Physics of ultrarelativistic heavy-ion collisions

Transcription

1 Physics of ultrarelativistic heavy-ion collisions Jean-Philippe Lansberg IPNO, Paris-Sud U. Taller de Altas Energías 2015, Benasque, Sep 20 - Oct 02, nd Lecture: September 29, 2015 J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

2 Part I Reminder J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

3 Evolution stages of a nucleus-nucleus collision J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

4 Evolution stages of a nucleus-nucleus collision 1 initial collision: t t coll 2R γ boost cms c J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

5 Evolution stages of a nucleus-nucleus collision 1 initial collision: t t coll 2R γ boost cms c 2 thermalisation: equilibrium is reached : t 1fm/c J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

6 Evolution stages of a nucleus-nucleus collision 1 initial collision: t t coll 2R γ boost cms c 2 thermalisation: equilibrium is reached : t 1fm/c 3 expansion and cooling : t 10 15fm/c J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

7 Evolution stages of a nucleus-nucleus collision 1 initial collision: t t coll 2R γ boost cms c 2 thermalisation: equilibrium is reached : t 1fm/c 3 expansion and cooling : t 10 15fm/c 4 hadronisation J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

8 Evolution stages of a nucleus-nucleus collision 1 initial collision: t t coll 2R γ boost cms c 2 thermalisation: equilibrium is reached : t 1fm/c 3 expansion and cooling : t 10 15fm/c 4 hadronisation 5 Chemical freeze-out: the inelastic collisions stop the yields are fixed J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

9 Evolution stages of a nucleus-nucleus collision 1 initial collision: t t coll 2R γ boost cms c 2 thermalisation: equilibrium is reached : t 1fm/c 3 expansion and cooling : t 10 15fm/c 4 hadronisation 5 Chemical freeze-out: the inelastic collisions stop the yields are fixed 6 Kinetic freeze-out : the elastic collisions stop the spectra are fixed : t 3 5fm/c J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

10 Evolution stages of a nucleus-nucleus collision 1 initial collision: t t coll 2R γ boost cms c 2 thermalisation: equilibrium is reached : t 1fm/c 3 expansion and cooling : t 10 15fm/c 4 hadronisation 5 Chemical freeze-out: the inelastic collisions stop the yields are fixed 6 Kinetic freeze-out : the elastic collisions stop the spectra are fixed : t 3 5fm/c Measurement at stage 5 & 6 to learn about stage 3 J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

11 Evolution stages: with or without QGP J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

12 It is always good to recall some obvious things Duration: about 10 fm/c (i.e s) Impossible to throw a probe, simultaneously, in the plasma 3-body collisions extremely rare between particles the probe should come from the collision itself... J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

13 It is always good to recall some obvious things Duration: about 10 fm/c (i.e s) Impossible to throw a probe, simultaneously, in the plasma 3-body collisions extremely rare between particles the probe should come from the collision itself... I would classify them in 3 categories: 1 enhancement/creation/emission what s the initial rate? 2 suppression/dissociation what s the initial rate? 3 quenching/shift in spectra what s the initial spectrum? J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

14 Part II How to probe the QGP from the inside J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

15 Probes to study the QCD phase diagram J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

16 Probes to study the QCD phase diagram Thermal emission: photons (as the black body radiation) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

17 Probes to study the QCD phase diagram Thermal emission: photons (as the black body radiation) Color screening: quarkonium melting J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

18 Probes to study the QCD phase diagram Thermal emission: photons (as the black body radiation) Color screening: quarkonium melting Chemical equilibrium,...: strangeness enhancement J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

19 Probes to study the QCD phase diagram Thermal emission: photons (as the black body radiation) Color screening: quarkonium melting Chemical equilibrium,...: strangeness enhancement Compression effect: azimuthal asymmetry (pressure gradient in the overlapping zone of the colliding nuclei) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

20 Probes to study the QCD phase diagram Thermal emission: photons (as the black body radiation) Color screening: quarkonium melting Chemical equilibrium,...: strangeness enhancement Compression effect: azimuthal asymmetry (pressure gradient in the overlapping zone of the colliding nuclei) Creation of a dense matter: jet quenching, heavy-quark energy loss,... J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

21 Need for proton-proton & proton-nucleus studies baselines p-p: p-p = QCD vacuum (reference) p,d-a: p,d-a = cold QCD medium (control) A-A: A-A = hot & dense QCD matter b Plasma volume dialed varying impact parameter b ( centrality ) time J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic 18/67 heavy-ion collisions September 29, / 30

22 Need for proton-proton & proton-nucleus studies baselines p-p: p-p = QCD vacuum (reference) p,d-a: p,d-a = cold QCD medium (control) A-A: A-A = hot & dense QCD matter b Plasma volume dialed varying impact parameter b ( centrality ) time J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic 18/67 heavy-ion collisions September 29, / 30

