How can resonances be used to explore dense and hot matter :

1. How can resonances be used to explore dense and hot matter : J. Aichelin Subatech/ Nantes/ France Austin, March 5-7

2. Physics to study Detector Austin, March 5-7

3. A lot of very interesting physics is taking place in the plasma • I will not discuss this physics • Rather I will discuss the question what information the resonances carry on the physics close the phase transition • More concrete: Having detectors only at T=μ= 0, how can they • observe the physics at T> 120 MeV and μ= several hundreds of MeV ? • C. Hartnack, H. Petersen, J. Steinheimer, S. Vogel, M. Bleicher • Centrality dependence of resonances is different than that of stable hadrons. • Resonances are not sensitive to the phase transition point • What information carry the resonances on high baryon density high temperature hadronic matter Austin, March 5-7

4. We expect that some resonances cannot be identified because the decay products rescatter but do otherwise behave resonances like all the stable particles? Austin, March 5-7

5. Centrality Dependence of Hadron Multiplicities In reality more complicated (EPOS) -shape fluctuations, finite particle number -some of the participants scatter only once (cannot equilibrate) separation of core and corona The Model Core – corona model Assumption: Nucleons with 1 initial coll: corona Nucleons with more: core Calculated in Glauber Model Austin, March 5-7

6. Phys.Rev.C79:064907 Mi (Npart) follows a very simple law The Model Calculation for Cu+Cu without any further input Austin, March 5-7

7. 200 AGeV Au+Au Cu+Cu Theory=lines works for non strange and for strange hadrons at 200 (and 62 and 17.3) AGeV Multiplicities Cu+Cu: completely predicted from Au+Au and pp Austin, March 5-7

8. Average pT <pT> = ficore(Npart)<pT>core + (1-ficore(Npart))<pT>corona Average pt p, Λ, Φ p, K, π Centrality dep. Of <pT > due to core-corona and not necessarily due to collective flow Particles with similar mass have widely different pT Austin, March 5-7

9. Core-corona single particle spectra STAR [0,5%] PHENIX Spectra [70-80%] Austin, March 5-7

10. K* Resonances behave differently as stable particles K* Austin, March 5-7

11. Can this be a consequence of rescattering ? no final state int p K+ Final state int Spectra K- ap Yes, there is final state interaction but only at low pT where no data exist Austin, March 5-7

12. First conclusion: The centrality dependence of spectra of resonances is different as compared to stable particles This cannot be due to rescattering Detailed investigation would be necessary but very time consuming Austin, March 5-7

13. Can resonancens measure the freeze out energy density in hydrodynamical approaches? Reasoning: Very late freeze out: all resonances can be identified Early freeze out: decay products rescatter Austin, March 5-7

14. hadronic decay K f signal measured late decay p K p L* re-scattering K signal lost p kinetic freeze-out L* p t signal measured K K regeneration e+ signal measured early decay f e- leptonic decay time Resonances (I) If we know how many resonances are produced (thermal model) the ratio of measured reconstructed /produced resonances allows to test the expansion phase If this ratio <1 we can use this information to understand the interaction of the decay products with the other particles: Information on ρ > 0 Austin, March 5-7

15. Resonances (II) Bleicher and Aichelin Phys. Lett. B530 (2002) 81. Bleicher and Stöcker J. Phys.G30 (2004) 111. Life-time [fm/c] : K(892) = 4.0 S(1385) = 5.7 L(1520) = 13  (1020) = 45 STAR Markert SQM07 This approach has been successful at RHIC: Resonances behave like predicted by the simulation program There is life after chemical freeze out!! The shorter the lifetime the more they should be suppressed but there is also recreation Austin, March 5-7

16. URQMD with hydro describes the resonances reasonably Austin, March 5-7

17. Multiplicity of Resonances are reasonably well reproduced but They are completely insensitive to the freeze out density in the Hydro calculations K* Reason : the resonance are formed and decay over a long time. No memory effect on transition Austin, March 5-7

