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A Promising Solution to the Elliptic Quench Puzzle at RHIC

A Promising Solution to the Elliptic Quench Puzzle at RHIC. William A. Horowitz Columbia University August 4-5, 2005. What is the Puzzle? – Data. Na ïvely combine published R AA (p T ) and v 2 (p T ) data Preliminary PHENIX p 0 data Data centrality classes: STAR 1,2 charged hadron

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A Promising Solution to the Elliptic Quench Puzzle at RHIC

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  1. A Promising Solution to the Elliptic Quench Puzzle at RHIC William A. Horowitz Columbia University August 4-5, 2005

  2. What is the Puzzle?–Data • Naïvely combine published RAA(pT) and v2(pT) data • Preliminary PHENIX p0 data • Data centrality classes: • STAR1,2 charged hadron • 0-5%, 10-20%, 20-30%, 30-40%, 40-60% • PHENIX3,4 charged hadron • 0-20%, 20-40%, 40-60% • PHENIX5p0 • 10-20%, 20-30%, …, 50-60% • Note: error regions are only a rough estimate

  3. What is the Puzzle?–Theory • Can’t fit the RHIC phenomena • Hydrodynamics • Not applicable at intermediate and higher pT • Parton Cascade and Energy Loss • Don’t work: jet quenching and anisotropy anti-correlated • Models over-suppress RAA in order to reproduce large observed v2

  4. GLV Energy Loss • A geometric approximation: the gGLV • Fractional energy loss: • Integral through the 1D expanding medium that captures the L2 dependence of energy loss in a static medium:

  5. The gGLV • Use Glauber, factorization, and power law spectrum to yield: • 10% difference between n=4 and n=5, use n=4 • To calculate RAA and v2, generate this at multiple values of f and find the Fourier modes • Use hard sphere nuclear geometry • Systematically enhances v26

  6. Model Failures • Models can’t match intended data point for any value of their free parameter (opacity of the medium) • MPC7: calculated for 25-35% centrality • gGLV: 40-50% centrality

  7. Modify gGLV • Absorption model: add thermal absorption and stimulated emission8, • Integral through 1D expanding medium that captures linear in L dependence of energy gain in static media: • Punch model: add a momentum boost (DpT) to the parton in the direction normal to the edge of emission

  8. Fixing the Parameters • As in Drees, et al.6, gGLV (k) model fit to PHENIX most central RAA • gGLV+abs (k, k) and gGLV+punch (k,DpT) parameters uniquely determined by a single (RAA,v2) point: • 20-30% centrality p0

  9. Success! • Having fixed the parameters for a single centrality, allow the impact parameter to vary

  10. But! • For radiative energy loss and thermal absorption, asymptotic expansions7 give: where

  11. Failure of Absorption • Too high a multiplicity required for absorption part of gGLV+absorption (k = .5 and k = .25): • For E = 6 GeV, L = 5 fm, l0 = .2 fm, and as = .4: • For E = 10 GeV, L = 5 fm , l0 = .2 fm, and as = .4:

  12. Success of the Punch • Reasonable multiplicity required for energy loss part of gGLV+punch (k = .18) • For E = 10 GeV, L = 5 fm, and as = .3: • Punch needed (DpT = .5 GeV) is on the order of the energy boost (~1 GeV) expected from deflagration, latent heat, or the effect of the bag constant

  13. Cu+Cu v2 vs. RAA: Centrality-binned Results: Cu+Cu Predictions Use parameters for Au+Au, apply models to Cu+Cu

  14. Conclusions • Previous theories don’t follow the elliptic quench pattern at RHIC • Energy loss modified with either absorption or a punch agrees with the RAA and v2 data • Absorption ruled out by the multiplicity results • Possible punch sources exist, with effects on the same order of magnitude • Smallness of punch (.5 GeV) should allow for necessary scaling when a more realistic nuclear density geometry is used and v2 enhancement is lost

  15. References

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