23 Need for proton-proton & proton-nucleus studies baselines p-p: p-p = QCD vacuum (reference) p,d-a: p,d-a = cold QCD medium (control) A-A: A-A = hot & dense QCD matter b Plasma volume dialed varying impact parameter b ( centrality ) time J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic 18/67 heavy-ion collisions September 29, / 30

24 Observables: nuclear modification factors dn AB b σ AB R AB = N coll dn pp ABσ pp For that, we need to know/measure σ pp dn pp J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

25 Observables: nuclear modification factors dn AB b σ AB R AB = N coll dn pp ABσ pp For that, we need to know/measure σ pp dn pp ( R CP (y) = dn dy / N coll ) ( ) dn 60 80% (or as a function of p dy / N 60 80% T ) coll [we could divide by the yield from another centrality bin or even do R PC (y)] no need of pp reference, but only sensitive on the b dependence J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

26 Observables: nuclear modification factors dn AB b σ AB R AB = N coll dn pp ABσ pp For that, we need to know/measure σ pp dn pp ( R CP (y) = dn dy / N coll ) ( ) dn 60 80% (or as a function of p dy / N 60 80% T ) coll [we could divide by the yield from another centrality bin or even do R PC (y)] no need of pp reference, but only sensitive on the b dependence for pa, one can also define R FB ( y CM ) dn pa(y CM ) dn pa ( y CM ) = R pa(y CM ) R pa ( y CM ) no need of pp reference, but only sensitive on the y dependence J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

27 Observables: nuclear modification factors dn AB b σ AB R AB = N coll dn pp ABσ pp For that, we need to know/measure σ pp dn pp ( R CP (y) = dn dy / N coll ) ( ) dn 60 80% (or as a function of p dy / N 60 80% T ) coll [we could divide by the yield from another centrality bin or even do R PC (y)] no need of pp reference, but only sensitive on the b dependence for pa, one can also define R FB ( y CM ) dn pa(y CM ) dn pa ( y CM ) = R pa(y CM ) R pa ( y CM ) no need of pp reference, but only sensitive on the y dependence The reason to use R AB (or R pa ) is that, for a rare/hard probe [σ probe NN << σnn inel ], the yield per AB collisions is proportional to the number of collisions. J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

28 Observables: nuclear modification factors dn AB b σ AB R AB = N coll dn pp ABσ pp For that, we need to know/measure σ pp dn pp ( R CP (y) = dn dy / N coll ) ( ) dn 60 80% (or as a function of p dy / N 60 80% T ) coll [we could divide by the yield from another centrality bin or even do R PC (y)] no need of pp reference, but only sensitive on the b dependence for pa, one can also define R FB ( y CM ) dn pa(y CM ) dn pa ( y CM ) = R pa(y CM ) R pa ( y CM ) no need of pp reference, but only sensitive on the y dependence The reason to use R AB (or R pa ) is that, for a rare/hard probe [σ probe NN << σnn inel ], the yield per AB collisions is proportional to the number of collisions. For a soft/frequent probe, the yield rather scales like N part [production on the surface rather than over the whole nuleus] J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

29 pp baseline RHIC QCD [jets, prompt vacuum γ, π, heavy-quarks, (p-p) references... ] vs. pqcd p-p X, s = 200 GeV Jets, high-p T hadrons, prompt-γ, heavy-q... High-quality measurements within p T ~2-45 GeV/c NLO [1], NLL [2] pqcd + recent PDFs, FFs in good agreement with all data. Slide borrowed from D. d Enterria [1] W. Vogelsang et al. [2] M. Cacciari et al. DdE, JPG34 (2007) S53-S81 TAE2010, Barcelona, 06/09/ /67 David d'enterria (CERN) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

30 Part III Thermal photons J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

31 Thermal Thermal photon photon measure radiation the = QGP temperature TAE2010, Barcelona, 06/09/ /67 David d'enterria (CERN) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

32 Thermal Thermal photon photon measure radiation the = QGP temperature Slide borrowed from D. d Enterria TAE2010, Barcelona, 06/09/ /67 David d'enterria (CERN) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

33 Thermal photon Thermal tophoton measure radiation the QGP from temperature QGP c 3 ) -2 (mb GeV 3 σ/dp 3 c 3 ) or Ed -2 (GeV 3 N/dp 3 Ed Hydrodynamical models vs. Au-Au γ,γ* excess over p-p & pqcd: Au-Au 200 GeV 4 AuAu Min. Bias x10 2 AuAu 0-20% x10 AuAu 20-40% x10 p+p Turbide et al. PRC69 QGP temperature <T 0 >~350 MeV NLO-pQCD Initial derived temperatures: T 0 = GeV well above latt. QCD T crit ~ GeV PHENIX, PRL 104 (2010) D.d'E, D.Peressounko, EPJC46 (2006) 451 p (GeV/c) T TAE2010, Barcelona, 06/09/ /67 David d'enterria (CERN) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30 τ 0 Slide borrowed from D. d Enterria