18. There are other particles which are sensitive to the energy density at freeze out : baryons and anti baryons Reason: Baryons annihilate with antibaryons N+Nbar – many mesons Inverse process very improbable No detailed balance as for resonances All ratios point to a freeze out at a TCF of about 145 MeV This explains the deficit of protons at LHC Austin, March 5-7

19. Second conclusion: Resonances are not sensitive to the freeze out when in the simulation programs hadrons are produced via a Cooper Frye formula Several generations of resonances are produced and decay and only at the end of the expansion rescattering of the decay products make a identification impossible and therefore the apparent deficit appears. Austin, March 5-7

20. Can we study high baryon densities with resonance? Austin, March 5-7

21. Freeze out curve in the thermodynamical model 30 AGeV Ekin = 30 AGeV Highest net baryon density Quite high energy density Strongly interacting system of mesons and baryons Resonance dynamics becomes very important Cleymans SQM07 Austin, March 5-7

22. Resonances (I) Can this be extended to 30 AGeV ? Vogel, Petersen, Aichelin, Bleicher ρ/ρ0 Reaction scenario At 11 AGeV ρMax at 4 fm/c ρMax/2 at 8 fm/c at 30 AGeV ρMax at 2.2 fm/c ρMax/2 at 4.4 fm/c ρmax/2 ρ/ρ0 2.1 Time [fm/c] UrQMD Austin, March 5-7

23. Resonances (II) coll 11 AGeV Δ decay Δ ρ < ρ0/2 coll At high density reabsorption is much more probably than decay Only if the system is at ρ < ρmax/4 decay dominates 30 AGeV Δ decay Austin, March 5-7 ρ < ρ0/2

24. Resonances (III) URQMD In reality even worse: the decay products may still scatter Only resonances which are created after around 20 fm/c have a chance to be seen in the detectors. Δ resonance is sensitive to the very final phase of the reaction No information on what has happened before 20 Austin, March 5-7

25. Resonances (III) This is not specific for the Δ but similar for all resonances Resonances measure system properties for t>20fm/c or densities around and below ρ0 ω ω 25 K* Σ* K* Σ Austin, March 5-7 25 150 25

26. Distribution of the density at the production vertex Almost all resonances which are seen finally are produced at very low baryon density Austin, March 5-7

27. Dileptons (I) EM probes have no final state interaction coll Au+Au There are two principal sources for dileptons Particle annihilation (either q’s or h’s) Particle decay (ρ,η,ω, Δ,π) The first process is similar for quark matter and for hadronic matter (Kämpfer) For the second we take the ρ decay as example 2 AGeV decay coll 11 AGeV decay At high energy collision loss dominates during the high density phase, only later decay becomes important coll 30 AGeV decay Austin, March 5-7

28. Dileptons (II) Only late time ρ’s have a change to decay (and not to be reabsorbed) This translates into a density: most of the ρ which decay come from low density coll decay 2AGeV coll decay 11AGeV Dileptons come from ρ’s which are produced at a quite low density Despite of being a leptonic probe it does not carry information on the high density phase Going from 2AGeV to 30 AGeV <ρB> decreases due to π+πρ coll decay 30AGeV ρB/ρ0 Austin, March 5-7 0 1 3 6 9

29. Dileptons (III) Although not sensitive to high density dileptons and resonance measurement may discover very interesting physics on in medium modification of hadron properties resonance production in a hadronic environment HADES C+C 2 AGeV Example: All simulation programs overpredict the dilepton yield in the ω mass region if they use as input free cross sections free hadron masses Thomere et al. nucl-th/0702004 Austin, March 5-7

30. Conclusion All resonance yields are sensitive to low density nuclear physics Special kinematical conditions may enhance the density to which they are sensitive (Vogel) Even dileptons do not carry information of on the high density region This is consistent with the independence of the resonance yield on the freeze out energy density Austin, March 5-7

31. Stable Particles (I) Weber et al. nucl-th/0209079 Two standard simulation codes give about the same multiplicity: π dynamics not really under control (already true at 2 AGeV) Resonances ? Austin, March 5-7

