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What can dileptons tell us about non-equilibrium QCD dynamics at RHIC?

What can dileptons tell us about non-equilibrium QCD dynamics at RHIC?. Gojko Vujanovic Thermal Photons and Dileptons Workshop 2014 Brookhaven National Laboratory August 21 st 2014. Outline. Motivation Hydrodynamics and hadronic observables Our model: Thermal Sources of Dileptons

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What can dileptons tell us about non-equilibrium QCD dynamics at RHIC?

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  1. What can dileptons tell us about non-equilibrium QCD dynamics at RHIC? Gojko Vujanovic Thermal Photons andDileptons Workshop 2014 Brookhaven National Laboratory August 21st 2014

  2. Outline Motivation • Hydrodynamics and hadronic observables Our model: Thermal Sources of Dileptons • QGP Rate (w/ viscous corrections) • Hadronic Medium Rates (w/viscous corrections) Dileptons & Out-of-Equilibrium Evolution • Effects of initial condition for the shear-stress tensor on vn • Effects of the relaxation time of the shear-stress tensor on vn • Effects of temperature dependent shear viscosity in the early phase on vn Conclusion and outlook

  3. How do we know that URHIC are creating a medium? • Hadronic observables played a crucial role in understanding properties of the medium created at RHIC/LHC. • MUSIC+MC Glauber: RHIC LHC Schenke, Jeon, and Gale, Phys. Rev. C 85, 024901 (2012) Schenke, Jeon, and Gale, Phys. Lett. B 702, 59 (2011)

  4. 3+1D Viscous Hydrodynamics • Israel-Stewart viscous hydrodynamics equations: • Lattice QCD EoS [P. Huovinen and P. Petreczky, Nucl. Phys. A 837, 26 (2010).] (s95p-PCE160) • Out-of-equilibrium part of Tmn, pmn, is less constrained by hadronic observables and is thus less known.

  5. 3+1D Viscous Hydrodynamics • Israel-Stewart viscous hydrodynamics equations: • Goals: • To study the effects of initial conditions [pmn (t0)] rel. to Bjorken flow Navier-Stoke value. • To explore the effects ofa transport coefficient [tp]. • We are changing one parameter at a time while keeping the others to their default values:

  6. 3+1D Viscous Hydrodynamics • Our choice of temperature dependent shear viscosity over entropy: • Goals: • To explore the consequences introducing a linear h/s(T) in the QGP phase: does the slope change flow coefficients? • To explore the consequences introducing quadratic h/s(T) in the QGP phase: does the shape affect the anisotropic flow? • Keep all other initial and freeze-out conditions set by MC-Glauber model [see Schenke, Jeon, and Gale, Phys. Rev. C 85, 024901 (2012)].

  7. Limited sensitivity of hadronic observables • Hadronic observables at RHIC:modest sensitivity to non-eq. init. cond. [pmn(t0)] and to departures from equilibrium in the evolution via tp. 20-40% 20-40%

  8. Limited sensitivity of hadronic observables • Hadronic observables at RHIC:modest sensitivity to non-eq. init. cond. [pmn(t0)] and to departures from equilibrium in the evolution via tp. 20-40% 20-40% x=y=2.625fm, z=0; in fluid rest frame x=y=2.625fm, z=0; in fluid rest frame • Reason: Hadrons are emitted at late times => sensitive to conditionson the freeze-out surface. Note the size of pmnthere.

  9. Limited sensitivity of hadronic observables • A subtle sensitivity to a temperature dependent h/s in the QGP phase, for energies probed by RHIC 20-40% 20-40% • Reason: Hadrons are emitted at late times => sensitive to conditionson the freeze-out surface.

  10. Motivation to study dilepton flow • Dileptons (and photons) are sensitive to non-equilibrium initial conditions [pmn(t0)] and to departures from equilibrium in the evolutiontp. • Also, they are directly sensitive to the temperature dependence of the shear viscosity, in particular that of the QGP. • Question: How much are dileptonssensitive topmn(t0),tp, & h/s(T)?

  11. Viscous corrections: HM rates • The rate involves (incl. VDM): • Self-Energy[Eletsky, et al., Phys. Rev. C, 64, 035202 (2001)] • Viscous extension to thermal distribution function • Therefore, the self-energy is • B2 was computed: G. Vujanovic et al., Phys. Rev. C 89, 034904 (2014) Israel-Stewart dn

  12. Viscous Corrections: QGP rates • Viscous correction to the Born rate in kinetic theory rate • Going beyond Israel- Stewart form: General form of dist. Function • G is computed using Boltzmann equation for a gas of massless particles with constant cross-section. Radial part Angular part

  13. Anisotropic Flow • To describe the flow of dileptons we use the usual Fourier decomposition, i.e. flow coefficients vn (per event): z • Flow coefficients • Two important notes: • Within an event: vn’s are a yieldweighted average of the different sources (e.g. HM, QGP, …). • Averaging over events: the flow coefficients (vn) are computed x