34 Thermal photon Thermal tophoton measure radiation the QGP from temperature QGP Hydrodynamical models vs. Au-Au γ,γ* excess over p-p & pqcd: Au-Au 200 GeV QGP temperature <T 0 >~350 MeV NLO-pQCD Initial derived temperatures: T 0 = GeV well above latt. QCD T crit ~ GeV PHENIX, PRL 104 (2010) D.d'E, D.Peressounko, EPJC46 (2006) 451 TAE2010, Barcelona, 06/09/ /67 David d'enterria (CERN) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30 τ 0 Slide borrowed from D. d Enterria

35 Part IV Hard probes: Heavy-flavour, heavy-quarkonia and jets J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

36 Hard probes Hard tomographic probes of QCD matter Hard-probes of QCD matter: _ jets, γ, QQ... well controlled experimentally & theoretically (pqcd) self-generated in collision at τ<1/q~0.1 fm/c, tomographic probes of hottest & densest phases of medium. QCD probe out QCD probe in Modification? QCD medium (possible quark-gluon plasma) Z, Slide borrowed from D. d Enterria TAE2010, Barcelona, 06/09/ /67 David d'enterria (CERN) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

37 Heavy-flavour Key points: J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

38 Heavy-flavour Key points: Conserved quantity (negligible thermal creation and late weak decay) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

39 Heavy-flavour Key points: Conserved quantity (negligible thermal creation and late weak decay) Produced at early times J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

40 Heavy-flavour Key points: Conserved quantity (negligible thermal creation and late weak decay) Produced at early times Interaction with nuclear/qgp matter might be tractable with pqcd J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

41 Heavy-flavour Key points: Conserved quantity (negligible thermal creation and late weak decay) Produced at early times Interaction with nuclear/qgp matter might be tractable with pqcd Abundance (mainly at low P T ) : J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

42 Quarkonia (Q Q) in the QGP Two families: Mass (MeV) Mass (MeV) ϒ(11020) X(4660) ψ (4415) ππ ϒ(10860) Thresholds: B sb s Thresholds: D s*d s* D s*d s D*D* D s D s D D* DD η c (2S) π π X(4360) X(4260) ψ (4160) ψ (4040) ψ (3770) π π η ψ (2S) π π π 0 η π π π π π 0 h c (1P) π π χ c0 (1P) X(3872) + (2?) χ c1 (1P) χ c2 χ c2 (2P) (1P) η b η b (3S) (2S) ππ KK ππ ππ η ππ ϒ(4S) ϒ(3S) ϒ(2S) ππ η ππ π 0 ππ ππ h b h b (2P) (1P) χ b0 χ b0 (2P) (1P) ω χ b (3P) χ (2P) b1 ππ χ (1P) b1 χ b2 ππ χ b2 (2P) (1P) π π B*B* BB 3 ϒ(1 D 2 ) η c (1S) (1S) J /ψ 9500 η b (1S) ϒ(1S) 9300 J PC = PC J = J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

43 Quarkonia (Q Q) in the QGP Two families: J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

44 Quarkonia (Q Q) in the QGP Two families: Expected to melt in the QGP by Debye screeening Matsui, Satz 1986 J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

45 Quarkonia: the QGP thermometer Different melting/dissociation (T d ) temperatures: depend on the size J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

46 Quarkonia: the QGP thermometer Different melting/dissociation (T d ) temperatures: depend on the size the observation of a sequential melting (directly or via feed-down) could be used as a thermometer of the GQP ψ χc J/ ψ T < T c ψ χc J/ ψ Τ χ < Τ < Τ ψ ψ χc J/ ψ Τ ψ < Τ < Τ χ ψ χc J/ ψ Τ > Τ ψ J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

47 Quarkonia: the QGP thermometer Different melting/dissociation (T d ) temperatures: depend on the size the observation of a sequential melting (directly or via feed-down) could be used as a thermometer of the GQP ψ χc J/ ψ T < T c ψ χc J/ ψ Τ χ < Τ < Τ ψ ψ χc J/ ψ Τ ψ < Τ < Τ χ ψ χc J/ ψ Τ > Τ ψ J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

48 Quarkonia: LHC results J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

49 Part V Some complications from cold nuclear matter effects J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

50 Expected nuclear effects on (involved in) quarkonium production in proton-nucleus collisions Nuclear modification of the parton densities, npdf: initial-state effect J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

51 Expected nuclear effects on (involved in) quarkonium production in proton-nucleus collisions Nuclear modification of the parton densities, npdf: initial-state effect Energy loss (w.r.t to pp collisions): initial-state or final-state effect J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

52 Expected nuclear effects on (involved in) quarkonium production in proton-nucleus collisions Nuclear modification of the parton densities, npdf: initial-state effect Energy loss (w.r.t to pp collisions): initial-state or final-state effect Break up of the meson in the nuclear matter: final-state effect J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

