Direct Photons in Heavy-Ion Collisions from Microscopic Transport Theory and Fluid Dynamics

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1 HGS-HIRe Helmholtz Graduate School for Hadron and Ion Research Direct Photons in Heavy-Ion Collisions from Microscopic Transport Theory and Fluid Dynamics Bjørn Bäuchle, Marcus Bleicher The UrQMD-Group Based on [arxiv: (hep-ph)] Winter Workshop on Nuclear Dynamics Jan 7 th 2010

2 Collaborators The UrQMD-Group Marcus Bleicher, Horst Stöcker, Gerhard Burau, Michael Mitrovski, Elvira Santini, Bjørn Bäuchle, Hannah Petersen, Tim Schuster, Thomas Lang, Stephan Endres, Jan Steinheimer-Froschauer, Gunnar Gräf, Timo Spielmann Sponsors HGS-HIRe Helmholtz Graduate School for Hadron and Ion Research

3 Table of Contents Direct Photons UrQMD and Hydro UrQMD and UrQMD + Hydro Photons from the model Results Epilogue Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

4 Interactions with photons Photons are the gauge bosons of electromagnetic interactions. Photons do not interact strongly Small production cross-section, but small rescattering rate Photons from hadronic decays make 97 % of all photons Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

5 Interactions with photons Photons are the gauge bosons of electromagnetic interactions. Photons do not interact strongly Small production cross-section, but small rescattering rate Photons from hadronic decays make 97 % of all photons Direct Photons All the photons that do do not come from hadronic decays are called direct photons. Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

6 Direct Photon Experiments Helios, WA 80, CERES (SPS) upper limits WA 93 (SPS) no results WA 98 first measurements at SPS PHENIX (RHIC) various results STAR (RHIC) spectra expected soon Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

7 Direct Photon Experiments Helios, WA 80, CERES (SPS) upper limits WA 93 (SPS) no results WA 98 first measurements at SPS PHENIX (RHIC) various results STAR (RHIC) spectra expected soon Photons from hadronic decays make 97 % of all photons Uncertainties in hadron yield significantly change direct photon yield Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

8 Existing models High p : yields calculated by NLO-pQCD 1. Important at RHIC- and LHC-energies! 1 E.g. Aurenche, Fontannaz et. al, PRD 73, (2006) Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

9 Existing models High p : yields calculated by NLO-pQCD 1. Important at RHIC- and LHC-energies! Hydrodynamics: naturally implement phase transition (QGP HG): e.g. Turbide, Liu, Vitev, Haglin, Srivastava 2 1 E.g. Aurenche, Fontannaz et. al, PRD 73, (2006) 2 Turbide, Rapp and Gale, PRC 69, (2004); Turbide, Gale et al., PRC 72, (2005); Liu and Werner, arxiv: [hep-ph]; Vitev and Zhang, arxiv: [hep-ph]; Haglin, PRC 50, 1688 (1994); Haglin, JPG 30, L27 (2004), Chatterjee et al., Nucl. Phys. A 830 (2009) 503C Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

10 Existing models High p : yields calculated by NLO-pQCD 1. Important at RHIC- and LHC-energies! Hydrodynamics: naturally implement phase transition (QGP HG): e.g. Turbide, Liu, Vitev, Haglin, Srivastava 2 Transport: Study non-equilibrium effects and effects from dilute system: e.g. Dumitru, Huovinen, Li, Bratkovskaya 3 1 E.g. Aurenche, Fontannaz et. al, PRD 73, (2006) 2 Turbide, Rapp and Gale, PRC 69, (2004); Turbide, Gale et al., PRC 72, (2005); Liu and Werner, arxiv: [hep-ph]; Vitev and Zhang, arxiv: [hep-ph]; Haglin, PRC 50, 1688 (1994); Haglin, JPG 30, L27 (2004), Chatterjee et al., Nucl. Phys. A 830 (2009) 503C 3 Dumitru, Bleicher, Bass, Spieles, Neise, Stöcker and Greiner, PRC 57, 3271 (1998); Huovinen, Belkacem, Ellis and Kapusta, PRC 66, (2002); Li, Brown, Gale and Ko, arxiv:nucl-th/ ; Bratkovskaya and Cassing, NPA 619, 413 (1997); Bratkovskaya, Kiselev and Sharkov, arxiv: [nucl.th] Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

11 UrQMD Non-equilibrium transport model Hadrons and resonances up to m = 2.2 GeV String excitation and fragmentation Cross sections are parametrized via AQM or calculated by detailed balance pqcd hard scattering at high energies UrQMD Ultra-Relativistic Quantum Molecular Dynamics Generates full space-time dynamics of hadrons and strings Version 3.3 out now! Go to Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

12 UrQMD+Hydro (new in u3.3) Non-equilibrium initial conditions from UrQMD Switching to ideal relativistic one-fluid hydrodynamics when the nuclei have passed each other Hydro evolution with variable Equation of State Transition to cascade when ǫ < 730 MeV/fm 3 ( 5ǫ 0 ) in all cells seperately for all z (gradual)... in complete system (isochronous) Rescatterings and decays with hadronic cascade (UrQMD) See also Petersen et al. Phys. Rev. C 78 (2008) Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

13 Equations of State Hadron Gas Includes all particles from UrQMD no phase transition Bag Model MIT Bag Model First Order Phase Transition at T C = 170 MeV Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

