PHENIX dileptons Thomas K. Hemmick Stony Brook University

The matter alters J/ , dissolve+regen, stopped? sQGP Properties The matter is so opaque that even a 20 GeV  0 is stopped. Even heavy quarks flow The matter modifies the shape of jets PHENIX preliminary Heavy quarks are stopped All these interesting measurements represent information recorded at the endpoint of the system evolution. Dilepton measurements probe the integral of the system evolution.

An Iconic Plot In-Medium  Spectral Function NA60: SPS In+In Is the spectral function the whole story? Other components appear in RHIC collisions!

A quite difficult measurement Same analysis on data sample with additional conversion material  Combinatorial background increased by 2.5 Good agreement within statistical error  signal /signal =  BG /BG * BG/signal large!!! 0.25% From the agreement converter/non- converter and the decreased S/B ratio scale error < 0.1% (well within the conservative 0.25% error we assigned) p+p Au+Au arXiv: arXiv:

The Reference: pp Mesonic Spectra Start from the π 0, assumption : π 0 = (π + + π - )/2 parameterize PHENIX pion data : Other mesons well measured in electronic and hadronic channel Other mesons are fit with: m T scaling of π 0 parameterization p T → √(p T 2 +m meson 2 -m π 2 ) fit the normalization constant  All mesons m T scale!!! PHENIX Preliminary arXiv:

p+p Cocktail Comparison Data absolutely normalized Excellent agreement data- cocktail Extract charm and bottom cross section Charm: integration after cocktail subtraction –  cc =544 ± 39 (stat) ± 142 (sys) ± 200 (model)  b Simultaneous fit of charm and bottom: –  cc =518 ± 47 (stat) ± 135 (sys) ± 190 (model)  b –  bb = 3.9 ± 2.4 (stat) +3/-2 (sys)  b submitted to Phys. Lett.B arXiv:

Charm and bottom cross sections CHARM BOTTOM Dilepton measurement in agreement with single electron, single muon, and with FONLL (upper end) Dilepton measurement in agreement with measurement from e-h correlation and with FONLL (upper end) First measurements of bottom cross section at RHIC energies!!!

Au+Au Cocktail Comparison Data absolutely normalized Cocktail filtered in PHENIX acceptance Charm from –PYTHIA –Single electron non photonic spectrum w/o angular correlations  cc = N coll x 567±57±193  b submitted to Phys. Rev. Lett arXiv: Low-Mass Continuum: enhancement 150 <m ee <750 MeV: 3.4±0.2(stat.) ±1.3(syst.)±0.7(model) Intermediate-Mass Continuum: Single-e  p T suppression & non-zero v 2 : charm thermalized? PYTHIA single-e p T spectra softer than p+p but coincide with Au+Au Angular correlations unknown Room for thermal contribution?

pp – AuAu comparison pp and AuAu normalized to  0 region p+p: follows the cocktail Au+Au: large Enhancement in Agreement in intermediate mass and J/  just for ‘coincidence’ (J/  happens to scale as  0 due to scaling with Ncoll + suppression) p+p NORMALIZED TO m ee <100 MeV submitted to Phys. Lett.B arXiv: submitted to Phys. Rev. Lett arXiv:

Centrality Dependency submitted to Phys. Rev. Lett arXiv:  0 region: Agreement with cocktail LOW MASS Low Mass: yield increases faster than proportional to N part  enhancement from binary annihilation (ππ or qq) ? Intermediate Mass: yield increase proportional to N coll  charm follows binary scaling

Theory comparison Freeze-out Cocktail + “random” charm +  spectral function Low mass M>0.4GeV/c 2 : some calculations OK M<0.4GeV/c 2 : not reproduced Intermediate mass Random charm + thermal partonic may work R.Rapp + H.vanHees K.Dusling + I.Zahed E.Bratkovskaja + W.Cassing Gluon Compton q  g q e+e+ e-e- q q HADRONIC PARTONIC  -  annihilation q-q annihilation

p T dependency p+p: follows the cocktail Au+Au: enhancement concentrated at low p T 0<p T <0.7 GeV/c 0.7<p T <1.5 GeV/c 1.5<p T <8 GeV/c All p T p+p Au+Au arXiv: arXiv:

p T dependency II p+p: follows the cocktail for all the mass bins Au+Au: significantly deviate at low p T p+p Au+Au