32. Decrease of baryon-chemical potential: transition from baryon-dominated to meson- dominated matter Stable particles (II) SQM04 The more strange the particle the more we have to learn still how they are produce and where they come from Austin, March 5-7

33. Stable particles (III) Also rapidity and pt distribution quite well reproduced This is good news and bad news at the same time: Good News: Basic dynamics of the reaction is under control Bad News: The result of the simulations for stable particles does not depend sensitively on the differences in the programs (early times): - different cross section parametrization for little known or unknown cross sections - different string fragmentation scenario at different densities The more strange the particle (Ω,Ξ) the more these differences play a role Epos = string decay UrQMD = hadronic rescattering Austin, March 5-7

34. The most reliable messenger from the high density zone will be charmed hadrons They play the same role as the strange hadrons have played at SIS energies They are probably even more interesting But also more difficult to detect We have a lot of things to do before we can even start to make predictions with transport theories Austin, March 5-7

35. Percentage of reconstructible baryon resonances coming from >2ρ0 Austin, March 5-7

36. Fraction of reconstructible resonances Austin, March 5-7

37. A closer look reveals that those resonances produced at higher baryon density have a higher momentum Triggering in high momenta on can enhance the probability to see early (at higher baryon density) produced resonances Austin, March 5-7

38. Cross section at E= 30 AGeV for D(cbar) corresponds to that for K+ at 700 AMeV ! (but due to high luminosity they will be copiously produced) Cassing Cassing et al. NPA786 (2007) 183 Cassing Austin, March 5-7

39. Good news: a) D meson mass does practically not change its mass b) Probably the D meson becomes unstable in the plasma Pion dressing No pion dressing Mocsy SQM07 Tolos nucl-th/0509054 c) hadronic phase: Rescattering of D-mesons plasma creation: Coalescence at freeze out No reason why pt spectrum should be similar Austin, March 5-7

40. Good News: d)Strong increase with yield (RAA) measures energy concentration in elementary reactions or signals a new reaction mechanism Cassing et al. NPA786 (2007) 183 Cross section Compilation Bad News: pN  D+Λc (dominant) unknown pN D/D+X only known at irrelevant NPA691 (2001) 753 Austin, March 5-7

41. Bad News (II) We have to have (indirect) experimental info on the σ (D(c) +N  π+Λc) Not hopeless: We are at a high net baryon density: Rescattering for D(cbar) and D(c) is most different WHY: a) e+ (e-) c (cbar) because BR ratios are different: b) K- π+ (K- π+ ) c (cbar) but (charm – Λc ) Thus without knowing how many charmed quarks are bound in Λc we should avoid to make prediction which would be nothing else than speculations. Austin, March 5-7

42. If the D-mesons are that complicated why not the J/Ψ? There are other dangers on the way to the detector: Rescattering J/Ψ + X  D(c) +D(cbar) +Y. pA collisions reveil only the X=p cross section In an expanding system X=ρ and X = N* are even more frequent X=N calculated by Barnot + Peskin in leading twist (NPB156,391) X=π by Gousset et al. (PRD65, 014005) In leading twist: Dissociation cross section is NOT a constant matrix element time phase space but depends on G(x), the gluon momentum distribution in the hadron p π Austin, March 5-7

43. Collective Variables : Softest point Rischke et al. (nucl-th/9505015) … Minimum of the excitation fct of the collective in-plane flow reflects the existence of a softest point (local minimum of P/ε as a fct of ε) and therefore for a long mixed phase. UrQMD: a minimum is a natural consequence of the energy dependence of elastic pp dσ/dΩ and of resonance production. same observation allows for different interpretations Austin, March 5-7

44. Conclusions The probably very rich physics close to the chiral phase transition is difficult to assess: Stable particles and resonances are produced late and are rather insensitive to what happens before. Dileptons from particle decay are also produced very late and carry no information on the high density. They reveal nevertheless very interesting and yet unknown physics. Charmed mesons will be sensitive to the high density zone Results can only interpreted after a)the elementary production cross sections b) the role of the Λc and c) Ψ+X D(c) +D(cbar)+Y have been experimentally explored. Austin, March 5-7