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Dielectron mass spectra from √s NN = 200 GeV heavy ion collisions at PHENIX

Dielectron mass spectra from √s NN = 200 GeV heavy ion collisions at PHENIX. Sarah Campbell APS April Meeting Washington, DC. Possible modifications. Chiral symmetry restoration Continuum enhancement Modification of vector mesons. Thermal radiation Charm modification.

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Dielectron mass spectra from √s NN = 200 GeV heavy ion collisions at PHENIX

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  1. Dielectron mass spectra from √sNN = 200 GeV heavy ion collisions at PHENIX Sarah Campbell APS April Meeting Washington, DC Sarah Campbell APS 2010

  2. Possible modifications Chiral symmetry restoration Continuum enhancement Modification of vector mesons Thermal radiation Charm modification Suppression Motivation • E&M probe – e+ e- • No color charge  No final state interactions • Integrated over the full time evolution of the system • Diverse Physics Signals • Direct virtual photons • Dalitz decays • Hadronic decays • Semi-leptonic heavy flavor decays • Medium mass modifications • Dropping mass • Mass broadening • Submitted paper Au+Au, p+p to PRC • Arxiv 0912.0244 • Cu+Cu preliminary results in centrality bins Sarah Campbell APS 2010

  3. p e+ e- PHENIX • Electron Tracks • Good quality tracks in DC-PC1 • pT /pT = 0.7%  1% pT • RICH ring, EMC shower • All possible electron pairs in an event are made • like-sign • unlike-sign • Conversion pairs removed by orientation angle cut • Overlapping pairs removed by track separation cut Sarah Campbell APS 2010

  4. Jet Background Pions in jets dalitz decay into electrons Like-sign and unlike-sign pairs produced at same rate Simulated with Pythia “Cross” pairs Decays that produce multiple lepton pairs Like-sign and unlike-sign pairs produced at same rate Simulated with Exodus Pions, etas only sizable source γ e- e+ e+ π0 e+ e- π0 π0 γ e- γ e+ 0 e-  e+ e- Background Types • Combinatorial Background • Largest background in HI events • Shape determined by event mixing • Normalization determined using the like-sign pairs in regions where combinatorial dominates Sarah Campbell APS 2010

  5. Full Background Removal 0-10% CuCu All like-sign pairs Combinatorial BG Correlated Pairs Cross Pairs Jet Pairs • In Cu+Cu and Au+Au jet awayside component (d > 90) altered to account for jet modificationin HI systems[1] • [1] PRC 78 014901 (2008), PRC 77 011901 (2008), J. Phys. G 35 No 10 (2008) 104033 0-10% CuCu All unlike-sign pairs Combinatorial BG Correlated Pairs Cross Pairs Jet Pairs Sarah Campbell APS 2010

  6. Hadronic pair sources Calculated with Exodus Pion pT spectra fit to a modified Hagedorn function mT scaling Normalized to measured mesons pT distributions when possible Charm correlation D mesons semi-leptonically decay Simulated with Pythia In p+p, measure the σcc from non-photonic single e-, σcc = 567 ± 57(stat) ± 193 (sys) μb Phys. Lett. B 670, 313 (2009) For Au+Au and Cu+Cu use NColl scaled p+p Cocktail Generation • σcc = 544 ± 39(stat) ± 142(sys) ± 200 (model) μb Sarah Campbell APS 2010

  7. p+p good agreement with cocktail AuAu MB LMR excess ~ 5X the expected yield p+p & Au+Au Results Sarah Campbell APS 2010

  8. Au+Au Centrality Dependence • Excess grows faster than Npart Sarah Campbell APS 2010

  9. Cu+Cu Centrality Spectra Sarah Campbell APS 2010

  10. Too Many Results Read the paper… Arxiv 0912.0244 Y. Akiba’s talk TEff ~ 100MeV Sarah Campbell APS 2010

  11. signal e- partner e+ needed for rejection Conclusions & Future • Conclusions • See a LMR excess • Au+Au: MB, 0-10%, 10-20% • Cu+Cu: 0-10% • LMR excess grows faster than Npart • More results than 10 min can hold • Future • d+Au analysis • J. Kamin talk today at 2:42pm in Maryland C • Hadron Blind Detector • B. Lewis and S. Rolnick’s talks earlier in this session • Low energy scan Sarah Campbell APS 2010

  12. Sarah Campbell APS 2010

  13. LMR has 2 components • There exists LMR excess in Au+Au at all pTs • LMR excess is largest low pair pT • Calculate local inverse slopes of mT spectra in ranges (0 - 0.6), (0.6 – 2.5) • Soft component at m ~ 0.5 • TEff ~ 100 MeV • Over 50% of the excess Sarah Campbell APS 2010

