mll≤ 1 GeV: Dalitz decays of mesons: of baryons: Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  31. Dilepton invariant mass spectra Characteristic features of dilepton invariant mass spectra Physics issues • Low mass: • continuum enhancement ? • modification of vector mesons ? • Intermediate mass: • thermal radiation ? • charm modification • High mass: • J/ suppression ? • enhancement ? • Drell-Yan In these lectures focus is on low mass region! Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  32. bb cc Dimuon sprectrum from p+p at LHC light quark states Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  33. N N N r e+ N e- The experimental challenge ... Must detect • e+e- pairs • μ+μ- pairs among large hadronic background! ► Seenext lecture… Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

  34. atSIS100 Overview (of HI expts.) CMS ATLAS LHC s Energy RHIC SPS CERES HELIOS 3 SIS 300 SIS 100AGS SIS18 Bevalac 1990 2000 2010 2018 Time + advance in technology Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI

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