  14. Effects of a non-zero initial pmn 20-40% 20-40% x=y=2.625fm, z=0; in fluid rest frame

  15. Effects of a non-zero initial pmn 20-40% 20-40% x=y=2.625fm, z=0; in fluid rest frame

  16. Effects of relaxation time tp 20-40% 20-40% x=y=2.625fm, z=0; in fluid rest frame • .

  17. Effects of relaxation time tp 20-40% 0 20-40% x=y=2.625fm, z=0; in fluid rest frame

  18. Effects of h/s(T) in the QGP 20-40% 0

  19. Effects of h/s(T) in the QGP P. Huovinen and P. Petreczky, Nucl. Phys. A 837, 26 (2010).

  20. Effects of h/s(T) in the QGP

  21. Effects of h/s(T) in the QGP

  22. Effects of h/s(T) in the QGP

  23. Effects of h/s(T) in the QGP 20-40% 0

  24. Higher flow harmonics 20-40% 20-40% • Higher flow harmonics are affected by pmn(t0),tp, & h/s(T). • Higher flow harmonics, at the current M, are rather large, which is encouraging from an experimental stand point. 20-40%

  25. Higher flow harmonics 20-40% 20-40% • Higher flow harmonics are affected by pmn(t0),tp, & h/s(T). • Higher flow harmonics, at the current M, are rather large, which is encouraging from an experimental stand point. 20-40%

  26. Higher flow harmonics • Photon-like behaviour • Dileptons provide a unique opportunity to exp’t constrain pmn(t0), tp, & h/s(T)… what about quadratic h/s(T)? 20-40% 20-40% 20-40%

  27. Higher flow harmonics for quadratic h/s(T) • Difficult to distinguish between linear and quadratic h/s(T) at low M. • For v2 shape is similar and only normalization changes. • For v3 and v4, vice versa => What about higher M? 20-40% 20-40% 20-40%

  28. Can we distinguish lin. vs quad. QGP h/s(T)? • The shape in v2is noticeably different though normalization (i.e. signal) is much smaller. • More studies are needed to optimize the magnitude of signal and effect; those are currently underway, so stay tuned! 20-40% 20-40% Combined 20-40%

  29. Bottom line • Dileptons & hadronic observables together can reduce degeneracy in “free” hydrodynamic parameters. 20-40% 20-40% 20-40%

  30. Conclusions & Outlook • Conclusion: • Dileptons provide us with a new handle on : • medium’s departure from equilibrium (initial pmn) early on, • the medium’s capacity to relax towards Navier-Stokes (tp), & • the temperature dependent h/s in the QGP phase & around Tc. • Experimental measurements of dilepton’s higher flow harmonics present a new opportunity to tightly constrain these parameters. • As hadronicobservables (at RHIC) are almost insensitive to these parameters, electromagnetic probes play a more central role in both our understanding of QCD’s out-of-equilibrium properties, and possible extraction of transport coefficients. • Outlook: • The inclusion of open charm hadrons is currently in progress. • Making predictions for: LHC, S-PHENIX, STAR’s m± telescope detector • Improving the HM rates (w/ R. Rapp), QGP rates (w/ M. Laine)

  31. Thank you

  32. Momentum anisotropy near freeze-out: Tfo±5 MeV

  33. Higher flow harmonics for quadratic h/s(T) 20-40% 20-40% 20-40%

  34. G(k0/T) • Viscous correction to the Born rate in kinetic theory rate

  35. Dilepton higher flow harmonics: Effect of pmn 20-40% 20-40% • Higher sensitivity of higher flow harmonics to pmn(t0),tp, & h/s(T). Expected as any viscous effect will mostly affect smaller anisotropies. • Only v2(M) and possibly v3(M) could be measured in the near future. 20-40%

  36. Dilepton higher flow harmonics: Effect of tp 20-40% 20-40% • Higher sensitivity of higher flow harmonics to pmn(t0),tp, & h/s(T). Expected as any viscous effect will mostly affect smaller anisotropies. • Only v2(M) and possibly v3(M) could be measured in the near future. 20-40%

  37. Dilepton higher flow harmonics: Effect of h/s(T) 20-40% 20-40% • Higher sensitivity of higher flow harmonics to pmn(t0),tp, & h/s(T). Expected as any viscous effect will mostly affect smaller anisotropies. • Only v2(M) and possibly v3(M) could be measured in the near future. 20-40%

  38. Effects of quadratic h/s(T) in the QGP 20-40% 20-40% • Higher sensitivity of higher flow harmonics to pmn(t0),tp, & h/s(T). Expected as any viscous effect will mostly affect smaller anisotropies. • Only v2(M) and possibly v3(M) could be measured in the near future. 20-40%

  39. Effects on pion yield 20-40% 20-40% 20-40% 20-40%

  40. Photon higher flow harmonics: tp and init. pmn 20-40% 20-40% Photons: Jean-François Paquet 20-40% 20-40%

  41. More on yield and v2vs pT 20-40% 20-40% 20-40% 20-40%

  42. Effects on dilepton yield 20-40% 20-40% 20-40% 20-40% [GeV-1] [GeV-1]

  43. Born, HTL, and Lattice QCD Ding et al., PRD 83 034504

  44. Viscous corrections to HM rates • Two modifications are plausible: • Self-Energy ; ;

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