Understanding the p T dependency Comparison with cocktail Single exponential fit: –Low-p T : 0<m T <1 GeV –High-p T : 1<m T <2 GeV 2-components fits –2exponentials –m T -scaling of  0 + exponential Low p T : –inverse slope of ~ 120MeV –accounts for most of the yield

Yields and Slopes Intermediate p T : inverse slope increase with mass, consistent with radial flow. Low p T : inverse slope of only ~ 120MeV!!! accounts for most of the yield!!! Cold and Bright SLOPESYIELDS Total yield (DATA) 2expo fit m T -scaling +expo fit Low-p T yield

Theory Comparison II Calculations from R.Rapp & H.vanHees K.Dusling & I.Zahed E.Bratovskaja & W.Cassing (in 4  ) The cold component is not yet explained

High p T Excess 0<p T <0.7 GeV/c 0.7<p T <1.5 GeV/c 1.5<p T <8 GeV/c 0<p T <8.0 GeV/c p+p Au+Au arXiv: arXiv: Au+Au Large enhancement at low p T Enhancement is also observed in p T above 1GeV/c in the low-mass below 300MeV

p+p Au+Au (MB) Dileptons at low mass and high p T Virtual Photons have a mass. The distribution of a virtual photon’s mass depends explicitly upon the parent mass. Thus, we can disentangle “Dalitz” virtual photons from direct virtual photons. 1 < p T < 2 GeV 2 < p T < 3 GeV 3 < p T < 4 GeV 4 < p T < 5 GeV 1.Decompose mass spectrum into Dalitz and direct components in each p T slice. 2.Determine the fraction of direct virtual photons in each slice. 3.Take this same fraction of REAL photons as a measurement of direct real photons.

Fraction of direct photons Compared to direct photons from pQCD p+p –Consistent with NLO pQCD –favors small μ Au+Au –Clear excess above pQCD μ = 0.5p T μ = 1.0p T μ = 2.0p T p+p Au+Au (MB) NLO pQCD calculation is provided by Werner Vogelsang

Direct  via  * for p+p, Au+Au New p+p result with  * method agrees with NLO pQCD predictions, and with the measurement by the calorimeter For Au+Au there is a significant low p T excess above p+p expectations The excess above TAA scaled p+p spectrum is characterized by the exponential fit explained in the previous slides. The inverse slope and the yield of the exponential is determined. NLO pQCD (W. Vogelsang) Fit to pp exp + TAA scaled pp

Theory comparison Hydrodynamical models are compared with the data D.d’Enterria &D.Peressounko T=590MeV,  0 =0.15fm/c S. Rasanen et al. T=580MeV,  0 =0.17fm/c D. K. Srivastava T= MeV,  0 =0.2fm/c S. Turbide et al. T=370MeV,  0 =0.33fm/c J. Alam et al. T=300MeV,  0 =0.5fm/c Hydrodynamical models are in qualitative agreement with the data Theory compilation by D. d’Enterria and D. Peressounko EPJC46, 451 (2006)

Summary-I First measurements of dielectron continuum at RHIC p+p Low mass Excellent agreement with cocktail Intermediate mass Extract charm and bottom –  c = 544 ± 39 (stat) ± 142 (sys) ± 200 (model)  b –  b = 3.9 ± 2.4 (stat) +3/-2 (sys)  b Au+Au Low mass Enhancement above the cocktail expectations: 3.4±0.2(stat.) ±1.3(syst.)±0.7(model) Centrality dependency: increase faster than N part p T dependency: enhancement concentrated at low p T Intermediate mass Agreement with PYTHIA: coincidence? First measurements of direct photons for p T ~1GeV at RHIC p+p Excellent agreement with NLO pQCD Au+Au above NLO pQCD  thermal radiation?

Summary-II 1.Intermediate p T shows similar shape to pp and mesonic cocktail. COLD 2. Enhancement is from COLD component -- May also be observed at SPS. -- Flow at these masses should exclude this. -- The real mystery. 3. Higher p T shows excess direct photon signal, perhaps direct thermal radiation from the early plasma -- Consistent with models of direct thermal emission from T i = MeV RHIC SPS