  14. signal e- partner e+ needed for rejection Conclusions & Future • Conclusions • See a LMR excess • Au+Au: MB, 0-10%, 10-20% • Cu+Cu: 0-10% • LMR excess grows faster than Npart • LMR excess has two sources • Quasi-real virtual photons at high pT • Mass modifications at low pt • looks soft, TEff ~ 100 MeV • Future • d+Au analysis • see talk by J. Kamin • Hadron Blind Detector • Reduce combinatorial background • Successfully took data in 2009 p+p • Data taking Au+Au in 2010 • Low energy scan Sarah Campbell APS 2010

  15. Conversion Pairs Opening angle in the plane perp. to B field Charges ordered by B field Mass of the pair is roughly proportional to the radius of the conversion point Overlapping Pairs RICH ring overlap Require pairs are separated by twice the nominal ring size Dalitz decay z z e- Conversion pair B B y y x x e- e+ e+ False Pair Rejection Sarah Campbell APS 2010

  16. Theory Comparison Hadronic gas VDM broadening HSD Dropping rho w/ broadening Current-current correl. func. Hadronic gas Hydro evol. • Fail to describe the excess Sarah Campbell APS 2010

  17. LMR m Spectra in pT Slices • p+p matches the cocktail fairly well • There exists LMR excess in Au+Au at all pTs • LMR excess is largest low pair pT Sarah Campbell APS 2010

  18. R. Rapp and H. van Hees K. Dusling and I. Zahed W. Cassing and E. Bratkovskaya LMR Theory pT Slices • In the high pT ranges, the theories are close but still low • Benefit from including virtual photon processes, q + g ->q e+ e- • At low pT, none describe the data Sarah Campbell APS 2010

  19. High pt (pT > 1) Quasi-real virtual photons mee << pT for mee < 0.3 Direct photon component, fdir, shape known: Filtered by acceptance Smeared by resolution PRL arXiv 0804.4168 R = (data - cocktail)/fdir flat even at higher masses Low pT (pT < 1) R is not flat Must be something other than quasi-real virtual photons Medium modified masses Two sources of LMR excess LMR Excess Sarah Campbell APS 2010

  20. pT Spectra of LMR • Corrected to the full 2 acceptance Solid lines cocktail Dashed lines cocktail + virtual photon Sarah Campbell APS 2010

  21. LMR pT Spectra  TEff • Calculate local inverse slopes in m ranges (0 - 0.6), (0.6 – 2.5) • Soft component at m ~ 0.5 • TEff ~ 100 MeV • Over 50% of the excess Sarah Campbell APS 2010

  22. R. Rapp and H. van Hees K. Dusling and I. Zahed W. Cassing and E. Bratkovskaya LMR Theory pT Spectra • None really describe the data • Cassing and Bratkovskaya closest • Benefit from including the virtual photon • q + g -> q + e+e- Sarah Campbell APS 2010

  23. Photons from dielectrons • m << pt  S=1, L=1 • From the fit, • r= direct /inclusive  • Extrapolate to m=0 Dashed Taa scaled p+p Solid Taa scaled p+p + exp T=233+/-14 +/-19 T=221+/-19+/-19 T=217+/-18+/-16 Sarah Campbell APS 2010

  24. Thermal Photon Theories • hi Sarah Campbell APS 2010

  25. R Rapp’s Theories • Hi • Turbide,Rapp,Gale PRC 69, 014903(2004) Sarah Campbell APS 2010

  26. More on the Conversion Photons Sarah Campbell APS 2010

  27. Like Sign subtraction Sarah Campbell APS 2010

  28. Jet treatment • In p+p full jet is used • In Au+Au, only “near-side” jet (dphi < 90) used • Good agreement b/w FG comby BG ratio at high masses • In Cu+Cu “away-side” jet is modified by measured Cu+Cu Iaa Sarah Campbell APS 2010

  29. p+p Normalization region Sarah Campbell APS 2010

  30. Reconstruction Efficiency Correction • Correct for eID efficiency and detector dead areas • In Au+Au • Single electron efficiencies folded into PHENIX aperture with EXODUS • Smaller stat errors • PISA GEANT simulation cross check • In p+p • Same method as Au+Au • Additional trigger efficiency correction • In Cu+Cu • PISA GEANT simulation Sarah Campbell APS 2010

  31. EMC RICH p+p Trigger Efficiency Correction Sarah Campbell APS 2010

  32. IMR vs Centrality • Different than the charm mass shape • Steeper shape Sarah Campbell APS 2010

  33. Cu+Cu Au+Au comparison Sarah Campbell APS 2010

  34. IMR Theory Sarah Campbell APS 2010

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