53 Expected nuclear effects on (involved in) quarkonium production in proton-nucleus collisions Nuclear modification of the parton densities, npdf: initial-state effect Energy loss (w.r.t to pp collisions): initial-state or final-state effect Break up of the meson in the nuclear matter: final-state effect Break up by comoving particles: final-state effect J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

54 Expected nuclear effects on (involved in) quarkonium production in proton-nucleus collisions Nuclear modification of the parton densities, npdf: initial-state effect Energy loss (w.r.t to pp collisions): initial-state or final-state effect Break up of the meson in the nuclear matter: final-state effect Break up by comoving particles: final-state effect Colour filtering of intrinsic QQ pairs: initial-state effect J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

55 Expected nuclear effects on (involved in) quarkonium production in proton-nucleus collisions Nuclear modification of the parton densities, npdf: initial-state effect Energy loss (w.r.t to pp collisions): initial-state or final-state effect Break up of the meson in the nuclear matter: final-state effect Break up by comoving particles: final-state effect Colour filtering of intrinsic QQ pairs: initial-state effect... J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

56 Expected nuclear effects on (involved in) quarkonium production in proton-nucleus collisions Nuclear modification of the parton densities, npdf: initial-state effect Energy loss (w.r.t to pp collisions): initial-state or final-state effect Break up of the meson in the nuclear matter: final-state effect Break up by comoving particles: final-state effect Colour filtering of intrinsic QQ pairs: initial-state effect... I will not speak about any QGP-like effect in pa collisions here J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

57 Typical gluon nuclear PDFs R g Pb (x,µr ) EPS09LO envelope EPS09LO: central EPS09LO: min. EMC EPS09LO: max. EMC EPS09LO: max. shad. EPS09LO: min. shad. ndsg 0.5 µ R =m J/ψ x J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

58 Typical gluon nuclear PDFs R g Pb (x,µr ) EPS09LO envelope EPS09LO: central EPS09LO: min. EMC EPS09LO: max. EMC EPS09LO: max. shad. EPS09LO: min. shad. ndsg µ R =m J/ψ x 4 regions: (i) Fermi-motion (x > 0.7), (ii) EMC (0.3 < x < 0.7), (iii) Anti-shadowing (0.05 < x < 0.3), (iv) Shadowing (x < 0.05) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

59 Typical gluon nuclear PDFs R g Pb (x,µr ) EPS09LO envelope EPS09LO: central EPS09LO: min. EMC EPS09LO: max. EMC EPS09LO: max. shad. EPS09LO: min. shad. ndsg µ R =m J/ψ x 4 regions: (i) Fermi-motion (x > 0.7), (ii) EMC (0.3 < x < 0.7), (iii) Anti-shadowing (0.05 < x < 0.3), (iv) Shadowing (x < 0.05) For the gluons, only the shadowing depletion is established although its magnitude is still discussed J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

60 Typical gluon nuclear PDFs R g Pb (x,µr ) EPS09LO envelope EPS09LO: central EPS09LO: min. EMC EPS09LO: max. EMC EPS09LO: max. shad. EPS09LO: min. shad. ndsg µ R =m J/ψ x 4 regions: (i) Fermi-motion (x > 0.7), (ii) EMC (0.3 < x < 0.7), (iii) Anti-shadowing (0.05 < x < 0.3), (iv) Shadowing (x < 0.05) For the gluons, only the shadowing depletion is established although its magnitude is still discussed The gluon antishadowing not yet observed although used in many studies; absent in some npdf fit J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

61 Typical gluon nuclear PDFs R g Pb (x,µr ) EPS09LO envelope EPS09LO: central EPS09LO: min. EMC EPS09LO: max. EMC EPS09LO: max. shad. EPS09LO: min. shad. ndsg µ R =m J/ψ x 4 regions: (i) Fermi-motion (x > 0.7), (ii) EMC (0.3 < x < 0.7), (iii) Anti-shadowing (0.05 < x < 0.3), (iv) Shadowing (x < 0.05) For the gluons, only the shadowing depletion is established although its magnitude is still discussed The gluon antishadowing not yet observed although used in many studies; absent in some npdf fit The gluon EMC effect is even less known, hence the uncertainty there J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

62 Generalities on the quarkonium break-up cross section As aforementionned: σ break up r 2 meson J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

63 Generalities on the quarkonium break-up cross section As aforementionned: σ break up r 2 meson 2S (and 3S states for Υ) should be more suppressed J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

64 Generalities on the quarkonium break-up cross section As aforementionned: σ break up r 2 meson 2S (and 3S states for Υ) should be more suppressed... provided that what propagates in the nucleus is already formed: τ f L J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

65 Generalities on the quarkonium break-up cross section As aforementionned: σ break up r 2 meson 2S (and 3S states for Υ) should be more suppressed... provided that what propagates in the nucleus is already formed: τ f L Heisenberg inequalities tell us: τ onia f fm/c [in the meson rest frame obviously] J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