14 Photons from the model Both models π + π γ + ρ, π + ρ γ + π Only Cascade Cross-sections from Kapusta, Lichard & Seibert (PRD 44 (1991) 2774) π + π γ + η, π + η γ + π, π + π γ + γ Only Hydro Parametrizations from Turbide, Rapp & Gale (PRC 69 (2004) ) π+k γ+k, π+k γ+k, ρ+k γ+k, K +K γ+π Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

15 Comparison of p -spectra 10 1 WA98 Pb+Pb 158 AGeV Pure UrQMD Isochronous transition Pb+Pb 158 AGeV b < 4.5 fm y cm < Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

16 Comparison of p -spectra 10 1 WA98 Pb+Pb 158 AGeV Pure UrQMD Hybrid, Hadron gas EoS Isochronous transition Pb+Pb 158 AGeV b < 4.5 fm y cm < Hybrid and pure cascade model produce similar spectra Hadronic spectra too low (no pqcd) Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

17 Comparison of p -spectra WA98 Pb+Pb 158 AGeV Pure UrQMD Hybrid, Hadron gas EoS Hybrid, Bag Model EoS Isochronous transition Pb+Pb 158 AGeV b < 4.5 fm y cm < Hybrid and pure cascade model produce similar spectra Hadronic spectra too low (no pqcd) Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

18 The dense stage pre-equilibrium (t < 1.4 fm) hydro (1.4 fm < t 13.3 fm) post-freeze-out (t > 13.3 fm) Hadron gas EoS Isochronous transition Pb+Pb 158 AGeV b < 4.5 fm, y cm < Pre-equilibrium dominates at high p Hydro and Afterburner contribute similarly For BM-EoS, hydro dominates up to p 3.5 GeV Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

19 Closer look: high p -photons temission [fm] sum πρ γπ ππ γρ Processes inv. η 158 AGeV b < 4.5 fm y cm < 0.5 UrQMD Flattening at high p corresponds to earlier emission times Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

20 Closer look: high p -photons temission [fm] sum πρ γπ ππ γρ Processes inv. η 158 AGeV b < 4.5 fm y cm < 0.5 UrQMD p γ [GeV] Flattening at high p corresponds to earlier emission times thermal emission from non-thermalized system! Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

21 Closer look: high p -photons sum Photon production at leading πρlog γπ ππ γρ Processes Annihilationinv. η Compton Photons 6 are completely out of equilibrium 2. At 16 leading log we have p µ 12 quark qµ photon temission [fm] from Kevin Dusling s talk (Tuesday) Their spectra only appears thermal since the quarks creating the photons are thermal so distribution of quarks matches spectra of photons AGeV b < 4.5 fm y cm < 0.5 UrQMD p γ [GeV] Flattening at high p corresponds to earlier emission times thermal emission from non-thermalized system! Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

22 Closer look: high p -photons sum Photon production at leading πρlog γπ ππ γρ Processes Annihilationinv. η Compton Photons 6 are completely out of equilibrium 2. At 16 leading log we have p µ 12 quark qµ photon temission [fm] from Kevin Dusling s talk (Tuesday) Their spectra only appears thermal since the quarks creating the photons are thermal so distribution of quarks matches spectra of photons AGeV b < 4.5 fm y cm < 0.5 UrQMD p γ [GeV] Flattening at high p corresponds to earlier emission times thermal emission from non-thermalized system! Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

23 Closer look: high p -photons sum Photon production at leading πρlog γπ ππ γρ Processes Annihilationinv. η Compton Photons 6 are completely out of equilibrium 2. At 16 leading log we have p µ 12 quark qµ photon temission [fm] from Kevin Dusling s talk (Tuesday) Their spectra only appears thermal since the quarks creating the photons are thermal so distribution of quarks matches spectra of photons AGeV b < 4.5 fm y cm < 0.5 UrQMD p γ [GeV] source not thermalized Flattening at high p corresponds to earlier emission times thermal emission from non-thermalized system! My Take: γ-spectra thermal even though Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

24 Taking ρ off its pole (on-off)/off m ρ fixed m 100 ρ Breit-Wigner UrQMD 10 Pb+Pb 158 AGeV b < 4.5 fm y c.m. < π ± π γρ π ± π 0 γρ ± π ± π 0 γρ ± π ± π γρ In channels that produce ρ-mesons: cross-section changes, channels also possible for s < m 0 ρ! Affects only very low p γ Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

25 Gradual transition Gradual Transition Isochronous Transition UrQMD+Hydro HadronGas 158 AGeV b < 4.5 fm y < preliminary No significant change between gradual and isochronous transition Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

26 Contribution of stages sum before hydro hydro after hydro UrQMD+Hydro HadronGas Isochronous 158 AGeV b < 4.5 fm y < preliminary Isochronous Transition: Hydro and post-transition contribute similarly Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

27 Contribution of stages sum before hydro hydro after hydro UrQMD+Hydro HadronGas Gradual 158 AGeV b < 4.5 fm y < preliminary Gradual Transition: hydro contribution enhanced, post-transition reduced! Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

28 Future: FAIR UrQMD preliminary sum πρ γπ ππ γx πη γπ 45 AGeV min. bias y cm < Very thermal spectrum, no high-p -tail Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19

29 Conclusion & Summary Hadronic Sources below Data at SPS Bag Model better, not sufficient pqcd! Emission from unthermalized system is exponential ρ-mass fixed or Breit-Wigner 10 % effect Gradual / isochronous transition: no effect on final spectra FAIR: No surprises expected Thanks for this Workshop, Scott and Roy! Bjørn Bäuchle, ITP Frankfurt Direct Photons in Heavy-Ion Collisions WWND / 19