66 Generalities on the quarkonium break-up cross section As aforementionned: σ break up r 2 meson 2S (and 3S states for Υ) should be more suppressed... provided that what propagates in the nucleus is already formed: τ f L Heisenberg inequalities tell us: τ onia f fm/c [in the meson rest frame obviously] At RHIC (200 GeV), for a particle with y = 0, γ = E beam,cms /m N 107! [= cosh(y beam ) = 5.36] It takes 30 fm/c for a quarkonium to form and to become distinguishable from its excited states J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

67 Generalities on the quarkonium break-up cross section As aforementionned: σ break up r 2 meson 2S (and 3S states for Υ) should be more suppressed... provided that what propagates in the nucleus is already formed: τ f L Heisenberg inequalities tell us: τ onia f fm/c [in the meson rest frame obviously] At RHIC (200 GeV), for a particle with y = 0, γ = E beam,cms /m N 107! [= cosh(y beam ) = 5.36] It takes 30 fm/c for a quarkonium to form and to become distinguishable from its excited states At the LHC (5 TeV), still for a particle with y = 0, γ = E beam,cms /m N 2660! [= cosh(y beam ) = 8.58] It takes fm/c for a quarkonium to form and to become distinguishable from its excited states J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

68 Generalities on the quarkonium break-up cross section As aforementionned: σ break up r 2 meson 2S (and 3S states for Υ) should be more suppressed... provided that what propagates in the nucleus is already formed: τ f L Heisenberg inequalities tell us: τ onia f fm/c [in the meson rest frame obviously] At RHIC (200 GeV), for a particle with y = 0, γ = E beam,cms /m N 107! [= cosh(y beam ) = 5.36] It takes 30 fm/c for a quarkonium to form and to become distinguishable from its excited states At the LHC (5 TeV), still for a particle with y = 0, γ = E beam,cms /m N 2660! [= cosh(y beam ) = 8.58] It takes fm/c for a quarkonium to form and to become distinguishable from its excited states Naive high energy limit: σ break up π/mq 2? 0.5 mb for charmonia? J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

69 Baseline: absorption and npdfs in a collinear pqcd framework See e.g. E.G. Ferreiro, F. Fleuret, J.P.L., A. Rakotozafindrabe, PLB 680 (2009) 50 J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

70 Baseline: absorption and npdfs in a collinear pqcd framework See e.g. E.G. Ferreiro, F. Fleuret, J.P.L., A. Rakotozafindrabe, PLB 680 (2009) 50 Parton densities in nuclei are modified (EMC effect); J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

71 Baseline: absorption and npdfs in a collinear pqcd framework See e.g. E.G. Ferreiro, F. Fleuret, J.P.L., A. Rakotozafindrabe, PLB 680 (2009) 50 Parton densities in nuclei are modified (EMC effect); Mesons may scatter inelastically with nucleons in the nuclear matter; J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

72 Baseline: absorption and npdfs in a collinear pqcd framework See e.g. E.G. Ferreiro, F. Fleuret, J.P.L., A. Rakotozafindrabe, PLB 680 (2009) 50 Parton densities in nuclei are modified (EMC effect); Mesons may scatter inelastically with nucleons in the nuclear matter; If the meson is formed, this should be described by σ break up r 2 meson J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

73 Baseline: absorption and npdfs in a collinear pqcd framework See e.g. E.G. Ferreiro, F. Fleuret, J.P.L., A. Rakotozafindrabe, PLB 680 (2009) 50 Parton densities in nuclei are modified (EMC effect); Mesons may scatter inelastically with nucleons in the nuclear matter; If the meson is formed, this should be described by σ break up rmeson 2 Any differential cross section can then be obtained from the partonic one: dσ pa QX = dx 1 dx 2 g(x 1, µ f ) dz A Fg A (x 2, b, zb, µ f )J dσ gg Q+g S A ( b, za ) dy dp T d b dˆt dσ gg Q+g dˆt from any pqcd-like production model J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

74 Baseline: absorption and npdfs in a collinear pqcd framework See e.g. E.G. Ferreiro, F. Fleuret, J.P.L., A. Rakotozafindrabe, PLB 680 (2009) 50 Parton densities in nuclei are modified (EMC effect); Mesons may scatter inelastically with nucleons in the nuclear matter; If the meson is formed, this should be described by σ break up rmeson 2 Any differential cross section can then be obtained from the partonic one: dσ pa QX = dx 1 dx 2 g(x 1, µ f ) dz A Fg A (x 2, b, zb, µ f )J dσ gg Q+g S A ( b, za ) dy dp T d b dˆt dσ gg Q+g from any pqcd-like production model dˆt the survival probability for a QQ produced at the point ( r A, z A ) to pass through the target unscathed can parametrised as ( S A ( r A, z A ) = exp A σ break up z A ) d z ρ A ( r A, z) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

75 Baseline: absorption and npdfs in a collinear pqcd framework See e.g. E.G. Ferreiro, F. Fleuret, J.P.L., A. Rakotozafindrabe, PLB 680 (2009) 50 Parton densities in nuclei are modified (EMC effect); Mesons may scatter inelastically with nucleons in the nuclear matter; If the meson is formed, this should be described by σ break up rmeson 2 Any differential cross section can then be obtained from the partonic one: dσ pa QX = dx 1 dx 2 g(x 1, µ f ) dz A Fg A (x 2, b, zb, µ f )J dσ gg Q+g S A ( b, za ) dy dp T d b dˆt dσ gg Q+g from any pqcd-like production model dˆt the survival probability for a QQ produced at the point ( r A, z A ) to pass through the target unscathed can parametrised as ( S A ( r A, z A ) = exp A σ break up z A ) d z ρ A ( r A, z) the nuclear PDF (+ b dependence), F A g (x 1, r A, z A, µ f ), assumed to be factorisable in terms of the nucleon PDFs : S.R. Klein, R. Vogt, PRL 91 (2003) F A g (x 1, r A, z A ; µ f ) = ρ A ( r A, z A ) g(x 1 ; µ f ) (1 + [R A g (x, µ f ) 1]N ρa dz ρa ( r A, z) dz ρa (0, z) ) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

76 J/ψ suppression Nuclear modification factor d-au s =200 GeV NN RHIC, inclusive J/ψ 0.6 SAT - Fujii et al. COH.ELOSS - Arleo et al. CEM EPS09 NLO - Vogt 0.4 KPS - Kopeliovich et al. EXT EKS98 LO - Ferreiro et al. EXT EKS98 LO ABS - Ferreiro et al y Plot from the Sapore Gravis Network review: arxiv: p-pb s =5.02 TeV NN ALICE, inclusive J/ψ LHCb, prompt J/ψ EXT EPS09 LO - Ferreiro et al y J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

77 J/ψ suppression: energy independent? Nuclear modification factor d-au s =200 GeV NN RHIC, inclusive J/ψ 0.6 SAT - Fujii et al. COH.ELOSS - Arleo et al. CEM EPS09 NLO - Vogt 0.4 KPS - Kopeliovich et al. EXT EKS98 LO - Ferreiro et al. EXT EKS98 LO ABS - Ferreiro et al y Plot from the Sapore Gravis Network review: arxiv: p-pb s =5.02 TeV NN ALICE, inclusive J/ψ LHCb, prompt J/ψ EXT EPS09 LO - Ferreiro et al Most models except maybe the Eloss without shadowing predicted an increase of the suppression Now... although they were done with care the LHC results rely on a pp cross section interpolation J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30 y

78 A puzzle with excited states? PRL 109, (2012) Selected for a Viewpoint in Physics P H Y S I C A L R E V I E W L E T T E R S week ending 30 NOVEMBER 2012 Observation of Sequential Suppression in PbPb Collisions S. Chatrchyan et al.* (CMS Collaboration) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

79 ) m µ + - µ ) A puzzle with excited states? CMS PRL (2012), JHEP04(2014)103 2 Events / ( 0.05 GeV/c 800 µ η < 1.93 CM µ 700 p > 4 GeV/c T CMS pp s = 2.76 TeV -1 L = 5.4 pb data total fit background 2 Events / ( 0.1 GeV/c CMS PbPb s NN = 2.76 TeV Cent %, y < 2.4 µ p > 4 GeV/c T -1 L int = 150 µb data total fit background (GeV/c ) Mass(µ + µ ) [GeV/c ] [Υ(nS)/Υ(1S)] ij [Υ(nS)/Υ(1S)] pp 2S 3S PbPb 0.21 ± 0.07 (stat.) ± 0.02 (syst.) 0.06 ± 0.06 (stat.) ± 0.06 (syst.) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

80 ) m µ + - µ ) A puzzle with excited states? CMS PRL (2012), JHEP04(2014)103 2 Events / ( 0.05 GeV/c 800 µ η < 1.93 CM µ 700 p > 4 GeV/c T CMS pp s = 2.76 TeV -1 L = 5.4 pb data total fit background 2 Events / ( 0.1 GeV/c CMS PbPb s NN = 2.76 TeV Cent %, y < 2.4 µ p > 4 GeV/c T -1 L int = 150 µb data total fit background (GeV/c ) Mass(µ + µ ) [GeV/c ] In addition to QGP formation, differences between quarkonium production yields in PbPb and pp collisions can also arise from cold-nuclear-matter effects [21]. However, such effects should have a small impact on the double ratios reported here. Initial-state nuclear effects are expected to affect similarly each of the three Υ states, thereby canceling out in the ratio. Final-state nuclear absorption becomes weaker with increasing energy [22] and is expected to be negligible at the LHC [23]. [Υ(nS)/Υ(1S)] ij [Υ(nS)/Υ(1S)] pp 2S 3S PbPb 0.21 ± 0.07 (stat.) ± 0.02 (syst.) 0.06 ± 0.06 (stat.) ± 0.06 (syst.) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

81 ) m µ + - µ ) ) m µ + - µ A puzzle with excited states? CMS PRL (2012), JHEP04(2014)103 2 Events / ( 0.05 GeV/c 800 µ η < 1.93 CM µ 700 p > 4 GeV/c T CMS pp s = 2.76 TeV -1 L = 5.4 pb data total fit background 2 Events / ( 0.1 GeV/c CMS PbPb s NN = 2.76 TeV Cent %, y < 2.4 µ p > 4 GeV/c T -1 L int = 150 µb data total fit background 2 Events / ( 0.05 GeV/c µ η < 1.93 CM µ p > 4 GeV/c T CMS ppb s NN = 5.02 TeV -1 L = 31 nb data total fit background (GeV/c ) Mass(µ + µ ) [GeV/c ] (GeV/c ) In addition to QGP formation, differences between quarkonium production yields in PbPb and pp collisions can also arise from cold-nuclear-matter effects [21]. However, such effects should have a small impact on the double ratios reported here. Initial-state nuclear effects are expected to affect similarly each of the three Υ states, thereby canceling out in the ratio. Final-state nuclear absorption becomes weaker with increasing energy [22] and is expected to be negligible at the LHC [23]. [Υ(nS)/Υ(1S)] ij [Υ(nS)/Υ(1S)] pp 2S 3S PbPb 0.21 ± 0.07 (stat.) ± 0.02 (syst.) 0.06 ± 0.06 (stat.) ± 0.06 (syst.) ppb 0.83 ± 0.05 (stat.) ± 0.05 (syst.) 0.71 ± 0.08 (stat.) ± 0.09 (syst.) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

82 ) m µ + - µ ) ) m µ + - µ A puzzle with excited states? CMS PRL (2012), JHEP04(2014)103 2 Events / ( 0.05 GeV/c 800 µ η < 1.93 CM µ 700 p > 4 GeV/c T CMS pp s = 2.76 TeV -1 L = 5.4 pb data total fit background 2 Events / ( 0.1 GeV/c CMS PbPb s NN = 2.76 TeV Cent %, y < 2.4 µ p > 4 GeV/c T -1 L int = 150 µb data total fit background 2 Events / ( 0.05 GeV/c µ η < 1.93 CM µ p > 4 GeV/c T CMS ppb s NN = 5.02 TeV -1 L = 31 nb data total fit background (GeV/c ) Mass(µ + µ ) [GeV/c ] (GeV/c ) In addition to QGP formation, differences between quarkonium production yields in PbPb and pp collisions can also arise from cold-nuclear-matter effects [21]. However, such effects should have a small impact on the double ratios reported here. Initial-state nuclear effects are expected to affect similarly each of the three Υ states, thereby canceling out in the ratio. Final-state nuclear absorption becomes weaker with increasing energy [22] and is expected to be negligible at the LHC [23]. [Υ(nS)/Υ(1S)] ij [Υ(nS)/Υ(1S)] pp 2S 3S PbPb 0.21 ± 0.07 (stat.) ± 0.02 (syst.) 0.06 ± 0.06 (stat.) ± 0.06 (syst.) ppb 0.83 ± 0.05 (stat.) ± 0.05 (syst.) 0.71 ± 0.08 (stat.) ± 0.09 (syst.) If the effects responsible for the relative ns/1s suppression in ppb collisions factorise, they could be responsible for half of the PbPb relative suppression!!! J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

83 Comover-interaction model (CIM) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

84 Comover-interaction model (CIM) In a comover model, suppression from scatterings of the nascent ψ with comoving [no boost] particles S. Gavin, R. Vogt PRL 78 (1997) 1006; A. Capella et al.plb 393 (1997) 431 J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

85 Comover-interaction model (CIM) In a comover model, suppression from scatterings of the nascent ψ with comoving [no boost] particles S. Gavin, R. Vogt PRL 78 (1997) 1006; A. Capella et al.plb 393 (1997) 431 Stronger comover suppression where the comover densities are larger. For asymmetric collisions as proton-nucleus, stronger in the nucleus-going direction J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

86 Comover-interaction model (CIM) In a comover model, suppression from scatterings of the nascent ψ with comoving [no boost] particles S. Gavin, R. Vogt PRL 78 (1997) 1006; A. Capella et al.plb 393 (1997) 431 Stronger comover suppression where the comover densities are larger. For asymmetric collisions as proton-nucleus, stronger in the nucleus-going direction Rate equation governing the charmonium density at a given transverse coordinate s, impact parameter b and rapidity y, τ dρψ dτ (b, s, y) = σco ψ ρ co (b, s, y) ρ ψ (b, s, y) where σ co ψ is the cross section of charmonium dissociation due to interactions with the comoving medium of transverse density ρ co (b, s, y). J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

87 Comover-interaction model (CIM) In a comover model, suppression from scatterings of the nascent ψ with comoving [no boost] particles S. Gavin, R. Vogt PRL 78 (1997) 1006; A. Capella et al.plb 393 (1997) 431 Stronger comover suppression where the comover densities are larger. For asymmetric collisions as proton-nucleus, stronger in the nucleus-going direction Rate equation governing the charmonium density at a given transverse coordinate s, impact parameter b and rapidity y, τ dρψ dτ (b, s, y) = σco ψ ρ co (b, s, y) ρ ψ (b, s, y) where σ co ψ is the cross section of charmonium dissociation due to interactions with the comoving medium of transverse density ρ co (b, s, y). Survival probability from integration over time (with τ fin /τ 0 = ρ co (b, s, y)/ρ pp (y)) [ Sψ { σ co(b, s, y) = exp co ψ ρ co ρ (b, s, y) co ]} (b, s, y) ln ρ pp (y) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

88 Comover-interaction model (CIM) In a comover model, suppression from scatterings of the nascent ψ with comoving [no boost] particles S. Gavin, R. Vogt PRL 78 (1997) 1006; A. Capella et al.plb 393 (1997) 431 Stronger comover suppression where the comover densities are larger. For asymmetric collisions as proton-nucleus, stronger in the nucleus-going direction Rate equation governing the charmonium density at a given transverse coordinate s, impact parameter b and rapidity y, τ dρψ dτ (b, s, y) = σco ψ ρ co (b, s, y) ρ ψ (b, s, y) where σ co ψ is the cross section of charmonium dissociation due to interactions with the comoving medium of transverse density ρ co (b, s, y). Survival probability from integration over time (with τ fin /τ 0 = ρ co (b, s, y)/ρ pp (y)) [ Sψ { σ co(b, s, y) = exp co ψ ρ co ρ (b, s, y) co ]} (b, s, y) ln ρ pp (y) ρ co (b, s, y) connected to the number of binary collisions and dn pp ch /dy J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

89 Comover-interaction model (CIM) In a comover model, suppression from scatterings of the nascent ψ with comoving [no boost] particles S. Gavin, R. Vogt PRL 78 (1997) 1006; A. Capella et al.plb 393 (1997) 431 Stronger comover suppression where the comover densities are larger. For asymmetric collisions as proton-nucleus, stronger in the nucleus-going direction Rate equation governing the charmonium density at a given transverse coordinate s, impact parameter b and rapidity y, τ dρψ dτ (b, s, y) = σco ψ ρ co (b, s, y) ρ ψ (b, s, y) where σ co ψ is the cross section of charmonium dissociation due to interactions with the comoving medium of transverse density ρ co (b, s, y). Survival probability from integration over time (with τ fin /τ 0 = ρ co (b, s, y)/ρ pp (y)) [ Sψ { σ co(b, s, y) = exp co ψ ρ co ρ (b, s, y) co ]} (b, s, y) ln ρ pp (y) ρ co (b, s, y) connected to the number of binary collisions and dn pp ch /dy σ co ψ fixed from fits to low-energy AA data N. Armesto, A. Capella, PLB 430 (1998) 23 [ σ co J/ψ = 0.65 mb for the J/ψ and σ co ψ(2s) = 6 mb for the ψ(2s)] J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

90 CIM result vs. data Theory: E.G. Ferreiro arxiv: ; Plot from the SGNR review: arxiv: ; PHENIX PRL 111, (2013); ALICE JHEP 02 (2014) 072 / [ψ(2s)/j/ ψ] [ψ(2s)/j/ ψ] pp ppb 1.6 d-au s =200 GeV NN p-pb s =5.02 TeV NN ALICE, inclusive J/ψand ψ(2s) PHENIX, inclusive J/ψand ψ(2s) N coll COMOV - Ferreiro Given that all the other models discussed so far predict no difference and that the comover cross sections from AA data at SPS were re-used, this is encouraging... y J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

91 Part VI Competing hot nuclear effects vs. the melting? J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

92 Competing hot nuclear effects vs. the melting? Opposite effect at high energy?: recombination/regeneration J/ Production Probability ψ 1 statistical regeneration sequential suppression Energy Density J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

93 Competing hot nuclear effects vs. the melting? Opposite effect at high energy?: recombination/regeneration J/ Production Probability ψ 1 statistical regeneration sequential suppression Energy Density Way out: p T cut: reduce recombination; look at b b: less recombination J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30

94 Competing hot nuclear effects vs. the melting? Opposite effect at high energy?: recombination/regeneration J/ Production Probability ψ 1 statistical regeneration sequential suppression Energy Density Way out: p T cut: reduce recombination; look at b b: less recombination Competing suppression effect as well: comovers (within a normal hadron phase) J.P. Lansberg (IPN Orsay, Paris-Sud U.) Physics of ultrarelativistic heavy-ion collisions September 29, / 30